Catalytic Hydrothermal Gasification Research Articles

Leaching char with acidic aqueous phase from biomass pyrolysis: Valorization of the leachate via catalytic hydrothermal gasification

Aqueous phase of bio-oil (APB) is a general stream of waste produced from biomass pyrolysis and fractional condensation of pyrolytic volatiles and has very limited applications. We have demonstrated a sequence of leaching of alkali and alkaline earth metallic species (AAEMs) from char and catalytic hydrothermal gasification (CHTG) for valorizing char and APB, respectively. The majority of AAEMs can be removed from the char by leaching with APB and the removal rates were almost equivalent to those leached with HCl (1.0 M). CHTG of an aqueous solution of the spent APB with a total organic carbon of 14,450 ppm was performed in a continuous flow reactor, employing an activated carbon-supported Ru catalyst (Ru loading, 4.6 wt%). The catalyst exhibited a stable activity for carbon conversion of 98.8 % at 350 °C for at least 360 min while gaseous product consisting of H2, CH4, and CO2 was produced with a cold gas efficiency of 101–103 %, on a higher heating value basis. The cold gas efficiency exceeding 100 % is mainly because of the generation of H2 from water through water-gas shift reaction. The CHTG performance of APB was enhanced by char leaching through the uptake of coke-forming precursors of APB onto char and the enrichment of AAEMs in the spent APB. These AAEMs played roles in suppressing coke formation and deposition onto the catalyst and maintaining Ru particle size by providing a less acidic hydrothermal environment.

The effect of Ni- and Mo-based materials on thermochemical sulfate reduction by glycerol under hydrothermal process conditions

Catalytic hydrothermal gasification (cHTG) is a sustainable and promising route to convert wet biomass into renewable methane, but the catalyst is deactivated by small amounts of soluble sulfate stemming from the biomass feedstock. Under hydrothermal conditions, sulfate can be converted to the strong catalyst poisons thiols or sulfides by thermochemical sulfate reduction (TSR). In this work, we explored the extent to which TSR occurs under conditions relevant to cHTG operation, along with the impact of various materials on the reaction. Our results indicated that within 60 min, an aqueous solution of 20 wt% glycerol and 10 mM potassium sulfate at 25 MPa started to produce organosulfur compounds at ca. 420–440 °C, with yields for the volatile ones of 3% and 6% at 440 °C and 490 °C, respectively. The main products were non-volatile organosulfur compounds (NVOSC), which were tentatively identified as sulfate esters of glycerol or of glycerol decomposition products. A smaller fraction of products consisted of volatile organosulfur compounds (VOSC). The VOSC identified from the TSR with glycerol were mostly alkyl thiophenes, as well as methanethiol, disulfides and trisulfides with no evidence of H2S formed. Ni-, Mo-, or NiMox-based materials did not show any catalytic effect on sulfate reduction, independent of the sulfidation of the material. Glycerol was proven to be much more reactive towards TSR than acetone, as no TSR products could be observed when acetone was used as a reducing agent. A reaction pathway for the formation of thiophenes from H2S and glycerol is proposed that consists of the dehydration of glycerol, the formation of CO and H2 from glycerol decomposition, hydroformylation of acrolein, and the Paal-Knorr synthesis with succinaldehyde and H2S as intermediates.

Evaluation on the characteristics of homogeneous catalytic hydrothermal gasification of waste rubber based on ReaxFF-MD simulation

Massive waste tires unrecycled will pose a significant threat to the urban environment. Hydrothermal gasification (HTG) is a promising technology converting polymer wastes into H2-rich syngas. The homogeneous catalytic hydrothermal gasification behavior of natural rubber (NR) and styrene-butadiene rubber (SBR) was estimated based on reactive force field molecular dynamics (ReaxFF-MD). KOH had the highest catalytic performance in enhancing the degradation efficiency (22.5 %) and H2 yield (27.4 %) in HTG of NR, and K2CO3 demonstrated the most optimal alkaline catalyst for SBR to enhance the degradation efficiency (27.2 %) and H2 yield (37.9 %). K2CO3 loading with 6 wt% manifested the optimum amount for lifting DE and H2 yield in HTG of SBR, while 10 wt% K2CO3 loading represented the best effect for lifting DE (26.5 %) and H2 yield (42.6 %) in HTG of NR. The activation energy of SBR in HTG was about 259 kJ/mol, which was about 72 kJ/mol higher than that of NR. With 6 wt% K2CO3, the activation energy of SBR and NR in HTG decreased to about 143 kJ/mol and 122 kJ/mol, respectively. The present work could provide essential theoretical support and fundamental data for the application of the homogeneous catalysts in HTG recycling of waste rubber materials.

Metal oxide nanoparticles embedded in porous carbon for sulfur absorption under hydrothermal conditions

MOx (M = Zn, Cu, Mn, Fe, Ce) nanoparticles (NPs) embedded in porous C with uniform diameter and dispersion were synthesized, with potential application as S-absorbents to protect catalysts from S-poisoning in catalytic hydrothermal gasification (cHTG) of biomass. S-absorption performance of MOx/C was evaluated by reacting the materials with diethyl disulfide at HTG conditions (450 °C, 30 MPa, 15 min). Their S-absorption capacity followed the order CuOx/C > CeOx/C ≈ ZnO/C > MnOx/C > FeOx/C. S was absorbed in the first four through the formation of Cu1.8S, Ce2S3, ZnS, and MnS, respectively, with a capacity of 0.17, 0.12, 0.11, and 0.09 molS molM−1. The structure of MOx/C (M = Zn, Cu, Mn) evolved significantly during S-absorption reaction, with the formation of larger agglomerates and separation of MOx particles from porous C. The formation of ZnS NPs and their aggregation in place of hexagonal ZnO crystals indicate a dissolution/precipitation mechanism. Note that aggregated ZnS NPs barely sinter under these conditions. Cu(0) showed a preferential sulfidation over Cu2O, the sulfidation of the latter seemingly following the same mechanism as for ZnO. In contrast, FeOx/C and CeOx/C showed remarkable structural stability with their NPs well-dispersed within the C matrix after reaction. MOx dissolution in water (from liquid to supercritical state) was modeled and a correlation between solubility and particle growth was found, comforting the hypothesis of the importance of an Ostwald ripening mechanism. CeOx/C with high structural stability and promising S-absorption capacity was suggested as a promising bulk absorbent for sulfides in cHTG of biomass.

Catalytic hydrothermal gasification of aqueous effluents obtained from microwave torrefaction of agricultural residue

A significant amount of aqueous liquids rich in organic, inorganic contents and leached metals is produced during torrefaction of biomass, which requires additional remediation before disposal. Hydrothermal gasification can produce H2-rich syngas from organic wastes, especially from feedstocks with high-water content. This study presents a novel method of valorizing liquid effluents produced from the torrefaction of oat hull and canola hull via microwave irradiation. Hydrothermal gasification of the liquid effluents (feedstock) was carried out at 375–525 °C for 15–60 min with 1:5 and 1:10 feed-to-water ratios under 22–25 MPa pressure to optimize the operating parameters of the process. Hydrothermal gasification of torrefaction effluents from canola hull and oat hull produced total gas yields of 6.6 mmol/g and 8.7 mmol/g, respectively without the addition of water at optimized conditions (525 °C and 45 min). However, with the addition of water (i.e., 1:10 feed-to-water ratio), the total gas yield increased to 12 mmol/g and 16.1 mmol/g from oat hull and canola hull effluents, respectively. The highest H2 yields (7.8 mmol/g) and carbon gasification efficiency (51%) were obtained at 525 °C in 60 min with a 1:10 feed-to-water ratio. Homogeneous catalysts including KOH, K2CO3 and Na2CO3 were used to improve the gas yields from torrefaction effluents from oat hull at optimal conditions. H2 gas yield increased by 58%, 65% and 66% in presence of K2CO3, Na2CO3 and KOH, respectively. KOH led to maximum H2 yield, hydrogen selectivity and carbon gasification efficiency of 12.8 mmol/g, 89% and 98%, respectively.

Economic and environmental analysis of algal biorefinery for the production of renewable fuels and co-product

• Techno-economic and life cycle analysis of spirulina-based algal biorefinery is developed. • A minimum selling price (MSP) and GHG emissions are calculated for various pathways. • MSP of renewable fuels is found in the range of US$ 2.5/GGE - $3.94/GGE for various pathways. • GHG emission is found in the range of −59.2 - 147.4 g CO 2-eq /MJ for various pathways. The present study involves techno-economic and life cycle analysis of the production of renewable fuels with co-product from Spirulina platensis using hydrothermal liquefaction method (HTL). In the baseline pathway, the production of renewable fuels from HTL of spirulina is considered along with the utilisation of HTL aqueous phase being recycled back to the algal cultivation system. Various other pathways such as the utilisation of aqueous phase from HTL by catalytic hydrothermal gasification (CHG) and anaerobic digestion (AD) and the production of co-product of C-Phycocyanin (C-PC) (food grade pigment) from the spirulina are studied. Mass and energy balances of the various pathways are conducted using process engineering data available in the literature. It is found that the minimum selling price (MSP) of renewable fuels for the baseline pathway is 3.94 US$/GGE, whereas other pathways show 3.81 US$/GGE, 3.97 US$/GGE, and 2.5US$/GGE for CHG, AD, and C-PC extraction pathways, respectively. A global warming potential of total GHG emissions shows −59.2 g CO 2-eq /MJ, −20.2 g CO 2-eq /MJ, −49.2CO 2-eq /MJ, and 147.4 g CO 2-eq /MJ for baseline, CHG, AD, and C-PC extraction pathways, respectively. These values match with the literature. Further, the sensitivity study is conducted to obtain the most important parameters which are influences the MSP of renewable fuels.

Techno-Economic and Life-Cycle Analyses of Sustainable Aviation Fuel Production Via Integrated Catalytic Deoxygenation and Hydrothermal Gasification

Techno-Economic and Life-Cycle Analyses of Sustainable Aviation Fuel Production Via Integrated Catalytic Deoxygenation and Hydrothermal Gasification

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

Hydrothermal processes are promising technologies for an efficient valorization of wet biomass feedstocks or wastes. Their performance strongly depends on the composition of the feedstock, and methods to analyze such complex mixtures along with the produced effluents are in constant progress. Herein, catalytic hydrothermal gasification (cHTG) was used to valorize process water produced from the hydrothermal liquefaction of pine wood. A detailed analysis of the effluents and streams at various points of the process was performed. About 54% of the feed’s chemical energy could be transferred to synthetic natural gas while an excellent extraction of minerals (98%) into a concentrated brine (27 wt % dry matter) could be achieved. The low gasification efficiency observed and the origin of the 41% and 44% loss of chemical energy and carbon in the brine, respectively, were investigated by high-pressure liquid chromatography–high-resolution mass spectrometry (HPLC–HRMS) analysis of the feed and the effluents from the salt separator. This allowed for identifying mono- and polycarboxylates accounting for 71% of the carbon in the brine. Increasing temperature in the salt separator to favor decarboxylation reaction was identified as pivotal to improve synthetic natural gas yields, with a 20-fold decrease of carboxylate concentration being reached with a temperature rise from 723 to 768 K. The use of two new approaches to estimate the high heating value (HHV) of this feed rich in volatile organic compounds is also reported.

An In-Depth Process Model for Fuel Production via Hydrothermal Liquefaction and Catalytic Hydrotreating

One of the more promising technologies for future renewable fuel production from biomass is hydrothermal liquefaction (HTL). Although enormous progress in the context of continuous experiments on demonstration plants has been made in the last years, still many research questions concerning the understanding of the HTL reaction network remain unanswered. In this study, a unique process model of an HTL process chain has been developed in Aspen Plus® for three feedstock, microalgae, sewage sludge and wheat straw. A process chain consisting of HTL, hydrotreatment (HT) and catalytic hydrothermal gasification (cHTG) build the core process steps of the model, which uses 51 model compounds representing the hydrolysis products of the different biochemical groups lipids, proteins, carbohydrates, lignin, extractives and ash for modeling the biomass. Two extensive reaction networks of 272 and 290 reactions for the HTL and HT process step, respectively, lead to the intermediate biocrude (~200 model compounds) and the final upgraded biocrude product (~130 model compounds). The model can reproduce important characteristics, such as yields, elemental analyses, boiling point distribution, product fractions, density and higher heating values of experimental results from continuous experiments as well as literature values. The model can be applied as basis for techno-economic and environmental assessments of HTL fuel production, and may be further developed into a predictive yield modeling tool.

Modeling of cost optimized process integration of HTL fuel production

Hydrothermal liquefaction (HTL) is an advanced biomass conversion process for biocrude production from a broad variety of organic feedstock, including wet waste streams. The intermediate biocrudes can be further upgraded to liquid hydrocarbon fuels and thereby contribute to the mitigation of greenhouse gases from the transport sector. This work investigates an optimized sub-system integration of transportation fuel production via sub-critical HTL of primary sewage sludge. The plant design integrates HTL conversion, biocrude upgrading via hydrotreatment, and an energetic valorization of the residual aqueous phase from HTL conversion via catalytic hydrothermal gasification (cHTG). The option of on-site hydrogen production via reforming of cHTG gas is examined for the purpose of biocrude upgrading. The modeling results show that the hydrogen demand for hydrotreatment could be covered by the valorization of the HTL by-products. The thermal management of an integrated biofuel plant is optimized with respect to subsystem cost based on in-depth process modeling to quantify mass and energy flows and principles of pinch analysis to design a heat exchanger network. The cost optimized configuration results in an overall process energy efficiency of 40.5%. The results provide a basis for design choices for future HTL plants.

Bioenergy with carbon emissions capture and utilisation towards GHG neutrality: Power-to-Gas storage via hydrothermal gasification

The low efficiency of renewable electricity storage has been considered as a bottleneck of the scalable and low-carbon Power-to-Gas energy transformation concept. This paper investigates the combination of CO2 biofixation using Spirulina platensis microalgae and catalytic hydrothermal gasification of wet organic feedstock for the storage of fluctuating electricity and direct utilisation of waste CO2. The presented method enables wet microalgae biomass conversion into H2 and C1-C2 rich fuel gas stream using hydrothermal conversion that is valorised further to methane. For bridging the gap between theoretical investigations and the application of this approach, experiments were carried out at elevated temperatures (632.9-717.0 °C) based on a central composite design of the experiment. Biogas upgrading was evaluated by ASPEN Plus flowsheeting software. The results show that the proposed storage cycle outperforms the state-of-the-art biological and chemical-based Sabatier methanations with an overall round-trip efficiency of 42.3%. The optimised thermo-chemical process enables to achieve simultaneously high H2 (9.05 mol kg−1) and CH4 (7.91 mol kg−1) yields with an enhanced 71.23% carbon conversion ratio. Moreover, the environmental and cost evaluations of the currently proposed bio-synthetic process indicate low associated CO2 equivalent emission (99.4 ± 12.6 g CO2,eq kWh−1) with 144.9 €MWh-1 normalised total annual natural gas production cost. Ideally the proposed storage cycle requires less H2 from external sources, effective CO2 utilisation becomes available through the biofixation and hydrothermal conversion of the wet organic feedstock and closed carbon emission cycle can be accomplished.

System Design and Performance Evaluation of Wastewater Treatment Plants Coupled With Hydrothermal Liquefaction and Gasification

Wastewater treatment and sludge disposal are responsible for considerable costs and emissions in a global scale. With population and urbanization growing, tackling the rational and efficient use of energy while fulfilling the desired effluent standards are imperatives. In this work, a superstructure-based approach is designed to incorporate alternative treatments for wastewater; in particular, technologies like hydrothermal liquefaction and gasification, coupled with technologies for CO2 conversion to value-added products are studied. Multi-objective optimization is applied as a way to generate multiple solutions that correspond to different system configurations. From a reference treatment cost of almost 0.16 $/m^3WW, an environmental impact of 0.5 kgCO2/m^3WW and an energy efficiency of 5%, different configurations are able to transform a waste water treatment plant (WWTP) to a net profit unit, with a net environmental benefit and energy efficiency close to 65%. The investment in hydrothermal liquefaction producing biocrude coupled with catalytic hydrothermal gasification, demonstrated to yield consistently better total costs and environmental impacts. Parametric analysis is performed in the inlet flow of wastewater, to account for different sizes of WWTPs, with smaller inlets achieving values closer to those of the state-of-the-art configuration.

Sequential conversion of lignite in alkaline water by oxidative degradation, dissolution and catalytic gasification

We have demonstrated a sequence of degradation, dissolution and catalytic hydrothermal gasification (CHTG) of lignite in alkaline water. A Victorian lignite was subjected to hydrothermal treatment (HT) in an aqueous solution of NaOH at 250 °C, and then oxidation with pressurized O2 at 100 °C. The sequential HT and oxidation solubilized a 95% portion of the lignite on mass/carbon bases. The resulting solution was further converted by CHTG in a flow reactor at 350 °C for 10 h, employing a ruthenium/activated-charcoal catalyst (ruthenium loading; 16 wt%). The initial carbon conversion to gas was as high as 98% while CH4, CO2 and H2 were produced. The conversion gradually decreased due to coke deposition over the catalyst but was near steady around 83% at 8–10 h. The solubilized lignite consisted of compounds with molecular mass up to 5,000. The heavier portion (molecular mass > 1,000) was responsible for the coke formation and accumulation that caused the catalyst deactivation.

Fate and transport of estrogenic compounds in an integrated swine manure treatment systems combining algal-bacterial bioreactor and hydrothermal processes for improved water quality.

An integrated manure treatment system, including a mixed algal-bacterial bioreactor (MABB) and hydrothermal processing of biomass solids, was found to remove 76.4-97.0% of the total estrogenic hormones (estrone (E1), 17β-estradiol (E2), and estriol (E3)) from the liquid portion of animal manure (LPAM). The mixed biomass was converted into either biocrude oil with a yield up to 40% via hydrothermal liquefaction (HTL) or syngas with a yield up to 54% yield via catalytic hydrothermal gasification (CHG). Adding granular activated carbon (GAC) in the MABB enhanced the removal of estrogenic hormones (+ 7.2%), cytotoxicity (+ 58%), and heavy metals (+ 10.5%). After the integrated system with the MABB, HTL, and CHG processes, the overall percent removal of heavy metals from the LPAM ranged from 27.1 to 40.3%. The concentrations of potentially toxic heavy metals (lead (Pb), copper (Cu), zinc (Zn), cadmium (Cd), nickel (Ni), chromium (Cr)) in the aqueous phase after HTL and CHG tests ranged from 0.01 to 25.3 mg/L.

Techno-economic analysis of alternative aqueous phase treatment methods for microalgae hydrothermal liquefaction and biocrude upgrading system

An economic analysis was conducted for an algae hydrothermal liquefaction (HTL) and biocrude upgrading system with alternative aqueous phase treatment methods. Using experimental data, three different methods were modeled and compared: 1) direct recycle of HTL aqueous phase to the algae farm, 2) catalytic hydrothermal gasification (CHG), and 3) anaerobic digestion (AD). Direct recycle consumes the most natural gas because unlike AD and CHG, no methane is generated from the aqueous phase organics conversion. However, direct recycle has the lowest cost compared to other two cases because it only requires the addition of pumps and buffer tankage related to the aqueous phase recycle. The CHG and AD cases require significant capital and operating costs for aqueous phase treatment, which increase the minimum fuel selling price (MFSP) over the direct recycle case by 11% and 2.9%, respectively. The CHG and AD respectively increase the conversion cost only (excludes the cost to grow, harvest, and dewater algae) by 75% and 21%. Sensitivity analysis suggests that the key factors affecting the total cost of fuel production are the feedstock cost, the biocrude yield, the plant scale, and the method of aqueous phase treatment.

Biohythane production of post-hydrothermal liquefaction wastewater: A comparison of two-stage fermentation and catalytic hydrothermal gasification

Developing efficient methods to recover energy from post-hydrothermal liquefaction wastewater (PHW) is critical for scaling up hydrothermal liquefaction (HTL) technology. Here we evaluated two-stage fermentation (TF) and catalytic hydrothermal gasification (CHG) for biohythane production using PHW. A hydrogen yield of 29 mL·g−1 COD and methane yield of 254 mL·g−1 COD were achieved via TF. In comparison, a higher hydrogen yield (116 mL·g−1 COD) and lower methane yield (65 mL·g−1 COD) were achieved during CHG. Further, a techno-economic and sensitivity analysis was conducted. The capital cost and operating cost for TF varied with the different reactor systems. TF with high-rate reactors suggested its promising commercialized application as it had a lower minimum selling price (−0.71 to 2.59 USD per gallon of gasoline equivalent) compared with conventional fossil fuels under both the best and reference market conditions. Compared with TF, CHG was only likely to be profitable under the best case conditions.

A two-step process for sewage sludge treatment: Hydrothermal treatment of sludge and catalytic hydrothermal gasification of its derived liquid

The worldwide increase in amount of sewage sludge has recently attracted considerable interest in developing an efficient and economical sludge disposal method. A sewage sludge treatment process combining the hydrothermal treatment (HT) of sludge and the catalytic hydrothermal gasification (CHTG) of its derived liquid (HT&CHTG-Process) is proposed in this paper. Liquid hourly space velocity (LHSV) value of 25–100 h−1 and liquid flow rate of 10–40 mL/min were employed with a self-designed CHTG experimental setup. During the first stage of the HT-Process, approximately 56% of the carbon in the sludge was transferred into the derived liquid at 300 °C. During the second stage of the CHTG-Process, the derived liquid was gasified into CH4, H2, and CO2 using a Ni/carbon catalyst, and the carbon conversion reached 88% at 350 °C and 20 MPa with a LHSV of 25 h−1. Using the integrated HT&CHGT-Process, approximately 0.78 Nm3 of CH4, 0.62 Nm3 of H2 and 0.31 Nm3 of CO2 were generated from 1 kg of carbon in the sewage sludge. The combined process was expected to be an efficient method for sewage sludge treatment due to its mild conditions (≤350 °C and ≤20 MPa) and high yield of fuel gases.

Influence of promoted bimetallic Ni-based catalysts and Micro/Mesopores carbonaceous supports for biomass hydrothermal conversion to H2-rich gas

We report herein, a green route of energy generation from lignocellulosic wastes, the production of H2 from catalytic hydrothermal gasification of Iranian canola stalks (CS). Firstly, we performed the non-catalytic tests in a stainless-steel batch micro reactor to determine the impacts of operational parameters (temperature, time and feedstock concentration) and optimize them. The achieved optimized control factors were found to be 440 °C and 20 min, and 2.5 wt% for temperature, reaction time, and feed concentration, respectively. Furthermore, the optimum control factors were used to examine the impacts of Ni catalysts supported on two different supports (activated carbon (AC) and Graphene Nano sheets (GNS)) on the mole fractions and yields of H2 in details. Hence, we investigated the impacts of novel bimetallic catalysts, (Ni-Ru, Ni-Co, and Ni-Cu) supported on GNS for the first time and the optimized catalyst promoter was also impregnated separately on AC to improve and achieve the highest H2 yield possible. Among the prepared catalysts, the Ni-Cu/AC catalyst showed the best performance with the highest H2 gas yield and lowest methane production of 20.96 and 2.19 (mmolgas. g−1CS), respectively. H2 gas production was monitored during the HTG process using gas chromatography and the physiochemical properties of the prepared catalysts were also examined by various techniques.

Comparative evaluation for catalytic gasification of petroleum coke and asphaltene in subcritical and supercritical water

Abstract Subcritical and supercritical water gasification of petroleum coke and asphaltene was performed at variable temperatures (350–650 °C), feed concentrations (15–30 wt%) and reaction times (15–60 min). Nickel-impregnated activated carbon (Ni/AC) was synthesized as a catalyst for enhancing syngas yields at optimal gasification conditions (650 °C, 15 wt% and 60 min). Structural chemistry of precursors and chars developed at different gasification temperatures was studied using physicochemical and synchrotron-based approaches such as carbon–hydrogen–nitrogen–sulfur (CHNS) analysis, thermogravimetric and differential thermogravimetric analysis (TGA/DTA), scanning electron microscopy (SEM), Fourier-Transform Infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Asphaltene testified to be a better precursor for catalytic hydrothermal gasification leading to 11.97 mmol/g of total gas yield compared to petroleum coke (8.04 mmol/g). In particular, supercritical water gasification using 5 wt% Ni/AC at 650 °C with 15 wt% feed concentration for 60 min resulted in 4.17 and 2.98 mmol/g of H2 from asphaltene and petroleum coke, respectively. Under the same conditions, the respective CH4 yields from catalytic gasification of asphaltene and petroleum coke were 2.54 and 1.07 mmol/g. Nonetheless, asphaltene also seemed to an attractive feedstock for the production of highly aromatic chars through hydrothermal gasification.

Bench-Scale Evaluation of Hydrothermal Processing Technology for Conversion of Wastewater Solids to Fuels.

Hydrothermal Liquefaction (HTL) and Catalytic Hydrothermal Gasification (CHG) proof-of-concept bench-scale tests were performed to assess the potential of hydrothermal treatment for handling municipal wastewater sludge. HTL tests were conducted at 300 to 350 °C and 20 MPa on three different feeds: primary sludge, secondary sludge, and digested solids. Corresponding CHG tests were conducted at 350 °C and 20 MPa on the HTL aqueous phase output using a ruthenium-based catalyst. Biocrude yields ranged from 25 to 37%. Biocrude composition and quality were comparable to biocrudes generated from algae feeds. Subsequent hydrotreating of biocrude resulted in a product with comparable physical and chemical properties to crude oil. CHG product gas methane yields on a carbon basis ranged from 47 to 64%. Siloxane concentrations in the CHG product gas were below engine limits. The HTL-CHG process resulted in a chemical oxygen demand (COD) reduction of > 99.9% and a reduction in residual solids for disposal of 94 to 99%.