Hydrothermal Liquefaction System Research Articles

Production of biocrude oils from various bio-feedstocks through hydrothermal liquefaction: Comparison of batch and continuous-flow operations

Laboratory- and pilot-scale hydrothermal liquefaction (HTL) of biomass has predominantly been carried out in batch reactor systems. However, the development of continuous-flow reactor systems is critical for industrial deployment of HTL technology in a cost-competitive manner. In this study, a continuous-flow HTL system (with a feed capacity up to 6 kg/h) was developed and employed to convert various types of bio-feedstocks (wood sawdust, cornstalk, and black liquor) into biocrudes in the presence of K2CO3 catalyst at 300 °C for 12 min. The produced biocrude oils were characterized in detail by using GC-MS, FT-IR, GPC, and elemental analysis. This work compared the performance of the continuous-flow HTL process with that of a batch HTL process under the same conditions in terms of the yields and chemistry of the biocrude products as well as the energy recovery potential. The results indicated that HTL of different bio-feedstocks, particularly cornstalk and pinewood, in the continuous-flow reactor led to a higher yield of biocrude (32.4 and 34.5 wt %, respectively) with lower molecular weights and less solid residue (2.9 and 4.6 wt%, respectively) as well as a higher energy recovery rate (53.3 and 52.0%, respectively) compared with those in the batch reactor (Cornstalk: 23.8 wt%, 6.2 wt% and 46.5%; Pinewood: 28.5 wt%, 10.3 wt% and 50.8%, respectively). These promising results shall advance the future development and deployment of the HTL technology in Canadian and global bioenergy sectors.

Improving yields, compatibility and tailoring the properties of hydrothermal liquefaction bio-crude using yellow grease

Low quality waste feedstocks like food wastes, waste fats, manures etc. offer huge potential for replacing an appreciable quantity of petroleum crude. Owing to high water content of some of these feedstocks, hydrothermal liquefaction is the preferred route for its transformation. The present work performed in a continuous pilot scale hydrothermal liquefaction system studies the influence of yellow grease on the yields and quality of bio-crude, properties of bio-crude/blends, and its compatibility with petroleum fractions. Blends of food waste, yellow grease, and algae were used as feedstocks. Key fuel properties such as density and viscosity of bio-crudes and its blends with diesel and butanol were evaluated. Compatibility of different bio-crudes with petroleum fraction was investigated using microscopy imaging of blends of bio-crude and commercial diesel. Enhanced yields of bio-crude and lower asphaltene content were observed with the addition of waste lipids in the form of yellow grease while also decreasing the viscosity and density of bio-crude. Bio-crude from food wastes showed regions of compatibility at higher bio-crude concentrations while lower concentrations of bio-crude were incompatible. A combination of feedstock mix and blending of bio-crude could be used to improve the properties and compatibility of bio-crude for specific end-use devices and processes.

Development of a rigorous and generalized model on the hydrothermal liquefaction (HTL) process for bio-oil production

A rigorous process model for hydrothermal liquefaction (HTL) of microalgae is proposed in this work. This research attempts to uncover a complicated simulation scenario for the characterization of microalgae, the development of suitable reaction pathways, kinetics, and thermodynamics. In this study, 55 model compounds and 41 individual reactions were used to describe an HTL system. The kinetic parameters were regressed using literature data, which reported the results under different operating conditions using the three species of microalgae. The proposed kinetic model revealed acceptable predictivity by predicting 117 published biocrude yields (total 160) to within ± 10 wt% and 28 published HHV (total 39) to within ± 5 MJ/kg. Finally, a continuous HTL process was conceptually designed. The trade-off between the biocrude yield and HHV was investigated via multi-objective optimization (MOO), which yielded the best trade-off between the biocrude yields (37.2–60.0 wt%) and HHV (27.5 and 33.5 MJ/kg). This work presents a satisfactory first attempt to rigorously simulate a very complex HTL process. Its application in the preliminary process design, optimization, and economic analysis is recommended.

Studies on Influence of Process Parameters in Upgradation of Bio-oil Derived from HTL of Domestic household waste: Application of Response Surface Methodology

<p>This research focuses on hydrothermal gasification (HTG) and hydrothermal liquefaction (HTL) studies to produce bio-hydrogen from domestic mixed waste. HTG and HTL studies were studied at temperatures of 300–450°C and 300–400°C, correspondingly, with a catalyst level of 6 wt %. The sol-gel technique was used to make the Bentonite/Nb-TiO2 catalyst. For a solvent-waste proportion of 14 millilitre/gram, an C2H5OH - water proportions of 2:2, and a period of one-hour, maximum H2 output from HTL was 30 wt % (catalyst loads: 4 wt %) and HTG was 40 wt % (catalyst loads: 5 wt %). As C2H5OH acts as half-solvent and ideal solvent to bio-mass capacity it shot up H2 result in the HTG procedure by methanation, gas water shift and improving responses in the organization. The second output of the HTL procedure was bio-oil, which yielded 35 wt % with O/C as well as H/C standards of 1.2 and 1.0, respectively, and an HHV of 42 Mega Joule/kilogram. In the HTL system, mechanistic procedures such depolymerization, hydration, reduction, and hydrolysis generated in a larger proportion of gaseous product. Thermal and the solvent-to-waste proportion is the ideal factors in the H2 synthesis procedure, according to experimental analysis. Energy nexuses from domestic mixed trash are taken over in this research.</p>

Biofuel potential of liquid products from protein- and lipid-rich biomass hydrothermal liquefaction

Hydrothermal liquefaction (HTL) of oleaginous microorganisms is an economical method with which to transform all compounds of wet biomass into competitive biofuels without the need for pretreatments such as feedstock drying and lipid extraction. In the present work, liquefaction of microalgae or yeasts in subcritical water is investigated in a self-built HTL system. Fractional yield distribution of the end-products and characterization of biocrudes from algae HTL are studied by considering the effects of the reaction temperature and residence time. The identified compounds in the biocrudes are compared to those in yeast-derived HTL biocrudes and the reaction scheme is reported. The present work reveals that no significant quality change of algae-derived HTL biocrudes is observed in a moderate temperature range thus the N-containing compounds vary complicatedly at different residence times. Compared to the pyrolysis biocrudes of algae and yeast, the collected HTL biocrudes do not perform the advantage, in terms of biofuel potential of a high portion of N-containing compounds, especially heterocyclic compounds. It should be noted that the low protein content in the feedstocks cannot definitely be proven to have led to the reduced heterocyclic compounds in HTL biocrudes. If lipids had been present, this would have enhanced the formation of N-containing heterocyclic compounds. Instead, amino acid degradation was accelerated by the high level of carbohydrates, forming amides. This paper presents a promising effort to develop an efficient route to transform oleaginous microorganisms into biofuels.

Rethinking quantified methods for arsenic speciation and risk in a biowaste hydrothermal liquefaction system

Controversy exists to quantify the fate and speciation of Arsenic (As). We investigated its characteristics by As-containing algae in various pH hydrothermal liquefaction (HTL) system, specifically via two classical methods, i.e. the European Community Bureau of Reference (BCR) and Wenzel's method. Solid residue immobilized 11.23–16.55% of As, and 88.07–82.44% was in aqueous by the pH regulators (e.g., CH3COOH, HCl, and KOH). ICP-MS and XRD analysis revealed that As (V) was converted into As (III) and As (0) in the solid residue, while the As (V) was mainly converted into As (III) in the aqueous phase during HTL. When the classified forms of As in solid residue are compared, Wenzel's method was more appropriate for dividing the bio-availability forms of As, whereas BCR was better for estimating the toxic-potential forms of As. Subsequently, pH regulators raised the risk of As in solid residue associated with the increasing of unstable forms. The amide was hydrolyzed to carboxylic acid with acidic additives, which weakened the reducing environment in the HTL process. In contrast, the amide was hydrolyzed to ammonia with the alkaline additives, which enhanced the reducing environment and increased the risk of As in products. This work provided a new insight in systematically evaluating the risk and speciation of As in HTL.

Performance evaluation of jet fuel production by hydrothermal liquefaction in Europe

The EU Horizon 2020 project HyFlexFuel successfully demonstrated hydrothermal liquefaction (HTL) fuel production chains from different feedstock types to upgraded kerosene products. Now the question arises which commercial scale HTL system design is associated with the lowest environmental impact and production costs. The contribution addresses this research question by establishing a comprehensive process model for different feedstock types (sewage sludge, straw, miscanthus and microalgae) based on experimental biocrude production and upgrading campaigns in pilot and laboratory scale. This model enables evaluating different process configurations and serves as basis for subsequent system analyses by applying techno-economic and life cycle analyses (TEA and LCA). Upgraded biocrude using sewage sludge, representing a waste stream in wastewater management, can be produced at near-competitive price levels. Compared to conventional jet fuel production, greenhouse gases are reduced significantly. However, sewage sludge is a limited resource and only limited amounts of jet fuel could be substituted. Lignocellulosic feedstock such as straw or miscanthus are available in larger quantities and provide the opportunity to produce large amounts of sustainable aviation fuels at moderate costs.

Processing of household waste via hydrothermal gasification and hydrothermal liquefaction for bio-oil and bio-hydrogen production: Comparison with RSM studies

This study focuses on bio-hydrogen production from household mixed waste via hydrothermal gasification (HTG) and hydrothermal liquefaction (HTL) experiments. HTG and HTL studies were performed at temperature 280–420 °C and 280–360 °C, catalyst of 1–5 wt% and varying solvent proportion. Bentonite/Nb-TiO2 catalyst was synthesized via sol-gel method. Maximum hydrogen yield from HTL was 26 wt% (catalyst load: 3 wt%) and HTG was 39 wt% (catalyst load: 4 wt%) for solvent to waste ratio of 13.33 mL/g, ethanol to water ratio of 1:1 and time of 60 min. Enhanced hydrogen yield in the HTG process was via gas water shift, methanation and reforming reactions in the system due to ethanol as half-solvent and optimum solvent to biomass load. Second product from HTL process was bio-oil which resulted in yield of 33 wt% with O/C and H/C values of 0.1 and 0.95 with HHV of 34.74 MJ/kg. Mechanistic reactions like depolymerisation, hydration, reduction and hydrolysis reaction in the HTL system resulted in higher proportion of gaseous product. Optimization studies showed that temperature and solvent to waste ratio are the desired variables in the hydrogen production process. This study provides support for energy nexuses from household mixed waste.

Machine learning prediction of biocrude yields and higher heating values from hydrothermal liquefaction of wet biomass and wastes

Machine learning (ML) approach was applied for the prediction of biocrude yields (BY) and higher heating values (HHV) from hydrothermal liquefaction (HTL) of wet biomass and wastes using 17 input features from feedstock characteristics (biological and elemental properties) and operating conditions. Several novel ML algorithms were evaluated, based on 10-fold cross-validation, with 3 different sets of input features. An extreme gradient boosting (XGB) model proved to give the best prediction accuracy at nearly 0.9 R2 with normal root mean square error (NRMSE) of 0.16 for BY and about 0.87 R2 with NRMSE of about 0.04 for HHV. Temperature was found to be the most influential feature on the predictions for both BY and HHV. Meanwhile, feedstock characteristics contributed to the XGB model for more than 55%. Individual effects and interactions of most important features on the predictions were also exposed, leading to better understanding of the HTL system.

Biocrude Production from Hydrothermal Liquefaction of Chlorella: Thermodynamic Modelling and Reactor Design

Hydrothermal liquefaction can directly and efficiently convert wet biomass into biocrude with a high heating value. We developed a continuous hydrothermal liquefaction model via Aspen Plus to explore the effects of moisture content of Chlorella, reaction pressure and temperature on thermodynamic equilibrium yields, and energy recoveries of biocrude. We also compared the simulated biocrude yield and energy recoveries with experiment values in literature. Furthermore, vertical and horizontal transportation characteristics of insoluble solids in Chlorella were analyzed to determine the critical diameters that could avoid the plugging of the reactor at different flow rates. The results showed that the optimum moisture content, reaction pressure, and reaction temperature were 70–90 wt%, 20 MPa, and 250–350 °C, respectively. At a thermodynamic equilibrium state, the yield and the energy recovery of biocrude could be higher than 56 wt% and 96%, respectively. When the capacity of the hydrothermal liquefaction system changed from 100 to 1000 kg·h−1, the critical diameter of the reactor increased from 9 to 25 mm.

Experimental investigation and comparison of bio-oil from hybrid microalgae via super/subcritical liquefaction

The development of liquid bioenergy bio-oil from microalgae has recently attracted much attention, while most of them focused on single feedstock. In this work, super/subcritical liquefaction was applied for bio-oil production from hybrid microalgae. The effects of liquefaction conditions on yield of products were investigated. The results show that the hybrid microalgae Chlorella and Spirulina with an appropriate mass ratio present synergistic effects for liquefaction. Lanthanum oxide as catalysts in hydrothermal liquefaction system can improve the quality of the bio-oil. Supercritical alcoholic liquefaction systems have much higher bio-oil yield, and the maximum yield of bio-oil reaches 74.71%. The solvent methanol and ethanol in supercritical conditions could upgrade the components of the bio-oils and enhance their combustion performances. The comprehensive properties of the bio-oil from hybrid microalgae under supercritical liquefaction conditions show a potential prospect for application.

Development of biomass-based hydrothermal liquefaction system for essential oil extraction

ABSTRACT The current research is to develop a hydrothermal liquefaction system for essential oil extraction from herbal biomass. The system was developed to operate on the batch type of capacity 5 kg for the farmers cultivating on a small scale. Herbal biomass selected for the experiment was Lemongrass (Cymbopogon). The developed system comprises biomass combustion chamber, boiler, charge reactor and condenser. Samples were shade-dried for 72 h before the use in the experiment and the fuel used was Babul (Acacia nilotica). The critical thickness of insulation was calculated as 0.03 m and the energy input from biomass fuel was 15716 kJ. The feed consumption for the reaction was 33.30 g/min and the volumetric air requirement was 0.19 m3. The essential oil yields obtained from the lemongrass were 1.15%, 0.95%, 1.20% and 1.065%. The cost analysis of the developed system calculated the payback period as 4 months, benefit–cost ratio as 1.48, net present worth as $21360.28 which proved that the developed system is cost effective.

Effects of the aqueous phase recycling on bio-oil yield in hydrothermal liquefaction of Spirulina Platensis, α-cellulose, and lignin

The utilization of hydrothermal liquefaction (HTL), an efficient thermochemical conversion technology, can produce biofuels from biomass, but also a large amount of processing wastewater. In the present paper, the aqueous phase from the HTL of Spirulina Platensis was recycled as the intermediate reactant and its effects on the bio-oil yield from the HTL of Spirulina Platensis, α-Cellulose, and Lignin were investigated. The results revealed that the best bio-oil yields obtained from HTL of Spirulina Platensis and α-Cellulose in pure water were 30 and 7.03 wt% at the optimized operation conditions. Aqueous phase obtained from HTL of Spirulina Platensis could be introduced return into HTL system and result in an obvious increase in the bio-oil yield by 10 wt% and 6 wt% from HTL of Spirulina Platensis and α-Cellulose, respectively. Energy recovery rates from bio-oil were improved greatly by applying aqueous phase recycling during HTL. However, aqueous phase recycling inhibited generation of bio-oil, suggesting the presence of the antagonistic reaction between protein aqueous and Lignin. Based on the gas chromatography-mass spectrometer (GC-MS) and fourier transform infrared spectroscopy (FT-IR) analysis of the aqueous phase and bio-oil, the possible reaction pathways were deduced.

Techno-economic uncertainty quantification of algal-derived biocrude via hydrothermal liquefaction

Using microalgae for fuel production via hydrothermal liquefaction (HTL) has received increasing attention in recent years because of its high biocrude productivity and quality, cultivation flexibility, and potential for large scale operation. Most of the current knowledge on algae HTL is based on laboratory benchtop findings and/or simulation models, while yield correlations or simplified kinetics models were usually developed based on small batch equipment. In this work, the lack of commercial experience and knowledge gaps of algae HTL process were addressed through techno-economic uncertainty quantification. Particularly, a “component additivity” model was developed to predict the yields and qualities of biocrude derived from a variety of algal biomass via HTL process with model uncertainty quantified based on the operating data of PNNL's continuous flow HTL system. Impacts of algae types on the biocrude yield and process economic were investigated by performing sensitivity analysis. Monte Carlo simulations were conducted using rigorous process and economic models developed in Aspen Plus and Excel to determine the process uncertainty. The results indicate that higher total lipid content (including membrane lipid) yields more biocrude, which directionally reduces biocrude production cost. For the base case scenario (Chlorella with 18.2 wt% lipid, capacity of 200 tpd daf algae, dewatered algae price of $1171/dry ton), the modeled biocrude production cost is approximately $11/gge, of which 90% is attributed to feedstock cost of dewatered algae. According to the Monte Carlo simulation, the modeled production cost for HTL biocrude production is between $5/gge and $16/gge when the algae price ranges from $400 to $1800/daf ton, of which an uncertainty (range between 10% and 90% percentiles) up to ±12% is observed. Tornado analysis suggested that the algae composition and capital investment are the two main contributors to the economic uncertainties of the algae conversion via HTL.

A simple modeling approach for characteristics analysis of hydrothermal liquefaction products from low-lipid aquatic plants

Hydrothermal liquefaction (HTL) product distributions highly depend on reaction temperature and holding time. This paper provided a new method to establish the isothermal model on the relationship between HTL product characteristics and severity factor (combined temperature and time). The results showed that the yields of the HTL bio-oil and aqueous-phase product presented strong correlations with reaction severity and could be modeled by Lorentz (or Gaussian) function, while the HTL solid char decreased gradually with increase of reaction severity, and could be modeled by the Dose-response function. All the mean adj. R2 values of the models were greater than 0.89. The H/C, O/C ratio, dry ash-free carbon recovery (energy recovery) could be described by Bi-Dose-response, Dose-response, Dose-response, and Lonrentz models, respectively. Low biomass/water ratio resulted in achieving the maximum bio-oil yield at low reaction severity. High bio-oil yield could be produced with low-ash feedstock. The maximum dry ash-free carbon recovery and energy recovery of Desmodesmus sp. (Dsp), Cyanobacteria sp. (Csp), Bacillariophyta sp. (Bsp), and Duckweed (Dw) dependeded less on the carbohydrate composition. The newly established models of the HTL yields provide a promising method for predicting the product characteristics, simulating, designing, and optimizing the HTL system.

Pilot-Scale Continuous-Flow Hydrothermal Liquefaction of Filamentous Fungi

This study examined the potential of using the filamentous fungus Rhizopus oligosporus as a feedstock for hydrothermal liquefaction (HTL). The fungal biomass, cultivated in thin stillage from a corn ethanol plant, was processed at pilot-scale using a 1.5-L capacity continuous-flow HTL system. HTL operating conditions of 300–400 °C at 27 MPa for 12–30 min were tested. Biocrude yields ranging from 48.2 to 60.9% were obtained. At low reaction temperatures (300 °C), yields as high as 59.9% could still be achieved. Aside from the least severe reaction condition studied (300 °C, 12 min), neither the yield nor elemental composition of the biocrude was significantly impacted by residence time or temperature, as is typically seen with batch reactors. Similarities in the biochemical and elemental composition between R. oligosporus and microalgae resulted in biocrude yields that were comparable to those previously reported for continuous-flow systems using microalgae. These findings demonstrate the viability of usin...

Product and Economic Analysis of Direct Liquefaction of Swine Manure

Direct hydrothermal liquefaction of biomass is a technology that has shown promising results in treating waste and producing oil. A batch hydrothermal liquefaction system was used to treat swine manure, and it successfully converted up to 70% of swine manure volatile solids into oil and reduced manure chemical oxygen demand by up to 75% (He et al., Trans ASAE 43(6):1827–1833, 2000). A continuous-flow reactor was developed and resulted in similar conversion rates to the batch process, indicating the potential for scale-up (Ocfemia, 2005). This study investigates the hydrothermal process in relation to a livestock system to determine the impact on oil yields and fertilizer values that might be realized in a farm-scale application. Oil products from the hydrothermal process are maximized using manure containing around 20% solids, but typical swine confinement facilities contain wetter manure slurries. A preliminary investigation of liquid–solid separation methods was conducted to determine the resultant oil yields and the effects of the hydrothermal process on fertilizer values in the wastewater as compared to the unprocessed manure. Energy and economic analyses of the liquid–solid separation and hydrothermal liquefaction processes were also conducted. The hydrothermal process results in an oil product as well as a fertilizer product that retains the majority of its nitrogen value with a reduced level of phosphorus (as compared to the unprocessed swine manure). The economic analyses indicate feasibility for several different liquid–solid separation methods, dependent on the equipment and maintenance costs assumed for each method. Conveyor-belt manure collection systems in conjunction with hydrothermal liquefaction are especially promising.