Acid-catalyzed alcoholysis of soybean oil

In an effort to increase utilization of fats and oils with high concentrations of FFA, acid catalysts were investigated at elevated temperatures to determine their efficacy under various operating conditions. Acid-catalyzed alcoholysis of soybean oil using sulfuric, hydrochloric, formic, acetic, and nitric acids was evaluated at 0.1 and 1 wt% loadings at temperatures of 100 and 120°C in sealed ampules, but only sulfuric acid was effective. Kinetic studies at 100°C, 0.5 wt% sulfuric acid catalyst, and nine times methanol stoichiometry provide >99 wt% conversion of TG in 8 h and less than 0.8 wt% FFA concentrations at less than 4 h. Reaction conditions near 100°C at 0.1 to 0.5 wt% were identified as providing the necessary conversions in a 24-h batch cycle while not darkening the product as is typical with high temperatures and catalyst loadings. The oxygen/air contained in the reaction ampules at the onset of the reaction was not sufficient to color the product, but the product darkened if atmospheric air contacted the reacting mixture. The presence of small amounts of stainless steel significantly decreased conversions.     

Evaluation of the effects of operational parameters in the pretreatment of sugarcane bagasse with diluted sulfuric acid using analysis of variance

The pretreatment of lignocellulosic residues has been extensively studied as a method to disrupt the cellulose–hemicelluloses–lignin complex in biomass to access the sugars in their respective components. In this work, we carried out a study using sulfuric acid pretreatment of sugarcane bagasse by varying the following operational parameters: solid loading (10–30% of bagasse relative to the volume of the sulfuric acid solution), sulfuric acid concentration (0.5–2.5% relative to the dry mass of bagasse), reaction time (5–25?min), and temperature (135–195°C). The obtained solids from each pretreatment condition were submitted to enzymatic hydrolysis under the same process conditions: 0.232?g of Celluclast 1.5?L and 0.052?g of Novozym 188 per g of pretreated sugarcane bagasse, 72?h of hydrolysis, and 200?rpm of agitation at 50°C. Using central composite rotational design configuration in the experiments and analysis of variance, the results indicate that the conditions that produced larger quantities of glucose by enzymatic hydrolysis (0.35?g glucose/g pulp) with minimum amounts of degradation products were as follows: 20% solids loading, 15?min of reaction time, 1.5% sulfuric acid, and a minimum temperature of reaction of 170°C.     

Kinetic studies of alkyl formate hydrolysis using formic acid as a catalyst

BACKGROUND: The hydrolysis of methyl formate is the major industrial process for the production of formic acid. The aim of the work is to determine the reaction kinetics quantitatively in the presence of formic acid catalyst, develop a mathematical model for the reaction system and estimate the kinetic parameters for the purpose of optimization. RESULTS: Liquid phase hydrolysis kinetics of alkyl formates (ethyl and methyl formate) was studied in an isothermal batch reactor at 80–110 °C and 20 bar nitrogen pressure. The catalyst of choice was formic acid. The reaction rate was enhanced but the formic acid product yield was slightly suppressed relative to the uncatalysed system. A kinetic model comprising mass balances and rate equations was developed and the kinetic and equilibrium parameters included in the rate equations were estimated from the experimental data with non‐linear regression analysis. CONCLUSION: The model was able to predict the experimental results successfully. The results obtained were compared quantitatively with an earlier model involving alkyl formate hydrolysis in a neutral aqueous solution. Copyright © 2011 Society of Chemical Industry     

秸秆中木质素对其超低酸水解过程的影响

以湖北稻草秸秆为研究对象,研究了超低酸水解木质纤维素的适宜条件,测定了适宜条件下的超低酸法水解15种不同种类秸秆的纤维素及半纤维素的转化率、还原糖得率及结晶度的变化。实验结果表明:秸秆投料量3 g、硫酸投料量45 mL(硫酸质量分数0.05%)、搅拌转速500 r/min、反应温度210 ℃、反应时间10 min为适宜的水解条件。对15种不同种类秸秆的水解结果统计得到,随着秸秆中木质素含量的增大,纤维素和半纤维素的转化率都逐渐降低,还原糖得率逐渐降低;通过SEM和X衍射分析水解前后的木质纤维素结构,得到了木质素影响水解过程的方式:1)木质素含量越大,纤维素的结晶度越大,纤维素的非晶化越困难,从而影响了纤维素的水解;2)原木质素不溶于反应体系且在酸性条件下相对稳定,富木质素层的木质素阻碍反应物与产物扩散,使富木质素层内的纤维素、半纤维素水解速率降低;3)木质素含量越高,木质纤维素的富木质素层越厚、强度越大,水解时难以从颗粒表面脱落,进一步降低水解速率。     

Delignification of intact biomass and cellulosic coproduct of acid‐catalyzed hydrolysis

The kinetics of acid‐catalyzed hemicellulose removal and also alkaline delignification of oat hull biomass were investigated. All three operational parameters namely, catalyst concentration (0.10–0.55 N H₂SO₄), temperature (110–130°C), and residence time (up to 150 min) affected the efficiency of hemicellulose removal, with 100% of hemicellulose removed by appropriate selection of process parameters. Analysis of delignification kinetics (in the temperature range of 30–100°C) indicated that it can be expressed very well by a two‐phase model for the crude biomass and also for the hemicellulose‐prehydrolyzed material. The application of acid‐catalyzed prehydrolysis improved the capacity of lignin dissolution especially at lower temperatures (30 and 65°C) and accelerated the dissolution of lignin. This acceleration of delignification by prehydrolysis was possible at all levels of temperature in the bulk phase; however, results were more significant at the lower temperatures in the terminal phase. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1783–1791, 2015     

Reaction mechanisms and kinetics of xylo‐oligosaccharide hydrolysis by dicarboxylic acids

Hydrothermal pretreatment of lignocellulosic materials generates a liquid stream rich in pentose sugar oligomers. Cost‐effective hydrolysis and utilization of these soluble sugar oligomers is an integral process of biofuel production. We report integrated rate equations for hydrolysis of xylo‐oligomers derived from pretreated hardwood by dicarboxylic maleic and oxalic acids. The highest xylose yield observed with dicarboxylic acids was 96%, and compared to sulfuric acid, was 5–15% higher with less xylose degradation. Dicarboxylic acids showed an inverse correlation between xylose degradation rates and acid loadings unlike sulfuric acid for which less acid results in less xylose degradation to aldehydes and humic substances. A combination of high acid and low‐temperature leads to xylose yield improvement. Hydrolysis time course data at three different acid concentrations and three temperatures between 140 and 180°C were used to develop a reaction model for the hydrolysis of xylo‐oligosaccharides to xylose by dicarboxylic acids. © 2012 American Institute of Chemical Engineers AIChE J, 59: 188–199, 2013     

Preparation of diacylglycerol‐enriched palm olein by phospholipase A1‐catalyzed partial hydrolysis

Partial hydrolysis of palm olein catalyzed by phospholipase A₁ (Lecitase Ultra) in a solvent‐free system was carried out to produce diacylglycerol (DAG)‐enriched palm olein (DEPO). Four reaction parameters, namely, reaction time (2–10 h), water content (20–60 wt‐% of the oil mass), enzyme load (10–50 U/g of the oil mass), and reaction temperature (30–60 °C), were investigated. The optimal conditions for partial hydrolysis of palm olein catalyzed by Lecitase Ultra were obtained by an orthogonal experiment as follows: 45 °C reaction temperature, 44 wt‐% water content, 8 h reaction time, and an enzyme load of 34 U/g. The upper oil layer of the reaction mixture with an acid value of 54.26 ± 0.86 mg KOH/g was first molecularly distilled at 150 °C to yield a DEPO with 35.51 wt‐% of DAG. The DEPO was distilled again at 250 °C to obtain a DAG oil with 74.52 wt‐% of DAG. The composition of the acylglycerols of palm olein and the DEPO were analyzed and identified by high‐performance liquid chromatography (HPLC) and HPLC/electrospray ionization/mass spectrometry. The released fatty acids from the partial hydrolysis of palm olein catalyzed by phospholipase A₁ showed a higher saturated fatty acid content than that of the raw material.     

Reaction Rates for the Partial Dehydration of Glucose to Organic Acids in Solid-Acid,Molecular-Sieving Catalyst Powders

Molecular-sieving catalysts have the potential to promote the production of oxygenated hydrocarbons from glucose. A kinetic model for the partial dehydration of glucose to organic acids by micro- and mesoporous aluminosilicate catalysts was developed. Kinetic parameters were estimated from glucose conversion and product yield versus time data at 150°C for HY-zeolite, aluminum-pillared montmorillonite, MCM-20 and MCM-41 catalyst powders of 0·5 mmol H⁺ g⁻¹ solid-acid activity. Rate constants for the partial dehydration of glucose to 5-hydroxymethylfurfural (HMF) and the rehydration and cleavage of HMF to formic acid and 4-oxopentanoic acid were maximized at catalyst pore diameters of 10–30 Å. The final organic acid product yields were low, less than 60% of theoretical for formic acid and 10% of theoretical for 4-oxopentanoic acid, due to significant coke formation. © 1997 SCI.     

小麦秸秆制备乙酰丙酸的动力学研究

Levulinic acid is considered as a promising green platform chemical derived from biomass. The kinetics of levulinic acid accumulation in the hydrolysis process of wheat straw was investigated in the study. Using dilute sulfuric acid as a catalyst, the ki-netic experiments were performed in a temperature range of 190-230C and an acid concentration range of 1%-5% (by mass). A simple model of first-order series reactions was developed, which provided a satisfactory interpretation of the experimental results. The kinetics of main intermediates including sugar and 5-hydroxymethylfurfural (5-HMF) were also established. The kinetic pa-rameters provided useful information for understanding the hydrolysis process.     

Modeling and optimization of dilute nitric acid hydrolysis on corn stover

BACKGROUND: Because of its high cost, nitric acid has not been widely employed as the catalyst for hydrolysis of lignocellulosic biomass to obtain fermentable sugars. However, recently more and more research results have reported that nitric acid was more effective than other acids for the hydrolysis of lignocellulose. Therefore, it is necessary to find an optimum condition for nitric acid pretreatment and a means of reducing the cost. RESULTS: In this work, low concentrations of nitric acid and short reaction times were considered to optimize the pretreatment process. The kinetic parameters of models to predict the concentrations of xylose, glucose, arabinose, acetic acid and furfural in the hydrolysates were obtained. Applying the kinetic models, the optimum conditions were: 150 °C, 0.6% HNO₃ and 1 min, which yielded a solution containing up to 22.01 g L^?1 xylose, 1.91 g L^?1 glucose, 2.90 g L^?1 arabinose, 2.42 g L^?1 acetic acid and 0.21 g L^?1 furfural, which were consistent with the predicted values. The influence of temperature was also studied using the Arrhenius equation. CONCLUSIONS: A combination of experimental data and model analysis suggested that 96% xylose yield can be achieved by using low concentration nitric acid for a short reaction time, which could greatly reduce the pretreatment cost. Therefore, dilute nitric acid could be considered a good choice for the hydrolysis of corn stover. Copyright © 2010 Society of Chemical Industry     

Hydrogen generation from noncatalytic hydrothermolysis of ammonia borane for vehicle applications

Ammonia borane (AB) is a promising hydrogen storage material as it contains 19.6 wt % hydrogen. In this article, our recently developed hydrothermolysis approach to release hydrogen is studied over a wide range of AB concentrations (6–88 wt %), at pressure 14.7 and 200 psia, and temperature 85–135°C. It is shown that with increasing AB concentration up to 77 wt %, the H₂ yield increases, and that the role of thermolysis, when compared with hydrolysis, increases. The maximum hydrogen storage capacity, obtained at 77 wt % AB and T_reactor ～ 85°C along with rapid kinetics, was 11.6 and 14.3 wt % at pressure 14.7 and 200 psia, respectively. To our knowledge, on a material basis, the AB hydrothermolysis process is the first one to provide such high hydrogen yield values at near PEM fuel cell operating temperatures without use of catalyst, and thus is promising for use in fuel cell‐based vehicle applications. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Production of furfural by acid hydrolysis of corncobs

Hydrolysis of corncobs for producing furfural was carried out in a pressurized batch reactor using superheated water and diluted sulphuric acid as catalyst. The range of experimental conditions was T=140–200°C and P=350–1550 kPa. Yields of furfural are reported as a function of reaction temperature, particle size, acid concentration and liquid/solid ratio. Attention has been focused on the solid residue remaining after the hydrolysis process, so that it can be further used as a humic fertilizer after oxiammoniation treatment.     

Efficient hydrolysis of cellulose over a magnetic lignin-derived solid acid catalyst in 1-butyl-3-methylimidazolium chloride

A green and efficient strategy for the hydrolysis of cellulose was developed by using a magnetic lignin-derived solid acid catalyst (MLC-SO₃H) in the presence of ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl). The results indicated that reaction temperature, reaction time, catalyst loading and water content have a big influence on the yield of total reducing sugars (TRS). By optimizing these reaction parameters, 69.3% TRS yield was observed at 140 °C for 150 min with the addition of 40 wt% MLC-SO₃H and 1 wt% water. More importantly, MLC-SO₃H could be easily separated from the reaction mixture with an external magnet and could be repeatedly used five times without an obvious loss of catalytic activity, demonstrating that it possessed excellent recyclability. Furthermore, a plausible mechanism involving three consecutive processes of dissolution, adsorption and catalysis for the hydrolysis of cellulose in [BMIM]Cl over a catalyst of MLC-SO₃H was also proposed.     

Low-Temperature Dilute Acid Hydrolysis of Oil Palm Frond

Oil palm frond (OPF) fiber, a lignocellulosic waste from the palm oil industry, contains high cellulose and hemicellulose content, thus it is a potential feedstock for simple sugars production. This paper describes the two-stage hydrolysis process focusing on the use of low-temperature dilute acid hydrolysis to convert the hemicellulose in OPF fiber to simple sugars (xylose, arabinose, and glucose). The objective of the present study was to evaluate the effect of operating conditions of dilute sulfuric acid hydrolysis undertaken in a 1 L self-built batch reactor on xylose production from OPF fiber. The reaction conditions were temperatures (100–140°C), acid concentrations (2–6%), and reaction times (30–240 min). The mass ratio of solid/liquid was kept at 1:30. Analysis of the three main sugars glucose, xylose, and arabinose were determined using high-pressure liquid chromatography. The optimum reaction temperature, reaction time, and acid concentration were found to be 120°C, 120 min, and 2% acid, respectively. Based on the potential amount of xylose (10.8 mg/mL), 94% conversion (10.15 mg/mL) was obtained under the optimum conditions with small amount of furfural (0.016 mg/mL). To enhance the effectiveness of dilute acid hydrolysis, the hydrolysis of OPF fiber was also performed using ultrasonic-pretreated OPF fiber. The effects of ultrasonic parameters power (40–80%) and ultrasonication times (20–60 min) were determined on sugar yields under optimum hydrolysis conditions (2% acid sulfuric, 120°C and 120 min). However, the use of ultrasonication was found to have detrimental effect on the yield of simple sugars due to the 10-fold increase in the formation of furfural.     

Kinetics of combined noncatalytic and catalytic hydrolysis of jute fiber under ultrasonic–far infrared energy synergy

Hydrolysis of pretreated waste jute fiber was intensified for maximizing reducing sugar (RS) yield deploying a novel reactor equipped with ultrasonic–far-infrared-waves (US–FIRW). At optimal 70°C temperature, 2.5 wt% Amberlyst-15 catalyst concentration, 15 min hydrolysis time and 10 (wt/wt) water loading; US–FIRW rendered significantly greater RS yield (74.82 mol%) compared to other reactors provided with far-infrared-wave (69.63 mol%), ultrasonication (50.34 mol%), and conventional thermal system (48.16 mol%). Kinetic models were developed considering noncatalytic-pseudo-homogenous (NCPH) in addition to the combined catalytic-pseudo-homogeneous (CPH) and catalytic heterogeneous (CHE) hydrolysis pathways. The results revealed that pseudo-homogenous–heterogeneous Eley–Rideal (PHHER) model could represent the hydrolysis kinetics most accurately. Remarkably, the lowest activation energy [16.75 kJ mol⁻¹ (NCPH), 13.82 kJ mol⁻¹ (CPH), 40.01 kJ mol⁻¹ (CHE)] required in US–FIRW evidently established its greater energy-efficiency among investigated reactors. The novel reactor and the simulated kinetic models can be applicable to other lignocellulosic biomass conversion for sustainable biorefinery.     

REACTIVITY AND MECHANISTIC STUDIES OF BASE-CATALYZED REACTION OF SOME DIHYDROXAMIC ACIDS

Kinetics and mechanism of the alkaline hydrolysis of two dihydroxamic acids, oxalo and malonodihydroxamic acids, have been studied in 25% (v/v) DMSO at 75°C. The solvent, salt, temperature, and solvent isotopic effects have been examined. Correlation of reaction rate with the acidity function (H–) and these effects indicate a pathway involving the rate-limiting formation of a tetrahedral intermediate that decomposes to give products.     

Molecular stability of chitosan in acid solutions stored at various conditions

The stability of chitosan with a degree of deacetylation (DD) of 88 and 81% was investigated in solution during storage for 60 days at various temperatures (60, 28, and 5°C) and acid concentrations (0.8M, 0.2M, and 0.1M). The first‐order rate constant of chain hydrolysis of 88%DD chitosan at 60°C was about 1.4 times higher than that of the 81%DD sample. At 28°C, the rates of hydrolysis for both chitosan samples were four to five times lower than those at 60°C and are similar. At 5°C, chain degradation was not significant. Although acetic acid caused significantly higher (P ≤ 0.05) chain scission than formic acid, no significant difference of rate change was observed among three different acid concentrations. Reprecipitation of dissolved chitosan was applied for its purification and to transfer dissolved chitosan to the solvent used to measure its molecular weight. Reprecipitation resulted in slightly lower molecular weight (P ≤ 0.05) for both 88%DD and 81%DD samples. The molecular weight of chitosan before and after reprecipitation had good linear relationship (r² > 0.9). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Hydrochloric acid‐catalyzed levulinic acid formation from cellulose: data and kinetic model to maximize yields

In this study, the kinetics of the acid catalyzed hydrolysis of microcrystalline cellulose (Avicel PH101) to levulinic (LA) and formic (FA) acids was investigated in a batch reactor over the following range of conditions: 160–200°C, hydrochloric acid concentrations of 0.309–0.927 M (11.3–33.8 g/l), cellulose concentrations of 49.8–149 mM (8.06–24.1 g/l), and residence times of 0–50 min. The maximum LA yield of around 60% of theoretical was achieved for an initial cellulose concentration of 99.6 mM, acid concentration 0.927 M, and 180–200°C. A mathematical model and its analytical solution were developed to predict conversion of cellulose to LA and FA through glucose and hydroxymethyl‐2‐furfural based on an irreversible pseudo‐first order reaction. Rate analysis of each reaction indicated that the rate‐controlling step shifted from LA formation initially to HMF formation later. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Pretreatment of <Emphasis Type="Italic">Helianthus tuberosus</Emphasis> residue by flow-through process for production of fermentable sugar

The pretreatment of Helianthus tuberosus residue was studied for fermentable sugar production. The pretreatment was performed by varying the temperature, type of chemical solution, and concentration. Two different catalytic pretreatments using sulfuric acid and aqueous ammonia were operated and compared in a flow-through column reactor system. The flow-through process was required to increase the sugar production yield of biomass. To selectively remove the lignin of biomass and achieve fractionation of hemicellulose in the liquid phase to produce pentose, the flow-through process could be controlled by the pretreatment conditions. Furthermore, the remaining solid underwent enzymatic hydrolysis for hexose production. The mass balances of biomass pretreated with aqueous ammonia and sulfuric acid solution were compared in terms of production of fermentable sugars. The glucose recovery compared to the initial biomass was 71.2% in the pretreatment using aqueous ammonia at 170 °C, and pretreatment using sulfuric acid solution at 150 °C was 52.3%.