Dilute Mineral Acid Research Articles

Applicability of new sustainable and efficient alginate-based composites for critical raw materials recovery: General composites fabrication optimization and adsorption performance evaluation

Based on the 2020 list of raw materials for the EU, there are 30 critical minerals on the critical raw materials list, among which the rare earth elements group is placed. This study demonstrates a viable approach to the increasing possibility of the critical materials recovery through biosorption. The environmentally friendly biosorbents were prepared modifying calcium alginate with biochar and clinoptilolite. Firstly, the optimization procedure was applied for obtaining new biocomposites. After that the adsorption studies of La(III), Ce(III), Pr(III), and Nd(III) ions as a function of solution pH, biosorbent mass, interaction time, initial metal concentration, temperature, and competing ions presence were carried out using the batch mode. The kinetic studies were analyzed using the pseudo-first order, pseudo-second order, Weber and Morris intraparticle diffusion, Boyd as well as Dumwald-Wagner kinetic models. The experimental equilibrium data were fitted using the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. The thermodynamic functions, i.e. ΔG°, ΔH°, and ΔS° were also determined. Importantly, the biocomposite beads were readily regenerated using diluted mineral acids (exemplary 0.1 mol/dm3 HNO3) and moreover, the adsorption effectiveness was very satisfactory even after six adsorption–desorption cycles (97%). New biocomposites as potential sorbents were characterized with ATR/FT-IR and XPS spectroscopy, SEM, EDX, OM and AFM microscopy, nitrogen adsorption, TG/DTG, CHNS, XRD as well as the sieve analysis and pHpzc measurements. After the interactions of the alginate composites with La(III) ions, a possible sorption mechanism was analyzed by ATR/FT-IR, XPS, and EDX spectroscopy.

Development of Analytical Method for Determination of Inorganic Constituents in Powder Refreshment using Dilute Mineral Acids and Detection by ICP OES

An analytical method for multi-elementary determination in powder refreshment, based on sample digestion using dilute mineral acids and detection by inductively plasma coupled optical emission spectrometry (ICP OES) is proposed. Chemometric tools, such as fractional factorial design and principal component analysis (PCA) and hierarchical cluster analysis (HCA) were applied to optimize the sample preparation conditions in closed block digester, and Doehlert design for spectrometer operation. Addition and recovery tests and analyses of certified reference material were performed to evaluate the precision and accuracy, and the results confirm the reliability of the proposed method. Limits of quantification (LOQ) between 0.02 and 36 μg g−1 were obtained. The analytical method was applied for determination of 24 inorganic constituents in 20 powder refreshment samples. Calcium, K, Mg, Na, P, S and Ti presented the highest concentrations. The analytical method was adequate for the determinations of inorganic constituents in powder refreshment samples by ICP OES.

Mild Synthesis of Cyclohexanol and Cyclohexanone Via Electrocatalytic Reduction of Phenols Using Dispersed Metal Catalysts

Cyclohexanol and cyclohexanone are industrially important chemicals for the synthesis of Nylon polymers. On the industrial scale, they are produced by thermocatalytic processes, either phenol hydrogenation (140–170 oC, 1 atm) or cyclohexane oxidation (140–180 oC, 0.8–2 MPa), which require high temperatures and external gas supply. This work demonstrates that electrosynthesis of cyclohexanol and cyclohexanone can be done at mild conditions using diverse aqueous electrolytes and dispersed metal catalysts (Pt/C, Ru/C, and Pd/C).Electrocatalytic hydrogenation (ECH) of lignin-derived phenols (e.g., guaiacol and phenol) is performed in a stirred slurry H-cell under potentiostatic or galvanostatic control. Dilute mineral acid (H2SO4, HClO4), organic acid (CH4SO3), and inorganic salt (NaCl) worked efficiently as the electrolyte solutions. In the ECH of guaiacol at low temperatures (35–40 oC) and low Pt/C loading, high guaiacol conversions (83–96%) and Faradaic efficiencies (40–70%) were achieved with significant cyclohexanol selectivities (45–53%) after 4 h reactions. In the ECH of phenol, full conversion to cyclohexanol was achieved after 2 h with high current efficiency (90%). Remarkably, by pairing the NaCl catholyte and H2SO4 anolyte, the activity of Ru/C and Pd/C can be dramatically improved, showing the importance of electrocatalyst and electrolyte synergy in the ECH of phenolic compounds.The stirred slurry catalyst allows the cell to operate at the industrially relevant current densities (in this work, between 100–300 mA cm-2). Dispersion of the negatively charged catalyst particles in the solution also facilitates the mass transfer between the organic molecules and chemisorbed hydrogens through physical collisions during the reaction, thereby improving the ECH efficiency. Mild electrocatalytic reduction of phenolic compounds represents a promising route for selective and efficient production of renewable chemicals from biomass.

Recovery of ammonia from wastewater through chemical precipitation

Chemical precipitation is a consolidated technique applied in wastewater treatment to remove and recover phosphorous and ammonium that remain in the effluent after the anaerobic digestion treatment. The precipitate is magnesium ammonium phosphate hexahydrate (MgNH4PO4·6H2O), also known as struvite, and it is sold as a slow-release fertiliser. However, the value of struvite is quite low and has a limited market. Furthermore, it precipitates with heavy metals and other impurities that need to be removed to make the fertiliser commercially viable. This study looked at the thermal decomposition of struvite to recover added value products and recycle the magnesium for further precipitation. A kinetic study was carried out to understand the mechanism of decomposition and the formation of the different solid phases, which is fundamental for the design and optimisation of the technology. The thermogravimetric study confirmed that thermal decomposition is possible, but ammonia could not be completely released below 250 °C. The thermal analysis also led to the determination of the energy required for the decomposition, found to be 1.87 kJ g−1, which also includes the evaporation of water and ammonia. The kinetic study through the isoconversional method showed the presence of two major reactions, and the model-fitting approach identified the diffusion model as the best fit for the first reaction. The activation energy of the first reaction found with this method was 0.24 kJ g−1, comparable with the data obtained from the isoconversional method. The two-stage decomposition reactions were proposed, and the final calcination product was confirmed as magnesium pyrophosphate, which could be used in agriculture or dissolved in diluted mineral acids solution to separate the phosphate from the magnesium.

Rocha contendo biotita como fonte alternativa de potássio para fertilizante após processamento térmico com aditivos

A biotita é um filossilicato ferromagnesiano que contém potássio. Ela é muito abundante e dispersa em todas as regiões do mundo. Formada secundariamente nos processos metamórficos constitui impureza em muitos processamentos minerais e descartada em bacias de estéreis ou de rejeito. É uma fonte alternativa de potássio para produção de fertilizante, porém, ainda sem exploração comercial em grande escala, para este propósito, por falta de tecnologia que torne o negócio viável economicamente. O objetivo deste trabalho foi investigar o efeito do processamento térmico, usando aditivos, na solubilização do potássio e impurezas em ácido mineral diluído, de rocha contendo biotita. Foi selecionada uma rocha da província mineral de Carajás–Pará – Brasil, com teor de 9,7% de K₂O e 70% de biotita. O processamento térmico foi executado em duas temperaturas, 800°C e 900°C, durante 6h, usando dois sistemas de misturas: (biotita+CaCO₃+MgCl2.6H2O) e (biotita+gesso+Na₂CO₃). A etapa de lixiviação ácida sulfúrica foi executada em pH mantido entre 2,0 e 3,0, temperatura de 85℃, durante 1h. As extrações, no sistema com cloreto de magnésio (800°C), chegaram a 63% do potássio e com solubilização máxima de 5% de Fe e Al. As extrações de potássio com gesso ficaram menores, 41%, mostrando tendência de melhor eficiência em temperaturas mais altas do que as escolhidas para este estudo, porém, com licor efluente da lixiviação isento de alumínio e 1,2% máximo de extração de ferro.

The role of electrolyte acid concentration in the electrochemical exfoliation of graphite: Mechanism and synthesis of electrochemical graphene oxide

Electrochemistry has emerged as a major route for graphene and graphene oxide synthesis from graphite. Anodic graphite oxidation is commonly used with dilute mineral acid or aqueous salt electrolytes. In this system, the electrolyte acid concentration appears to be a critical parameter. However, the effect of the acid concentration, particularly at low concentrations, is still not fully understood. To address this issue, we used a packed bed electrochemical reactor to synthesize seven different electrochemical graphite oxide (EGO) products in 2–16 M sulfuric acid. Detailed XRD, XPS, Raman, conductivity and optical microscopy analysis of the products was carried out. We found dilute acid (<10 M) graphite oxides were less crystalline and less oxidized than those produced in stronger acids. The oxygen evolution reaction at the graphite surface appears to affect the structural changes, oxidation mechanism, and electrochemical corrosion of the anode. EGO conductivity is also strongly affected by the electrolyte’s acidity. We show that well oxidized, yet reasonably conductive, single layer graphene oxide can be produced from 7.1 M acid. These results broaden our understanding of graphite electrochemistry and will serve to inform future electrochemical graphene synthesis efforts.

Levulinic Acid Production from the Green Macroalgae Chaetomorpha Linum and Valonia Aegagropila Harvested in the Orbetello Lagoon

In recent years, the replacement of fossil resources with renewable ones has received great interest, especially as regards the production of new valuable bio-products and bio-fuels, in order to replace the traditional petroleum-based ones. In this context, the exploitation of waste biomasses into added-value bio-chemicals is strongly encouraged. Among these ones, the algae ones are attracting considerable attention, in particular macroalgae which cause eutrophication problems in estuaries and lagoons, due to the drastic reduction of dissolved oxygen during their decomposition. This is true for Orbetello lagoon (Italy), where a large amount of algal biomasses is removed every year through an expensive practice, with consequent environmentally serious disposal problems. In this work, for the first time, the acid-catalyzed conversion of two different macroalgae harvested in Orbetello lagoon, Chaetomorpha linum (Muller) Kutzing and Valonia aegagropila C. Agardh, into levulinic acid was studied and optimized, adopting a one-pot hydrothermal treatment, under microwave heating and in the presence of aqueous diluted mineral acids, H2SO4 and HCl. Levulinic acid is a versatile platform chemical, classified by the United States Department of Energy as one of the top-12 promising bio-based building blocks. The effect of the main reaction parameters to give levulinic acid was investigated and discussed, in particular the type and concentration of the acid catalyst, the temperature and the reaction time. The highest levulinic acid yields of 19 wt% for Chaetomorpha linum and 16 wt% for Valonia aegagropila, calculated respect to the weight of the starting dried biomass, were reached. The achieved results are very promising and confirm the significant potential of these green algae as renewable starting feedstocks for levulinic acid production.

An investigation of poultry farm waste as potential fuel and source of nutrients for agricultural land

ABSTRACTPoultry litter was subjected to water and diluted mineral acids leaching for nutrients extraction followed by its thermal and kinetic analysis. Nitric acid treatment yielded optimum results showing an increase of 33%, 30%, and 60%, in fixed carbon, volatile matter, and gross calorific values, respectively. Macronutrients prior and after the leaching process were found to be decreased to 50% in leached samples. Ignition and burn out temperatures were not affected with heating rates, whereas an inverse effect was found for activation energy during thermogravimetric and kinetic analysis. However, peak temperature was increased to 100°C and 50°C in case of water treated and untreated & nitric acid treated samples, respectively. The results showed potential utilization of extracted poultry litter in the energy matrix.

Laboratory Leaching Tests to Investigate Mobilisation and Recovery of Metals from Geothermal Reservoirs

The H2020 project “Combined Heat, Power and Metal extraction” (CHPM2030) aims at developing a novel technology which combines geothermal energy utilisation with the extraction of metals in a single interlinked process. In order to improve the economics of geothermal-based energy production, the project investigates possible technologies for the exploitation of metal-bearing geological formations with geothermal potential at depths of 3–4 km or deeper. In this way, the coproduction of energy and metals would be possible and could be optimized according to market demands in the future. This technology could allow the mining of deep ore bodies, particularly for critical metals, alongside power production, while minimizing environmental impact and costs. In this paper, we describe laboratory leaching experiments aimed at quantifying the relative rates and magnitudes of metal release and seeing how these vary with different fluids. Specific size fractions (250–500 μm) of ground mineralised rock samples were investigated under various pressures and temperatures up to 250 bar and 250°C. Initial experiments involved testing a variety of potential leaching fluids with various mineralised samples for a relatively long time (up to 720 h) in batch reactors in order to assess leaching effectiveness. Selected fluids were used in a flow-through reactor with shorter contact time (0.6 h). To ensure possible application in a real geothermal reservoir, a range of fluids were considered, from dilute mineral acid to relatively environmentally benign fluids, such as deionised water and acetic acid. The main findings of the study include fast reaction time, meaning that steady-state fluid compositions were reached in the first few hours of reaction and enhanced mobilisation of Ca, Cd, Mn, Pb, S, Si, and Zn. Some critical elements, such as Co, Sr, and W, were also found in notable concentrations during fluid-rock interactions. However, the amount of these useful elements released is much less compared to the common elements found, which include Al, Ca, Fe, K, Mg, Mn, Na, Pb, S, Si, and Zn. Even though concentrations of dissolved metals increased during the tests, some remained low, and this may present technical challenges for metal extraction. Future efforts will work toward attaining actual fluids from depth to more tightly constrain the effect of parameters such as salinity, which will also influence metal solubility.

Phase Crystallization in the CePO4–NaF System

The phase crystallization in the CePO4–NaF system was studied in order to develop an industrial process for rare earth metal recovery from a phosphate salt melt formed upon liquation of the rare earth ores from the weathering crust of the Tomtor deposit. The phosphate salt melt accumulated TR2O3, P2O5, Sc2O3, and Y2O3, and the silicate melt contained Fe2O3 and Nb2O5. Chemical reactions between CePO4 and NaF in the phosphate salt melt induced crystallization of the double phosphate Na3Ce[PO4]2 and the fluoride phosphate Na2CePO4F2. The products of melt crystallization in the CePO4–NaF system incongruently decomposed in dilute mineral acids (HNO3) to give an insoluble precipitate containing CeO2 and CeF3.

A new approach to recycle oxalic acid during lignocellulose pretreatment for xylose production

BackgroundDilute oxalic acid pretreatment has drawn much attention because it could selectively hydrolyse the hemicellulose fraction during lignocellulose pretreatment. However, there are few studies focusing on the recovery of oxalic acid. Here, we reported a new approach to recycle oxalic acid used in pretreatment via ethanol extraction.ResultsThe highest xylose content in hydrolysate was 266.70 mg xylose per 1 g corncob (85.0% yield), which was achieved using 150 mmol/L oxalic acid under the optimized treatment condition (140 °C, 2.5 h). These pretreatment conditions were employed to the subsequent pretreatment using recycled oxalic acid. Oxalic acid in the hydrolysate could be recycled according to the following steps: (1) water was removed via evaporation and vacuum drying, (2) ethanol was used to extract oxalic acid in the remaining mixture, and (3) oxalic acid and ethanol were separated by reduced pressure evaporation. The total xylose yields could be stabilized by intermittent adding oxalic acid, and the yields were in range of 46.7–64.3% in this experiment.ConclusionsThis sustainable approach of recycling and reuse of oxalic acid has a significant potential application for replacing traditional dilute mineral acid pretreatment of lignocellulose, which could contribute to reduce CO2 emissions and the cost of the pretreatment.

Insights into the Inhibition of Acidic Hydrolysis of Cellulose by Its Solation

Cellulose hydrolysis in dilute mineral acids was investigated, and a plateau in cellulose conversion was observed such that an extended reaction time did not result in further conversion of cellulose, which severely reduced the hydrolysis efficiency of cellulose. The characterization results indicated that the crystallinity indexes of cellulose and the deposition of humins were not the key factors inhibiting the reaction but rather the solation of cellulose in the presence of water, protons, and anions was the key. The hydrolysis reaction proceeded after the solated state of cellulose was disrupted by means of filtration, increased temperature, or the addition of organic solvents and inorganic salts. However, a new plateau in cellulose conversion eventually formed and inhibited the hydrolysis reaction again. Therefore, continuous disruption of the solated system of cellulose is the key strategy to achieve high cellulose conversion under even mild reaction conditions.

Separation of 89Zr from irradiated yttrium targets by extraction chromatography

In this work, the separation of 89Zr, a radionuclide promising for positron-emission tomography, from an irradiated yttrium target using different extraction-chromatographic resins (TEVA, UTEVA, TRU, and LN resins ©Triskem) was studied. Distribution coefficients of Zr(IV) onto TEVA, LN (in HCl solutions), and onto TRU (in HCl and HNO3) were determined. The optimum conditions for the separation of Zr(IV) and Y(III) using these resins were proposed. In each case, the maximum separation factor was higher than 105. The developed separation procedures allow to obtain 89Zr of high radiochemical purity for dilute mineral acids.

Production of 5‐hydroxymethyl furfural and levulinic acid from lignocellulose in aqueous solution and different solvents

AbstractWith the continuous development of society and a serious energy crisis, renewable energy has become highly important. As platform compounds that can produce large amounts of chemical products, 5‐hydroxymethyl furfural (5‐HMF) and levulinic acid (LA) have attracted the attention of many researchers. Production of 5‐HMF and LA with lignocellulose is currently one of the most promising research directions in biomass energy. Conventionally, production of 5‐HMF and LA with lignocellulose is typically performed in aqueous solutions containing dilute mineral acids as catalysts. Recently, advances have been reported in the use of heterogeneous catalysts for conversion of lignocellulose into 5‐HMF and LA in different solvents to eliminate the use of mineral acids. In this paper, the merits, demerits, and requirements for commercialization are outlined for 5‐HMF and LA production from lignocellulose in aqueous solution, and different solvents are reviewed. Special attention is focused on the use of green chemicals (such as γ‐valerolactone) and ionic liquids as solvents due to their clean and recoverable characteristics. © 2016 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

Influence of Residues Contained in Softwood Hemicellulose Hydrolysates on the Catalytic Oxidation of Glucose to Glucarate in Alkaline Aqueous Solution

The hydrolysate recovered after acid hydrolysis of the hemicellulose fraction of softwood represents a renewable and low-cost source of sugars which can be used for the production of chemicals such as glucaric acid. In this paper we first re-evaluated the metal-catalyzed aerobic oxidation of gluconate and one-step oxidation of glucose to glucarate in alkaline aqueous solution at 60 °C using air as oxidant. Then, we investigated the possible inhibitory effect of some inherent side (or by)-products liberated during the dilute mineral acid hydrolysis. High conversion efficiencies were obtained in glucose oxidation; however, the maximum glucarate yield was 54% over Pt/C since overoxidation products were formed under these conditions. As regards the residues in the hydrolysate, sodium salts (acetate and sulfate) or disaccharides (cellobiose and maltose) were without significant effect on the course of the reaction, whereas furan aldehydes (5-hydroxymethylfurfural and furfural) appeared to significantly slow do...

English

The surface composition and surface properties of water hyacinth (Eichhornia crassipes) root biomass were studied before and after extraction with dilute nitric acid and toluene/ethanol (2/1, v/v) followed by ethanol, using Fourier Transform Infra-red (FT-IR) spectroscopy, thermogravimetric analysis, x-ray diffraction, scanning electron microscopy. FT-IR absorption bands were obtained at 3421, 2855, 1457 and 1035 cm-1 (O-H stretch, C-H vibration, C-H asymmetric deformation, and C-O stretch, respectively) and 1508, 1541 and 1559 cm-1 (all aromatic skeletal vibrations characteristic of lignin), as well as a C=O carboxylate stretch vibrational band at 1654 cm-1. Scanning electron microscopy confirmed the root biomass to be amorphous and not to have a strongly structured surface. The dilute mineral acid and organic solvent treatment increased crystallinity. Thermogravimetric analysis Studies show that the treated biomass are more thermally stable than the untreated biomass. Data are presented showing that dilute mineral acid and organic solvent treatment resulted in a decrease in the amount of lignin in the biomass. The implications of the decrease in the percentage of lignin on the adsorption of volatile polar organic solvents and non-polar n-alkane hydrocarbons is discussed. Key words: Water hyacinth, biomass, surface composition, Fourier Transform Infra-red (FT-IR) spectroscopy, scanning electron microscopy, x-ray diffraction spectroscopy, thermo gravimetric analysis.

Complete chemical hydrolysis of cellulose into fermentable sugars through ionic liquids and antisolvent pretreatments.

This work describes a relatively simple methodology for efficiently deconstructing cellulose into monomeric glucose, which is more easily transformed into a variety of platform molecules for the production of chemicals and fuels. The approach undertaken herein first involves the dissolution of cellulose in an ionic liquid (IL), followed by a second reconstruction step aided by an antisolvent. The regenerated cellulose exhibited strong structural and morphological changes, as revealed by XRD and SEM analyses. These changes dramatically affect the hydrolytic reactivity of cellulose with dilute mineral acids. As a consequence, the glucose yield obtained from the deconstructed-reconstructed cellulose was substantially higher than that achieved through hydrolysis of the starting cellulose. Factors that affect the hydrolysis reaction include the type of cellulose substrate, the type of IL used in pretreatment, and the type of acid used in the hydrolysis step. The best results were obtained by treating cellulose with IL and using phosphotungstic acid (0.067 mol L(-1) ) as a catalyst at 413 K. Under these conditions, the conversion of cellulose was almost complete (>99%), with a glucose yield of 87% after only 5 h of reaction.

Enhanced Chromium Recovery from Tannery Waste by Acid-Alkali Reaction in China

Leather processing is an important industry in China, and the discharge of chromium waste has been severely circumscribed. Though traditional processes for treating chromium waste have been widely used in tannery plants, technology adopting high efficiency and economic simultaneously is deficient. In order to develop an economic treatment for tannery waste, a mixed alkali of sodium hydroxide and magnesium oxide and diluted mineral acids were tested to improve the sedimentation effect of trivalent chromium from tannery wastewater. The results showed that the most feasible alkali was a mixture of sodium hydroxide and magnesium oxide with a mass ratio of 5:1 to balance the cost performance. The high chromium removal as 99.1% was obtained with a mixed alkali dosage only 0.2 g/L at pH 9.5, with a very low Cr-sludge yield. The effects of various factors on the extraction of trivalent chromium from Cr-sludge using mineral acids were investigated further more, and the results indicated that the feasible condition for chromium recovery from wet chromium sludge was as follows: 4% sulfuric acid as the leaching acid, chromium sludge (dry weight) load 23.55 g/L, extraction time 60 min, and reaction temperature 30°C. A chromium recovery of 20.86 mg/g was obtained under the feasible condition with a recovery rate of 91.8%. The method developed in the present study provided an effective solution to balance the cost performance for tannery waste treatment.

Simultaneous detoxification, saccharification, and ethanol fermentation of weak-acid hydrolyzates

Lignocellulosic feedstocks can be prepared for ethanol fermentation by pre-treatment with a dilute mineral acid catalyst that hydrolyzes the hemicellulose and opens up the plant cell wall fibers for subsequent enzymatic saccharification. The acid catalyzed reaction scheme is sequential whereby released monosaccharides are further degraded to furans and other chemicals that are inhibitory to the next fermentation step. This work evaluated the use of agricultural residue (flax shive) as starting material for making activated biochar to adsorb these degradation products. Results show that both furfural and hydroxymethylfurfural (HMF) are adsorbed by steam-activated biochar prepared from flax shive. Decontamination of the hydrolyzate significantly improved the fermentation behavior by Saccharomyces cerevisiae yeast, including significantly reducing the lag phase of the fermentation, when the amount of biochar added to the fermentation broth was 2.5% (w/v). No negative effects were noted from addition of activated char to the process.

Reactive high pressure carbonated water pretreatment prior to enzymatic saccharification of biomass substrates

Abstract Pretreatment of biomass substrates is critical in their use for generating monomeric sugars for conversion to transport fuels, such as bioethanol. In this study, high pressure reactive pretreatment and hydrolysis of cellulose- and hemicellulose-containing substrates, principally corn stover and switchgrass, were conducted over the temperature range of 150–190 °C utilizing carbon dioxide pressures ranging from 150 to 450 bar. Experimental protocol was guided by the development of an orthogonal design criteria consisting of temperature, CO2 pressure, time of pretreatment-hydrolysis, and substrate particle size. High pressure carbonation of the subcritical water-biomass mixtures were conducted in a small batch reactor and the resultant hydrolyzate mixtures were analyzed for sugar content using SEC and HPLC-RI detection. Also, the resultant hydrolyzates after carbonated water pretreatment were further hydrolyzed using commercial enzymes to saccharify the remaining oligomeric sugars to xylose and glucose. The resultant % sugar content of the carbonated water – versus dilute mineral acid – pretreated biomass mixtures were compared as well as the corresponding final enzymatically saccharified hydrolyzates for switchgrass and corn stover. High pressure carbonated water pretreatment yielded 9–13% less sugars than the sulfuric acid-derived hydrolyzate and relatively 6–10% less sugars were found in the final carbonated water treated hydrolyzates after further enzymatic treatment. It was also found that carbonated water pretreated switchgrass hydrolyzate required 33% lesser amount of enzyme for saccharification when compared to that obtained using dilute sulfuric acid pretreatment. The supercritical carbon dioxide dissolved in water provides an environmentally benign and “green” pretreatment method for depolymerization of the sugars present in biomass substrates and to facilitate further saccharification without the necessity of base neutralization, or pH adjustment prior to application of enzyme-initiated hydrolysis.