Isothermal Hydrothermal Liquefaction Research Articles

Integration of hydrothermal liquefaction of Cyanophyta and supercritical water oxidation of its aqueous phase products: Biocrude production and nutrient removal

Cyanophyta has the potential to produce biocrude via hydrothermal liquefaction (HTL). However, aqueous phase products (APs), as by-products of HTL, pose a risk of eutrophication for the high levels of carbon, nitrogen, and phosphorus. Supercritical water oxidation (SCWO) can efficiently convert organics into small molecules, offering a technique for the harmless treatment of APs. Effects of holding time, pressure, and moisture content on the biocrude yields from isothermal HTL (300 °C) and fast HTL (salt bath temperature of 500 °C) were comprehensively investigated. Biocrude properties were characterized by elemental analysis, FT-IR and GC–MS. Subsequently, the APs obtained under the conditions producing the highest biocrude yield were subjected to SCWO at 550 °C with different oxidation coefficients (n) from 0 to 2. Removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH3−N), and total phosphorus (TP) were further explored. The results show that the highest biocrude yields from isothermal HTL and fast HTL were 24.2 wt% (300 °C, 1800 s, 25 MPa, and 80 wt% moisture content) and 21.9 wt% (500 °C, 40 s, 25 MPa, and 80 wt% moisture content), respectively. The biocrude primarily consisted of N-containing heterocyclic compounds, amides, and acids. SCWO effectively degraded the COD and TP in APs, while the NH3-N required further degradation. At n = 2, the highest removal rates of COD, NH3-N and TP were 98.5 %, 22.6 % and 89.1 %, respectively.

Machine learning models for fast and isothermal hydrothermal liquefaction of biomass: Comprehensive experiment and prediction of various product fraction yields

Hydrothermal liquefaction (HTL) shows promise in biocrude productions from wet biomass. In this study, phycocyanin conversion was performed under an extensive range of conditions (set-point temperatures of 300–500 °C and holding times of 20–1800 s), covering both isothermal and fast HTL processes. Based on 226 sets of product fraction yields obtained from this study and literature, machine learning models, such as multiple linear regression, decision regression tree, random forest, gradient boosting regression, and support vector regression were developed. The model with the highest predictive accuracy for biocrude yield was further used to perform both single and multi-task predictions of other product yields. The results show that fast HTL at 500 °C and 40 s produced the highest biocrude yield (35.0 wt%) and energy recovery (55.2%), which were 11.9 wt% and 15.9% higher than those obtained by conventional isothermal HTL at 300 °C and 1800 s. Biocrude predominantly consisted of nitrogenous heterocyclic compounds, leading to its high nitrogen content (∼10 wt%). In addition, water quality analysis shows that the chemical oxygen demand, ammonia and total phosphorus contents of the aqueous phase by-products were much higher than the discharge standards and required further treatments. Cross-validation and testing error analysis show that the random forest model exhibited the highest predictive accuracy for the biocrude yield, with a testing R2 of 0.93. Additionally, the random forest model could predict other product fraction yields with desirable accuracies. According to the feature importance analysis, the most important factor for biocrude production from fast HTL was the residence time, followed by the reaction temperature.

Reaction kinetics for hydrothermal liquefaction of Cu-impregnated water hyacinth to bio-oil with product characterization

Hydrothermal liquefaction is a promising technology for the conversion of biomass to bio-oil and gaseous fuels. In the present work, isothermal hydrothermal liquefaction experiments of Cu-impregnated water hyacinth were conducted at 280 °C and investigated the effect of reaction time (10 min to 45 min) on bio-oil, carbon hybrids, aqueous products, and gas yields. A short residence time of 15 min was found to be optimum to achieve a maximum total bio-oil yield of 34.82% and analyzed by GC-MS and NMR for identification of compounds. Solid residues were analyzed by FESEM, XPS, XRD, and BET for morphological study, Cu loading, and its transition in the hydrothermal environment. Based on experimental data, reaction kinetics was developed and compared for hydrothermal liquefaction of Cu-impregnated water hyacinth with raw water hyacinth to predict the influence of Cu metal on reaction rate constants during hydrothermal liquefaction. From the kinetic modeling, it was found that the presence of Cu promoted the biomass conversion to bio-oil with light oil to heavy oil ((k4) 0.24404 min−1) conversion being the dominating reaction path. In contrast to catalytic degradation, the light oil conversion to aqueous phase components with a rate constant of 0.26323 min−1 is the most prevailing step for non-catalytic hydrothermal liquefaction.

Fast and isothermal hydrothermal liquefaction of sludge at different severities: Reaction products, pathways, and kinetics

Hydrothermal liquefaction has emerged as a preferred means of converting wet biomass to biocrude. In this study, we examined the hydrothermal conversion of sludge over a large range of conditions (300–600 °C, 1–60 min) that included both nominally isothermal processing and non-isothermal processing (rapid heating, short times). An empirical severity index was employed to combine the effects of reaction temperature and holding time into a single parameter. The highest biocrude yields (20.1–30.9 wt%) were achieved at 10−1 < severity index < 102 and about 32% and 63% of the nitrogen in sludge transferred into the biocrude and aqueous phase products, respectively. A Van Krevelen diagram illustrated that dehydration and decarboxylation pathways were important for biocrude and light biocrude formation whereas dehydration paths were more important for heavy biocrude. We developed a quantitative kinetics model that faithfully correlated the effects of time and temperature on the yields of biocrude, aqueous phase products, solid, gas, and volatiles. It also accurately predicted the yields of the product fractions from hydrothermal liquefaction at 350 °C.

Hydrothermal Liquefaction of Model Food Waste Biomolecules and Ternary Mixtures under Isothermal and Fast Conditions

We subjected potato starch, casein, and sunflower oil to both isothermal and fast hydrothermal liquefaction (HTL), both individually and as ternary mixtures in different proportions. Fast HTL (15 wt % biomass loading, 600 °C set-point temperature, 1 min) of sunflower oil produced the highest biocrude yield (91 wt %), followed by casein (23 wt %) and potato starch (19 wt %). Up to 21% of the phosphorus and 57% of the nitrogen in casein are distributed to the aqueous phase after fast HTL and can potentially be recovered as fertilizer for growing more food. Fast HTL (600 °C, 1 min) provided higher biocrude energy recoveries than did isothermal HTL (350 °C, 60 min) for all three feedstocks. Potato starch showed the greatest increase in energy recovery with fast (46%) vs isothermal (32%) HTL, and fast HTL of the ternary mixture rich in potato starch produced biocrude with the largest higher heating value (HHV) (42 MJ/kg). The results indicate that fast HTL is particularly beneficial for polysaccharides compared to the other biomolecules. Biocrude yields produced from fast HTL of ternary model mixtures were within two standard deviations of the yields estimated on the basis of individual biomolecules. The presence of pyrrolidines, pyrazines, fatty acid alkyl esters, and fatty acid amides indicate that chemical reactions occur between molecules derived from the different feedstocks during HTL of mixtures.

Metals and Other Elements in Biocrude from Fast and Isothermal Hydrothermal Liquefaction of Microalgae

We determined the effects of different hydrothermal liquefaction (HTL) process variables (temperature, holding time, algae loading, and water loading) on 13 different elements in biocrude and the aqueous phase co-product. Reaction conditions included both fast and isothermal HTL. The concentrations of P, Mg, Na, and Ca in the biocrude had their highest values at the mildest HTL conditions explored, and the concentrations decreased precipitously as even moderate HTL conditions were used. The concentrations of Zn, Cu, and Ni do not show much variation with HTL severity, whereas the concentration of Fe in the biocrude first increases and then decreases. P and Na were the most abundant elements in the biocrude from fast HTL, but Fe was the most abundant from isothermal HTL. These results show that the HTL conditions can influence the concentrations of different metals and inorganic species in algal biocrude from HTL.

Hydrothermal liquefaction of sewage sludge under isothermal and fast conditions

We investigated the effects of water loading, sludge moisture content, recovery solvent, and additives on the product yields and compositions from isothermal (673K, 60min) and fast (773K, 1min) hydrothermal liquefaction (HTL) of sewage sludge. The water loading (which affects pressure within the reactor) plays a small role in product yields. The sludge moisture content had a larger effect with the highest biocrude yields (26.8wt% from isothermal HTL and 27.5wt% from fast HTL) being produced from sludge that was 85wt% moisture. The HTL biocrude from sludge mainly contains long-chain aliphatic hydrocarbon moieties and aliphatic acids. Dichloromethane recovered more biocrude and energy content (∼50%) than did the other solvents tested. Added K2CO3, Na2CO3, HCOOH, CH3COOH, MoO3-CoO/γ-Al2O3 and Ru/C significantly decrease the biocrude yield when their loadings are 50wt% of the dried sludge. The additives, excepting carbonates, enhance gasification of sludge.

Products, Pathways, and Kinetics for the Fast Hydrothermal Liquefaction of Soy Protein Isolate

We conducted nonisothermal fast hydrothermal liquefaction (HTL) of soy protein isolate (SPI) for batch holding times of 10–300 s and at temperatures up to 500 °C. The SPI solids rapidly formed water-soluble products, some of which subsequently formed biocrude. The highest biocrude yields (38–40 wt %) were obtained within 45–120 s, at which times the reactor temperatures had reached 375–435 °C. The highest recovery of nitrogen in the aqueous-phase products (80% of that present in SPI) occurred prior to formation of high biocrude yields. Ammonia formation was significant when the hydrothermal reaction medium reached supercritical conditions; over 50% of the atomic N appeared as ammonia under such conditions. We deduced the reaction pathways and developed a kinetic model from the experimental data. The reaction network includes two types of aqueous-phase products formed during HTL of protein. The first type arises directly from the SPI and the second arise from biocrude. The model accurately correlated the product yields under the fast HTL experimental conditions studied, and it accurately predicted the yields of product fractions from isothermal HTL of SPI at 300 and 350 °C.

A quantitative kinetic model for the fast and isothermal hydrothermal liquefaction of Nannochloropsis sp.

Hydrothermal liquefaction (HTL) is a technology for converting algal biomass into biocrude oil and high-value products. To elucidate the underlying kinetics for this process, we conducted isothermal and non-isothermal reactions over a broad range of holding times (10s–60min), temperatures (100–400°C), and average heating rates (110–350°Cmin−1). Biocrude reached high yields (⩾37wt%) within 2min for heat-source set-point temperatures of 350°C or higher. We developed a microalgal HTL kinetic model valid from 10s to 60min, including significantly shorter timescales (10s–10min) than any previous model. The model predicts that up to 46wt% biocrude yields are achievable at 400°C and 1min, reaffirming the utility of short holding times and “fast” HTL. We highlight potential trade-offs between maximizing biocrude quantity and facilitating aqueous phase recovery, which may improve biocrude quality.

Products and Kinetics for Isothermal Hydrothermal Liquefaction of Soy Protein Concentrate

Soy protein concentrate was hydrothermally treated at isothermal temperatures of 200, 250, 300, and 350 °C for times up to 60 min to produce a crude bio-oil. Additional product fractions included water-soluble products, gases, and residual solids. We report herein the conversion of protein and gravimetric yields of the different product fractions. The biocrude yield generally increased with both time and temperature as did the yield of gaseous products. The highest biocrude yield was 34%, produced from liquefaction at 350 °C for 60 min. Chemical and physical characterization of the biocrude revealed how its composition and boiling point range changed with reaction time. Finally, we report a reaction network and the parameters for a phenomenological kinetics model that captures the influence of time and temperature on the yields of gas, solid, biocrude, and aqueous-phase products from isothermal hydrothermal liquefaction (HTL) of soy protein concentrate. The reaction network comprised a sole primary path, ...

Characterization of products from fast and isothermal hydrothermal liquefaction of microalgae

We investigated nonisothermal (fast) and nominally isothermal hydrothermal liquefaction (HTL) of Nannochloropsis sp. microalgae for the production of biocrude. Biocrude yields ranged from 36 to 45 wt % (dry weight), with fast HTL with low mass loading giving the highest yield. This condition also gave the biocrude with the lowest heating value, which indicates there are compromises to be made between biocrude quantity and quality. The aqueous phase and biocrude product fractions were characterized using elemental analysis and Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS). This detailed level of analysis identified more than 30,000 unique molecular products. The aqueous phase products included compounds with the same molecular formulae as known herbicides, which may inform efforts in genetic engineering of algae and/or bacteria for cultivation on the aqueous phase. This detailed molecular‐level characterization provides some clues regarding the types of reactions that may take place during HTL. © 2016 American Institute of Chemical Engineers AIChE J, 62: 815–828, 2016

A general kinetic model for the hydrothermal liquefaction of microalgae.

We developed a general kinetic model for hydrothermal liquefaction (HTL) of microalgae. The model, which allows the protein, lipid, and carbohydrate fractions of the cell to react at different rates, successfully correlated experimental data for the hydrothermal liquefaction of Chlorella protothecoides, Scenedesmus sp., and Nannochloropsis sp. The model can faithfully account for the influence of time and temperature on the gravimetric yields of gas, solid, biocrude, and aqueous-phase products from isothermal HTL of a 15 wt% slurry. Examination of the rate constants shows that lipids and proteins are the major contributors to the biocrude, while other algal cell constituents contribute very little to the biocrude.

Hydrothermal Liquefaction of Bacteria and Yeast Monocultures

We hydrothermally treated monocultures of Escherichia coli, Pseudomonas putida, Bacillus subtilis, and Saccharomyces cerevisiae at isothermal (350 °C for 60 min) and fast (rapid heating for 1 min) liquefaction conditions. Fast hydrothermal liquefaction (HTL) of P. putida and S. cerevisiae produced the highest biocrude yields of 47 ± 13 and 48 ± 9 wt %, respectively. Biocrudes generated via fast HTL were always richer in O and N and had a higher yield of hexane-insoluble products. Isothermal HTL of all microorganisms always produced an aqueous phase richer in NH3 than the aqueous phase from fast HTL. Up to 62 ± 9% of the chemical energy in the biomass could be recovered in the biocrude product fraction. These results demonstrate the feasibility of applying HTL to produce high yields of biocrude from bacteria and yeast that are high in protein [>80 wt %, dry and ash-free basis (daf)] and low in lipids (<3 wt %, daf). Such microorganisms could serve as a renewable feedstock for biofuels.