Conventional technologies for the removal/remediation of toxic metal ions from wastewaters are proving expensive due to non-regenerable materials used and high costs. Biosorption is emerging as a ...technique offering the use of economical alternate biological materials for the purpose. Functional groups like carboxyl, hydroxyl, sulphydryl and amido present in these biomaterials, make it possible for them to attach metal ions from waters.
Every year, large amounts of straw and bran from
Triticum aestivum (wheat), a major food crop of the world, are produced as by-products/waste materials. The purpose of this article is to review rather scattered information on the utilization of straw and bran for the removal/minimization of metal ions from waters. High efficiency, high biosorption capacity, cost-effectiveness and renewability are the important parameters making these materials as economical alternatives for metal removal and waste remediation. Applications of available adsorption and kinetic models as well as influences of change in temperature and pH of medium on metal biosorption by wheat straw and wheat bran are reviewed. The biosorption mechanism has been found to be quite complex. It comprises a number of phenomena including adsorption, surface precipitation, ion-exchange and complexation.
Hydrogen from waste biomass is considered to be a clean gaseous fuel and efficient for heat and power generation due to its high energy content. Supercritical water gasification is found promising in ...hydrogen production by avoiding biomass drying and allowing maximum conversion. Waste biomass contains cellulose, hemicellulose and lignin; hence it is essential to understand their degradation mechanisms to engineer hydrogen production in high-pressure systems. Process conditions higher than 374 °C and 22.1 MPa are required for biomass conversion to gases. Reaction temperature, pressure, feed concentration, residence time and catalyst have prominent roles in gasification. This review focuses on the degradation routes of biomass model compounds such as cellulose and lignin at near and supercritical conditions. Some homogenous and heterogeneous catalysts leading to water–gas shift, methanation and other sub-reactions during supercritical water gasification are highlighted. The parametric impacts along with some reactor configurations for maximum hydrogen production and technical challenges encountered during hydrothermal gasification processes are also discussed.
•Gasification of biomass model compounds in supercritical water for H2 synthesis.•Effect of temperature, pressure and feed concentration on H2 production.•Improvement of H2 yields in presence of catalysts during biomass gasification.•Reactor configuration and residence time impact supercritical water gasification.•Challenges and future prospective of supercritical water gasification is presented.
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•Waste cooking oil was gasified in supercritical water for hydrogen production.•Effects of temperature, feed concentration, reaction time and catalysts were studied.•High H2 yields ...were obtained at 675 °C and 60 min with 25 wt% of waste cooking oil.•Ru/Al2O3 maximized H2 yields due to decarboxylation, decarbonylation and water-gas shift reaction.•Glycerol, acetic acid and propionic acid were obtained as the main degradation products of cooking oil.
Substantial amounts of waste cooking oil are obtained worldwide from household and catering enterprises because of deep-frying and other cooking activities. Supercritical water gasification is considered as an aqueous phase reforming process to produce hydrogen enriched syngas from biomass and other organic wastes. In this study, waste cooking oil was gasified at variable temperatures (375–675 °C), feed concentration (25–40 wt%) and reaction time (15–60 min) to investigate their effects on syngas yield and composition. Maximum yields of hydrogen (5.16 mol/kg) and total gases (10.5 mol/kg) were obtained at optimal temperature, feed concentration and reaction time of 675 °C, 25 wt% and 60 min, respectively. At 5 wt% loading, Ru/Al2O3 enhanced hydrogen yield (10.16 mol/kg) through water-gas shift reaction, whereas Ni/Si-Al2O3 improved methane yield (8.15 mol/kg) via methanation reaction. The trend of hydrogen production from catalytic supercritical water gasification of waste cooking oil at 675 °C, 25 wt% and 60 min decreased as Ru/Al2O3 > Ni/Si-Al2O3 > K2CO3 > Na2CO3. The results indicate the recycling potential of waste cooking oil for hydrogen production through hydrothermal gasification.
5-Hydroxymethylfurfural (HMF) is a platform chemical derived from C6 sugars, which can be transformed into various important chemicals and fuels because of the presence of C&z.dbd;O, C-O and furan ...ring functional groups. In this review, the selective tailoring of these groups in HMF to form 2,5-dimethylfuran, 2,5-dihydromethylfuran, 2,5-dihydromethyltetrahydrofuran, 5-ethoxymethylfurfural, 1,6-hexanediol, long-chain alkanes, 3-(hydroxy-methyl)cyclopentanone,
p
-xylene, 2,5-diformylfuran, 2,5-furandicarboxylic acid and maleic anhydride will be described to gain more insight into the transformation of HMF under various conditions. The focus of this review is on the mechanisms of the catalytic processes and potential design strategies for future catalysts. The activation of the functional groups and the key challenges involved in the precise design of bifunctional catalysts are highlighted. Some examples of "one-pot" transformations of fructose into various chemicals using the HMF platform are also presented.
The catalytic mechanisms and catalyst design strategies for 5-hydroxymethylfural conversion are summarized.
•Renewable fuel ashes from different origin were analyzed.•Characterization and comparison of studied ashes were given.•Transformation of inorganic components was determined using XRD and FTIR.•The ...ash fusion behaviour of ashes was studied experimentally.•Empirical indices were calculated indicating slagging and fouling propensities.
The paper is focused on the characterization of renewable fuel ashes and their impact on fouling and slagging during combustion. Biomass (A1) and sewage sludge (A2, A3) ashes were investigated for characterization of their corrosive properties. The chemical and phasemineral composition of ashes were studied using a variety of analytical techniques including XRF, ICP-MS, XRD, SEM–EDS, and the ash fusion characteristics by using a thermal microscope. The slagging and fouling indices, as well as thermal conductivity, were calculated and the sintering properties were predicted. The studied ashes had different concentrations of the main chemical compounds and mineral phases. The XRF results showed that CaO, SiO2, K2O, MgO, P2O5 and Al2O3 are the main compounds of A1 and A3 ashes, whereas Na2O and SO3 dominated in A2. Consequently, SEM images showed surface differences between ash particles. Phase analyses indicated the existence of corrosive phases containing potassium and sodium K2Ca(CO3)2, KAlSi2O6, KCl, NaAlSiO4 (A1) and Na2SO4, NaCl (A2). Such compounds can decrease the sintering temperature due to formation of low temperature eutectics. The lowest fusion temperatures below 1000°C were detected from the sewage sludge ash A2 and above 1200°C from A1 and A2 with high Ca, Si and Al contents.
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•Supercritical water gasification of various fruit wastes and agro-food residues.•Coconut shell had superior carbon content and calorific value due to high lignin.•Maximum H2 yields ...at 600°C with 1:10 biomass-to-water ratio, 45min and 23–25MPa.•High H2 yields from coconut shell, bagasse and aloe vera rind with 2wt% K2CO3.•High CH4 yields from coconut shell with 2wt% NaOH due to methanation reaction.
Considerable amounts of fruit wastes and agro-food residues are generated worldwide as a result of food processing. Converting the bioactive components (e.g., carbohydrates, lipids, fats, cellulose, hemicellulose and lignin) in food wastes to biofuels is a potential remediation approach. This study highlights the characterization and hydrothermal conversion of several fruit wastes and agro-food residues such as aloe vera rind, banana peel, coconut shell, lemon peel, orange peel, pineapple peel and sugarcane bagasse to hydrogen-rich syngas through supercritical water gasification. The agro-food wastes were gasified in supercritical water to study the impacts of temperature (400–600°C), biomass-to-water ratio (1:5 and 1:10) and reaction time (15–45min) at a pressure range of 23–25MPa. The catalytic effects of NaOH and K2CO3 were also investigated to maximize the hydrogen yields and selectivity. The elevated temperature (600°C), longer reaction time (45min) and lower feed concentration (1:10 biomass-to-water ratio) were optimal for higher hydrogen yield (0.91mmol/g) and total gas yield (5.5mmol/g) from orange peel. However, coconut shell with 2wt% K2CO3 at 600°C and 1:10 biomass-to-water ratio for 45min revealed superior hydrogen yield (4.8mmol/g), hydrogen selectivity (45.8%) and total gas yield (15mmol/g) with enhanced lower heating value of the gas product (1595kJ/Nm3). The overall findings suggest that supercritical water gasification of fruit wastes and agro-food residues could serve as an effective organic waste management technology with regards to bioenergy production.
•Physico–chemical studies of bio-chars produced from waste biomasses at 400–550°C.•Abundant alkaline elements in biochars showed their potential for soil application.•All biochars, except poultry ...litter-based are suitable precursors for activated carbon.•Larger carbon content and compact aromatic structure in biochars produced at 550°C.•Biochars prepared at 550°C have better potential for soil application.
Bio-chars are produced by means of a mobile pyrolysis unit from fast pyrolysis of different types of Canadian waste biomass including agricultural waste (wheat straw and flax straw), forest residue (sawdust) and animal manure (poultry litter). They were analyzed for their physicochemical changes with pyrolysis temperature (400–550°C). To study the chemical nature of bio-char samples, analyses such as XRD, FTIR, Raman spectroscopy, XPS, SEM, ICP, TGA and electrical conductivity measurements were performed. ICP-MS analysis showed that poultry litter-derived bio-char had the largest concentration of inorganic elements (∼200,000ppm) followed by wheat straw, flax straw and sawdust derived bio-chars. In addition, the alkaline elements were 4–14times that of essential elements (Fe and P) and 18–57times that of heavy elements. Electrical conductivity of bio-chars, a measure of their salinity, was maximum for all samples prepared at 400°C. SEM showed that sawdust derived bio-chars retained relatively less dissociated surfaces compared with other bio-chars. XRD confirmed the presence of sylvite, dolomite and quartz in the bio-chars. The deconvoluted XPS spectra indicated that for all precursors except poultry litter, aromatic/aliphatic carbon portion increased in the corresponding bio-char with the pyrolysis temperature. For all precursors, O/C mass ratio decreased with an increase in the pyrolysis temperature due to the development of compact aromatic structure in bio-char. This result was confirmed by a drastic increase in ID/IG (defect to graphitic carbon) ratio of bio-char samples produced at 550°C from the deconvolution results of Raman spectroscopy. Thermogravimetric analysis showed that biomass decomposition started at lower temperatures for the following order: poultry litter, wheat straw, flax straw and sawdust.
Biofuels and biomaterials are gaining increased attention because of their ecofriendly nature and renewable precursors. Biochar is a recalcitrant carbonaceous product obtained from pyrolysis of ...biomass and other biogenic wastes. Biochar has found many notable applications in diverse areas because of its versatile physicochemical properties. Some of the promising biochar applications discussed in this paper include char gasification and combustion for energy production, soil remediation, carbon sequestration, catalysis, as well as development of activated carbon and specialty materials with biomedical and industrial uses. The pyrolysis temperature and heating rates are the limiting factors that determine the biochar properties such as fixed carbon, volatile matter, mineral phases, surface area, porosity and pore size distribution, alkalinity, electrical conductivity, cation-exchange capacity, etc. A broad investigation of these properties determining biochar application is rare in literature. With this objective, this paper comprehensively reviews the evolution of biochar from several lignocellulosic biomasses influenced by pyrolysis temperature and heating rate. Lower pyrolysis temperatures produce biochar with higher yields, and greater levels of volatiles, electrical conductivity and cation-exchange capacity. Conversely, higher temperatures generate biochar with a greater extent of aromatic carbon, alkalinity and surface area with microporosity. Nevertheless, this coherent review summarizes the valorization potentials of biochar for various environmental, industrial and biomedical applications.
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•Soybean straw and flax straw were gasified under hydrothermal conditions.•Optimal temperature (500 °C), biomass-to-water ratio (1:10), biomass particle size (0.13 mm) and residence ...time (45 min).•Higher H2 yield from soybean straw (6.62 mmol/g) than flax straw (3.82 mmol/g).•KOH catalyst enhanced H2 and total gas yields from soybean straw and flax straw.•Experimental results show a slight deviation from thermodynamic yields.
Biofuels produced from lignocellulosic feedstocks are gaining popularity because of the elevating energy demand, increasing greenhouse gas emissions, escalating fuel prices and dwindling fossil fuel resources. Therefore, it has become important to seek alternative energy resources from renewable waste biomass. In this study, agricultural crop residues such as soybean straw and flax straw were gasified in subcritical water (300 °C) and supercritical water (400 and 500 °C) for H2 production. To maximize the non-catalytic process, the impacts of temperature (300–500 °C), biomass-to-water ratio, BTW (1:5 and 1:10), biomass particle size (0.13 mm and 0.8 mm) and residence time (30–60 min) on H2 production were studied at a pressure range of 22–25 MPa. Maximum H2 yield and total gas yields of 6.62 mmol/g and 14.91 mmol/g, respectively were obtained from soybean straw at the highest temperature (500 °C), lower feed concentration (1:10 BTW), smaller particle size biomass (0.13 mm) and longer residence time (45 min). To evaluate the drift in the experimental H2 yield from the theoretical values, thermodynamic modeling using Gibbs free minimization method was performed. The experimental results showed slight deviations from the thermodynamic models due to the temperature gradient and absence of agitation in the tubular batch reactor. However, the KOH catalyst was found to elevate the H2, CO2 and CH4 yields for soybean straw and flax straw. The findings suggest that supercritical water gasification could be an efficient green technology for H2 production from waste biomass.
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•Design for hydrothermal gasification of 56,000 metric tons/year of soybean straw.•Aspen Plus-designed plant can process 170 metric tons/day of soybean straw.•Breakeven cost of H2 was ...U.S. $1.94/kg excluding storage and transportation cost.•Tax rate and costs of feedstock, catalyst and labor impact breakeven cost of H2.•Cash flow analysis was used to evaluate profitability of the project.
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.
