Hydrothermal Liquefaction Experiments Research Articles

Reaction kinetics and characterisation of species in renewable crude from hydrothermal liquefaction of monomers to represent organic fractions of biomass feedstocks

Hydrothermal liquefaction (HTL) can be used to convert a range of biomass feedstocks to a renewable crude with solid, aqueous and gas co-products. In order to characterise the HTL process so that the products can be predicted for a range of reaction conditions from varying feedstock, bulk kinetic models that predict the yield of each phase from the organic composition of the feed biomass, including carbohydrate, lipid, protein and lignin components are required. Due to the complexity of the reactions and variation in the organically rich wet feedstocks being considered for HTL, investigations using model compounds have been performed by numerous researchers. In the current work monomer model compounds including glucose, oleic acid, alanine and guaiacol have been used in multivariate HTL experiments in a batch reactor at reaction temperatures of 250, 300 and 350 °C for reaction times of 5 to 60 min. The resulting yields of renewable crude, solid, aqueous and gas products allowed a model to be developed for HTL of these monomer model compounds that could be compared to a second model previously developed for products from HTL of polymer compounds from the same families. Gas chromatography-mass spectrometry analysis of renewable crude products identified that lipid produced fatty acids. Carbohydrates produced crude consisting of phenol, furans, aldehydes, aromatics and ketones. HTL of the protein monomer resulted in a renewable crude composed of amides, aromatics, amines, carboxylic acids and short hydrocarbon chains and phenolic compounds made up the majority of the renewable crude from the lignin model compound.

Hydrothermal Liquefaction of an Animal Carcass for Biocrude Oil

This study investigated the optimum operating conditions on hydrothermal liquefaction (HTL) for the production of biocrude oil from animal carcass. HTL experiments were carried out at various reaction temperatures (230−350 °C), residence times (10−80 min), solid concentrations (5−20 wt%), and pressures (15−30 MPa). Detailed chemical composition analysis of biocrude oil was performed by gas chromatography-mass spectrometry, Fourier transform infrared spectroscopic analysis, and element analysis. The results showed that the biocrude oil was composed of fatty acids, hydrocarbons, amides, esters, and N-heterocyclic compounds. The maximum biocrude oil yield of 55.6 wt% was obtained at 320 °C, 10 wt% solid concentration for a residence time of 60 min. Pressure imparts little on the yield of biocrude oil. The higher heating value of the biocrude oil ranging from 39.7 to 42.5 MJ·kg−1 was comparable to that of petroleum crude (42.9 MJ·kg−1). What is more, the general reaction pathways for HTL of animal carcass was...

Impact of time on yield and properties of biocrude during downstream processing of product mixture derived from hydrothermal liquefaction of microalga

This paper is a study on effects of separation procedures on yield and characteristics of biocrude derived from hydrothermal liquefaction (HTL) of Tetraselmis sp. microalgae. The algae was grown and cultivated in outdoor open raceway ponds. The HTL experiments were performed using 1 l custom built high pressure–temperature reactor with inbuilt magnetic stirrer. HTL experimental studies were conducted at reaction temperature of 350 °C and 15 min holding time using alga solids loading of 16 w/v%. HTL product mixture diluted with dichloromethane (ratio 1:1) was allowed to stand for 1 h, 3 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h and 15 h at room temperature. The result showed that varying stand times for product mixture separation influenced yields in biocrude, solid residue and dissolved aqueous solids. Biocrude yields were in the range of 30 wt% to 56 wt% characterised with higher heating value of ~ 35 to 37 MJ/kg and hydrogen to carbon atomic ratios of 1.56 to 1.95. Maximum yield of biocrude was obtained after 9 h stand time for product mixture and dichloromethane (PM–DCM) mixture. Although, varying PM–DCM mixture stand times showed variation in product yields, there was no clear trend in distribution of elemental contents. Majority of alkali metals distributed in aqueous phase and solid residue, which could be used as nutrients, an alternative to conventional fertiliser.

Hydrothermal liquefaction of protein-containing biomass: study of model compounds for Maillard reactions

The potential application of bio-oil production from nitrogen-containing biomass via hydrothermal liquefaction (HTL) may be limited due to high nitrogen content, making this product oil unsuitable for fuel-related uses. The Maillard reaction is expected to play a most significant role in the interaction between proteins and carbohydrates during the hydrothermal treatment. To evaluate the Maillard reaction network in this process, lactose, maltose, and lysine were employed as model substances and tested individually and in binary mixtures. HTL experiments were conducted at temperatures between 250 and 350 °C and at 20 min reaction time. When treated individually, conversion of lysine leads to higher bio-oil yields (5–17 wt.%) than the model carbohydrates (6–10 wt.%) during HTL. In mixtures with carbohydrates, the measured bio-oil yields exceeded those obtained from conversion of the single substances (10–39 wt.%). Both yields and the relative nitrogen content of the bio-oil, increase with rising reaction temperature. The composition of the bio-oils obtained through HTL experiments was investigated in more detail: cyclopentenes and furfurals were obtained from disaccharide decomposition, piperidines and quinolines in the bio-oil originate from lysine, pyrazine and its derivatives are obtained from the mixture of lysine and disaccharides. A reaction scheme based on key chemical compounds accompanied with functional groups identified by FT-IR and NMR was developed to provide a better understanding of the Maillard reaction and its impact during HTL of protein-containing biomass.

Effect of ultrasound pretreatment of municipal sewage sludge on characteristics of bio-oil from hydrothermal liquefaction process

Hydrothermal liquefaction experiments with a moist (water content 80.64 wt%) municipal sewage sludge (SS) were conducted at 280, 300, 320, 340 and 360 °C for raw and ultrasound pretreated (energy input 4500 kJ/kg of solid matter) sludge. The main aim of the experiments was to explore the effects of ultrasounds on yields and composition of bio-oil and liquefaction by-products (gas and char). The bio-oils obtained were viscous, dark brown liquids with a specific odor and heating values in the range 31.39–37.35 MJ/kg. A temperature of 320 °C was found to be the optimum for the maximum yields of the SS-derived bio-oil. During the tests a significant effect of ultrasounds on bio-oil yields was proven. A positive effect of ultrasound energy input was observed at each of the liquefaction temperatures and the maximum effect (increase of 19 wt% in bio-oil yield) was achieved at 320 °C. The GC–MS analysis revealed that the bio-oils were complex mixtures of many chemical compounds belonging to different chemical classes: aliphatic hydrocarbons, fatty alcohols, N-aliphatics, phenols, aromatic esters, aldehydes, ketones, alcohols and carboxylic acids. It was found that influence of ultrasounds on the chemical composition of the bio-oils was negligible.

Hydrothermal Liquefaction of Loblolly Pine: Effects of Various Wastes on Produced Biocrude.

In this study, feedstock interaction of cow manure and digested sewage sludge on hydrothermal liquefaction (HTL) of loblolly pine (LP) was evaluated. Noncatalytic HTL experiments were performed at reaction temperatures of 250, 275, and 300 °C at a constant reaction time of 30 min. Cyclohexane and acetone were used for biocrude extraction separately. The study focuses on the characteristics of the produced biocrude, and thus, physicochemical properties of biocrudes were examined by gas chromatography–mass spectrometry, Fourier-transform infrared spectroscopy, density, and viscosity measurements, in addition to comparing mass and energy yields. On a LP basis, the biocrude yield reached as high as 30 and 17% for acetone and cyclohexane extraction, respectively, at the highest reaction temperature. Elemental carbon and energy contents increased with increasing HTL temperature for all cases. Alkalinity of the HTL process liquid (aqueous phase) increases from the HTL of sludge, and thus, it favored the formation of nonpolar compounds in biocrude. On the other hand, acidity of the reaction medium increases with the HTL of manure and pine, and thus, phenolic compounds in biocrude were increasing. Cyclohexane was more effective for sludge/LP biocrude extraction, whereas acetone was effective for manure/LP. Density of cyclohexane extracted sludge/LP biocrudes at 300 °C was less than 1000 kg m–3, whereas acetone-extracted biocrudes had densities greater than 1000 kg m–3. For all the biocrudes, viscosity was reduced considerably for the mixtures when compared to biocrudes from LP alone.

Characterization of Aqueous Products Obtained from Hydrothermal Liquefaction of Rice Straw: Focus on Product Comparison via Microwave-Assisted and Conventional Heating

This paper focuses on the comparison of aqueous products obtained from hydrothermal liquefaction (HTL) of rice straw via microwave (MW)-assisted and conventional heating treatments. A systematic investigation of HTL experiments of rice straw via MW-assisted and conventional heating treatments has been carried out, covering a broad but mild temperature range from 150 to 230 °C at 20 °C intervals. In addition, different reaction times were studied when the HTL reaction temperature was 210 °C. In comparison to conventional HTL, considerable aqueous products could be obtained for MW-assisted HTL, which consumes less time, and in addition, repolymerization behavior could be efficiently decreased and high saccharide yields could be obtained with MW-assisted heating. Besides, the HTL temperature appeared to be the dominant factor, while the increased residence time slightly changed the contents of total organic carbon (TOC) and typical sugars and acids for both conventional and MW-assisted HTL heating.

Investigation of aqueous phase recycling for improving bio-crude oil yield in hydrothermal liquefaction of algae

In this study, the aqueous phase obtained from catalytic/non-catalytic hydrothermal liquefaction (HTL) of Chlorella vulgaris was recycled as the reaction medium with an aim to reduce water consumption and increase bio-crude oil yield. Although both Na2CO3 and HCOOH catalysts have been proven to be effective for promoting biomass conversion, the bio-crude oil yield obtained from HTL with Na2CO3 (11.5wt%) was lower than that obtained from the non-catalytic HTL in pure water at 275°C for 50min. While, the HCOOH led to almost the same bio-crude yield from HTL (29.4wt%). Interestingly, bio-crude oil yield obtained from non-catalytic or catalytic HTL in recycled aqueous phase was much higher than that obtained from HTL in pure water. Recycling aqueous phase obtained from catalytic HTL experiments resulted in a sharp increase in the bio-crude oil yield by 32.6wt% (Na2CO3-HTL) and 16.1wt% (HCOOH-HTL), respectively.

Techno-economic and life-cycle assessment of an attached growth algal biorefinery

This study examined the sustainability of generating renewable diesel via hydrothermal liquefaction (HTL) of biomass from a rotating algal biofilm reactor. Pilot-scale growth studies and laboratory-scale HTL experiments were used to validate an engineering system model. The engineering system model served as the foundation to evaluate the economic feasibility and environmental impact of the system at full scale. Techno-economic results indicate that biomass feedstock costs dominated the minimum fuel selling price (MFSP), with a base case of $104.31per gallon. Life-cycle assessment results show a base-case global warming potential (GWP) of 80gCO2-eMJ−1 and net energy ratio (NER) of 1.65 based on a well-to-product system boundary. Optimization of the system reduces MFSP, GWP and NER to $11.90Gal−1, −44gCO2-eMJ−1, and 0.33, respectively. The systems-level impacts of integrating algae cultivation with wastewater treatment were found to significantly reduce environmental impact. Sensitivity analysis showed that algal productivity most significantly affected fuel selling price, emphasizing the importance of optimizing biomass productivity.

Temperature effect on hydrothermal liquefaction of Nannochloropsis gaditana and Chlorella sp.

Temperature effect on hydrothermal liquefaction (HTL) of Nannochloropsis gaditana and Chlorella sp. was investigated with 10% biomass loading at HTL temperatures of 180–330°C, and reaction time of 30min. Maximum yields of 47.5% for Nannochloropsis sp. and 32.5% biocrude oil yields for Chlorella sp. were obtained at 300°C. The higher heating values of biocrude oils produced in this work ranged between 34 and 39MJ/kg. 79% of energy in the Nannochloropsis sp. was recovered at 300°C and 62% of energy recovery from Chlorella sp. was achieved at 200°C. Valuable nutrients (NH3–N and PO43−) produced during the HTL process were quantified from the aqueous phase for both strains of biomass. The aqueous phase samples obtained at all temperatures were also analyzed for amino acids and carbohydrates. The suitable temperatures for extraction of lipids, amino acids and carbohydrates have been identified. Sequential HTL experiments conducted have shown the prospect of recovering nutrients and other valuable byproducts along with biocrude oil. The experimental results and analysis indicate that sustainable biofuel production requires the development of strain based strategies for the hydrothermal liquefaction process.

Life cycle assessment of bio-jet fuel from hydrothermal liquefaction of microalgae

Bio-jet fuel is increasingly being produced from feedstocks such as algae and tested in flight. As the industry adopts bio-jet fuels from various feedstocks and conversion processes, life cycle assessment (LCA) is necessary to determine whether these renewable fuels result in lower life cycle greenhouse gas (LC-GHG) emissions than conventional jet fuel. An LCA was performed for a functional unit of 1 GJ of bio-jet fuel produced through thermochemical conversion (hydrothermal liquefaction (HTL)) of microalgae cultivated in wastewater effluent. Two pathways were analyzed to compare the impacts of siting HTL at a wastewater treatment plant (WWTP) to those of siting HTL at a refinery. Base cases for each pathway were developed in part using primary data from algae production in wastewater effluent and HTL experiments of this algae at the University of Kansas. The LC-GHG emissions of these cases were compared to those of conventional jet fuel, and a sensitivity analysis and Monte Carlo analyses were performed. When algal conversion using HTL was modeled at a refinery versus at the WWTP site, the transportation steps of biomass and waste nutrients were major contributors to the LC-GHG emissions of algal bio-jet fuel. The LC-GHG emissions were lower for the algal bio-jet fuel pathway that performs HTL at a WWTP (35.2kg CO2eq/GJ for the base case) than for the pathway for HTL at a refinery (86.5kg CO2eq/GJ for the base case). The LCA results were particularly sensitive to the extent of heat integration, the source of the heat for HTL, and the solids content of dewatered algae. The GHG emissions of algal bio-jet fuel can be reduced by 76% compared to conventional jet fuel with feasible improvements in those sensitive parameters and siting HTL at a WWTP. Therefore, it is critical that transportation logistics, heat integration of biomass conversion processes, and nutrient supply chains be considered as investment and production of bio-jet fuels increase.

Hydrothermal wood processing using borax decahydrate and sodium borohydride

Hydrothermal liquefaction experiments were carried out at 250, 300 and 350°C with the use of an additive (either borax decahydrate (Na2B4O7·10H2O) or sodium borohydride (NaBH4)). The effects of both temperature and types of additives on the product distributions and bio-crude compositions were viewed. The use of additives (either Na2B4O7·10H2O or NaBH4) increased bio-crude yields at all liquefaction temperatures. The highest bio-crude yield was achieved with Na2B4O7·10H2O at 300°C. The use of additives (either Na2B4O7·10H2O or NaBH4) decreased the char yield at 300 and 350°C. The heating values of ether extracts from all experimental runs including the run without additives were close to each other. However, the heating values of the acetone extract from chemical runs were higher than the heating values of the non-chemical run. The highest heating value of the acetone extract was 28.05MJkg−1 and it was obtained from the run with Na2B4O7·10H2O at 300°C. The identified compounds in ether extracts and acetone extracts were mainly oxygenated compounds. The compositions of ether extract and acetone extract were affected when using additives.

ASI: Hydrothermal extraction and characterization of bio‐crude oils from wet chlorella sorokiniana and dunaliella tertiolecta

In this research, the potential of geothermal water as an alternative water source was tested for the production of algal bio‐fuels. Two algal species, Chlorella Sorokiniana and Dunaliella Tertiolecta were cultivated in a photo‐bioreactor with tap water and geothermal water. The freshly harvested wet algae samples were used to produce bio‐crude oil samples in a high pressure reactor under a hydrothermal liquefaction (HTL) condition (300°C, 90 bar and solid loading of 9 wt %). Supernatant water obtained after harvesting was used in the HTL experiments. A thermogravimetric analyzer was used to determine the moisture and ash content of the algal biomass. It was observed that the bio‐crude oil yield could be higher than the lipid content in the algae. The GC‐MS analysis of biocrude oils showed the contribution of both lipids and proteins to the yield of biocrude. The highest bio‐crude oil yield of 30 wt % (of dry algae) was obtained with a Dunaliella Tertiolecta sample cultivated in a regular tap water medium. A similar amount of biocrude was achieved with a geothermal water medium. Using a calorie meter, the high heating values of bio‐crude oils were measured and these values ranged from 36 to 38 MJ/kg, which are close to that of crude petroleum oils. © 2013 American Institute of Chemical Engineers Environ Prog, 32: 910–915, 2013

Hydrothermal liquefaction of Spirulina and Nannochloropsis salina under subcritical and supercritical water conditions

Six hydrothermal liquefaction experiments on Nannochloropsis salina and Spirulina platensis at subcritical and supercritical water conditions (220–375°C, 20–255bar) were carried out to explore the feasibility of extracting lipids from wet algae, preserving nutrients in lipid-extracted algae solid residue, and recycling process water for algae cultivation. GC–MS, elemental analyzer, FT-IR, calorimeter and nutrient analysis were used to analyze bio-crude, lipid-extracted algae and water samples produced in the hydrothermal liquefaction process. The highest bio-crude yield of 46% was obtained on N. salina at 350°C and 175bar. For S. platensis algae sample, the optimal hydrothermal liquefaction condition appears to be at 310°C and 115bar, while the optimal condition for N. salina is at 350°C and 175bar. Preliminary data also indicate that a lipid-extracted algae solid residue sample obtained in the hydrothermal liquefaction process contains a high level of proteins.

A synergistic combination of algal wastewater treatment and hydrothermal biofuel production maximized by nutrient and carbon recycling

This study introduces and analyzes a novel system for algal biofuel production that synergistically integrates algal wastewater treatment with hydrothermal liquefaction (HTL) of wastewater biosolids and algae into bio-crude oil. This system maximizes the biofuel potential of wastewater inputs by internally capturing and recycling carbon and nutrients – a powerful concept referred to as multi-cycle nutrient reuse, which amplifies waste nutrients into multiple cycles of algal biomass and bioenergy production. We call this system “Environment-Enhancing Energy” (E2-Energy) because it can simultaneously improve conventional wastewater treatment by nutrient removal and production of a large amount of biofuel co-products. Moreover, E2-Energy resolves several key bottlenecks commonly associated with large-scale algal biofuel production including: contamination of target high-oil algal cultures, high nutrient costs/usage, unsustainable fresh water usage, and large energy inputs for dewatering/extraction. A series of algal cultivation and HTL experiments were conducted to confirm the primary steps and performance characteristics of the E2-Energy system. These experiments showed: (1) low-oil, mixed algal–bacterial biomass can be successfully cultured with the recycled HTL aqueous product; (2) both organics and nutrients are removed from wastewater during algal–bacterial biomass production (63–95% reduction); (3) this low-oil, algal–bacterial biomass can be converted into bio-crude oil via HTL with a high yield (∼50%) and a net positive energy balance; and (4) the HTL step re-releases nutrients to an aqueous phase product that can be recycled back to step (1). This repeating loop of steps 1–4 facilitates multi-cycle reuse of nutrients and thus provides biomass amplification. A mathematical model was also developed using STELLA® to simulate mass balances for long-term E2-Energy operations with internal recycling of nutrients and carbon. The model results showed that E2-Energy can amplify the biomass and biofuel production from wastewater by up to 10 times, which gives it the potential to replace all US petroleum imports using only current wastewater feedstocks and carbon dioxide from the atmosphere or point sources. Thus, E2-Energy represents a major paradigm shift—where wastewater treatment systems become optimized biofuel producers with enhanced effluent quality, which provides a viable and advantageous pathway to sustainable, carbon-neutral energy independence.

Hydrothermal liquefaction of beech wood using a natural calcium borate mineral

This study reports the effects of a natural calcium borate mineral, colemanite, on the hydrothermal liquefaction of beech wood biomass. Hydrothermal liquefaction experiments were performed at 250, 300 and 350°C with and without colemanite. The highest light bio-oil yield (11.1wt%) and the highest heavy bio-oil yield (29.8wt%) were obtained at 300°C with colemanite. The total bio-oil yields were 22wt% and 41wt% ca. at 300°C without and with colemanite, respectively. The highest heating values were obtained from the hydrothermal liquefaction of biomass using colemanite at 350°C: 23.81MJ/kg for LBO and 27.53MJ/kg for HBO. Most of the identified compounds in the light bio-oils were phenols. The light bio-oil obtained without the catalyst at 300°C contained furfurals. However, these compounds were not observed in the run with colemanite at the same temperature. The heavy bio-oils from the runs both without and with colemanite are composed of phenols, aldehydes, ketones, acids, and benzene derivatives. 4-Methyl-3-penten-2-one was the major compound in the heavy bio-oils produced in the catalytic runs.