Optimizing Dilute-Acid Pretreatment of Rapeseed Straw for Extraction of Hemicellulose

Biological conversion of biomass into fuels and chemicals requires hydrolysis of the polysaccharide fraction into monomeric sugars prior to fermentation. Hydrolysis can be performed enzymatically or with mineral acids. In this study, dilute sulfuric acid was used as a catalyst for the pretreatment of rapeseed straw. The purpose of this study is to optimize the pretreatment process in a 15-mL bomb tube reactor and investigate the effects of the acid concentration, temperature, and reaction time. These parameters influence hemicellulose removal and production of sugars (xylose, glucose, and arabinose) in the hydrolyzate as well as the formation of by-products (furfural, 5-hydroxymethylfurfural, and acetic acid). Statistical analysis was based on a model composition corresponding to a 3³ orthogonal factorial design and employed the response surface methodology to optimize the pretreatment conditions, aiming to attain maximum xylan, mannan, and galactan (XMG) extraction from hemicellulose of rapeseed straw. The obtained optimum conditions were: H₂SO₄ concentration of 1.76% and temperature of 152.6 °C with a reaction time of 21 min. Under these optimal conditions, 85.5% of the total sugar was recovered after acid hydrolysis (78.9% XMG and 6.6% glucan). The hydrolyzate contained 1.60 g/L glucose, 0.61 g/L arabinose, 10.49 g/L xylose, mannose, and galactose, 0.39 g/L cellobiose, 0.94 g/L fructose, 0.02 g/L 1,6-anhydro-glucose, 1.17 g/L formic acid, 2.94 g/L acetic acid, 0.04 g/L levulinic acid, 0.04 g/L 5-hydroxymethylfurfural, and 0.98 g/L furfural.     

A Comparison of Simple Rheological Parameters and Simulation Data for Zymomonas mobilis Fermentation Broths with High Substrate Loading in a 3-L Bioreactor

Traditionally, as much as 80% or more of an ethanol fermentation broth is water that must be removed. This mixture is not only costly to separate but also produces a large aqueous stream that must then be disposed of or recycled. Integrative approaches to water reduction include increasing the biomass concentration during fermentation. In this paper, experimental results are presented for the rheological behavior of high-solids enzymatic cellulose hydrolysis and ethanol fermentation for biomass conversion using Solka Floc as the model feedstock. The experimental determination of the viscosity, shear stress, and shear rate relationships of the 10 to 20% slurry concentrations with constant enzyme concentrations are performed with a variable speed rotational viscometer (2.0 to 200 rpm) at 40 °C. The viscosities of enzymatic suspension observed were in range of 0.0418 to 0.0144, 0.233 to 0.0348, and 0.292 to 0.0447 Pa s for shear rates up to 100 reciprocal seconds at 10, 15, and 20% initial solids (w/v), respectively. Computational fluid dynamics analysis of bioreactor mixing demonstrates the change in bioreactor mixing with increasing biomass concentration. The portion-loading method is shown to be effective for processing high-solids slurries.     

Effect of Pretreatment Severity on Accumulation of Major Degradation Products from Dilute Acid Pretreated Corn Stover and Subsequent Inhibition of Enzymatic Hydrolysis of Cellulose

The concept of reaction severity, which combines residence time and temperature, is often used in the pulp and paper and biorefining industries. The influence of corn stover pretreatment severity on yield of sugar and major degradation products and subsequent effects on enzymatic cellulose hydrolysis was investigated. The pretreatment residence time and temperature, combined into the severity factor (Log R _o), were varied with constant acid concentration. With increasing severity, increasing concentrations of furfural and 5-hydroxymethylfurfural (5-HMF) coincided with decreasing yields of oligosaccharides. With further increase in severity factor, the concentrations of furans decreased, while the formation of formic acid and lactic acid increased. For example, from severity 3.87 to 4.32, xylose decreased from 6.39 to 5.26?mg/mL, while furfural increased from 1.04 to 1.33?mg/mL; as the severity was further increased to 4.42, furfural diminished to 1.23?mg/mL as formate rose from 0.62 to 1.83?mg/mL. The effects of dilute acid hydrolyzate, acetic acid, and lignin, in particular, on enzymatic hydrolysis were investigated with a rapid microassay method. The microplate method gave considerable time and cost savings compared to the traditional assay protocol, and it is applicable to a broad range of lignocellulosic substrates.     

Effect of potassium on alumina supported chromium oxide catalysts for methylene chloride oxidation

Alumina supported chromium oxide catalysts added potassium were prepared and tested for methylene chloride oxidation. They were investigated by XRD, BET, XPS, chemisorption. Chromium oxide catalyst added potassium of 1 wt.% has a large beneficial effect on activity. This revised version was published online in August 2006 with corrections to the Cover Date.     

Acid Hydrolysis of Hemicellulose in Green Liquor Pre-Pulping Extract of Mixed Northern Hardwoods

Forest biomass is a promising resource for future biofuels and bioproducts. Pre-pulping extraction of hemicellulose by alkaline (Green Liquor) pretreatment produces a neutral-pH extract containing hemicellulose-derived oligomers. A near-term option for use of this extract is to hydrolyze the oligomers to fermentable monomer sugars. Chips of mixed northern hardwoods were cooked in a rocking digester at 160 °C for 110 min in Green Liquor at a concentration of 3% Na₂O equivalent salts on dry wood. The mass of wood extracted into the Green Liquor extract was approximately 11.4% of the debarked wood mass, which resulted in a dilute solution of oligomeric hemicelluloses sugars. The concentration of the extract was increased through partial evaporation prior to hydrolysis. Dilute sulfuric acid hydrolysis was applied at conditions ranging from 100 to 160 °C, 2% to 6% (w/v) H₂SO₄, and 2- to 258-min residence time. The maximum fermentable sugar concentration achieved from evaporated extract was 10.7 g/L, representing 90.7% of the maximum possible yield. Application of the biomass pretreatment severity function to the hydrolysis results proved to offer a relatively poor prediction of temperature and reaction time interaction. The combined severity function, which incorporates reaction time, temperature, and acid concentration, did prove to provide a useful means of trading off the combined effects of these three variables on total sugar yields.     

Effect of sulfuric and phosphoric acid pretreatments on enzymatic hydrolysis of corn stover

The pretreatment of corn stover with H₂SO₄ and H₃PO₄ was investigated. Pretreatments were carried out from 30 to 120 min in a batch reactor at 121°C, with acid concentrations ranging from 0 to 2% (w/v) at a solid concentration of 5% (w/v). Pretreated corn stover was washed with distilled water until the filtrate was adjusted to pH 7.0, followed by surfactant swelling of the cellulosic fraction in a 0–10% (w/v) solution of Tween-80 at room temperature for 12 h. The dilute acid treatment proved to be a very effective method in terms of hemicellulose recovery and cellulose digetibility. Hemicellulose recovery was 62–90%, and enzymatic digestibility of the cellulose that remained in the solid was >80% with 2% (w/v) acid. In all cases studied, the performance of H₂SO₄ pretreatment (hemicellulose recovery and cellulose digestibility) was significantly better than obtained with H₃PO₄. Enzymatic hydrolysis was more effective using surfactant than without it, producing 10–20% more sugar. Furthermore, digestibility was investigated as a function of hemicellulose removal. It was found that digestibility was more directly related to hemicellulose removal than to delignification.     

Effect of oxychlorination treatment on the regeneration of Pt–Sn/Al2O3 catalyst for propane dehydrogenation

Research on Chemical Intermediates - Propane dehydrogenation and regeneration of Pt–Sn/θ-Al2O3 catalysts was evaluated with oxychlorination treatment. It was observed that the catalytic...     

Determination of226Ra in environmental samples using high-resolution inductively coupled plasma mass spectrometry

A time-saving and accurate technique for determining²²⁶Ra in groundwater and soil was examined, using high-resolution inductively coupled plasma-mass spectrometry (HR-ICP-MS). The technique was applied to the determination of²²⁶Ra in groundwater and soil samples and compared with the conventional liquid scintillation counting method. This technique was capable of completing²²⁶Ra counting within 3 minutes, without the in-growth period to allow radon and its progeny to achieve secular equilibrium with the parent²²⁶Ra. The detection limits of HR-ICP-MS for²²⁶Ra in groundwater and soil were 0.19 mBq·1⁻¹ and 0.75 Bq·kg⁻¹, respectively, which were about 10 times lower than that of the liquid scintillation counter. The results obtained from HR-ICP-MS in groundwater and soil were in accordance with those of LSC within a relative error of about 13%.     

Evaluation of Enzyme Mixtures in Releasing Fermentable Sugars from Pre-pulping Extracts of Mixed Northeast Hardwoods

One near-term option to developing a forest product biorefinery is to derive pre-pulping extract from incoming wood chips before the main pulping step. The release of monomer sugars from a xylan-rich extract, creating a fermentable substrate is a prerequisite for utilization of pre-pulping extract for production of ethanol or other value-added products. This study examined the individual and mixture efficiencies of two hemicellulolytic microbial enzymes and two xylanase preparations in catalyzing degradation of green liquor (GL) and hot water (HW) pre-pulping extracts. The effects of four commercial enzyme preparations were determined by assessing yields of xylose + galactose + mannose (xmg) obtained under different reaction conditions. Of the individual enzyme preparations tested, a sample NS 50012 was superior to the other enzyme preparations in releasing xmg under conditions optimized for separate hydrolysis and fermentation and for simultaneous saccharification and fermentation. In comparison to pre-pulping extracts treated with HW, extract treated with GL was found to inhibit the action of all tested enzymes. This inhibition may be related to higher salt and lignin phenol in the GL extract. On both types of extracts, the mixture constituted by NS 50012 and NS 50030 provided the highest yield of hemicellulose conversion at 55 °C and pH 5.5. The generated digestibility thus signified that the synergistic effectiveness in xylan + galactan + mannan (XMG) hydrolysis between NS 50012 (from Aspergillus aculeatus) and NS 50030 (from Aspergillus oryzae) is the result of an interaction mechanism involving different XMG-degrading enzyme activities in the two enzyme preparations.