Hydrothermal conversion of biomass to fuels, chemicals and materials: A review holistically connecting product properties and marketable applications.

Biomass is a renewable and carbon-neutral resource with good features for producing biofuels, biochemicals, and biomaterials. Among the different technologies developed to date to convert biomass into such commodities, hydrothermal conversion (HC) is a very appealing and sustainable option, affording marketable gaseous (primarily containing H2, CO, CH4, and CO2), liquid (biofuels, aqueous phase carbohydrates, and inorganics), and solid products (energy-dense biofuels (up to 30 MJ/kg) with excellent functionality and strength). Given these prospects, this publication first-time puts together essential information on the HC of lignocellulosic and algal biomasses covering all the steps involved. Particularly, this work reports and comments on the most important properties (e.g., physiochemical and fuel properties) of all these products from a holistic and practical perspective. It also gathers vital information addressing selecting and using different downstream/upgrading processes to convert HC reaction products into marketable biofuels (HHV up to 46 MJ/kg), biochemicals (yield >90 %), and biomaterials (great functionality and surface area up to 3600 m2/g). As a result of this practical vision, this work not only comments on and summarizes the most important properties of these products but also analyzes and discusses present and future applications, establishing an invaluable link between product properties and market needs to push HC technologies transition from the laboratory to the industry. Such a practical and pioneering approach paves the way for the future development, commercialization and industrialization of HC technologies to develop holistic and zero-waste biorefinery processes.

Algal biomass valorisation to high-value chemicals and bioproducts: Recent advances, opportunities and challenges.

Algae are considered promising biomass resources for biofuel production. However, some arguments doubt the economical and energetical feasibility of algal cultivation, harvesting, and conversion processes. Beyond biofuel, value-added bioproducts can be generated via algae conversion, which would enhance the economic feasibility of algal biorefineries. This review primarily focuses on valuable chemical and bioproduct production from algae. The methods for effective recovery of valuable algae components, and their applications are summarized. The potential routes for the conversion of lipids, carbohydrates, and proteins to valuable chemicals and bioproducts are assessed from recent studies. In addition, this review proposes the following challenges for future algal biorefineries: (1) utilization of naturally grown algae instead of cultivated algae; (2) fractionation of algae to individual components towards high-selectivity products; (3) avoidance of humin formation from algal carbohydrate conversion; (4) development of strategies for algal protein utilisation; and (5) development of efficient processes for commercialization and industrialization.

Production of Nitrogen-Containing Compounds via the Conversion of Natural Microalgae from Water Blooms Catalyzed by ZrO2.

Utilizing the inherent high nitrogen content in natural microalgae to produce value-added nitrogen-containing compounds such as fatty amides and fatty nitriles is a promising method. Herein, a method for producing value-added fatty amides and nitriles by liquefaction of natural microalgae from water blooms in n-heptane was developed. The effects of temperature, metal oxide catalyst (ZrO2 , Al2 O3 , TiO2 , ZnO, MgO, CaO), catalyst amount, and reaction time on the preparation of value-added nitrogen-containing compounds were studied. Under the optimized conditions (0.3 g ZrO2 , 300 °C, 6 h), the total yield of fatty amides was 6.9 wt %, and the yield of fatty nitriles was 1.9 wt %. Compared with the results obtained in the absence of ZrO2 , after adding ZrO2 the total yield of fatty acids was reduced by 4.7 wt % (18.5 to 13.8 wt %), while the total yield of fatty amides only increased by 0.9 wt % (6.0 to 6.9 wt %) and fatty nitriles was increased by 1.5 wt % (0.4 to 1.9 wt %). Exploring the role of ZrO2 by using model compounds (i. e., palmitic acid and palmitamide) revealed that ZrO2 could promote the dehydration of fatty amides to form fatty nitriles, but had limited effect on the reaction of fatty acid and NH3 .

Selective Conversion of Hemicellulose in Macroalgae Enteromorpha prolifera to Rhamnose.

Direct hydrothermal conversion (HC) of macroalgae Enteromorpha prolifera was conducted over the temperature range of 140-240 °C. At 160 °C, monosaccharides and small molecular acids began to generate. A high yield (18.8%) of monosaccharides was obtained at 180 °C, whereas 29.6% of small molecular organic acids was attained at 200 °C. Formic acid (FA) was then employed as a catalyst, which could selectively catalyze the conversion of hemicellulose at low temperature (94.1%, 140 °C). Rhamnose (45.2%) based on the mass of carbohydrates in E. prolifera was produced by the catalysis of 0.7 mL of FA (160 °C, 60 min, 1 g of biomass loading). A low ratio of biomass amount to water was beneficial to the solution of water-soluble components of hemicellulose in E. prolifera to get high yields to monosaccharides. HC showed promise to be an applicable and efficient method in the treatment of E. prolifera with high conversion of carbohydrates.

Fractional conversion of microalgae from water blooms.

Fractional conversion of natural algae cyanobacteria from Taihu Lake was conducted. The raw Taihu Lake algae (TLA) and pretreated samples were pyrolyzed at 290 °C and 450 °C according to the TGA results. Extraction of lipids or saccharides from the TLA was performed as a pretreatment to obtain lipid extracted algae (LEA) or saccharide extracted algae (SEA). The total yields of bio-oil from fractional pyrolysis were 40.9 wt% from TLA, 42.3 wt% from LEA, and 48.5 wt% from SEA. From TLA, the major components of the bio-oil were fatty acids, amides and hydrocarbons (heptadecane) at 290 °C whereas those at 450 °C were phenols and C10-C15 hydrocarbons. Following the lipid extraction, acids, amides and indoles accounted for a large proportion at 290 °C, while the main products obtained at 450 °C were phenols, indoles and pyrroles. It is worth mentioning that the yield of bio-oil from the LEA had increased, and the composition of the bio-oil was simplified. Moreover, the average molecular weight of the bio-oil obtained from LEA had decreased. Interestingly, the extraction of saccharides inhibited pyrolysis of the lipids, so the distribution of the bio-oil from SEA changed only a little. Fractional pyrolysis of pretreated microalgae not only increased the bio-oil yield but also improved the quality of the bio-oil.