Pyrolysis of sugarcane bagasse pretreated with sulfuric acid

Pyrolysis is a promising technique for the recovery of useful gas, tar, and solid products from biomass waste. However, the low tar yields obtained from lignocellulosic biomass are a significant drawback. To enhance tar yields, sugarcane bagasse, which is the most abundant agricultural waste in Fiji, was pretreated at ambient temperature and atmospheric pressure using various sulfuric acid (H₂SO₄) concentrations. Here, the ether bonds of cellulose, hemicellulose, and lignin were partially hydrolyzed. The pretreated samples were then pyrolyzed at 500 °C, and it was confirmed that H₂SO₄-pretreatment disrupted the bagasse cell structure, with the thermogravimetry and differential thermogravimetry results confirming that decomposition occurred at lower temperatures after pretreatment. In addition, tar yields were significantly enhanced from 5.6 wt% to 13.4 wt% for the untreated and 3 M H₂SO₄-pretreated samples respectively. The main components detected in this tar product were levoglucosan, andcellulose-and hemicellulose-derived products, whose proportions were increased following pretreatment. Thus, our work demonstrates that dilute acid pretreatment enhances tar production from sugarcane bagasse due to the production of shorter chain components via the partial hydrolysis of ether bonds.     

Efficient sugar production from sugarcane bagasse by microwave assisted acid and alkali pretreatment

Sugarcane bagasse represents one of the best potential feedstocks for the production of second generation bioethanol. The most efficient method to produce fermentable sugars is by enzymatic hydrolysis, assisted by thermochemical pretreatments. Previous research was focused on conventional heating pretreatment and the pretreated biomass residue characteristics. In this work, microwave energy is applied to facilitate sodium hydroxide (NaOH) and sulphuric acid (H₂SO₄) pretreatments on sugarcane bagasse and the efficiency of sugar production was evaluated on the soluble sugars released during pretreatment. The results show that microwave assisted pretreatment was more efficient than conventional heating pretreatment and it gave rise to 4 times higher reducing sugar release by using 5.7 times less pretreatment time. It is highlighted that enrichment of xylose and glucose can be tuned by changing pretreatment media (NaOH/H₂SO₄) and holding time. SEM study shows significant delignification effect of NaOH pretreatment, suggesting a possible improved enzymatic hydrolysis process. However, severe acid conditions should be avoided (long holding time or high acid concentration) under microwave heating conditions. It led to biomass carbonization, reducing sugar production and forming ‘humins’. Overall, in comparison with conventional pretreatment, microwave assisted pretreatment removed significant amount of hemicellulose and lignin and led to high amount of sugar production during pretreatment process, suggesting microwave heating pretreatment is an effective and efficient pretreatment method.     

Effect of aluminium sulphate-catalysed hydrolysis process on furfural yield and cellulose degradation of Cannabis sativa L. shives

Commercially, furfural is produced from pentosan-rich biomass using mineral acids as homogeneous catalysts. This study investigated a novel hydrolysis method that allows to obtain furfural from hemp shives with high yield and also to preserve the cellulose in the remaining biomass for other bioconversion processes. To date, hemp shives have not been investigated for furfural production. Cannabis sativa L. (“Bialobrzeskie” variety) shives were used as a feedstock due to the high content of pentosan (17.6% of oven-dried biomass). It means that the theoretically possible amount of furfural was 12.8% of oven-dried hemp shives. The effect of temperature (140–180 °C), the amount of catalyst (3–7% of oven-dried biomass) and the treatment time (10–90 min) on the furfural formation were studied. Whereas, the effect of the same temperature and the amount of catalyst on the changes of lignocellulose were studied after 90 min treatment time. Al₂(SO₄)₃*18H₂O was used as a catalyst for the conversion of C5-sugars to furfural. To show the catalytic properties of Al₂(SO₄)₃*18H₂O, autocatalysis was performed as a reference process using the same parameters. The highest yield of furfural, 73.7% of the theoretical yield, was obtained at 180 °C, 5% Al₂(SO₄)₃*18H₂O of oven-dried mass and 90 min. From the biorefinery perspective, the optimal hydrolysis parameters were 160 °C, 5% Al₂(SO₄)₃*18H₂O of oven-dried mass and 90 min. With these parameters, the yield of furfural was 62.7% of the theoretical yield, 99.2% of hemicelluloses were removed and 95.8% of cellulose was preserved and slightly depolymerized.     

Numerical Modeling of Bayonet-Type Heat Exchanger and Decomposer for the Decomposition of Sulfuric Acid to Sulfur Dioxide

The growth of global energy demand during the 21st century, combined with the necessity to master greenhouse gas emissions, has led to the introduction of a new and universal energy carrier: hydrogen. The Department of Energy (DOE) proposed using a bayonet-type heat exchanger as a silicon carbide integrated decomposer (SID) to produce the sulfuric acid decomposition product sulfur dioxide, which can be used for hydrogen production within a sulfur–iodine thermochemical cycle. A two-dimensional computational model of SID having a boiler, superheater and decomposer was developed using GAMBIT and fluid. The thermal and chemical reaction analyses were carried out in FLUENT. The main purpose of this study is to obtain the decomposition percentage of sulfur trioxide for the integrated unit. Sulfuric acid (H₂SO₄), sulfur trioxide (SO₃), sulfur dioxide (SO₂), oxygen (O₂), and water vapor (H₂O) are the working fluids used in the model. Concentrated sulfuric acid liquid of 40 mol% was pumped into the inlet of the boiler and the mass fraction of concentrated sulfuric acid vapor obtained was then fed into the superheater to obtain sulfur trioxide. The decomposer region, which houses the pellets, placed on the top of the bayonet heat exchanger acts as the porous medium. As the decomposition takes place, the mass fraction of SO₃ is reduced and mass fractions of SO₂ and O₂ are increased. The percentage of SO₃ obtained from the integrated decomposer was compared with the experimental results obtained from Sandia National Laboratories (SNL). Further, effects of various pressures, flow rates, and acid concentrations on the decomposition percentage of sulfur trioxide were studied.     

Kinetics of furfural production from pre-hydrolysis liquor (PHL) of a kraft-based hardwood dissolving pulp production process

The kinetics of C-5 sugars (xylose/xylan) conversion to furfural in an industrial pre-hydrolysis liquor (PHL) in both acetic acid (HAc)-catalyzed system and sulfuric acid (H₂SO₄)-catalyzed system, were determined in a temperature range of 150–190 °C. The main reactions involved during the process included: 1) C-5 sugars consumption for furfural formation and side reactions; 2) furfural degradation. It was found that these reactions followed first order kinetics. A consecutive reaction model (from xylose to furfural, then to degradation products) fitted into the data obtained in the H₂SO₄-catalyzed system; while a consecutive/parallel model suited for the HAc-catalyzed system due to side reactions, which also consumed C-5 sugars. The activation energy for C-5 sugar disappearance, and the furfural degradation, was 151 kJ mol⁻¹ and 115 kJ mol⁻¹, respectively, in the HAc-catalyzed system.     

Assessment of sugarcane bagasse gasification in supercritical water for hydrogen production

Sugarcane bagasse is one of the major resources of agricultural biomass waste in the world. In this work, supercritical water gasification characteristics of sugarcane bagasse were investigated. The effect of temperature (600–750 °C), concentration (3–12 wt%), residence time (5–20 min) and catalysts (Raney-Ni, K₂CO₃ and Na₂CO₃) on bagasse gasification were studied. A kinetic study on the non-catalytic and Na₂CO₃ catalytic bagasse gasification was conducted to describe the kinetic information of the bagasse gasification reaction. The results showed that a higher reaction temperature, a lower bagasse concentration and a longer residence time could favor the gasification of bagasse, leading to a higher hydrogen yield. Bagasse was nearly completely gasified at 750 °C without using any catalyst and the carbon gasification efficiency could reach up to 96.28%. The addition of employed catalysts remarkably promoted the bagasse gasification reactivity. The maximum hydrogen yield (35.3 mol/kg) was achieved at 650 °C with the Na₂CO₃ loading of 20 wt%. The experimental data fitted well with a homogeneous model based on a Pseudo-first-order reaction hypothesis. The kinetic study showed that Na₂CO₃ catalyst could lower the activation energy E_a of bagasse gasification from 117.88 kJ/mol to 78.25 kJ/mol.     

Catalyzed thermal decompositon of H2SO4 and production of HBr by the reaction of SO2 with Br2 and H2O

Decomposition of H₂SO₄ and production of HBr have been studied as a part of the research and development of the thermochemical hydrogen production from water. The catalytic activities of various metals and metal oxides on a porous alumina support were studied for the thermal decomposition of sulfuric acid in a fixed bed reactor. A Pt-Al₂O₃ catalyst gave a conversion of SO₃ close to the equilibrium at temperatures from 1073 to 1173 K and at a space velocity below 10 000 h^?1. It was also found that metal oxide catalysts such as CuO and Fe₂O₃ were as active as the Pt catalyst. To prepare SO₂-free HBr gas by the reaction between SO₂, Br₂ and H₂O, vapor-liquid equilibrium determinations for SO₂/Br₂/HBr/H₂SO₄/H₂O system were carried out at 298 K under atmospheric pressure. The unconverted SO₂ can be effectively removed by contacting the effluent gases with a HBr saturated aqueous solution containing an excess of Br₂.     

Influence of impregnation with lactic acid on sugar yields from steam pretreatment of sugarcane bagasse and spruce, for bioethanol production

Lignocellulosic biomass can be utilized to produce ethanol, a promising alternative energy source produced through fermentation of sugars. However, in order to achieve high sugar and ethanol yields, the lignocellulosic material must be pretreated before the enzymatic hydrolysis and fermentation. Dilute acid pretreatment, using SO₂, is one of the most promising methods of pretreatment for softwood and agricultural residues. However, handling the high acidity of the slurry obtained from pretreatment and difficulty in recycling/degradation of the impregnating agent are some of the drawbacks of the dilute acid processes. In the present study the influence of utilization of a weak organic acid (lactic acid), as impregnating agent, on the sugar yield from pretreatment, with and without addition of SO₂, was investigated. The efficiency of pretreatment was assessed by enzymatic hydrolysis of the slurry obtained by pretreatment, using sugarcane bagasse and spruce, stored for one and two months in the presence of lactic acid separately, as feedstocks. Pretreatment of bagasse after storage with 0.5% lactic acid resulted in an overall glucose yield, i.e. after enzymatic hydrolysis, of 79% of theoretical based on the amount available in the raw material. This was as good as pretreatment using SO₂ as impregnating agent. However, storage of spruce with lactic acid before pretreatment, with and without addition of SO₂, was not efficient and resulted in lower sugar yields than pretreatment using SO₂ only.     

Low voltage H2O electrolysis for enhanced hydrogen production

In this study, we report the ability to split H₂O into hydrogen at a reduced voltage by the influence of sulfur dioxide (SO₂) and anode tolerance materials. This will improve the energy consumption for the production of hydrogen. Hydrogen is produced at the cathode while the anode electrode is bathed in sulfur dioxide and water to form sulfuric acid by the application of potential in the form of electrical energy. In the presence of SO₂, the theoretical equilibrium voltage requirement is 0.19 V, thereby reducing the thermochemical free energy to less than one-sixth of its initial value, that is, from 56 to 9.18 kcal/mole. By using SO₂ to scavenge the anode we have in practice reduced the equilibrium voltage to 0.6 V. Based on different electrode configurations, ruthenium oxide (RuO₂) electrocatalyst deposited on silicon (Si) electrode exhibited superior performance for the low voltage H₂O electrolysis.     

Kinetic studies of sulfuric acid decomposition over Al–Fe2O3 catalyst in the sulfur-iodine cycle for hydrogen production

The decomposition of H₂SO₄ to produce SO₂ is the reaction with the highest energy demand in the sulfur-iodine cycle and it shows a large kinetic barrier. In the present study, alumina supported iron (III) oxide has been chosen for a detailed kinetic study. Experiments were carried out in the temperature range of 1023 K–1173 K using space hour velocities in the range of 0.146–0.731 kmol/kg-h in a quartz tube double stage continuous flow fixed bed reactor with 98% sulfuric acid feed over alumina supported Fe₂O₃ catalyst, nitrogen as inert carrier gas. From the homogeneous kinetic analysis, the apparent activation energy (E_A) was found to be 138.6 kJ/mol. This high activation energy indicates that the experiments were conducted in a kinetic controlled regime. The catalyst was well characterized by XRD, BET, TPR/TPO, SEM and FT-IR before and after reaction.     

Exergy analysis of hydrogen production from different sulfur-containing compounds based on H2S splitting cycle

There is a tremendous demand for hydrogen production worldwide but the current H₂ production routes from natural gas and other carbon fuels lead to large greenhouse gas emissions. Intentionally coupled with nuclear power, the sulfur–iodine (S–I) thermochemical water splitting cycle is one of the most widely studied cycles for the large-scale hydrogen production that has environmental benignity. Based on the inspiration of the S–I cycle, a novel chemical cycle called hydrogen sulfide splitting cycle has been proposed for hydrogen production. In addition to the SO₂ production from the reaction of H₂S and sulfuric acid, SO₂ can be produced from the burning (direct oxidation) of hydrogen sulfide or elemental sulfur. And it can also be provided by SO₂ capture from flue gas or other SO₂-containing waste gases. This paper performs exergy analysis on the various SO₂ provisions to the Bunsen reaction that make different routes for hydrogen production from waste sulfur-containing compounds as feedstock. It has been found that the route including SO₂ from direct H₂S oxidation potentially makes the best energy-efficient process of H₂ production. The heat that is generated from H₂S oxidation can be recovered and used to support the energy requirements for other steps of the cycle, making the entire hydrogen production cycle more energy-efficient.     

Overview of nuclear hydrogen production research through iodine sulfur process at INET

Thermochemical water-splitting cycle is a promising process to produce hydrogen using solar or nuclear energy. R&D on hydrogen production through iodine sulfur (IS) thermochemical cycle was initiated in 2005 at INET. Fundamental studies on the three reactions of IS cycle, i.e., Bunsen reaction, HI decomposition reaction, sulfuric acid decomposition reaction, and related techniques, such as separation, concentration and purification, were carried through. In Bunsen section, the reaction kinetics and separation characteristics of H₂SO₄ and HIx phases were studied. In HI section, Pt catalysts were loaded on different supporters by various methods and used for HI decomposition; and electro-electrodialysis(EED) was developed for concentration of HI acid. In sulfuric acid section, non-Pt catalysts were developed for SO₃ decomposition. Based on fundamental researches, a closed-loop test apparatus of 10 NL/h H₂ was designed and established. The current status of IS process research is summarized in this paper. In addition, R&D plan of IS process at INET is presented.     

Waste biomass to liquids: Low temperature conversion of sugarcane bagasse to bio-oil. The effect of combined hydrolysis treatments

This article describes the influence of different sugarcane bagasse hydrolysis pretreatments on modifications to biomass feedstock and the characteristics of the resultant pyrolysis products. Sugarcane bagasse was pretreated with acid, alkaline or sequential acid/alkaline solutions and pretreated samples were then subjected to a low temperature conversion (LTC) process under He or O₂/He atmospheres at 350-450 °C. Both pretreated samples and sugarcane bagasse in natura were analyzed by determination of their chemical composition and by thermogravimetric, FTIR and SEM analyses. The gases yielded during LTC were monitored on-line by quadrupole mass spectrometry, and the liquid fractions obtained were characterized by FTIR and ¹H and ¹³C NMR. Irrespective of the sugarcane bagasse pretreatment applied, the main bio-oil component obtained was levoglucosan. However, the LTC yield of bio-oil depended on the hydrolysis treatment of the biomass and decreased in the presence of O₂. The acid hydrolysis pretreatment increased the LTC bio-oil yield notably.     

Activated carbon from grass – A green alternative catalyst support for water electrolysis

Grass blades (turf grass) have been selected as a cheap biomass source of producing activated carbon for supporting Pt particles for utilizing as electrocatalyst for H₂ generation through electrolysis of water. Activation is done using ZnCl₂ followed by thermal processing at 250 °C. 1% Pt was supported over the grass derived activated biomass carbon (G-ABC) powder to result in Pt@G-ABC. After physical characterization, Pt@G-ABC sample has been tested for its catalytic activity in 1 M sulfuric acid solution for H₂ gas generation through Linear Sweep & Cyclic Voltammetry. Cost factor involved in the production of G-ABC has also been compared with the traditional commercially available carbon support. The studies suggest that grass may be considered not only as a potential alternative source for producing carbon supported catalyst for H₂ generation but also highlight the production of low-cost carbon for further applications like electrode materials, adsorbent for color, odor and hazardous pollutants.     

Preliminary results from bench-scale testing of a sulfur-iodine thermochemical water-splitting cycle

Portions of a bench-scale model of a sulfur-iodine thermochemical water-splitting cycle have been operated at General Atomic Company as part of a comprehensive program to demonstrate the technology for hydrogen production from non-fossil sources. The bench-scale model consists of three subunits which can be operated separately or together and is capable of producing as much as 4 l/min^?1 (6.7 × 10^?5m³s^?1) at standard conditions of gaseous hydrogen. One subunit (main solution reaction) reacts liquid water, liquid iodine (I₂) and gaseous sulfur dioxide (SO₂) to form two separable liquid phases: 50 wt % sulfuric acid (H₂SO₄) and a solution of iodine in hydroiodic acid (HI_x). Another subunit (H₂SO₄ concentration and decomposition) concentrates the H₂SO₄ phase to the azeotropic composition, then decomposes it at high temperature over a catalyst to form gaseous SO₂ and oxygen. The third subunit (HI separation and decomposition) separates the HI from water and I₂ by extractive distillation with phosphoric acid (H₃PO₄) and decomposes the HI in the vapor phase over a catalyst to form I₂ and product hydrogen. This paper presents the results of ongoing parametric studies to determine the operating characteristics, performance, and capacity limitations of major components.     

Thermophilic hydrogen fermentation from Korean rice straw by Thermotoga neapolitana

Rice straw, a low-cost lignocellulosic biomass was used as feedstock for thermophilic hydrogen fermentation by Thermotoga neapolitana. Hydrogen production, the growth and cellulose digestibility of the hyperthermophile in batch mode from untreated as well as chemically pretreated (ammonia and dilute sulfuric acid) Korean rice straws were investigated. Pretreatment method using combination of 10% ammonia and 1.0% dilute sulfuric acid was developed to increase the digestibility of rice straw for the hyperthermophilic H₂ fermentation and to decrease the time consumption. In a typical fermentation using raw rice straw, 29% of the substrate was digested and 2.3 mmol H₂/g straw of hydrogen yield was consistently obtained. Compared with the pretreatments using only ammonia or dilute sulfuric acid, the combined pretreatment method using both chemical agents significantly increases the digestibility of rice straw with 85.4% of substrate consumption. H₂ production on rice straw from this combined pretreatment showed the highest yield (2.7 mmol H₂/g straw) and the highest sugar conversions (72.9% of glucose and 95.7% of xylose).     

In situ reactive extraction of Jatropha curcas L. seeds assisted by ultrasound: Preliminary studies

Esterification is required to reduce the high free fatty acid (FFA) content of crude Jatropha oil to below 3% prior to transesterification. In this study, raw decorticated Jatropha seeds were employed as the feedstock in in situ reactive extraction assisted by ultrasound in the presence of sulfuric acid (H₂SO₄) as a catalyst. Extraction efficiency, esterification efficiency, and fatty acid methyl ester (FAME) yield were optimized as a function of ultrasonic pulse mode, amplitude, and H₂SO₄ amount. The optimum extraction efficiency of 83.96%, esterification efficiency of 71.10%, and FAME yield of 38.58% were achieved at a pulse mode of 5 s on/2 s off, an ultrasonic amplitude of 60%, and an H₂SO₄ amount of 5 mL in reaction time of 150 min.     

Analysis of gas dissociation solar thermal power system

Energy collected at high temperatures in a set of scattered solar furnaces can be delivered to a central facility at intermediate temperature by using a polyatomic gas in a closed cycle circulation system. For example, gaseous SO₃ dissociates at 800 to 1000°C to form SO₂ + O₂ with absorption of heat; the products recombine in the presence of a catalyst at 500 to 600°C liberating the heat of recombination. A system using SO₃ for energy transfer and scaled for production of a continuous 100 MW of electrical power with 3 days of cloudy weather storage is outlined.Alternate working fluids CH₄ + H₂O, COCl₂ and NF₃ are compared. Selected design options, potential problem areas, and possibilities of utilizing the collected heat for chemical processing are discussed.     

Simulation and experimental study on the sulfuric acid decomposition process of SI cycle for hydrogen production

This work is concerned with customization of the existing electrolyte thermodynamic model for process simulation and experimental studies on the sulfuric acid decomposition process of the SI cycle, using a commercial steady state simulator. An electrolyte thermodynamic model for the sulfuric acid–water system was tailored with four candidates available in commercial software, utilizing data from Perry's Handbook. Simulation of the sulfuric acid decomposition process comprising a flash separator, distillation column and decomposer was validated with the experimental results. To facilitate the lumped-parameter steady-state model-based simulation of sulfuric acid decomposition, the decomposer was conceptually decoupled into three sections: evaporation, H₂SO₄ dissociation, and SO₃ catalytic reduction to SO₂. The process simulation results exhibited good agreement with experimental data. This work contributes to future work on simulation and experimental study of a scaled-up process system and exergy analysis for an optimal energy-efficient sulfuric acid decomposition process in the SI cycle.     

Effect of sodium sulfite on acid pretreatment of wheat straw with respect to its final conversion to ethanol

A pretreatment process that combines dilute acid and sodium sulfite has been applied to wheat straw to study the effect of temperature (120–180 °C) and sodium sulfite concentration (0–3%) on the yield of glucose in subsequent enzymatic hydrolysis and ethanol production by fermentation. The results were compared with both dilute acid pretreatment (without Na₂SO₃ addition) and hot water pretreatment. Formation of furfural and hydroxymethylfurural, which can inhibit ethanol-producing microorganisms, were measured and the ethanol yield in a subsequent fermentation was evaluated. The results indicate that a combination of 180 °C, 30 min, 1% H₂SO₄ and 2.4% Na₂SO₃ during pretreatment produced the highest ethanol yield; 17.3 g/100 g dry weight of initial biomass, which corresponds to 75% of the theoretical yield from glucose. 28 mg of furan inhibitors (sum of furfural and hydroxymethylfurfural) per gram dry weight of initial wheat straw were generated under this condition. Increasing sulfite loading up to 2.4% decreased inhibitor formation, leading to increased delignification and preservation of cellulose from dissolution. On the other hand, an elevated temperature in combination with low pH reduced the amount of solid phase after pretreatment, increased the level of inhibitors and reduced the concentration of ethanol produced by fermentation.