Research Progress, Trends, and Future Prospects on Hydrothermal Liquefaction of Algae for Biocrude Production: A Bibliometric Analysis

May combine two claims.

The most significant and recent topics on liquefaction based on author keywords include technical-economic analysis, nutrient and energy recovery, response surface methodology, and kinetic model.

“Among them, technical-economic analysis, nutrient, and energy recovery, response surface methodology, and kinetic model are highlighted.”

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China is the country with the most contributions, with 201 publications (33.11%) and a local h-index of 46.

“As shown in Fig. 3a, China is the country with the most contributions, with 201 publications (33.11%) and local h-index of 46.”

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The number of publications did not exceed the maximum, reaching 77 papers published in 2017 and 75 papers published in 2021.

“Thereafter, the number of publications did not exceed the maximum reaching 77 papers published in 2017 and 75 papers published in 2021.”

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The co-authorship network includes 32 countries with a minimum of four documents of a country.

“Figure 4 shows the clustered co-authorship considering 32 countries and the minimum of four documents of a country.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Biller and Ross [12] is highlighted by the number of citations, with 690 citations.

“Some studies are highlighted by the number of citations, such as Biller and Ross [12], with 690 citations.”

• cites [12] Biller P, Ross AB (2011) Potential yields and properties of oil from the hydrothermal liquefaction of microalgae with different biochemical content. Bioresour Technol 102:215–225. https://doi.org/10.1016/j.biortech.2010.06.028 sourceNot checked yet

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The USA had an earlier and rapid increase in contributions compared to China until reaching the peak in 2017 with 27 publications.

“The USA had an earlier and rapid increase in contributions when compared to China until reaching the peak in 2017 with 27 publications.”

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The words algae and macroalgae appear in the network with 76 and 29 occurrences respectively.

“Moreover, the presence of the words “algae” and “macroalgae” is also noticed in the network, with 76 and 29 occurrences respectively.”

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In the selected database for liquefaction to produce biocrude, 85.29% of papers are articles, 7.52% are reviews, and 7.15% are proceedings papers.

“The documents type of the papers in the selected database was analyzed and it was found that 85.29% of the papers are articles, 7.52% are reviews, and 7.15% are proceedings papers.”

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Zhou et al. (2010) [43] and Shuping et al. (2010) [44] are the most-cited Chinese articles with 380 and 304 citations respectively.

“On the other hand, Zhou et al. (2010) [43] and Shuping et al., (2010) [44] are the most-cited Chinese articles with 380 and 304 citations respectively.”

• cites [43] Zhou D, Zhang L, Zhang S et al (2010) Hydrothermal liquefaction of macroalgae enteromorpha prolifera to bio-oil. Energy and Fuels 24:4054–4061. https://doi.org/10.1021/ef100151h sourceNot checked yet

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• cites [44] Shuping Z, Yulong W, Mingde Y et al (2010) Production and characterization of bio-oil from hydrothermal liquefaction of microalgae Dunaliella tertiolecta cake. Energy 35:5406–5411. https://doi.org/10.1016/J.ENERGY.2010.07.013 sourceNot checked yet

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The USA is linked with five other clusters, and China is linked only with four clusters.

“The USA is linked with other five clusters expressed in green, red, yellow, and purple, and China is linked only with four clusters colored with cyan, yellow and green.”

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In the past four years, China has exceeded the number of publications, reaching a peak in 2020 with 28 publications.

“However, in the past four years, China has exceeded the number of publications, reaching a peak in 2020 with 28 publications.”

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From 2009, a new phase characterized by an accentuated rising started, reaching 79 productions in 2017.

“However, from 2009 started a new phase characterized by an accentuated rising, reaching 79 productions in 2017.”

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The USA is the second most relevant country in this field, with 197 publications (32.45%) and a local h-index of 59.

“The USA is the second most relevant country in this field, with 197 (32.45%) with local h-index of 59”

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The sum of algae-related keywords is 303 occurrences, which is more expressive than the keyword biomass.

“It is clear the eminent importance of this feedstock in the process since its sum is given in 303 occurrences, being more expressive than the keyword “biomass.””

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There was a growth in the number of patent filings from 2018, with 57.15% of documents published after 2018.

“There was a growth in the number of patent filings from 2018, with 57.15% of documents published after 2018.”

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The main patents depositing country is China, which is also the country with the highest number of articles published on the topic.

“The main patents depositing country is China, which is also the country with the highest number of articles published on the topic.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Table 2 shows 13 relevant authors in the studied area according to their local h-index, with the number equal to or higher than 10.

“Table 2 shows the 13 relevant authors in the studied area according to their local h-index, which is shown in decreasing order with the number equal to or higher than 10.”

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The algal biomass database is composed of 87.97% articles, 9.06% reviews, and 97% proceedings papers.

“The database is composed of 87.97% of articles, 9.06% of reviews, and 97% proceedings papers.”

Probably not a substantial claim: may not pass S3 (load-bearing).

The University of Jiangsu is a reference in the development of patents related to bio-oil production from microalgae via hydrothermal liquefaction.

“Finally, it is noteworthy that the University of Jiangsu is a reference in the development of patents related to bio-oil production from microalgae via hydrothermal liquefaction.”

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The restricted search for liquefaction using algal biomass as feedstock found 607 papers since 2000, which is 25.36% of the articles published regarding the liquefaction process.

“Given the restricted search to select articles relating to the liquefaction process using algal biomass as feedstock, 607 papers were found since 2000, in other words, 25.36% of the articles published regarding the liquefaction process deal with algal biomass.”

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Brown et al. (2010) [38] and Vardon et al. (2011) [15] are the most-cited American articles published, with 512 and 416 citations respectively.

“Brown et al. (2010) [38] and Vardon et al. (2011) [15], which study focuses on the HTL of Spirulina algae, swine manure, and digested sludge at 300 °C for 30 min, are the most-cited American articles published, with 512 and 416 citations respectively.”

• cites [38] Brown TM, Duan P, Savage PE (2010) Hydrothermal liquefaction and gasification of Nannochloropsis sp. Energy and Fuels 24:3639–3646. https://doi.org/10.1021/ef100203u sourceNot checked yet

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• cites [15] Vardon DR, Sharma BK, Scott J et al (2011) Chemical properties of biocrude oil from the hydrothermal liquefaction of Spirulina algae, swine manure, and digested anaerobic sludge. Bioresour Technol 102:8295–8303. https://doi.org/10.1016/j.biortech.2011.06.041 sourceNot checked yet

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Other feedstocks used in HTL include lignin with 45 occurrences, lignocellulosic biomass with 28 occurrences, and sewage sludge with 48 occurrences.

“In addition, other feedstocks have been used in the HTL, such as lignin and lignocellulosic biomass, with 45 and 28 occurrences respectively [28–32], and sewage sludge, with 48 [16, 33–36].”

• cites [28] Kang S, Li X, Fan J, Chang J (2013) Hydrothermal conversion of lignin: a review. Renew Sustain Energy Rev 27:546–558. https://doi.org/10.1016/J.RSER.2013.07.013 sourceNot checked yet

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• cites [29] Brand S, Susanti RF, Kim SK et al (2013) Supercritical ethanol as an enhanced medium for lignocellulosic biomass liquefaction: influence of physical process parameters. Energy 59:173–182. https://doi.org/10.1016/J.ENERGY.2013.06.049 sourceNot checked yet

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• cites [30] Huang H, jun, Yuan X zhong, Zhu H na, et al (2013) Comparative studies of thermochemical liquefaction characteristics of microalgae, lignocellulosic biomass and sewage sludge. Energy 56:52–60. https://doi.org/10.1016/J.ENERGY.2013.04.065 sourceNot checked yet

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• cites [31] Cao L, Zhang C, Chen H et al (2017) Hydrothermal liquefaction of agricultural and forestry wastes: state-of-the-art review and future prospects. Bioresour Technol 245:1184–1193. https://doi.org/10.1016/j.biortech.2017.08.196 sourceNot checked yet

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• cites [32] Sharma K, Shah AA, Toor SS, et al (2021) Co-hydrothermal liquefaction of lignocellulosic biomass in supercritical water. Energies 2021, Vol 14, Page 1708 14:1708. https://doi.org/10.3390/EN14061708 sourceNot checked yet

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• cites [16] Huang HJ, Yuan XZ (2015) Recent progress in the direct liquefaction of typical biomass. Prog Energy Combust Sci 49:59–80. https://doi.org/10.1016/j.pecs.2015.01.003 sourceNot checked yet

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• cites [33] Leng L, Li J, Yuan X et al (2018) Beneficial synergistic effect on bio-oil production from co-liquefaction of sewage sludge and lignocellulosic biomass. Bioresour Technol 251:49–56. https://doi.org/10.1016/J.BIORTECH.2017.12.018 sourceNot checked yet

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• cites [34] Rahman T, Jahromi H, Roy P et al (2021) Hydrothermal liquefaction of municipal sewage sludge: effect of red mud catalyst in ethylene and inert ambiences. Energy Convers Manag 245:114615. https://doi.org/10.1016/J.ENCONMAN.2021.114615 sourceNot checked yet

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• cites [35] Leng L, Yuan X, Huang H et al (2014) The migration and transformation behavior of heavy metals during the liquefaction process of sewage sludge. Bioresour Technol 167:144–150. https://doi.org/10.1016/J.BIORTECH.2014.05.119 sourceNot checked yet

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• cites [36] Zhai Y, Chen H, Xu BB et al (2014) Influence of sewage sludge-based activated carbon and temperature on the liquefaction of sewage sludge: yield and composition of bio-oil, immobilization and risk assessment of heavy metals. Bioresour Technol 159:72–79. https://doi.org/10.1016/J.BIORTECH.2014.02.049 sourceNot checked yet

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Bioresource Technology has contributed over the years since 2011 and reached the peak of 16 papers published in 2017.

“This journal has contributed over the years since 2011 and it reached the peak of 16 papers published in 2017.”

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The first publication in the selected database in Fuel journal was in 2010, and later the number of annual contributions increased, with a maximum of eight papers in 2020.

“The first publication in the selected database in Fuel journal was in 2010 [60, 73], and later, the number of annual contributions in the field has increased, with a maximum of eight papers in 2020.”

• cites [60] Ross AB, Biller P, Kubacki ML et al (2010) Hydrothermal processing of microalgae using alkali and organic acids. Fuel 89:2234–2243. https://doi.org/10.1016/J.FUEL.2010.01.025 sourceNot checked yet

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• cites [73] Tran NH, Bartlett JR, Kannangara GSK et al (2010) Catalytic upgrading of biorefinery oil from micro-algae. Fuel 89:265–274. https://doi.org/10.1016/J.FUEL.2009.08.015 sourceNot checked yet

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From 2018 to 2020, the number of publications in Bioresource Technology decreased until reaching three publications, and in 2021, five papers were published.

“From 2018 to 2020, the number decreased until reaching three publications, and, in 2021, five papers were published [39, 68–71].”

• cites [39] Wang S, Zhao S, Cheng X et al (2021) Study on two-step hydrothermal liquefaction of macroalgae for improving bio-oil. Bioresour Technol 319:124176. https://doi.org/10.1016/j.biortech.2020.124176 sourceNot checked yet

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• cites [68] Nguyen ST, Le TM, Van Nguyen H (2021) Iron-catalyzed fast hydrothermal liquefaction of Cladophora socialis macroalgae into high quality fuel precursor. Bioresour Technol 337:125445. https://doi.org/10.1016/J.BIORTECH.2021.125445 sourceNot checked yet

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• cites [69] Li Y, Zhu C, Jiang J et al (2021) Catalytic hydrothermal liquefaction of Gracilaria corticata macroalgae: effects of process parameter on bio-oil up-gradation. Bioresour Technol 319:124163. https://doi.org/10.1016/J.BIORTECH.2020.124163 sourceNot checked yet

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• cites [70] Munasinghe-Arachchige SP, Abeysiriwardana-Arachchige ISA, Delanka-Pedige HMK, Nirmalakhandan N (2021) Biofertilizer recovery from organic solid wastes via hydrothermal liquefaction. Bioresour Technol 338:125497. https://doi.org/10.1016/J.BIORTECH.2021.125497 sourceNot checked yet

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• cites [71] Zhang W, Li J, Liu T et al (2021) Machine learning prediction and optimization of bio-oil production from hydrothermal liquefaction of algae. Bioresour Technol 342:126011. https://doi.org/10.1016/J.BIORTECH.2021.126011 sourceNot checked yet

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The University of Illinois is the most relevant institution for the sector considering the number of publications, with about 48 papers published (7.91%) and a local h-index of 25.

“The University of Illinois is the most relevant for the sector considering the number of publications, which has about 48 papers published (7.91%) and a local h-index of 25 (Figure 6b).”

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The University of Michigan publishes articles in the field since 2010 and has decreased its contribution since its peak in 2014 with six publications.

“This institution publishes articles in the field since 2010 [38] and has decreased its contribution since its peak, in 2014 with six publications.”

• cites [38] Brown TM, Duan P, Savage PE (2010) Hydrothermal liquefaction and gasification of Nannochloropsis sp. Energy and Fuels 24:3639–3646. https://doi.org/10.1021/ef100203u sourceNot checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

Keywords with bigger darker nodes indicate a solid topic in the studied field, such as biofuel (70 occurrences) and biomass (27 occurrences).

“In contrast, the keywords with bigger darker nodes indicate a solid topic in the studied field, such as “biofuel” (70 occurrences) and “biomass” (27 occurrences), which turn visible the high concern about the replacement of fossil fuels with alternative energy sources.”

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New Mexico State University has 28 studies in the field (4.61%), with an h-index of 18, and it started publishing in 2013.

“Next, the New Mexico State University has 28 studies in the field (4.61%), with an h-index of 18, and it started publishing in 2013 [77, 78].”

• cites [77] Reddy HK, Muppaneni T, Rastegary J et al (2013) ASI: Hydrothermal extraction and characterization of bio-crude oils from wet chlorella sorokiniana and dunaliella tertiolecta. Environ Prog Sustain Energy 32:910–915. https://doi.org/10.1002/EP.11862 sourceNot checked yet

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• cites [78] Toor SS, Reddy H, Deng S et al (2013) Hydrothermal liquefaction of Spirulina and Nannochloropsis salina under subcritical and supercritical water conditions. Bioresour Technol 131:413–419. https://doi.org/10.1016/J.BIORTECH.2012.12.144 sourceNot checked yet

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In the following years, University of Illinois decreased its number of publications, varying between one and seven papers, but two were already published in 2022.

“In the following years, the university has decreased its number, varying between one and seven papers, but two were already published in 2022 [75, 76].”

• cites [75] Lu J, Watson J, Liu Z, Wu Y (2022) Elemental migration and transformation during hydrothermal liquefaction of biomass. J Hazard Mater 423:126961. https://doi.org/10.1016/j.jhazmat.2021.126961 sourceNot checked yet

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• cites [76] Xia C, Pathy A, Paramasivan B et al (2022) Comparative study of pyrolysis and hydrothermal liquefaction of microalgal species: analysis of product yields with reaction temperature. Fuel 311:121932. https://doi.org/10.1016/J.FUEL.2021.121932 sourceNot checked yet

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Bioresource Technology is the journal with the highest number of published documents (87 articles, 14.33%) and also with the highest local h-index in the sector of 42.

“Bioresource Technology is the journal with the highest number of published documents (87 articles,14.33%) as shown in Fig. 6a, and also with the highest local h-index in the sector of 42.”

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The University of Michigan is the second organization with the highest number of publications, with about 33 (5.44%) and its local h-index is 25.

“The University of Michigan is the second organization with the highest number of publications, with about 33 (5.44%) and its local h-index is 25.”

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Algal Research-Biomass Biofuels and Bioproducts has had publications since 2012, but the maximum annual production was in 2015 with twelve papers.

“The Algal Research-Biomass Biofuels and Bioproducts journal has had publications since 2012 [72], but the maximum annual production was in 2015 with twelve papers.”

• cites [72] Biller P, Ross AB, Skill SC et al (2012) Nutrient recycling of aqueous phase for microalgae cultivation from the hydrothermal liquefaction process. Algal Res 1:70–76. https://doi.org/10.1016/J.ALGAL.2012.02.002 sourceNot checked yet

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Ross A. B. occupies the third position with an h-index of ten and ten publications.

“When the authors are arranged in citations descending order, Ross A. B. occupies the third position with an h-index of ten and ten publications, since the author has contributed to the field with significant contributions [12, 60, 61].”

• cites [12] Biller P, Ross AB (2011) Potential yields and properties of oil from the hydrothermal liquefaction of microalgae with different biochemical content. Bioresour Technol 102:215–225. https://doi.org/10.1016/j.biortech.2010.06.028 sourceNot checked yet

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• cites [60] Ross AB, Biller P, Kubacki ML et al (2010) Hydrothermal processing of microalgae using alkali and organic acids. Fuel 89:2234–2243. https://doi.org/10.1016/J.FUEL.2010.01.025 sourceNot checked yet

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• cites [61] Anastasakis K, Ross AB (2011) Hydrothermal liquefaction of the brown macro-alga Laminaria Saccharina: effect of reaction conditions on product distribution and composition. Bioresour Technol 102:4876–4883. https://doi.org/10.1016/J.BIORTECH.2011.01.031 sourceNot checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

Figure 7 shows 37 authors' keywords considering a minimum of six occurrences.

“Figure 7 shows 37 authors’ keywords considering a minimum of six occurrences.”

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New Mexico State University's annual contribution increased, with a maximum of five publications in 2019 and 2020 equally.

“Later, annual contribution increased, with a maximum of five publications in 2019 and 2020 equally.”

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Xi'an Jiaotong University and China Agricultural University are in fourth and fifth positions with 22 and 20 publications and a local h-index of twelve and ten, respectively.

“On the other hand, the fourth and fifth positions are from Chinese institutions, Xi'an Jiaotong University and China Agricultural University with 22 and 20 publications and a local h-index of twelve and ten, respectively, as shown in Fig. 6b.”

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Algal Research-Biomass Biofuels and Bioproducts has 60 publications (9.88%) and an h-index of 29.

“Algal Research-Biomass Biofuels and Bioproducts, with 60 publications (9.88%) and an h-index of 29”

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The first publications from University of Illinois were in 2011 and the maximum annual production was in 2014 with nine contributions.

“The first publications were in 2011 [15, 74] and the maximum annual production was in 2014 with nine contributions.”

• cites [15] Vardon DR, Sharma BK, Scott J et al (2011) Chemical properties of biocrude oil from the hydrothermal liquefaction of Spirulina algae, swine manure, and digested anaerobic sludge. Bioresour Technol 102:8295–8303. https://doi.org/10.1016/j.biortech.2011.06.041 sourceNot checked yet

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• cites [74] Yu G, Zhang Y, Schideman L et al (2011) Hydrothermal liquefaction of low lipid content microalgae into bio-crude oil. Trans ASABE 54:239–246. https://doi.org/10.13031/2013.36241 sourceNot checked yet

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Fuel has 44 articles (7.25%) and an h-index of 19.

“Fuel with 44 articles (7.25%) and an h-index of 19”

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American institutions are present in the top three positions even though the number of Chinese publications has exceeded in the past four years.

“It is noticeable the presence of American institutions in the top three positions even though the number of Chinese publications has exceeded in the past four years.”

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Biorefinery (21 occurrences), biodiesel (20), algal biofuel (10), biochar (10), and bioenergy (10) are described in the network.

“Converging to it, “biorefinery” (21 occurrences), “biodiesel” (20), “algal biofuel” (10), “biochar” (10), and “bioenergy” (10) are also described in the network.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Zhang Y. H.'s most-cited paper was the second American article most-cited in the database.

“Zhang Y. H.’s most-cited paper was also described above as the second American article most-cited in the database [15].”

• cites [15] Vardon DR, Sharma BK, Scott J et al (2011) Chemical properties of biocrude oil from the hydrothermal liquefaction of Spirulina algae, swine manure, and digested anaerobic sludge. Bioresour Technol 102:8295–8303. https://doi.org/10.1016/j.biortech.2011.06.041 sourceNot checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

The keyword "response surface methodology" appears in the network with six occurrences.

“the “response surface methodology” (the keyword with six occurrences)”

• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.
• AssumptionRests on an assumption: Author keywords accurately represent the content of the studies.

Probably not a substantial claim: may not pass S3 (load-bearing).

The keyword "life cycle analysis" appears in the network with twelve occurrences.

““life cycle analysis” (LCA), a keyword expressed in the network with twelve occurrences.”

• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.
• AssumptionRests on an assumption: Author keywords accurately represent the content of the studies.

Probably not a substantial claim: may not pass S3 (load-bearing).

The keyword "catalytic upgrading" appears in the network with six occurrences.

““catalytic upgrading” (six occurrences) [104, 105]”

• cites [104] Pongsiriyakul K, Kiatkittipong W, Adhikari S et al (2021) Effective Cu/Re promoted Ni-supported γ-Al2O3 catalyst for upgrading algae bio-crude oil produced by hydrothermal liquefaction. Fuel Process Technol 216:106670. https://doi.org/10.1016/J.FUPROC.2020.106670 sourceNot checked yet

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• cites [105] Li Z, Savage PE (2013) Feedstocks for fuels and chemicals from algae: treatment of crude bio-oil over HZSM-5. Algal Res 2:154–163. https://doi.org/10.1016/J.ALGAL.2013.01.003 sourceNot checked yet

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• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.
• AssumptionRests on an assumption: Author keywords accurately represent the content of the studies.

May combine two claims.

Other studies focus on TEA and LCA for different scenarios to conciliate biorefinery approaches and improve the viability of algae to biofuel production in environmental, economic, and technological aspects.

“Other studies also focus on TEA and LCA for different scenarios to conciliate biorefinery approaches and to improve the viability of algae to biofuel production in terms of environment, economics, and technology aspects [91, 106, 108, 111].”

• cites [91] Gu X, Martinez-Fernandez JS, Pang N et al (2020) Recent development of hydrothermal liquefaction for algal biorefinery. Renew Sustain Energy Rev 121:109707. https://doi.org/10.1016/J.RSER.2020.109707 sourceNot checked yet

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• cites [106] Beal CM, Gerber LN, Sills DL et al (2015) Algal biofuel production for fuels and feed in a 100-ha facility: a comprehensive techno-economic analysis and life cycle assessment. Algal Res 10:266–279. https://doi.org/10.1016/J.ALGAL.2015.04.017 sourceNot checked yet

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• cites [108] Liu X, Saydah B, Eranki P et al (2013) Pilot-scale data provide enhanced estimates of the life cycle energy and emissions profile of algae biofuels produced via hydrothermal liquefaction. Bioresour Technol 148:163–171. https://doi.org/10.1016/J.BIORTECH.2013.08.112 sourceNot checked yet

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• cites [111] Zhu Y, Albrecht KO, Elliott DC et al (2013) Development of hydrothermal liquefaction and upgrading technologies for lipid-extracted algae conversion to liquid fuels. Algal Res 2:455–464. https://doi.org/10.1016/J.ALGAL.2013.07.003 sourceNot checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

The keyword "upgrading" appears in the network with 13 occurrences.

“the keywords “upgrading” (13 occurrences) [102, 103]”

• cites [102] Duan P, Bai X, Xu Y et al (2013) Catalytic upgrading of crude algal oil using platinum/gamma alumina in supercritical water. Fuel 109:225–233. https://doi.org/10.1016/J.FUEL.2012.12.074 sourceNot checked yet

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• cites [103] Patel B, Arcelus-Arrillaga P, Izadpanah A, Hellgardt K (2017) Catalytic hydrotreatment of algal biocrude from fast hydrothermal liquefaction. Renew Energy 101:1094–1101. https://doi.org/10.1016/J.RENENE.2016.09.056 sourceNot checked yet

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• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.
• AssumptionRests on an assumption: Author keywords accurately represent the content of the studies.

Probably not a substantial claim: may not pass S3 (load-bearing).

The keyword "techno-economic analysis" appears in the network with 13 occurrences.

“Also, “techno-economic analysis” (TEA), with 13 occurrences, is also a recently discussed topic among academics”

• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.
• AssumptionRests on an assumption: Author keywords accurately represent the content of the studies.

Probably not a substantial claim: may not pass S3 (load-bearing).

TEA is a recently discussed topic among academics to overcome challenges that remain as a barrier to industrial-scale dissemination.

“Also, “techno-economic analysis” (TEA), with 13 occurrences, is also a recently discussed topic among academics to overcome the challenges that remain as a barrier to industrial-scale dissemination”

• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.
• AssumptionRests on an assumption: Author keywords accurately represent the content of the studies.

May combine two claims.

Research has intensified in the last ten years and advanced mainly in technical-operational aspects on a bench scale.

“Although research has intensified in the last ten years and advanced mainly in the technical-operational aspects on a bench scale”

• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.

Probably not a substantial claim: may not pass S3 (load-bearing).

The keyword "heterogeneous catalysts" appears in the network with nine occurrences.

“The use of the “heterogeneous catalysts” keyword appears in the network with nine occurrences [100, 101]”

• cites [100] Xu D, Guo S, Liu L et al (2019) Heterogeneous catalytic effects on the characteristics of water-soluble and water-insoluble biocrudes in chlorella hydrothermal liquefaction. Appl Energy 243:165–174. https://doi.org/10.1016/J.APENERGY.2019.03.180 sourceNot checked yet

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• cites [101] Han FY, Komiyama M, Uemura Y, Rabat NE (2020) Catalytic alcohothermal liquefaction of wet microalgae with supercritical methanol. J Supercrit Fluids 157:104704. https://doi.org/10.1016/J.SUPFLU.2019.104704 sourceNot checked yet

  Not checked in the free run.

• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.
• AssumptionRests on an assumption: Author keywords accurately represent the content of the studies.

Probably not a substantial claim: may not pass S3 (load-bearing).

In Masoumi and Dalai's LCA, GHG emissions were 5.2 g CO2-eq/MJ for the combustion route.

“which resulted in 5.2 g CO2-eq/MJ for combustion”

• cites [107] Masoumi S, Dalai AK (2021) Techno-economic and life cycle analysis of biofuel production via hydrothermal liquefaction of microalgae in a methanol-water system and catalytic hydrotreatment using hydrochar as a catalyst support. Biomass and Bioenergy 151:https://doi.org/10.1016/J.BIOMBIOE.2021.106168 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Researchers have been focusing on achieving economic viability of HTL to biocrude production, making it necessary to find alternatives that minimize operating costs and increase HTL productivity.

“Regarding the current interest in HTL to biocrude production, researchers have been focusing their efforts on achieving the economic viability of the process, making it necessary to find alternatives that minimize operating costs and increase HTL productivity.”

• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.

May combine two claims.

Techno-economic analysis, life cycle analysis, energy recovery, and nutrient recycling are becoming hot research topics in HTL.

“In this way, “techno-economic analysis,” “life cycle analysis,” “energy recovery,” and “nutrient recycling” are becoming hot research topics.”

• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.
• AssumptionRests on an assumption: Author keywords accurately represent the content of the studies.

May combine two claims.

Research in the field has been progressing mainly on algae screening, evaluation of HTL conditions (temperature, pressure, time), use of catalysts, analysis of HTL products, biocrude oil upgrade, and understanding of reaction pathways.

“The research in the field has been progressing mainly about algae screening, study, and evaluation of HTL conditions such as temperature, pressure, and time reaction, use of catalysts, analysis of HTL products, biocrude oil upgrade, and, understanding of reaction pathways.”

• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.

Probably not a substantial claim: may not pass S3 (load-bearing).

The keyword/theme "catalysis" appears in the bibliometric network with 31 occurrences.

“Another basic theme expressed in a big darker node presented in the network is “catalysis,” with 31 occurrences.”

• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.
• AssumptionRests on an assumption: Author keywords accurately represent the content of the studies.

Probably not a substantial claim: may not pass S3 (load-bearing).

In Masoumi and Dalai's TEA, the minimum fuel selling price (MFSP) was $2.4/L for the combustion scenario.

“the results showed a minimum fuel selling price (MFSP), as an economic parameter, of $2.4/L for combustion”

• cites [107] Masoumi S, Dalai AK (2021) Techno-economic and life cycle analysis of biofuel production via hydrothermal liquefaction of microalgae in a methanol-water system and catalytic hydrotreatment using hydrochar as a catalyst support. Biomass and Bioenergy 151:https://doi.org/10.1016/J.BIOMBIOE.2021.106168 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

In Masoumi and Dalai's LCA, GHG emissions were 50 g CO2-eq/MJ for the activation route.

“and 50 g CO2-eq/MJ for the activation route.”

• cites [107] Masoumi S, Dalai AK (2021) Techno-economic and life cycle analysis of biofuel production via hydrothermal liquefaction of microalgae in a methanol-water system and catalytic hydrotreatment using hydrochar as a catalyst support. Biomass and Bioenergy 151:https://doi.org/10.1016/J.BIOMBIOE.2021.106168 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

In Masoumi and Dalai's TEA, the MFSP was $2.2/L for the activation scenario.

“a lower MFSP of $2.2/L for activation.”

• cites [107] Masoumi S, Dalai AK (2021) Techno-economic and life cycle analysis of biofuel production via hydrothermal liquefaction of microalgae in a methanol-water system and catalytic hydrotreatment using hydrochar as a catalyst support. Biomass and Bioenergy 151:https://doi.org/10.1016/J.BIOMBIOE.2021.106168 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

The keyword "kinetic model" appears in the network with seven occurrences.

“the keyword “kinetic model” (with seven occurrences)”

• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.
• AssumptionRests on an assumption: Author keywords accurately represent the content of the studies.

Classified as probably not a substantial claim. May combine two claims.

Bottlenecks preventing diffusion of the technology are developing operation methodology for harvesting algae, performing HTL at industrial scale, and producing high-quality and multiple products to favor the process technically and economically.

“some bottlenecks that prevent the diffusion of the technology are the developing of operation methodology for harvesting algae, performing HTL in an industrial scale, and producing high-quality and multiple products in order to favor the process technically and economically.”

• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.

Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

These challenging aspects are still a gap in the literature.

“These challenging aspects are still a gap in the literature.”

• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.

May combine two claims.

Biocrude produced by liquefaction has an oxygen content of 10-20 wt.% and a heating value of about 30-36 MJ/kg.

“The biocrude produced by the liquefaction process has an oxygen content of 10–20 wt.% and a heating value of about 30–36 MJ/kg, which can be further improved to liquids similar to diesel and jet fuel [3, 6, 7].”

• cites [3] Xiu S, Shahbazi A (2012) Bio-oil production and upgrading research: A review. Renew Sustain Energy Rev 16:4406–4414. https://doi.org/10.1016/j.rser.2012.04.028 sourceNot checked yet

  Not checked in the free run.

• cites [6] Demirbas A (2011) Competitive liquid biofuels from biomass. Appl Energy 88:17–28. https://doi.org/10.1016/j.apenergy.2010.07.016 sourceNot checked yet

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• cites [7] Peterson AA, Vogel F, Lachance RP et al (2008) Thermochemical biofuel production in hydrothermal media: a review of sub- and supercritical water technologies. Energy Environ Sci 1:32–65. https://doi.org/10.1039/b810100k sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

HTL operates in the presence of a solvent at temperatures between 250 and 550°C and pressures 5-28 MPa, with or without added catalyst, during a residence time between 10 and 60 min.

“HTL is a technique that works in the presence of a solvent at temperatures between 250 and 550°C and pressures 5–28 MPa with or without added catalyst during a residence time between 10 and 60 min.”

• cites [12] Biller P, Ross AB (2011) Potential yields and properties of oil from the hydrothermal liquefaction of microalgae with different biochemical content. Bioresour Technol 102:215–225. https://doi.org/10.1016/j.biortech.2010.06.028 sourceNot checked yet

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• cites [16] Huang HJ, Yuan XZ (2015) Recent progress in the direct liquefaction of typical biomass. Prog Energy Combust Sci 49:59–80. https://doi.org/10.1016/j.pecs.2015.01.003 sourceNot checked yet

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• cites [17] Tian C, Li B, Liu Z et al (2014) Hydrothermal liquefaction for algal biorefinery: a critical review. Renew Sustain Energy Rev 38:933–950. https://doi.org/10.1016/j.rser.2014.07.030 sourceNot checked yet

  Not checked in the free run.

May combine two claims.

Microalgae biofuels are not competitive compared to conventional fuels and have many challenges to achieve marketable low-cost.

“However, economic analyses conclude that microalgae biofuels are not competitive compared to conventional fuels and have many challenges to achieve marketable low-cost [10, 13].”

• cites [10] Brindhadevi K, Anto S, Rene ER et al (2021) Effect of reaction temperature on the conversion of algal biomass to bio-oil and biochar through pyrolysis and hydrothermal liquefaction. Fuel 285:119106. https://doi.org/10.1016/j.fuel.2020.119106 sourceNot checked yet

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• cites [13] Brennan L, Owende P (2010) Biofuels from microalgae-a review of technologies for production, processing, and extractions of biofuels and co-products. Renew Sustain Energy Rev 14:557–577. https://doi.org/10.1016/j.rser.2009.10.009 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The price of fuel has reached records triggered by geopolitical conflicts, rising demand, and environmental concerns.

“However, the price of fuel has reached records triggered by geopolitical conflicts, rising demand, and environmental concerns [1, 2].”

• cites [1] Alonso DM, Bond JQ, Dumesic JA (2010) Catalytic conversion of biomass to biofuels. Green Chem 12:1493–1513. https://doi.org/10.1039/c004654j sourceNot checked yet

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• cites [2] Akhtar J, Amin NAS (2011) A review on process conditions for optimum bio-oil yield in hydrothermal liquefaction of biomass. Renew Sustain Energy Rev 15:1615–1624. https://doi.org/10.1016/j.rser.2010.11.054 sourceNot checked yet

  Not checked in the free run.

Classified as probably not a substantial claim.

The highlighted recent topics may indicate a new direction being taken by researchers besides operational parameters studies.

“This may indicate a new direction being taken by researchers besides the operational parameters’ studies.”

May combine two claims.

The HTL process does not require drying biomass as a pretreatment, saving investments, energy, and time, and produces biocrude as the main product.

“However, the HTL process has been widely studied as it is not necessary to dry the biomass as a pretreatment, saving investments, energy, and time in the operation, and also because it produces the biocrude as the main product [9, 12, 15].”

• cites [9] Toor SS, Rosendahl L, Rudolf A (2011) Hydrothermal liquefaction of biomass: a review of subcritical water technologies. Energy 36:2328–2342. https://doi.org/10.1016/j.energy.2011.03.013 sourceNot checked yet

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• cites [12] Biller P, Ross AB (2011) Potential yields and properties of oil from the hydrothermal liquefaction of microalgae with different biochemical content. Bioresour Technol 102:215–225. https://doi.org/10.1016/j.biortech.2010.06.028 sourceNot checked yet

  Not checked in the free run.

• cites [15] Vardon DR, Sharma BK, Scott J et al (2011) Chemical properties of biocrude oil from the hydrothermal liquefaction of Spirulina algae, swine manure, and digested anaerobic sludge. Bioresour Technol 102:8295–8303. https://doi.org/10.1016/j.biortech.2011.06.041 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

The authors' names were corrected manually in the .txt file because some redundancy was found in word order, different names, and abbreviations for the same author.

“the authors’ names were corrected manually in the .txt since some redundancy was found, in order of words, different names and abbreviations for the same author.”

May combine two claims.

China and the USA are in separate clusters, meaning that although there is collaboration between the countries, they work more independently in the development of technology.

“As shown in Fig. 4, China and the USA are in separate clusters. This means that although there is a collaboration between the countries, they work more independently in the development of technology.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

For keyword analysis, the network and table were settled excluding the words used in the search equation, and a thesaurus file was created to avoid redundancies between words by replacing similar words with a representative one.

“Aiming to better analyze the keywords, the network and table were settled excluding the words used in the search equation, and a thesaurus file was created to avoid redundancies between words (e.g., “microalgal” and “microalgae”) replacing all similar words with a representative one.”

Probably not a substantial claim: may not pass S3 (load-bearing).

The fact that China and the USA are interested in the development of microalgae liquefaction to produce bio-oil reinforces the worldwide relevance of this topic.

“Therefore, the fact that these two economic powers are interested in the development of microalgae liquefaction to produce bio-oil reinforces the worldwide relevance of this topic.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Missing data such as year of publication, institution, and country were completed by accessing the paper and obtaining the information manually.

“In Excel, some missing data, such as year of publication, institution, and country, were completed by accessing the paper and obtaining the information manually.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

China and the USA are the largest economies in the world.

“Nevertheless, China and the USA are the largest economies in the world [45].”

• cites [45] International Monetary Fund (2021) World Economic Outlook - GDP, current prices. https://www.imf.org/external/datamapper/NGDPD@WEO/OEMDC/ADVEC/WEOWORLD. Accessed 27 dez 2022Not checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Populous countries such as China and the USA have a larger scientific community and tend to have less motivation for international collaboration when compared to smaller countries such as Italy, Germany, the Netherlands, and Poland.

“According to Glanzel [46], populous countries such as China and the USA have a larger scientific community and tend to have less motivation for international collaboration when compared to smaller countries such as Italy, Germany, the Netherlands, and Poland, which can be found together in the same cluster (red).”

• cites [46] Glänzel W, Schubert A, Czerwon HJ (1999) A bibliometric analysis of international scientific cooperation of the European Union (1985–1995). Scientometrics 45:185–202. https://doi.org/10.1007/BF02458432/METRICS sourceNot checked yet

  Not checked in the free run.

Classified as probably not a substantial claim. May combine two claims.

The search queries were structured using strategic keywords related to the research field, and a preliminary analysis of the WoS database was performed to validate the search queries.

“The search queries were structured using strategic keywords that are related to the research field and a preliminary analysis of the WoS database was performed aiming to validate the SQ.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The 973 Plan is a program launched in 2011 by the Chinese government aimed to reduce the high cost of large-scale algal-biodiesel production, advancing the technology readiness levels of the studied processes.

“In this context, the “973 Plan,” for example, is a program launched in 2011 by the Chinese government. This initiative aimed to reduce the high cost of large-scale algal-biodiesel production, advancing the technology readiness levels (TRLs) of the studied processes [47, 48].”

• cites [47] Djandja OS, Wang Z, Chen L et al (2020) Progress in hydrothermal liquefaction of algal biomass and hydrothermal upgrading of the subsequent crude bio-oil: a mini review. Energy and Fuels 34:11723–11751. https://doi.org/10.1021/ACS.ENERGYFUELS.0C01973/ASSET/IMAGES/MEDIUM/EF0C01973_0010.GIF sourceNot checked yet

  Not checked in the free run.

• cites [48] Chen H, Wang X, Wang Q (2020) Microalgal biofuels in China: the past, progress and prospects. GCB Bioenergy 12:1044–1065. https://doi.org/10.1111/GCBB.12741 sourceNot checked yet

  Not checked in the free run.

May combine two claims.

The researched area is a current and developing technology with new application possibilities.

“It reinforces that the researched area is a current and developing technology with new application possibilities.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Institutions located in the eastern and southeastern coastal Chinese areas, such as Jiangsu, Zhejiang, and Guangdong Provinces, are leading in technology layout related to microalgal biofuels.

“As discussed by Chen [48], institutions located in the eastern and southeastern coastal Chinese areas, such as Jiangsu, Zhejiang, and Guangdong Provinces, are leading in technology layout related to microalgal biofuels.”

• cites [48] Chen H, Wang X, Wang Q (2020) Microalgal biofuels in China: the past, progress and prospects. GCB Bioenergy 12:1044–1065. https://doi.org/10.1111/GCBB.12741 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

Biochar and biorefinery are represented by lighted nodes, showing recent scientific interest in such terms as alternative sub-products.

““Biochar” and “biorefinery” are represented by lighted nodes, showing recent scientific interest in such terms as alternative sub-products.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Many authors reinforce the importance of algal biomass in the sector as being the most important biofuel source in the near future for its flexibility in producing different biofuels through different routes.

“Allied with this, many authors reinforce the importance of algal biomass in the sector as being the most important biofuel source in the near future for its flexibility in producing different biofuels (e.g. bioethanol, biodiesel, bio-oil, bio-syngas, bio-hydrogen) through different routes [17, 18, 79].”

• cites [17] Tian C, Li B, Liu Z et al (2014) Hydrothermal liquefaction for algal biorefinery: a critical review. Renew Sustain Energy Rev 38:933–950. https://doi.org/10.1016/j.rser.2014.07.030 sourceNot checked yet

  Not checked in the free run.

• cites [18] Chen H, Zhou D, Luo G et al (2015) Macroalgae for biofuels production: progress and perspectives. Renew Sustain Energy Rev 47:427–437. https://doi.org/10.1016/j.rser.2015.03.086 sourceNot checked yet

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• cites [79] Demirbas A (2010) Use of algae as biofuel sources. Energy Convers Manag 51:2738–2749. https://doi.org/10.1016/j.enconman.2010.06.010 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

70-75% of nitrogen and 35-80% of phosphorus, with amounts of other inorganic nutrients that remained in the aqueous phase, could be inserted into the algae cultivation system with the gaseous product, which contains about 75% of CO2.

“For example, 70–75% of nitrogen and 35–80% of phosphorus—with amounts of other inorganic nutrients that remained in the aqueous phase—could be inserted into the algae cultivation system with the gaseous product, which contains about 75% of CO2 [17]”

• cites [17] Tian C, Li B, Liu Z et al (2014) Hydrothermal liquefaction for algal biorefinery: a critical review. Renew Sustain Energy Rev 38:933–950. https://doi.org/10.1016/j.rser.2014.07.030 sourceNot checked yet

  Not checked in the free run.

May combine two claims.

Different approaches are discussed in recent scientific literature to improve economic issues, such as using co-HTL to cover algal reduced productivity in colder seasons or algal cultivation costs and previously extracting valuable compounds from algae then converting residual biomass into biofuel.

“Different approaches are also discussed in the recent scientific literature and aim to improve the economic issues, such as using the co-HTL process to cover algal reduced productivity in colder seasons [87, 88] or algal cultivation costs [89] and previously extracting valuable compounds from the algae and then converting the residual biomass into biofuel [90–92].”

• cites [87] Pereira AP, Dong T, Knoshaug EP et al (2020) An alternative biorefinery approach to address microalgal seasonality: blending with spent coffee grounds. Sustain Energy Fuels 4:3400–3408 sourceNot checked yet

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• cites [88] Mishra S, Mohanty K (2020) Co-HTL of domestic sewage sludge and wastewater treatment derived microalgal biomass – an integrated biorefinery approach for sustainable biocrude production. Energy Convers Manag 204:112312. https://doi.org/10.1016/j.enconman.2019.112312 sourceNot checked yet

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• cites [89] Islam MB, Khalekuzzaman M, Bin Kabir S et al (2022) Substituting microalgal biomass with faecal sludge for high-quality biocrude production through co-liquefaction: a sustainable biorefinery approach. Fuel Process Technol 225:107063. https://doi.org/10.1016/j.fuproc.2021.107063 sourceNot checked yet

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• cites [90] López Barreiro D, Samorì C, Terranella G et al (2014) Assessing microalgae biorefinery routes for the production of biofuels via hydrothermal liquefaction. Bioresour Technol 174:256–265. https://doi.org/10.1016/J.BIORTECH.2014.10.031 sourceNot checked yet

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• cites [91] Gu X, Martinez-Fernandez JS, Pang N et al (2020) Recent development of hydrothermal liquefaction for algal biorefinery. Renew Sustain Energy Rev 121:109707. https://doi.org/10.1016/J.RSER.2020.109707 sourceNot checked yet

  Not checked in the free run.

• cites [92] Alba Laura Garcia, Torri Cristian, Samor Chiara et al (2012) Hydrothermal treatment (HTT) of microalgae: evaluation of the process as conversion method in an algae biorefinery concept. Energy & Fuels 26:642–657 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The use of biofuels has benefits over traditional fuels, such as higher energy security, reduced environmental impact and socioeconomic issues, and foreign exchange savings.

“The use of biofuels has benefits over traditional fuels, such as higher energy security, reduced environmental impact and socioeconomic issues, and foreign exchange savings [79].”

• cites [79] Demirbas A (2010) Use of algae as biofuel sources. Energy Convers Manag 51:2738–2749. https://doi.org/10.1016/j.enconman.2010.06.010 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

Keywords with recent average years and a small number of occurrences might suggest they are being selected in current research and possibly being a trend.

“The keywords with recent average years and a small number of occurrences might suggest they are being selected in current research and possibly being a trend.”

Probably not a substantial claim: may not pass S3 (load-bearing).

The integration of HTL wastewater algae growth could lead to an increase of biomass up to ten times.

“Nutrients, wastewater, and chemicals could be directed to support the next cycle of algae growth since a study indicated the integration of HTL wastewater algae growth could lead to an increase of biomass up to ten times.”

• cites [86] Zhou Y, Schideman L, Yu G, Zhang Y (2013) A synergistic combination of algal wastewater treatment and hydrothermal biofuel production maximized by nutrient and carbon recycling. Energy Environ Sci 6:3765–3779. https://doi.org/10.1039/C3EE24241B sourceNot checked yet

  Not checked in the free run.

May combine two claims.

Practical biorefinery approaches have shown successful results from a techno-economical point of view since algae production has been reported as the main bottleneck that makes the process challenging from a sustainability perspective.

“Practical biorefinery approaches have shown successful results from a techno-economical point of view since algae production has been reported as the main bottleneck that makes the process challenging from a sustainability perspective [85].”

• cites [85] Kumar M, Sun Y, Rathour R, et al (2020) Algae as potential feedstock for the production of biofuels and value-added products: opportunities and challenges. Sci Total Environ 716:https://doi.org/10.1016/J.SCITOTENV.2020.137116 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

According to Das et al. [90], recovery of 59% of energy from the HTL process was possible using municipal sewage sludge.

“and according to Das et al. [90], recovery of 59% of energy from the HTL process was possible using municipal sewage sludge.”

• cites [90] López Barreiro D, Samorì C, Terranella G et al (2014) Assessing microalgae biorefinery routes for the production of biofuels via hydrothermal liquefaction. Bioresour Technol 174:256–265. https://doi.org/10.1016/J.BIORTECH.2014.10.031 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

Response surface methodology is used to anticipate optimum parameter conditions for HTL.

“Moreover, this methodology is the anticipation of optimum parameter conditions [114, 115].”

• cites [114] Kohansal K, Tavasoli A, Bozorg A (2019) Using a hybrid-like supported catalyst to improve green fuel production through hydrothermal liquefaction of Scenedesmus obliquus microalgae. Bioresour Technol 277:136–147. https://doi.org/10.1016/J.BIORTECH.2018.12.081 sourceNot checked yet

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• cites [115] Kandasamy S, Zhang B, He Z et al (2020) Effect of low-temperature catalytic hydrothermal liquefaction of Spirulina platensis. Energy 190:116236. https://doi.org/10.1016/J.ENERGY.2019.116236 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

Homogeneous catalysts are often more difficult to separate from reaction products than heterogeneous catalysts.

“Homogenous catalysts have been more used for HTL than heterogeneous catalysts, even though homogeneous catalysts are often more difficult to separate from the reaction products [94].”

• cites [94] Yeh TM, Dickinson JG, Franck A et al (2013) Hydrothermal catalytic production of fuels and chemicals from aquatic biomass. J Chem Technol Biotechnol 88:13–24. https://doi.org/10.1002/JCTB.3933 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

Homogeneous catalysts are generally more active than heterogeneous catalysts due to diffusion properties.

“This occurs because homogeneous catalysts are generally more active due to diffusion properties [95].”

• cites [95] Zhao B, Li H, Wang H et al (2021) Synergistic effects of metallic Fe and other homogeneous/heterogeneous catalysts in hydrothermal liquefaction of woody biomass. Renew Energy 176:543–554. https://doi.org/10.1016/J.RENENE.2021.05.115 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Optimizing HTL operational conditions using catalysts, robust kinetic models, and response surface methodology are ways to improve the economic viability of the process.

“Some ways to improve the economic viability process include optimizing HTL operational conditions using “catalyst,” “robust kinetics model,” and “response surface methodology.””

May combine two claims.

Total solids of harvested algae are usually 10-25%, making drying of feedstock unnecessary and improving overall thermal efficiency of HTL.

“total solids of harvested algae are usually 10-25% being unnecessary drying process of feedstock and improving the overall thermal efficiency of the HTL process”

• cites [17] Tian C, Li B, Liu Z et al (2014) Hydrothermal liquefaction for algal biorefinery: a critical review. Renew Sustain Energy Rev 38:933–950. https://doi.org/10.1016/j.rser.2014.07.030 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Research on HTL and its importance has increased in the last decades due to the high price of petroleum since 2010.

“However, the research on the field and the importance of HTL has increased in the last decades due to the high price of petroleum since 2010.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Microalgae have great potential for biofixation of CO2 due to high photosynthetic efficiency.

“great potential for biofixation of CO2 due to high photosynthetic efficiency”

• cites [17] Tian C, Li B, Liu Z et al (2014) Hydrothermal liquefaction for algal biorefinery: a critical review. Renew Sustain Energy Rev 38:933–950. https://doi.org/10.1016/j.rser.2014.07.030 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

The keyword "kinetic model" indicates concern about understanding how feedstock composition affects HTL kinetics.

“the keyword “kinetic model” (with seven occurrences) indicates the concern about understanding how feedstock composition affects the HTL kinetic.”

• AssumptionRests on an assumption: The Web of Science (WoS) database comprehensively covers all relevant papers on HTL of algae for biocrude production.
• AssumptionRests on an assumption: Author keywords accurately represent the content of the studies.

Probably not a substantial claim: may not pass S3 (load-bearing).

TEA is considered the most useful tool to determine the commercial feasibility of the HTL process.

“TEA is considered the most useful tool to determine the commercial feasibility of the process [107].”

• cites [107] Masoumi S, Dalai AK (2021) Techno-economic and life cycle analysis of biofuel production via hydrothermal liquefaction of microalgae in a methanol-water system and catalytic hydrotreatment using hydrochar as a catalyst support. Biomass and Bioenergy 151:https://doi.org/10.1016/J.BIOMBIOE.2021.106168 sourceNot checked yet

  Not checked in the free run.

May combine two claims.

Technical challenges in the field include finding an efficient technology for algae harvesting, downstream process, and a continuous operation HTL system with improved heat transfer.

“technical aspects are also highlighted as challenges in the field, such as finding an efficient technology for algae harvesting [119], downstream process, and a continuous operation HTL system with improved heat transfer [117].”

• cites [119] Chen CY, Yeh KL, Aisyah R et al (2011) Cultivation, photobioreactor design and harvesting of microalgae for biodiesel production: a critical review. Bioresour Technol 102:71–81. https://doi.org/10.1016/J.BIORTECH.2010.06.159 sourceNot checked yet

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• cites [117] Marzbali MH, Kundu S, Halder P, et al (2021) Wet organic waste treatment via hydrothermal processing: a critical review. Chemosphere 279: https://doi.org/10.1016/J.CHEMOSPHERE.2021.130557 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S2 (checkable).

The increase in publications reflects the concern of academic experts on overcoming barriers and finding a feasible sustainable energy source.

“the considerable increase in publications for the last twelve years on this topic reflects the concern of academic experts on overcoming these barriers and finding a sustainable source of energy that is feasible.”

Probably not a substantial claim: may not pass S3 (load-bearing).

LCA studies are increasingly important to evaluate environmental impacts related to the processes studied.

“LCA (life cycle assessment) studies are also increasingly important to evaluate the environmental impacts related to the processes studied [106, 121, 122].”

• cites [106] Beal CM, Gerber LN, Sills DL et al (2015) Algal biofuel production for fuels and feed in a 100-ha facility: a comprehensive techno-economic analysis and life cycle assessment. Algal Res 10:266–279. https://doi.org/10.1016/J.ALGAL.2015.04.017 sourceNot checked yet

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• cites [121] Marangon BB, Castro JS, Assemany PP et al (2022) Environmental performance of microalgae hydrothermal liquefaction: life cycle assessment and improvement insights for a sustainable renewable diesel. Renew Sustain Energy Rev 155:111910. https://doi.org/10.1016/J.RSER.2021.111910 sourceNot checked yet

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• cites [122] Chen PH, Quinn JC (2021) Microalgae to biofuels through hydrothermal liquefaction: open-source techno-economic analysis and life cycle assessment. Appl Energy 289:116613. https://doi.org/10.1016/J.APENERGY.2021.116613 sourceNot checked yet

  Not checked in the free run.

May combine two claims.

Biocrude quality can be improved by blending different biomass (co-HTL) or using catalysts.

“On the other hand, biocrude quality can be improved by blending different biomass (co-HTL) or using catalysts.”

Classified as probably not a substantial claim. May combine two claims.

The recent topics reinforce the importance of improving the technology and explain new studies focusing on optimization analysis to shorten the path toward industrial applications.

“These words reinforce the importance of improving the technology and explain the occurrence of new studies focusing not only on operational parameters but also on optimization analysis aiming to shorten the path toward industrial applications.”

May combine two claims.

Catalyst type, quantity, price, bottlenecks in recovery, and deactivation process after a certain period in continuous operation are difficulties appointed in the literature.

“the catalyst type, quantity, price, bottlenecks in recovery, and the deactivation process after a certain period in a continuous operation are also difficulties appointed in the literature [116–118].”

• cites [116] Li Q, Yuan X, Hu X et al (2022) Co-liquefaction of mixed biomass feedstocks for bio-oil production: a critical review. Renew Sustain Energy Rev 154:111814. https://doi.org/10.1016/J.RSER.2021.111814 sourceNot checked yet

  Not checked in the free run.

• cites [117] Marzbali MH, Kundu S, Halder P, et al (2021) Wet organic waste treatment via hydrothermal processing: a critical review. Chemosphere 279: https://doi.org/10.1016/J.CHEMOSPHERE.2021.130557 sourceNot checked yet

  Not checked in the free run.

• cites [118] Zuorro A, García-Martínez JB, Barajas-Solano AF (2020) The application of catalytic processes on the production of algae-based biofuels: a review. Catal 2021, Vol 11, Page 22 11:22. https://doi.org/10.3390/CATAL11010022 sourceNot checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

High reactor volumes may increase both capital and operating costs.

“the high reactor volumes may increase both capital and operating costs.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Many researchers have proposed the E2E concept, based on energy and nutrient recovery, as a promising alternative to overcome drawbacks and achieve techno-economic feasibility.

“many researchers have proposed a promising alternative to overcome these drawbacks under the E2E concept (presented in topic 3.4), which is based on energy and nutrient recovery mainly to achieve techno-economic feasibility.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The use of biochar from microalgae is a promising application because production of multiple high-value products can improve overall techno-commercial feasibility.

“the use of biochar from microalgae is a promising application, since the production of multiple high-value products can improve overall techno-commercial feasibility.”