H2SO4 Impregnation Research Articles

Preparation, characterization, and catalytic properties of SO42-/SnO2-Hangjin2#Clay solid superacid catalyst

A new sulfate oxide solid acid catalyst SO42-/SnO2-Hangjin2# clay was compounded with Hangjin2#clay, activated by sulfuric acid, as a carrier. In the catalysis of Xanthoceras sorbifolium Bunge, using the yield of oil and methanol synthesis of biodiesel as an index, the effect of SO42-/SnO2–Hangjin2#clay and the preparation conditions on the activity of solid acid were investigated. The variables included in the optimization process were concentration of Sn, impregnation sulfuric acid concentration, and calcination temperature. The optimal conditions were found as 0.4 M SnCl4, 3.0 M H2SO4 impregnation, and 350 °C calcination temperature. The catalyst was examined by scanning electron microscope, X-ray diffraction meter, Fourier transform infrared spectroscopy, surface area, and thermal weight analysis. The results showed that the introduction of Hangjin2#clay in the SO42--SnO2 solid acid catalyst improves its catalytic activity.

Preparation of coal fly ash-based Fenton-like catalyst and its application for the treatment of organic wastewater under microwave assistance

In order to realize the high value-added reuse of coal fly ash (CFA), a reusable CFA catalyst (AFA) for a Fenton-like process conducted under microwave (MW) assistance was prepared by H2SO4 impregnation. The optimal AFA preparation conditions included an impregnation time of 60 min, H2SO4 dosage of 0.5 mol/L, impregnation temperature of 303 K, and solid–liquid ratio of 1 g:5 mL. In addition, several AFA critical parameters such as specific surface area, pore size distribution, particle size distribution, surface morphology, relative content, chemical states of the elements on the AFA surface, mass fractions of various AFA oxides, crystal composition, surface chemical bonds, and coordination structure of Si were determined. The dynamic treatment conditions of organic wastewater were optimised using a continuous wastewater treatment system with MW assistance, and the removal efficiency of p-nitrophenol (PNP) exceeded 90% at a hydraulic retention time of 40 min. The AFA was successfully reused three times while retaining a PNP removal efficiency of 90%. The relationship between the PNP removal rate and the utilised treatment conditions was −d[PNP]dt=0.32⋅[H2O2]0.374⋅[AFA]0.337⋅[H+]0.445⋅[PNP]0.475. Furthermore, the AFA surface played the main role and ·OH was the most reactive oxidative radical. Hence, real coking wastewater can be effectively treated by the AFA-catalysed Fenton-like process under MW assistance.

Response Surface Methodology Optimization of Methylene Blue Removal by Activated Carbon Derived from Foxtail Palm Tree Empty Fruit Bunch

The release of dyes in form of wastewater causes serious environmental problems such as retards photosynthesis, inhibit growth of aquatic biota by blocking out sunlight and utilizing dissolved oxygen. In this study, activated carbon derived from foxtail palm (Wodyetia bifurcata) empty fruit bunch (EFB) was used as an adsorbent to remove methylene blue in aqueous solution. The preparation process of activated carbon consisted of H2SO4 impregnation followed by carbonization at 300ºC for 24 hours. The optimization adsorption process was carried out using Response Surface Methodology (RSM) via Box-Behnken design. Three important operating variables namely dye concentration, contact time and adsorbent dosage were studied. The optimum conditions obtained were 100 ppm of methylene blue, 13 h of contact time and 2 g of activated carbon with the highest percentage of methylene blue removal of 99.9%. Based on the study, activated carbon derived from foxtail palm EFB showed good potential as an adsorbing agent.

Bioprospecting Sulfuric Acid Assisted Hydrothermal Pretreatment of Sugarcane Bagasse and Microbial Community Structure for Methane Production

The complex chemical and structural arrangement of lignocellulosic biomass demand a pretreatment step to dismantle its coherent nature. The current study was designed to study H2SO4 impregnation before hydrothermal pretreatment (HP) of sugarcane bagasse for biogas production using response surface methodology based on defining factors: temperature (160, 180, 200 °C), time (5, 12, 19 min), and H2SO4 concentration (1, 2, 3% w/v). The H2SO4 impregnation had a paramount impact in combination with temperature and treatment time parameters. The lowest solid yield 12.3% was recorded in pretreatment run A-HSO (200 °C, 19 min, 3% H2SO4), up to 100% xylan removal was noted in four pretreatment runs (A-HSO; 200 °C, 19 min, 3% H2SO4, B-HSO; 200 °C, 19 min, 1% H2SO4, C-HSO; 200 °C, 5 min, 3% H2SO4, and O-HSO; 213.6 °C, 12 min, 2% H2SO4), maximum klason lignin increase in insoluble solid fraction (ISF) verified was 358.85% in pretreatment run O-HSO at 213.6 °C, while glucan content reduction (33.18–74.14%) was also observed in pretreatment runs A-HSO, C-HSO, and O-HSO. Results verified maximum methane recovery of 160.16 NmL (g TVS)−1 in pretreatment run I-SHO (180 °C, 12 min, 2% H2SO4). Microbial community analysis observed the predominance of Flavobacterium and Desulfosporosinus genera of Bacterial domain and Methanolinea of Archaea domain. H2SO4 impregnation before HP though not suitable for methane production from ISF could be employed in a biorefinery perspective to obtain valuables (chemicals and fuels) due to the production of organic acids rich liquid stream and lignin-rich solid fraction.

Synergistic Catalytic Effect of Sulphated Zirconia—HCl System for Levulinic Acid and Solid Residue Production Using Microwave Irradiation

The synergistic conversion of Miscanthus xGiganteous with sulphated zirconia and dilute hydrochloric acid was investigated. The sulphated zirconia was prepared using H2SO4 impregnation and characterised using X-ray Diffraction (XRD), Energy-dispersive X-ray (EDX), Scanning Electron Miscroscope (SEM) spectroscopy and nitrogen adsorption–desorption measurements. The microwave-assisted reaction was evaluated at various temperatures, reaction times and catalyst-to-biomass ratios, with and without the presence of trace HCl in the solution medium for the conversion of Miscanthus xGiganteous to levulinic acid. The highest levulinic acid yield of 63.8% was achieved at 160 °C, 80 min and a 2:1 catalyst-to-biomass ratio, with 10 mM HCl. The catalyst recyclability was investigated with and without calcination, finding that significant humin deposition on the catalyst surface likely caused catalyst deactivation. The post-reaction solid residue was also characterised using SEM, EDX, XRD, elemental composition and nitrogen adsorption–desorption measurements. Findings indicate that this residue could potentially be used as a soil amendment or as a fuel source. The synergistic conversion of real lignocellulosic biomass with sulphated zirconia and trace hydrochloric acid showed remarkable promise and should be investigated further.

Directional valorization of eucalyptus waste into value-added chemicals by a novel two-staged controllable pyrolysis process

Fast pyrolysis is a promising way to convert biomass waste into value-added chemicals, but current approaches give poor yield and selectivity for the desired chemicals (e.g. anhydrosugars). This study reported a novel two-staged controllable pyrolysis process consisting of torrefaction of H2SO4-impregnated eucalyptus waste and subsequent fast pyrolysis for achieving directional valorization of eucalyptus waste. Under different torrefaction temperature and holding time, the performance of two-staged controllable pyrolysis of 0.5%H2SO4-impregnated eucalyptus waste was evaluated. The highest total yield of levoglucosan (82.4%, based on cellulose) was obtained by torrefaction at 300 °C with a holding time of 240 s followed by fast pyrolysis at 550 °C, while the highest total yield of xylosan (17.0%, based on hemicellulose) was obtained from torrefaction at 280 °C with a holding time of 20 s combined with subsequent fast pyrolysis at 550 °C. It is demonstrated that H2SO4 impregnation can achieve the directional valorization of holocellulose into anhydrosugars during torrefaction at low temperature, while evidently inhibiting the degradation of lignin and the formation of non-condensable gas and C1-C4 light oxygenates. The unreacted holocellulose and lignin in torrefied eucalyptus waste can be further converted into anhydrosugars and phenols via subsequent fast pyrolysis. This study provides a very simple and efficient strategy to achieve staged and directional valorization of holocellulose and lignin in biomass waste into value-added chemicals.

Treatment of polymer-flooding wastewater by a modified coal fly ash-catalysed Fenton-like process with microwave pre-enhancement: System parameters, kinetics, and proposed mechanism

Raw coal fly ash (RCFA) was modified by H2SO4 impregnation, and the modified RCFA (ACFA) was then used as a Fenton-like catalyst to treat polymer-flooding wastewater (PW) with microwave (MW) pre-enhancement. The characterisation results revealed that H2SO4 impregnation can damage the surface structure of RCFA, increase its specific surface area, and release active sites, thereby improving its catalytic potential. Under optimal experimental conditions (ACFA loading = 20 g/L, H2O2 dosage = 18 mmol/L, pH = 3, MW pre-enhancement duration = 7 min, and formal treatment duration = 50 min), the removal rate of polyacrylamide (PAM) in PW reached 70.3%. The degradation of PAM followed pseudo-first-order kinetics: lnC0C=0.0290∙t, and the relationship between the reaction rate constant, H2O2, and ACFA was kap,1=4355·e-4724.8T·[ACFA]0.411·[H2O2]0.947. MW pre-enhancement could remarkably enhance the OH generation, while the generation path of OH could be changed by the leaching behaviour of ACFA.

Delonix regia heterogeneous catalyzed two-step biodiesel production from Pongamia pinnata oil using methanol and 2-propanol

The study described here was focussed on preparing heterogeneous catalysts (acid and base) by H2SO4 and KOH wet impregnation technique from raw Delonix regia pods after carbonization and steam activation, which was used in converting free fatty acids and glycerides in karanja oil into fuel-grade esters. Resistance to thermal degradation of the precursor material was evaluated by TGA analysis, while catalyst characterization was done through BET, EDAX, FT-IR, SEM and XRD. These helped in estimating efficient surface modification and efficient doping of functional groups. Optimization of both esterification and transesterification steps is done through L16 Taguchi matrices, with the following process parameters: agitation speed, alcohol to oil ratio, catalyst concentration, reaction duration, reaction temperature. With a maximum FFA conversion of 99.86%, the biodiesel yield was 99.39%. Fuel characterization tests and GC analyses for residual glycerides showed that the fuel has acceptable physico-chemical properties according to ASTM standards with low residual glycerides. Catalysts show significant reusability with sulfonated (H2SO4 impregnated) catalyst retaining efficiency up to 3 uses and base catalyst (KOH doped) up to 7 uses. A cost analysis of catalyst preparation shows that the indigenously developed catalysts reduce production costs by a significant margin, proving to be lucrative for commercialization.

Superprotonic conductivity of Ti-based MOFs with Brønsted acid–base pairs

Fuel cells technology demands high and stable proton-conductivity electrolyte materials. Here we show an effective approach of H2SO4 impregnation into Ti-based metal–organic framework (Ti-MOFs, (NH2)x-MIL-125 (x = 0, 1 or 2)), attains high proton-conductivity. The proton conductivity increases for increased amino functional groups on H2SO4@(NH2)x-MIL-125 (x = 0,1 or 2). The superproton conductivity, attributed to the abundant dangled amino functional groups, through an enhanced Brønsted acid–base pairs with sulfonic acid. Notably, the H2SO4@(NH2)2-MIL-125 measured to be superprotonic conductivity of 2.2 × 10−2 S cm−1 under 98% RH &80 °C, thus competes with the most popular electrolyte, such as Nafion. In addition, the composite appeals required characteristics of easy operation, and good stability.

Sulfonated catalytic esterification of Madhuca indica oil using waste Delonix regia: L16 Taguchi optimization and kinetics

The reported study discusses fuel-grade mahua oil methyl esters production from Madhuca indica oil, utilizing Delonix regia pods as a precursor to develop activated carbon support for preparing sulfonated carbon catalyst by H2SO4 impregnation. Raw pods were found to be thermally stable based on TGA analysis, making it suitable as raw material for catalyst synthesis. The catalyst is characterized using BET, XRD, SEM and FT-IR to check desired properties like surface area, porosity enhancement and doping of required functional groups. MOME production is optimized through L16 Taguchi design. Optimum yield of 97.04% is observed at 50 °C for 1 h with 4% w/w catalyst, methanol:oil of 6:1 and 1000 rpm. Catalyst load (1−4% w/w) affects the reaction most prominently, while methanol to oil molar ratio (3:1–12:1) is insignificant. The optimal product is characterized through ASTM standardized tests and gas chromatography analysis and conforms to acceptable biodiesel properties. The reaction adheres to pseudo-first order kinetics with low EA (4.257 kJ/mol) and high A (174.66 min−1). Catalyst shows appreciable reusability with >85% yield after 4 uses. Cost analysis of catalyst preparation shows that indigenously developed catalyst cuts down biodiesel production costs, thus the production process discussed is lucrative for commercialization.

Selective production of anhydrosugars and furfural from fast pyrolysis of corncobs using sulfuric acid as an inhibitor and catalyst

The objective of this study was to selectively coproduce anhydrosugars and furfural from the fast pyrolysis of biomass by H2SO4 impregnation. The pyrolysis behaviors of raw and H2SO4-impregnated corncobs, cellulose and xylan were systematically studied by a thermogravimetric analyzer (TGA) and commercial pyroprobe reactor. The results demonstrate that H2SO4 impregnation can reduce the formation of char and drastically improve the yield of anhydrosugars and furfural. The maximum yields of levoglucosan (38.45 wt% based on cellulose), furfural (19.18 wt% based on hemicellulose) and xylosan (9.49 wt% based on hemicellulose) were obtained by fast pyrolysis of corncobs impregnated with 2.75 wt% H2SO4. By comparing the product distributions from fast pyrolysis of H2SO4-impregnated cellulose, xylan, and raw and demineralized corncobs, it is concluded that H2SO4 can act as an inhibitor to suppress the catalytic functions of structural alkali and alkaline earth metals (AAEM) to improve the yield of anhydrosugars, and H2SO4 can also act as a catalyst to accelerate the dehydration of hemicellulose to form more furfural. It is speculated that H2SO4 could first react with structural AAEM in lignin to form lignosulfonates (e.g., potassium lignosulfonate), thus reducing the catalytic functions of structural AAEM during fast pyrolysis of corncobs. These findings provide a simple and efficient method for the selective coproduction of anhydrosugars and furfural from waste biomass.

Biodiesel Production From Waste Palm Oil Using Palm Empty Fruit Bunch-Derived Novel Carbon Acid Catalyst

Production of biodiesel from waste palm oil (WPO) can provide alternative energy and at the same time reduce the problems created by disposal of WPO. In this study, a novel, inexpensive, and environmental benign carbon acid catalyst is prepared by direct in situ concentrated H2SO4 impregnation of palm empty fruit bunch (PEFB) powder and employed for biodiesel production using WPO. The structure and the physiochemical properties of the prepared catalyst (PEFB-DS-SO3H) are analyzed by acid-base back titration data, energy dispersive X-ray spectroscopy (scanning electron microscopy (SEM)-EDS), SEM, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and using N2 adsorption and desorption isotherm data. It is observed that the catalyst has a unique amorphous structure with total acid density of 5.40 mmolg−1, surface area of 5.5 m2g−1, and 0.31 cm3g−1 pore volume. In addition, FT-IR, XPS, and EDS results confirm a successful sulfonation during the catalyst preparation. It is found that fatty acid methyl ester (FAME) yield increases with increasing methanol:oil (molar ratio) and reaction time up to an optimum value. The highest biodiesel yield of 91% is reported under reaction conditions of 5 wt % catalyst, 14:1 methanol: oil (molar ratio), at 65–70 °C after 14 h in an open reflux system. Results show that the catalyst can be reused for four consecutive cycles without significant loss of catalytic activity. Fuel properties of the produced biodiesel are compatible with the international fuel standards for biodiesel.

Effect of Iodination Temperature on the Polyvinyl Alcohol Based Carbon Nanofiber for Lithium Ion Battery Anodes

Nanofibers has broad application areas including energy, filtration, biomedical and many other engineering fields due to their high porosity, high surface area to volume ratio. Researchers studied several materials and production methods in order to obtain different superior properties from nanofibers. Recently, lithium ion batteries has achieved huge importance due to growing demand for portable electronics, electric vehicles and grid energy storage,etc. Batteries have different components among them anodes have crucial importance on the battery capacity, cycle life and rate capability. One of the promising 1D anode material as carbon nanofibers can provide fast electron transport, reduced lithium ion diffusion lenghts and enhanced surface area comparing to commercial electrodes. There are several carbon nanofiber precursors, such as polyacrylonitril(PAN), lignin, pitch, polyimide(PI).. etc. among them polyvynil alcohol has important advantage because of their environmentally friendly, water soluble and low cost properties. Polyvinyl alcohol (PVA) is a water-soluble polyhydroxy polymer with a broad range of industrial and technical applications. It has been used as a carbon precursor or directly used as anode, cathode or separator in Li-ion batteries. PVA based carbon nanofibers can be easily obtained by electrospinning and subsequent carbonization PVA might be an environmentally friendly alternative material for PAN based carbon fibers. However rather than oxidative stabilization in PAN based precursors, linear PVA chains must be stabilized via other suitable processes. There are various routes that have been proposed to suppress the thermal degradation of PVA before carbonization step, such as using HCl, H2SO4, NH4 vapour or chemical impregnation into different salts. Stabilization of PVA under iodine vapour is a promising approach with high carbon yield for obtaining carbon nanofibers. In this study, we investigated the effect of iodination temperature on the morphology, chemical structure, and electrical properties of carbon nanofiber webs fabricated from electrospun PVA nanofibers. Obtained nanofibers were subjected to different iodination temperature and then converted into carbon nanofibers. It was found that increasing the iodination temperature provides higher carbon yield. Carbon nanofibers were used as binder free, self- standing anode for lithium ion battery. Battery performances showed that PVA based carbon nanofibers are promising anode materials for lithium ion batteries.

Esterification of oily-FFA and transesterification of high FFA waste oils using novel palm trunk and bagasse-derived catalysts

Waste cooking oil is increasingly becoming a significant component of biodiesel feedstock and its conversion to FAME requires coupling of esterification and transesterification processes. In this study, new environmentally benign catalysts were prepared from oil palm trunk and sugarcane bagasse, which are sustainable because of the superfluity of oil palm trunk and abundant supply of bagasse. Effect of preparation variable, surface acidity and textural properties, pre-esterification of FFA in oil matrices and transesterification of waste oil under pseudo-infinite methanol and conventional methods were investigated. The preparation variable, H2SO4 impregnation time showed marginal effect on sulfonic acid density after 6h, and the corresponding values for 6–10h impregnations were 1.33±0.01–1.41±0.01mmolg−1 for OPT and 1.44±0.01–1.48±0.01mmolg−1 for SCB catalysts. In esterification of palmitic acid, activity of catalysts with different H2SO4 impregnation time correlates with their sulfonic acid density. The catalysts demonstrated rapid esterification of FFA in oil matrices under pseudo infinite methanol, reducing its content from 42wt.% to <1wt.% in just 15min. Similarly, the conversions of waste oil by OPT and SCB derived catalysts were 80.6% and 83.2%, respectively after 4h under pseudo-infinite methanol, and 43.7% and 45%, respectively after 6h under conventional method. These catalysts have shown remarkable properties that are suitable for biodiesel production from waste oil.

Impact of Sulfur Oxides on Mercury Capture by Activated Carbon

Recent field tests of mercury removal with activated carbon injection (ACI) have revealed that mercury capture is limited in flue gases containing high concentrations of sulfur oxides (SOx). In order to gain a more complete understanding of the impact of SOx on ACl, mercury capture was tested under varying conditions of SO2 and SO3 concentrations using a packed bed reactor and simulated flue gas (SFG). The final mercury content of the activated carbons is independent of the SO2 concentration in the SFG, but the presence of SO3 inhibits mercury capture even at the lowest concentration tested (20 ppm). The mercury removal capacity decreases as the sulfur content of the used activated carbons increases from 1 to 10%. In one extreme case, an activated carbon with 10% sulfur, prepared by H2SO4 impregnation, shows almost no mercury capacity. The results suggest that mercury and sulfur oxides are in competition for the same binding sites on the carbon surface.

Equilibrium, Kinetic and Mass Transfer Studies and Column Operations for the Removal of Arsenic(III) from Aqueous Solutions using Acid Treated Spent Bleaching Earth

In the present study, a new adsorbent was produced from spent bleaching earth by H2SO4 impregnation method. The sorption of arsenic(III) by acid treated spent bleaching earth was studied to examine the possibility of utilizing this material in water treatment systems. The effect of time, pH, initial concentration, temperature on the adsorption of arsenic(III) was studied. Maximum adsorption was found to occur at pH 9.0. The adsorption process followed the first order Lagergren equation. Mass transfer coefficients and rate constants of intraparticle diffusion were calculated. The experimental data points were fitted to the Langmuir equation in order to calculate the adsorption capacity (Q0) of the adsorbent and the value of Q0 was found to be 0.46 mmol g–1. In order to understand the adsorption mechanism, Dubinin-Radushkevich (DR) isotherm was used. The magnitude of E calculated from DR equation was found to be 5.12 kJ mol–1. The heat of adsorption (ΔH0 = –30367 J mol–1) implied that the adsorption was physical exothermic adsorption. The column studies were also carried out to simulate water treatment processes. The capacity values obtained in column studies were found to be greater than the capacity values obtained in batch studies. This result was explained by the difference between batch system and column system. The factors that affect the capacity values of column and batch systems were explained. The effect of other anions on the adsorption of arsenic(III) in the presence of NO3 –, SO4 2–, Cl–, Br– was studied. The presence of these anions did not affect the adsorption of arsenic(III) significiantly.

Combined use of H2SO4 and SO2 impregnation for steam pretreatment of spruce in ethanol production.

Fuel ethanol can be produced from softwood through hydrolysis in an enzymatic process. Prior to enzymatic hydrolysis of the softwood, pretreatment is necessary. In this study, two-step steam pretreatment employing dilute H2SO4 impregnation in the first step and SO2 impregnation in the second step, to improve the overall sugar and ethanol yield, was investigated. The first pretreatment step was performed under conditions of low severity (180 degrees C, 10 min, 0.5% H2SO4) to optimize the amount of hydrolyzed hemicellulose. In the second step, the washed solid material from the first pretreatment step was impregnated with SO2 and pretreated under conditions of higher severity to make the cellulose more accessible to enzymatic attack, as well as to hydrolyze a portion of the cellulose. A wide range of conditions was used in the second step to determine the most favorable combination. The temperatures investigated were between 190 and 230 degrees C, the residence times were 2, 5, and 10 min; and the SO2 concentration was 3%. The effect of pretreatment was assessed by both enzymatic hydrolysis of the solids and by simultaneous saccharification and fermentation (SSF) of the whole slurry, after the second pretreatment step. For each set of pretreatment conditions, the liquid fraction was also fermented to determine any inhibitory effects. Ethanol yield using the SSF configuration reached 66% of the theoretical value for pretreatment conditions in the second step of 210 degrees C and 5 min. The sugar yield using the separate hydrolysis and fermentation configuration reached 71% for pretreatment conditions of 220 degrees C and 5 min.

SO4–ZrO2 catalysts for the esterification of benzoic acid to methylbenzoate

SO4–ZrO2 catalysts, prepared by varying the conditions of oxide preparation and H2SO4 impregnation, have been characterized by means of different techniques (XRD, BET, Hammett–Bertolacini technique, XPS). The esterification of benzoic acid to methylbenzoate has been used to test the different catalysts and their catalytic performance has been discussed in the light of their bulk and surface properties.

Comparison of SO2 and H2SO4 impregnation of softwood prior to steam pretreatment on ethanol production

The pretreatment of softwood with sulfuric acid impregnation in the production of ethanol, based on enzymatic hydrolysis, has been investigated. The parameters investigated were: H2SO4 concentration (0.5–4.4% w/w liquid), temperature (180–240°C), and residence time (1-20 minutes). The combined severity (log Ro-pH) was used to combine the parameters into a single reaction ordinate. The highest yields of fermentable sugars, i.e., glucose and mannose, were obtained at a combined severity of 3. At this severity, however, the fermentability declined and the ethanol yield decreased. In a comparison with previous results, SO2 impregnation was found to be preferable, since it resulted in approximately the same sugar yields, but better fermentability.

Effect of Sulphur Dioxide and Sulphuric Acid on Steam Explosion of Aspenwood

Abstract The use of steam explosion as a pretreatment for woody biomass prior to enzymatic hydrolysis has been proposed in the past. In this study the effect of SO2 impregnation (1.6% SO2 on dry wood input) and H2SO4 impregnation (0.58% H2SO4 on dry wood input) on the exploded substrates produced are compared with the case where no acid was added. Both acid catalysts substantially improve the survival of pentose sugars when treatments of equal severity are compared. H2SO4 however reduces the extent to which lignin may be extracted from the water washed exploded substrates with caustic. The mode of action of the SO2 has been examined and, at the levels used in this work, approximately 50% of the input sulphur is shown to bind to the substrate forming, most likely, ligno-sulphonates. The enzymic digestibilities of the acid impregnated steam exploded substrates are compared with those of the non-acid impregnated material and are shown to be more easily saccharified.