Kinetic modeling of hemicellulose hydrolysis in the presence of homogeneous and heterogeneous catalysts

Kinetic models were developed for the hydrolysis of O‐acetyl‐galactoglucomannan (GGM), a hemicellulose appearing in coniferous trees. Homogeneous and heterogeneous acid catalysts hydrolyze GGM at about 90°C to the monomeric sugars galactose, glucose, and mannose. In the presence of homogeneous catalysts, such as HCl, H₂SO₄, oxalic acid, and trifluoroacetic acid, the hydrolysis process shows a regular kinetic behavior, while a prominent autocatalytic effect was observed in the presence of heterogeneous cation‐exchange catalysts, Amberlyst 15 and Smopex 101. The kinetic models proposed were based on the reactivities of the nonhydrolyzed sugar units and the increase of the rate constant (for heterogeneous catalysts) as the reaction progresses and the degree of polymerization decreases. General kinetic models were derived and special cases of them were considered in detail, by deriving analytical solutions for product distributions. The kinetic parameters, describing the autocatalytic effect were determined by nonlinear regression analysis. The kinetic model described very well the overall kinetics, as well as the product distribution in the hydrolysis of water soluble GGM by homogeneous and heterogeneous catalysts. The modelling principles developed in the work can be in principle applied to hydrolysis of similar hemicelluloses as well as starch and cellulose. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1066–1077, 2014     

Numerical investigation on the number of active surface sites of carbon catalysts in the decomposition of methane

The number of active sites on the surface of carbon catalysts is an important factor in determining their activity in the decomposition of methane. Although several studies have been performed to identify the nature of these sites, no method has been established to estimate their number. A method is presented to estimate this value, and its effect on hydrogen production is evaluated, along with that of temperature and residence time. For this purpose, the thermocatalytic decomposition of methane is modeled with the inclusion of the number of active sites of the catalyst in the kinetics. The results of the model indicate the high influence of variations of small residence times in this process, and the reduction of this effect at high temperatures. Also, the effect of the number of surface sites is shown to be more prominent at low residence times and temperatures. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2228–2234, 2014     

Comparison of Soybean and Cottonseed Oils upon Hydrogenation with Nickel,Palladium and Platinum Catalysts

There is current interest in reducing the trans fatty acids (TFA) in hydrogenated vegetable oils because consumption of foods high in TFA has been linked to increased serum cholesterol content. In the interest of understanding the TFA levels, hydrogenation was carried out in this work on soybean oil and cottonseed oil at two pressures (2 and 5 bar) and 100 °C using commercially available Ni, Pd, and Pt catalysts. The TFA levels and the fatty acid profiles were analyzed by gas chromatography. The iodine value of interest is ~70 for all-purpose shortening and 95–110 for pourable oil applications. In all cases, higher hydrogen pressures produced lower levels of TFA. In the range of 70–95 iodine values for the hydrogenated products, the Pt catalyst gave the least TFA, followed closely by Ni, and then Pd, for both oils. For all three catalysts at 2- and 5-bar pressures and 70–95 iodine values, cottonseed oil contained noticeably less TFA than soybean oil; this is probably because cottonseed oil contains a lower total amount of olefin-containing fatty acids relative to soybean oil. Approximate kinetic modeling was also done on the hydrogenation data that provided additional confirmation of data consistency.     

The Optimization of the Production of Methyl Esters from Corn Oil Using Barium Hydroxide as a Heterogeneous Catalyst

In recent years, vegetable oils, as renewable raw materials, became a promising feedstock for chemicals and biodiesel production. The main products derived from oils are esters of fatty acids, especially methyl esters, obtained by their transesterification with methanol, in presence of acid or alkaline catalysts. The use of such catalysts implies the need for washing operations, which leads to environmental pollution. In the present paper, the response surface methodology based on a central composite design, has been developed to optimize the process of transesterification of corn oil. Ba(OH)₂ in presence of diethyl ether was used as catalyst. A quadratic polynomial equation was obtained. It correlates the reaction parameters [methanol/oil molar ratio (x _r), reaction time (x _t) and catalyst concentration (x _c)] with methyl esters yield. Analysis of variance analysis showed that only methanol/oil molar ratio and catalyst concentration have had the most significant influences on the conversion. The maximum methyl esters yield was obtained using the following optimum parameters: methanol/corn oil ratio of 11.32, reaction time of 118 min and catalyst concentration of 3.6 wt%.     

Effect of Constant‐Rate Reduction on the Performance of a Ternary Cu/ZnO/Al2O3 Catalyst in Methanol Synthesis

A multi‐functional flow set‐up was developed for the rate‐ and temperature‐controlled reduction of copper catalysts, their application in high‐pressure methanol synthesis and the determination of the copper surface area by N₂O frontal chromatography. The influence of constant‐rate reduction on the catalytic properties of a ternary Cu/ZnO/Al₂O₃ catalyst was investigated. The temperature during the constant‐rate reduction was found to decrease, indicating autocatalytic kinetics, but no significant catalytic effect of the milder reduction conditions was observed compared with a slow linear heating ramp.     

Preparation and Application of Perovskite Catalysts for Diesel Soot Emissions Control: An Overview

The diesel engines are energy efficient (1), but their particulate matter (soot) emissions are still a matter of concern even though major advances in their control are being made. For soot abatement, catalytic diesel particulate filter (DPF) technique is widely employed to trap and burn the soot. Many types of catalysts have been investigated for the soot combustion i.e. platinum group metal (PGM) based, perovskite-type oxides, spinel-type oxides, rare earth metal oxides, and mixed transient metal oxides etc. The cost of PGM catalysts is high and their availability is questionable. Further they are susceptible to poisoning and have low thermal stability. On the other hand perovskite catalysts show potential as effective soot oxidation catalyst for the DPF because of their low cost, high thermal stability and tailoring flexibility. Many papers related to soot oxidation over perovskite catalysts have been published but no review paper appears in the literature that is dedicated to soot oxidation. Thus, this article provides a summary of published information regarding pure and substituted perovskite catalyst, preparation methods, properties, and their application for diesel soot emission control.     

Mo-Ni纳米自组装催化剂的表征与活性评价

以二次纳米自组装氧化铝为载体,浸渍以氨为溶剂、双金属活性组分配比不同的钼镍铵溶液,制备一种新型加氢催化剂,并对制得的催化剂进行表征和评价。结果表明,钼镍催化剂的孔性质稳定,孔径大小集中在3~10 nm和30~100 nm,其中在30~100 nm的孔道占33.70%~39.47%。以劣质催化裂化柴油为原料,对催化剂进行加氢活性评价,催化剂的脱硫率为81%~93%,脱氮率为87%~97%,芳烃饱和率为56%~67%,在催化剂运行时间内无明显结焦现象且活性较好。结合钼镍催化剂的表征数据及加氢活性评价结果发现钼镍质量比为7∶1时催化剂的性质最适宜,并且催化剂活性最优。     

CO、CO_2及其共存体系的甲烷化反应

介绍了甲烷化的反应体系,CO、CO2甲烷化反应的机理;比较了CO体系、CO2体系和CO、CO2共存体系的甲烷化反应特点以及三种反应体系对催化剂的要求;综述了适用于不同体系催化剂的研究进展,并重点介绍了多种催化剂的载体、助剂与活性组分之间的相互作用方式以及几种催化剂对碳氧化物甲烷化反应的催化机理;甲烷化反应的应用方向逐步从合成氨、合成气制天然气向燃料电池、焦炉煤气等方向扩展,对反应体系的研究也由CO甲烷化体系向CO2甲烷化体系和共存体系方向发展;复合载体负载的多金属催化剂成为现在甲烷化催化剂的主要研究方向,纳米颗粒催化剂、等离子体等技术开始应用于甲烷化催化剂。