Supercritical water gasification of lignocellulosic biomass materials for hydrogen production

The primary aim of this research is to optimize supercritical water gasification process operating conditions and develop a cost effective heterogeneous catalyst to reduce reaction temperature and improve H2 yield. Furthermore, a detailed techno- economic feasibility study was performed to evaluate the economic feasibility of SCWG process. The work plan is divided into five phases. In the phase one, model lignocellulosic biomass comprising of cellulose, hemicellulose and lignin were selected as the feedstock for SCWG process optimization. The objective of the study was to optimize the process conditions, propose a detailed reaction pathway for model compounds and understand how each intermediate product behaves under subcritical and supercritical conditions. The response surface methodology using the Box-Behnken design was applied for the first time to optimize the process parameters during subcritical and supercritical water gasification of cellulose. The process parameters investigated include temperature (300-500 °C), reaction time (30-60 min) and feedstock concentration (10-30 wt%). Temperature was found to be the most significant factor that influenced the yields of hydrogen and total gas yield. Among the three model compounds, hydrogen yields increased in the order of lignin (0.73 mmol/g) < cellulose (1.95 mmol/g) < xylose (2.26 mmol/g). Based on the gas yields from these model compounds, a reaction pathway of model lignocellulosic biomass decomposition in supercritical water was proposed. The results from the first phase raised several research questions, for example, does biomass heterogeneity have an effect on product yield? How far are the batch experimental results from equilibrium values when considering a real feedstock? Lignocellulosic biomass is heterogeneous in nature and it comprises of several molecules of different compounds including cellulose, hemicellulose, and lignin along with extractives. Lignocellulosic biomass (soybean straw and flax straw) were gasified under similar conditions as those of the model compounds in Phase two. Soybean straw exhibited superior H2 yield (6.62 mmol/g) and total gas yield (14.91 mmol/g). Similarly, the gaseous products from soybean straw showed improved lower heating value (1592 kJ/Nm3). The experimental results showed slight deviations from the thermodynamic models which could be as a result of temperature gradient and absence of agitation in the batch reactor. In the third phase, several Ni-based catalysts were screened and tested for SCWG of soybean straw. The aim is to develop a cost-effective heterogeneous catalyst that could improve the gas yields towards equilibrium values and lower the reaction temperature. All experiments were performed at the desired operating conditions identified in Phase 2. A comprehensive screening of different support materials ranging from activated carbon (AC), carbon nanotubes (CNT), ZrO2, Al2O3, SiO2 and Al2O3-SiO2 was performed at 10 wt% Ni loading. The effectiveness of each support in improving H2 yield and selectivity was in the order: ZrO2 > Al2O3 > AC > CNT > SiO2 > Al2O3-SiO2. The effect of three promoters (i.e. Na, K and Ce) added to the supported Ni/ZrO2 catalysts was evaluated. Ce promoter was found to be the best for ZrO2 supported Ni catalysts. The performance of Ce was attributed to its high capacity for storing oxygen species which have the ability to react with the carbon deposits on the surface of the catalysts thereby preventing carbon deposition. The objective of the fourth phase was to study the kinetics of Ni - Ce/ZrO2 catalyzed SCWG of soybean straw. The lumped parameter kinetics method was employed with several reactions resulting from the experimental results in Phase three and the proposed reaction pathway in Phase one. The pathways were used to develop the kinetic equations. Kinetic model results were found to correlate with experimental results. Furthermore, the kinetic model was used to predict experimental yields for long residence time. The kinetics results are also in agreement with thermodynamic predictions. In the last phase, a detailed techno-economic evaluation and sensitivity analysis was performed for a conceptual design for hydrogen production from soybean straw gasification in SCW. The economic feasibility of hydrogen production was evaluated based on a discounted cash flow analysis. Economic analysis suggested a minimum selling price of U.S. $1.94/kg for hydrogen. The cost is relatively low when compared with that of hydrogen produced from 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

Introduction to Process Simulation with Aspen Plus: Instructor's Guide

Process simulation entails the representation of a chemical process by using mathematical equations. Process simulation in Aspen Plus offers the advantages of optimizing plant performance, reducing operational costs, and improving product quality through precise modeling and analysis of chemical processes. This book was written as an educational material to help Chemical/ Environmental/Process Engineering students working on their capstone project to learn more about process design. Capstone courses are designed to help students understand process design, preliminary economic assessment and process plant optimization. The book delves into the fundamentals of process design and offers practical examples for easy understanding. This book was used with ENGR 3440, mentored research course on process design at the University of Oklahoma.This project was funded by the University of Oklahoma Libraries' Alternative Textbook Gran

Generalizability of empirical correlations for predicting higher heating values of biomass

Designing efficient biomass energy systems requires a thorough understanding of the physicochemical, thermodynamic, and physical properties of biomass. One crucial parameter in assessing biomass energy potential is the higher heating value (HHV), which quantifies its energy content. Conventionally, HHV is determined through bomb calorimetry, but this method is limited by factors such as time, accessibility, and cost. To overcome these limitations, researchers have proposed a diverse range of empirical correlations and machine-learning approaches to predict the HHV of biomass based on proximate and ultimate analysis results. The novelty of this research is to explore the universal applicability of the developed empirical correlations for predicting the Higher Heating Value (HHV) of biomass. To identify the best empirical correlations, nearly 400 different biomass feedstocks were comprehensively tested with 45 different empirical correlations developed to use ultimate analysis (21 different empirical correlations), proximate analysis (16 different empirical correlations) and combined ultimate-proximate analysis (8 different empirical correlations) data of these biomass feedstocks. A quantitative and statistical analysis was conducted to assess the performance of these empirical correlations and their applicability to diverse biomass types. The results demonstrated that the empirical correlations utilizing ultimate analysis data provided more accurate predictions of HHV compared to those based on proximate analysis or combined data. Two specific empirical correlations including coefficients for each element (C, H, N) and their interactions (C*H) demonstrate the best HHV prediction with the lowest MAE (~0.49), RMSE (~0.64), and MAPE (~2.70%). Furthermore, some other empirical correlations with carbon content being the major determinant also provide good HHV prediction from a statistical point of view; MAE (~0.5–0.8), RMSE (~0.6–0.9), and MAPE (~2.8–3.8%)

Techno – Economic analysis of activated carbon production from spent coffee grounds: Comparative evaluation of different production routes

2590-1745/© 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).Natural Sciences and Engineering Research Council of Canada (NSERC), BioFuel Net, and Canada Research Chair (CRC)Peer ReviewedActivated carbon (AC) has gained immense popularity owing to its excellent physicochemical properties and its ability to remove carbon dioxide (CO2) from flue gas stream. This study examines the potential of spent coffee grounds (SCG) as a precursor for activated carbon (AC) production via prominent thermochemical conversion technologies. Different production routes, such as slow pyrolysis, activation, and deep eutectic solvent (DES) functionalization were compared in terms of their economic viability. Three scenarios (Scenario 1–3) involving combinations of the technologies and production routes were evaluated. Scenario 1 comprises of slow pyrolysis, CO2 activation and flue gas recycling for activation. Scenario 2 includes flue gas combustion while the third scenario comprise of flue gas combustion and DES impregnation. All processes were simulated with Aspen plus, while a detailed cash flow analysis was used to estimate the profitability parameters. The price of AC was found to be the most crucial determinant of an AC production plant’s viability and feasibility. The minimum selling price (MSP) of AC samples produced from scenarios 1,2 and 3 are U.S $0.15/kg,$0.21/kg, $0.28/kg respectively. The price of pristine AC and DES treated AC were lower than the commercially available activated carbon (U.S$0.45/kg)

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

Copyright © 2022 The Authors. Published by American Chemical Society. This publication is licensed under CC-BY-NC-ND 4.0.Natural Sciences and Engineering Research Council of Canada (NSERC), BioFuel Net, and Canada Research Chair (CRC)Peer ReviewedTorrefaction 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

Ozone application in different industries:a review of recent developments

Ozone – a powerful antimicrobial agent, has been extensively applied for decontamination purposes in several industries (including food, water treatment, pharmaceuticals, textiles, healthcare, and the medical sectors). The advent of the COVID-19 pandemic has led to recent developments in the deployment of different ozone-based technologies for the decontamination of surfaces, materials and indoor environments. The pandemic has also highlighted the therapeutic potential of ozone for the treatment of COVID-19 patients, with astonishing results observed. The key objective of this review is to summarize recent advances in the utilisation of ozone for decontamination applications in the above-listed industries while emphasising the impact of key parameters affecting microbial reduction efficiency and ozone stability for prolonged action. We realise that aqueous ozonation has received higher research attention, compared to the gaseous application of ozone. This can be attributed to the fact that water treatment represents one of its earliest applications. Furthermore, the application of gaseous ozone for personal protective equipment (PPE) and medical device disinfection has not received a significant number of contributions compared to other applications. This presents a challenge for which the correct application of ozonation can mitigate. In this review, a critical discussion of these challenges is presented, as well as key knowledge gaps and open research problems/opportunities

Low-temperature chemical looping oxidation of hydrogen for space heating

Chemical looping combustion (CLC) is an advanced combustion process in which the combustion reaction splits into two parts; in the first reaction metal oxides are used as oxygen suppliers for fuel combustion and then in the second reaction, reduced metal oxides are re-oxidised in an air reactor. Although this technology could be applicable for the safe implication of “low-temperature oxidation of hydrogen”, there is limited understanding of oxygen carrier reduction stages and the oxidation mechanism of hydrogen throughout the process. The novelty of this research lies in its pioneering investigation of low-temperature oxidation of hydrogen through chemical looping technology as a safe and alternative heating system, using three distinct metal oxide oxygen carriers: CuO, Co3O4, and Mn2O3. The oxidation of hydrogen over these oxygen carriers was comprehensively studied in a fixed-bed reactor operating at 200–450 °C. XRD analysis demonstrates that CuO directly reduced to metallic Cu at 200–450 °C, instead of following a sequential reduction step CuO→Cu4O3→Cu2O→Cu throughout the temperature. Co3O4 was reduced to a mixture CoO and Co at 450 °C, which may refer to a sequential reduction step Co3O4→CoO→Co with increasing the temperature. Decreasing the reduction temperature led to an elevation in CoO formation. Mn2O3 can also reduce to a mixture of Mn3O4 and MnO at temperatures between 250 and 400 °C. Compared to temperature, the increase in the residence time did not show any further reduction in Mn2O3. SEM results showed that most of the metal oxide particles were evenly dispersed on the supports. Based on the experimental results, a potential reduction stage of CuO, Co3O4 and Mn2O3 was proposed for low-temperature hydrogen oxidation, which could be a potential application for space heating using safe hydrogen combustion