Catalytic hydrothermal liquefaction of Spirulina platensis : Focusing on aqueous phase characterization

Abstract

Summary Hydrothermal liquefaction of microalgae under alkaline and acidic conditions has been widely investigated. However, limited data are available on the mechanism of aqueous phase formation during liquefaction. In the present work, we conducted a detailed characterization of the aqueous phase from hydrothermal liquefaction of Spirulina platensis using acetic acid and potassium hydroxide as the catalyst. GC‐MS analysis revealed that a large proportion of nitrogen‐based heteroatom compounds and few oxygen‐based heterocycle compounds were presented in all the aqueous phase. All the aqueous phase displayed alkalescence and a high level of total organic carbon. Whereas, the addition of potassium hydroxide reduced the total organic carbon and the average molecular weight of the aqueous phase. The conventional liquefaction converted the Spirulina platensis to plenty of water‐soluble amides, while these compounds were apt to form acids under both the alkaline and acidic catalysts. Based on the analyses, the general reaction frameworks for the catalytic liquefaction were also proposed.

A Review of Hydrothermal Biomass Liquefaction: Operating Parameters, Reaction Mechanism, and Bio-Oil Yields and Compositions

“…Zhang et al proved the catalytic HTL of Dunaliella tertiolecta with the addition of 5% Na 2 CO 3 and found that the use of Na 2 CO 3 catalyst can increase the yield of biocrude oil by 25.8%, which can significantly improve the yield of bio-oil and promote the decomposition of carbohydrates. 188 Na 2 CO 3 can significantly enhance the quality of biocrude oil by promoting reactions such as denitrification, deoxygenation, desulfurization, and decarboxylation. This leads to an increase in the C and H content while reducing the O, N, and S content in the bio-oil, ultimately improving its heating value.…”

“…K 2 CO 3 catalyst promoted the bio-oil yield but inhibited the desulfurization process. Zhang et al proved the catalytic HTL of Dunaliella tertiolecta with the addition of 5% Na 2 CO 3 and found that the use of Na 2 CO 3 catalyst can increase the yield of biocrude oil by 25.8%, which can significantly improve the yield of bio- oil and promote the decomposition of carbohydrates . Na 2 CO 3 can significantly enhance the quality of biocrude oil by promoting reactions such as denitrification, deoxygenation, desulfurization, and decarboxylation.…”

Review of Studies on Joint Recovery of Macroalgae and Marine Debris by Hydrothermal Liquefaction

“…The use of alkalis only provides a decrease in the likelihood of repolymerization of products, which ensures a decrease in the yield of biochar and an increase of liquid fuel yield. Acid catalysis, as a rule, leads to negative consequences, increasing the rate of repolymerization of molecules in solution, reducing the yield of biofuel, and increasing the yield of the solid fraction [31,69,72].…”

Advanced Analytical Study of Process Streams for a Rational Optimization of Hydrothermal Gasification

“…The evaluation of the chemical composition of the products from hydrothermal conversion, and in particular HTL aqueous phase, is a challenging task first because of the extreme complexity of the mixture and second due to the high share of nonvolatile compounds. , Many studies have been performed with the aim to better understand the chemical composition of this effluent with the use of conventional methods such as gas chromatography coupled to mass spectrometry. − The identification of small organic acids, alcohols, ketones, and phenolic compounds was reported; however, those species correspond only to ca. 30 wt % of the organics present in the HTL-aqueous phase at a temperature of 280 °C, which is the typical gas chromatography (GC) injection condition . More advanced analytical techniques should be used to study the global composition of the aqueous phase.…”

“…30 wt % of the organics present in the HTL-aqueous phase at a temperature of 280 °C, which is the typical gas chromatography (GC) injection condition. 23 More advanced analytical techniques should be used to study the global composition of the aqueous phase. High-pressure liquid chromatography (HPLC) coupled to high-resolution mass spectrometry (HRMS) with soft ionization methods such as electrospray is a promising way to evaluate the composition of hydrothermal process products.…”