Prediction of Individual Gas Yields of Supercritical Water Gasification of Lignocellulosic Biomass by Machine Learning Models.

Supercritical water gasification (SCWG) of lignocellulosic biomass is a promising pathway for the production of hydrogen. However, SCWG is a complex thermochemical process, the modeling of which is challenging via conventional methodologies. Therefore, eight machine learning models (linear regression (LR), Gaussian process regression (GPR), artificial neural network (ANN), support vector machine (SVM), decision tree (DT), random forest (RF), extreme gradient boosting (XGB), and categorical boosting regressor (CatBoost)) with particle swarm optimization (PSO) and a genetic algorithm (GA) optimizer were developed and evaluated for prediction of H2, CO, CO2, and CH4 gas yields from SCWG of lignocellulosic biomass. A total of 12 input features of SCWG process conditions (temperature, time, concentration, pressure) and biomass properties (C, H, N, S, VM, moisture, ash, real feed) were utilized for the prediction of gas yields using 166 data points. Among machine learning models, boosting ensemble tree models such as XGB and CatBoost demonstrated the highest power for the prediction of gas yields. PSO-optimized XGB was the best performing model for H2 yield with a test R2 of 0.84 and PSO-optimized CatBoost was best for prediction of yields of CH4, CO, and CO2, with test R2 values of 0.83, 0.94, and 0.92, respectively. The effectiveness of the PSO optimizer in improving the prediction ability of the unoptimized machine learning model was higher compared to the GA optimizer for all gas yields. Feature analysis using Shapley additive explanation (SHAP) based on best performing models showed that (21.93%) temperature, (24.85%) C, (16.93%) ash, and (29.73%) C were the most dominant features for the prediction of H2, CH4, CO, and CO2 gas yields, respectively. Even though temperature was the most dominant feature, the cumulative feature importance of biomass characteristics variables (C, H, N, S, VM, moisture, ash, real feed) as a group was higher than that of the SCWG process condition variables (temperature, time, concentration, pressure) for the prediction of all gas yields. SHAP two-way analysis confirmed the strong interactive behavior of input features on the prediction of gas yields.

Catalytic Supercritical Water Gasification of Canola Straw with Promoted and Supported Nickel-Based Catalysts.

Lignocellulosic biomass such as canola straw is produced as low-value residue from the canola processing industry. Its high cellulose and hemicellulose content makes it a suitable candidate for the production of hydrogen via supercritical water gasification. However, supercritical water gasification of lignocellulosic biomass such as canola straw suffers from low hydrogen yield, hydrogen selectivity, and conversion efficiencies. Cost-effective and sustainable catalysts with high catalytic activity for supercritical water gasification are increasingly becoming a focal point of interest. In this research study, novel wet-impregnated nickel-based catalysts supported on carbon-negative hydrochar obtained from hydrothermal liquefaction (HTL-HC) and hydrothermal carbonization (HTC-HC) of canola straw, along with other nickel-supported catalysts such as Ni/Al2O3, Ni/ZrO2, Ni/CNT, and Ni/AC, were synthesized for gasification of canola straw on previously optimized reaction conditions of 500 °C, 60 min, 10 wt%, and 23-25 MPa. The order of hydrogen yield for the six supports was (10.5 mmol/g) Ni/ZrO2 > (9.9 mmol/g) Ni/Al2O3 > (9.1 mmol/g) Ni/HTL-HC > (8.8 mmol/g) Ni/HTC-HC > (7.7 mmol/g) Ni/AC > (6.8 mmol/g) Ni/CNT, compared to 8.1 mmol/g for the non-catalytic run. The most suitable Ni/ZrO2 catalyst was further modified using promotors such as K, Zn, and Ce, and the performance of the promoted Ni/ZrO2 catalysts was evaluated. Ni-Ce/ZrO2 showed the highest hydrogen yield of 12.9 mmol/g, followed by 12.0 mmol/g for Ni-Zn/ZrO2 and 11.6 mmol/g for Ni-K/ZrO2. The most suitable Ni-Ce/ZrO2 catalysts also demonstrated high stability over their repeated use. The superior performance of the Ni-Ce/ZrO2 was due to its high nickel dispersion, resilience to sintering, high thermal stability, and oxygen storage capabilities to minimize coke deposition.

A Review of the Design and Performance of Catalysts for Hydrothermal Gasification of Biomass to Produce Hydrogen-Rich Gas Fuel.

Supercritical water gasification has emerged as a promising technology to sustainably convert waste residues into clean gaseous fuels rich in combustible gases such as hydrogen and methane. The composition and yield of gases from hydrothermal gasification depend on process conditions such as temperature, pressure, reaction time, feedstock concentration, and reactor geometry. However, catalysts also play a vital role in enhancing the gasification reactions and selectively altering the composition of gas products. Catalysts can also enhance hydrothermal reforming and cracking of biomass to achieve desired gas yields at moderate temperatures, thereby reducing the energy input of the hydrothermal gasification process. However, due to the complex hydrodynamics of supercritical water, the literature is limited regarding the synthesis, application, and performance of catalysts used in hydrothermal gasification. Hence, this review provides a detailed discussion of different heterogeneous catalysts (e.g., metal oxides and transition metals), homogeneous catalysts (e.g., hydroxides and carbonates), and novel carbonaceous catalysts deployed in hydrothermal gasification. The article also summarizes the advantages, disadvantages, and performance of these catalysts in accelerating specific reactions during hydrothermal gasification of biomass, such as water-gas shift, methanation, hydrogenation, reforming, hydrolysis, cracking, bond cleavage, and depolymerization. Different reaction mechanisms involving a variety of catalysts during the hydrothermal gasification of biomass are outlined. The article also highlights recent advancements with recommendations for catalytic supercritical water gasification of biomass and its model compounds, and it evaluates process viability and feasibility for commercialization.

Valorization of Wild-Type Cannabis indica by Supercritical CO2 Extraction and Insights into the Utilization of Raffinate Biomass

Supercritical CO2 extraction (SCCO2) extraction of cannabis oil from Indian cannabis (Cannabis indica) leaves was optimized through a central composite design using CO2 pressure (150-250 bar), temperature (30-50 °C) and time (1-2 h). From the regression model, the optimal CO2 pressure, extraction temperature and time were 250 bar, 43 °C and 1.7 h, respectively resulting in the experimental yield of 4.9 wt% of cannabis oil via SCCO2 extraction. The extract contained cannabidiol, tetrahydrocannabivarin, Δ9-tetrahydrocannabinol and Δ8-tetrahydrocannabinol as well as two terpenoids such as cis-caryophyllene and α-humulene. Besides SCCO2 extraction of cannabis oil, the raffinate biomass was utilized to extract polyphenols using water as the extraction medium. Cannabis oil and water extractive were investigated for their half-maximal inhibitory concentration (IC50) values, which were found to be 1.3 and 0.6 mg/mL, respectively. This is comparable to the commercially available antioxidant such as butylated hydroxytoluene with an IC50 value of 0.5 mg/mL. This work on SCCO2 extraction of cannabinoids and other valuable bioactive compounds provides an environmentally sustainable technique to valorize cannabis leaves.

Innovations in applications and prospects of bioplastics and biopolymers: a review.

Non-biodegradable plastics are continually amassing landfills and oceans worldwide while creating severe environmental issues and hazards to animal and human health. Plastic pollution has resulted in the death of millions of seabirds and aquatic animals. The worldwide production of plastics in 2020 has increased by 36% since 2010. This has generated significant interest in bioplastics to supplement global plastic demands. Bioplastics have several advantages over conventional plastics in terms of biodegradability, low carbon footprint, energy efficiency, versatility, unique mechanical and thermal characteristics, and societal acceptance. Bioplastics have huge potential to replace petroleum-based plastics in a wide range of industries from automobiles to biomedical applications. Here we review bioplastic polymers such as polyhydroxyalkanoate, polylactic acid, poly-3-hydroxybutyrate, polyamide 11, and polyhydroxyurethanes; and cellulose-based, starch-based, protein-based and lipid-based biopolymers. We discuss economic benefits, market scenarios, chemistry and applications of bioplastic polymers.

Reactive adsorption of Safranin O: surface - pore diffusion modeling and degradation study.

Granular activated carbon was doped with iron (Fe-AC) and was used to study the removal of Safranin O (SO) using the Fe-AC/H2O2 system for reactive adsorption and Fe-AC for adsorption. Fe-AC and H2O2 doses were optimized to obtain maximum removal of SO. Maximum removal was found to be 96.1% after 5 h using 1.0 g/L Fe-AC and 5.0 mM hydrogen peroxide doses for 10 mg/L initial SO concentration. Kinetic study suggested the suitability of the pseudo-first-order model for reactive adsorption. The Langmuir isotherm explained well the sorption of SO onto Fe-AC. Parallel-pore-reactive adsorption model was applied and validated. By fitting the experimental data to the model, it is observed that the surface reaction rate coefficient, kr, was found to be five times that of the apparent rate constant, kapp. Parameters such as the external liquid film mass transfer coefficient, macro-pore and micro-pore diffusivities were estimated by regression analysis. Pore diffusion and surface reaction were found to be rate controlling for adsorption and reactive adsorption, respectively. An oxidative degradation of SO took place via hydroxylation and ring cleavage processes.

Review of post-combustion carbon dioxide capture technologies using activated carbon.

Carbon dioxide (CO2) is the largest anthropogenic greenhouse gas (GHG) on the planet contributing to the global warming. Currently, there are three capture technologies of trapping CO2 from the flue gas and they are pre-combustion, post-combustion and oxy-fuel combustion. Among these, the post-combustion is widely popular as it can be retrofitted for a short to medium term without encountering any significant technology risks or changes. Activated carbon is widely used as a universal separation medium with series of advantages compared to the first generation capture processes based on amine-based scrubbing which are inherently energy intensive. The goal of this review is to elucidate the three CO2 capture technologies with a focus on the use of activated carbon (AC) as an adsorbent for post-combustion anthropogenic CO2 flue gas capture prior to emission to atmosphere. Furthermore, this coherent review summarizes the recent ongoing research on the preparation of activated carbon from various sources to provide a profound understanding on the current progress to highlight the challenges of the CO2 mitigation efforts along with the mathematical modeling of CO2 capture. AC is widely seen as a universal adsorbent due to its unique properties such as high surface area and porous texture. Other applications of AC in the removal of contaminants from flue gas, heavy metal and organic compounds, as a catalyst and catalyst support and in the electronics and electroplating industry are also discussed in this study.

Breakthrough CO2 adsorption in bio-based activated carbons.

In this work, the effects of different methods of activation on CO2 adsorption performance of activated carbon were studied. Activated carbons were prepared from biochar, obtained from fast pyrolysis of white wood, using three different activation methods of steam activation, CO2 activation and Potassium hydroxide (KOH) activation. CO2 adsorption behavior of the produced activated carbons was studied in a fixed-bed reactor set-up at atmospheric pressure, temperature range of 25-65°C and inlet CO2 concentration range of 10-30 mol% in He to determine the effects of the surface area, porosity and surface chemistry on adsorption capacity of the samples. Characterization of the micropore and mesopore texture was carried out using N2 and CO2 adsorption at 77 and 273 K, respectively. Central composite design was used to evaluate the combined effects of temperature and concentration of CO2 on the adsorption behavior of the adsorbents. The KOH activated carbon with a total micropore volume of 0.62 cm(3)/g and surface area of 1400 m(2)/g had the highest CO2 adsorption capacity of 1.8 mol/kg due to its microporous structure and high surface area under the optimized experimental conditions of 30 mol% CO2 and 25°C. The performance of the adsorbents in multi-cyclic adsorption process was also assessed and the adsorption capacity of KOH and CO2 activated carbons remained remarkably stable after 50 cycles with low temperature (160°C) regeneration.

Hydrothermal Carbonization of Green Harvesting Residues (GHRs) from Sugar Cane: Effect of Temperature and Water/GHR Ratio on Mass and Energy Yield.

The Valle del Cauca region in Colombia is a significant producer of sugar cane, resulting in large quantities of agricultural residues (green harvesting residues (GHRs)). To ensure sustainable management of these residues, it is crucial to implement proper treatment and disposal technologies while also reusing waste to produce biogas, bioelectricity, or biofuels. The biomass hydrothermal carbonization process offers a means to convert these residues into useful products that serve as fuels or valuable energy materials. This thermal treatment involves the use of water as a solvent and reagent within the biomass's internal structure. In this study, sugar cane cutting residues were collected with relatively high moisture content of 8.5% wt. These residues were subjected to carbonization temperatures ranging from 200 to 300 °C, along with water/GHR ratios between 5/1 and 10/1. The properties of the resulting hydrocarbons were analyzed by using proximate and ultimate analysis. The objective was to produce hydrochar samples with the highest higher heating value (HHV) and energy density compared with the GHRs. The HHV value of the hydrochar showed a significant increase of 69.6% compared with that of the GHRs, reaching 43.5 MJ/kg. Besides, process parameters were optimized for mass yields, energy yields, and ash content. This exploration led us to investigate a new temperature range between 280 and 320 °C, allowing us to establish an optimal value for the hydrochar's properties.

Occurrence, distribution, and toxicity assessment of polycyclic aromatic hydrocarbons in biochar, biocrude, and biogas obtained from pyrolysis of agricultural residues.

Occurrence, distribution, and toxicity assessment of polycyclic aromatic hydrocarbons (PAHs) in pyrolysis steams (biochar, biocrude, and biogas) of three agricultural residues was investigated at pyrolysis temperatures of 400-800 °C. Increasing PAHs formation was observed in the narrow temperature range (500-600 °C) in all feedstocks due to temperature-induced dehydration, decarboxylation, and dehydrogenation reactions. Low molecular weight PAHs (naphthalene, phenanthrene) were dominant in all product streams while high molecular weight PAHs were found in negligible concentrations. Leaching studies showed that pyrolyzed biochars produced at lower temperatures are more prone to leaching due to the presence of hydrophilic amorphous uncarbonized structures, while the presence of hydrophobic carbonized matrix with denser and stronger polymetallic complex prevents the leaching of PAHs in the high temperature pyrolyzed biochar. Low leaching potential, low toxic equivalency, and permissible total PAHs values in biochar derived from all three feedstocks warrant the broader application and ensure ecological safety.

Energy recovery from agro-forest wastes through hydrothermal carbonization coupled with hydrothermal co-gasification: Effects of succinic acid on hydrochars and H2 production.

Aiming to upgrade agro-forest wastes into value-added solid and gaseous fuels in the present investigation, hydrothermal carbonization (HTC) of spruce (SP), canola hull (CH), and canola meal (CM) was optimized in terms of operating conditions, maximizing the higher heating value of hydrochars. The optimal operating conditions were achieved at HTC temperature, reaction time, and solid-to-liquid ratio of 260 °C, 60 min, and 0.2 g mL-1, respectively. At the optimum condition, succinic acid (0.05-0.1 M) was used as HTC reaction medium to investigate the effects of acidic medium on the fuel characteristics of hydrochars. The succinic acid assisted HTC was found to eliminate ash-forming minerals e.g., K, Mg, and Ca from hydrochar backbones. The calorific values, H/C and O/C atomic ratios of hydrochars were in the range of 27.6-29.8 MJ kg-1, 0.8-1.1, and 0.1-0.2, respectively, indicating the biomass upgrading into coal-like solid fuels. Finally, hydrothermal gasification of hydrochars with their corresponding HTC aqueous phase (HTC-AP) was assessed. Gasification of CM resulted in a relatively high H2 yield of 4.9-5.5 mol kg-1 followed by that for SP with 4.0-4.6 mol H2 per kg of hydrochars. Results suggest that hydrochars and HTC-AP have a great potential for H2 production via hydrothermal co-gasification, while suggesting HTC-AP reuse.

Perspectives on Thermochemical Recycling of End-of-Life Plastic Wastes to Alternative Fuels.

Due to its resistance to natural degradation and decomposition, plastic debris perseveres in the environment for centuries. As a lucrative material for packing industries and consumer products, plastics have become one of the major components of municipal solid waste today. The recycling of plastics is becoming difficult due to a lack of resource recovery facilities and a lack of efficient technologies to separate plastics from mixed solid waste streams. This has made oceans the hotspot for the dispersion and accumulation of plastic residues beyond landfills. This article reviews the sources, geographical occurrence, characteristics and recyclability of different types of plastic waste. This article presents a comprehensive summary of promising thermochemical technologies, such as pyrolysis, liquefaction and gasification, for the conversion of single-use plastic wastes to clean fuels. The operating principles, drivers and barriers for plastic-to-fuel technologies via pyrolysis (non-catalytic, catalytic, microwave and plasma), as well as liquefaction and gasification, are thoroughly discussed. Thermochemical co-processing of plastics with other organic waste biomass to produce high-quality fuel and energy products is also elaborated upon. Through this state-of-the-art review, it is suggested that, by investing in the research and development of thermochemical recycling technologies, one of the most pragmatic issues today, i.e., plastics waste management, can be sustainably addressed with a greater worldwide impact.

Techno-economic analysis of torrefied fuel pellet production from agricultural residue via integrated torrefaction and pelletization process.

Torrefied pellets have gained more commercial importance due to their excellent performance in combustion, co-firing and gasification. The present investigation provides a conceptual design for torrefied fuel pellets production via combined torrefaction and pelletization technologies with and without additives. The entire design contains torrefaction unit, grinding, preparation of pellet formulation, pelletizing, and finally cooling of pellets. Two scenarios, scenario 1 (pelletization of torrefied biomass with additives) and scenario 2 (pelletization of torrefied biomass without any external additives) were tested and compared. The economic analysis suggests that both scenarios are profitable. Both scenarios were simulated using Aspen plus™, and economic feasibility was estimated using a complete cash flow analysis for a base case plant with 40,080 tonne/y capacity. For both cases, a discounted cash flow is a useful tool for estimating the minimal selling price for torrefied pellets as well as the capital investment, production cost and operating costs. The cost of the reactor used for torrefaction was found to be the most important component of combined torrefaction and pelletization system. The lowest selling price of generated torrefied pellets was found to be $103.4 and $105.1 per tonne at the plant gate for scenarios 1 and 2, respectively. Sensitivity analysis shows that, among all variable costs, labor cost has the highest influence on both net present value (NPV) and minimum selling price (MSP) in making pellets for both the scenarios. Furthermore, the internal rate of return was found to be25% and 22% at 10% discounted cash flow rate for scenarios 1 and 2, respectively. The framework that was created was found to lessen over-dependence on wood or fossil fuels and facilitate the promotion of bioenergy in rural areas.

Experimental and Modeling Studies of Torrefaction of Spent Coffee Grounds and Coffee Husk: Effects on Surface Chemistry and Carbon Dioxide Capture Performance.

Torrefaction of biomass is a promising thermochemical pretreatment technique used to upgrade the properties of biomass to produce solid fuel with improved fuel properties. A comparative study of the effects of torrefaction temperatures (200, 250, and 300 °C) and residence times (0.5 and 1 h) on the quality of torrefied biomass samples derived from spent coffee grounds (SCG) and coffee husk (CH) were conducted. An increase in torrefaction temperature (200-300 °C) and residence time (0.5-1 h) for CH led to an improvement in the fixed carbon content (17.9-31.8 wt %), calorific value (18.3-25 MJ/kg), and carbon content (48.5-61.2 wt %). Similarly, the fixed carbon content, calorific value, and carbon content of SCG rose by 14.6-29 wt %, 22.3-30.3 MJ/kg, and 50-69.5 wt %, respectively, with increasing temperature and residence time. Moreover, torrefaction led to an improvement in the hydrophobicity and specific surface area of CH and SCG. The H/C and O/C atomic ratios for both CH- and SCG-derived torrefied biomass samples were in the range of 0.93-1.0 and 0.19-0.20, respectively. Moreover, a significant increase in volatile compound yield was observed at temperatures between 250 and 300 °C. Maximum volatile compound yields of 11.9 and 6.2 wt % were obtained for CH and SCG, respectively. A comprehensive torrefaction model for CH and SCG developed in Aspen Plus provided information on the mass and energy flows and the overall process energy efficiency. Based on the modeling results, it was observed that with increasing torrefaction temperature to 300 °C, the mass and energy yield values of the torrefied biomass samples declined remarkably (97.3% at 250 °C to 67.5% at 300 °C for CH and 96.7% at 250 °C to 75.1% at 300 °C for SCG). The SCG-derived torrefied biomass tested for CO2 adsorption at 25 °C had a comparatively higher adsorption capacity of 0.38 mmol/g owing to its better textural characteristics. SCG would need further thermal treatment or functionalization to tailor the surface properties to attract more CO2 molecules under a typical post-combustion scenario.

Cannabis: Chemistry, extraction and therapeutic applications.

Cannabis, a genus of perennial indigenous plants is well known for its recreational and medicinal activities. Cannabis and its derivatives have potential therapeutic activities to treat epilepsy, anxiety, depression, tumors, cancer, Alzheimer's disease, Parkinson's disease, to name a few. This article reviews some recent literature on the bioactive constituents of Cannabis, commonly known as phytocannabinoids, their interactions with the different cannabinoids and non-cannabinoid receptors as well as the significances of these interactions in treating various diseases and syndromes. The biochemistry of some notable cannabinoids such as tetrahydrocannabinol, cannabidiol, cannabinol, cannabigerol, cannabichromene and their carboxylic acid derivatives is explained in the context of therapeutic activities. The medicinal features of Cannabis-derived terpenes are elucidated for treating several neuro and non-neuro disorders. Different extraction techniques to recover cannabinoids are systematically discussed. Besides the medicinal activities, the traditional and recreational utilities of Cannabis and its derivatives are presented. A brief note on the legalization of Cannabis-derived products is provided. This review provides comprehensive knowledge about the medicinal properties, recreational usage, extraction techniques, legalization and some prospects of cannabinoids and terpenes extracted from Cannabis.

Comparative study on fuel characteristics and pyrolysis kinetics of corn residue-based hydrochar produced via microwave hydrothermal carbonization.

Corn residues are an important source of bioenergy. Due to their highly diverse lignocellulosic structures, the hydrochar produced from microwave-assisted carbonization of different corn residues may have distinct fuel properties and pyrolysis kinetics. This study comprehensively investigated the effect of processing temperature on the basic fuel properties of hydrochar and examined the pyrolysis behavior of hydrochar as a precursor through kinetic analysis. The results indicate that the fuel quality of corn straw hydrochar prepared by microwave-assisted hydrothermal carbonization at 230 °C was significantly improved over that of its feedstock, with a higher heating value of approximately 20.7 MJ/kg. Hydrochar prepared by microwave-assisted hydrothermal carbonization of corn cob at 230 °C presents noticeable environmental advantages because it contains the lowest ash and nitrogen contents (0.5% and 0.5%, respectively) and lower sulfur content (0.05%). Moreover, regarding the kinetic modeling, the Doyle and Coats-Redfern models, which are both first-order and single-step kinetic models, were identified as satisfactory in interpreting the key pyrolysis kinetic parameters. Additionally, the microwave-assisted hydrothermal process increased the apparent activation energy of hydrochar due to the increase in crystallinity and the increase in the number of CC and CO bonds.

Hydrothermal flames for subaquatic, terrestrial and extraterrestrial applications.

Hydrothermal flames are formed in supercritical water in the presence of a fuel and an oxidant (usually air or oxygen). Integrating hydrothermal flames as the heat source for supercritical water oxidation helps to minimize the reaction time (to milliseconds), improve the reaction kinetics and reduce the chances of corrosion and reactor plugging. This review outlines state-of-the-art research on hydrothermal flames including the impacts of process parameters on flame ignition. The ignition and sustainability of hydrothermal flames are dependent on several factors such as the type of fuel and its concentration, type of oxidant (air and oxygen) as well as the temperatures and flow rate of the feed and oxidant. The article describes some novel applications of hydrothermal flames for clean energy production, geothermal energy recovery, deep well spallation, wastewater treatment, degradation of recalcitrant nitrogen-containing compounds and heavy oil upgrading. Finally, the challenges and future perspectives of hydrothermal flame applications are discussed. This review also highlights some technical considerations relating to hydrothermal flames such as the choice of organic solvent and its characteristics, preheating, ignition mechanism, flame stability and propagation, advanced reactor configurations, mixing with subcritical and supercritical components, recirculation zones, cooling mechanisms, corrosion and salt precipitation.

Thermal and Kinetic Studies on Biomass Degradation via Thermogravimetric Analysis: A Combination of Model-Fitting and Model-Free Approach.

Thermal degradation behavior and kinetics of two agricultural (soy and oat hulls) and two forestry biomass (willow and spruce) residues were investigated using a unique combination of model-fitting and model-free methods. Experiments were carried out in an inert atmosphere at different heating rates. Both single step and multistep models were explored in deriving activation energies, frequency factors, and mechanisms of all four biomass residues. For the single step models, activation energy values ranged from 107.2 kJ/mol for willow and 139.7 kJ/mol for soy hull, and the frequency factors for both materials were 1.1 × 109 and 2.66 × 1012 s-1, respectively. The multistep models gave further insight into the different mechanisms across the full degradation spectrum. There was an observed difference between the number of distinct steps/mechanisms for the agriculture-based versus wood-based biomass materials, with pyrolysis occurring in three distinct steps for the agricultural biomass residues while the woody residues degraded in two steps. The difference in the number of distinct steps can be attributed to the composition and distribution of components of the biomass, which would differ based on the nature and source of the biomass.

Techno-economic evaluation and sensitivity analysis of a conceptual design for supercritical water gasification of soybean straw to produce hydrogen.

This paper proposes a conceptual design for the catalytic supercritical water gasification of soybean straw. The design consists of four process units for pretreatment, gasification, separation, purification and combustion. The economic feasibility of hydrogen production was evaluated based on a comprehensive cash flow analysis. The economic analysis suggested a minimum selling price of U.S. $1.94/kg for hydrogen. The cost of hydrogen produced is relatively lower compared to that of other biomass conversion processes. Besides, the net rate of return (NRR) estimated was 37.1%. A positive NRR value indicates that the project is profitable from an economic perspective. Sensitivity analysis indicates that the minimum selling price of hydrogen is affected by the feedstock price, utility cost, tax rate and labor cost. Moreover, feedstock price and labor cost show the greatest effect. Other factors such as land cost, working capital and utility cost showed the least effect on the minimum selling price.

Optimization studies for hydrothermal gasification of partially burnt wood from forest fires for hydrogen-rich syngas production using Taguchi experimental design.

Forest fires significantly affect the wildlife, vegetation, composition and structure of the forests. This study explores the potential of partially burnt wood recovered in the aftermath of a recent Canadian forest fire incident as a feedstock for generating hydrogen-rich syngas through hydrothermal gasification. Partially burnt wood was gasified in hydrothermal conditions to study the influence of process temperature (300-500 °C), residence time (15-45 min), feed concentration (10-20 wt%) and biomass particle size (0.13 mm and 0.8 mm) using the statistical Taguchi method. Maximum hydrogen yield and total gas yield of 5.26 mmol/g and 11.88 mmol/g, respectively were obtained under optimized process conditions at 500 °C in 45 min with 10 wt% feed concentration using biomass particle size of 0.13 mm. The results from the mean of hydrogen yield show that the contribution of each experimental factors was in the order of temperature > feed concentration > residence time > biomass particle size. Other gaseous products obtained at optimum conditions include CO2 (3.43 mmol/g), CH4 (3.13 mmol/g) and C2-C4 hydrocarbons (0.06 mmol/g).