Enzymes immobilized on montmorillonite: comparison of performance in batch and packed-bed reactors

Summary The enzymes a-amylase, invertase and glucoamylase were immobilized on acid activated montmorillonite using two techniques, viz. adsorption and covalent binding, and their activities were tested in a batch and packed-bed reactor and were compared. The packed-bed reactor showed an improved performance for all immobilized enzymes, which was attributed to lowering of diffusional restrictions to mass transfer. Lower activity in case of batch reactor for immobilized invertase was due to a combined effect of loss of native conformation of enzyme on account of immobilization and mass transfer resistances due to improper diffusion of substrate to the active site of enzyme. For immobilized glucoamylase, the packed-bed reactor demonstrated exceptionally high activity that was very close to the free enzyme. Covalently bound glucoamylase showed higher activity than the free enzyme.     

Production of citric acid using immobilized conidia of Aspergillus niger

Conidia of Aspergillus niger were immobilized in calcium alginate gel for the production of citric acid. First, the type of the preactivation medium, together with the preactivation period, was investigated. It was found that A. niger requires a 2-d preactivation period at a 0.05 g/L NH₄NO₃ concentration. Second, preactivated cells were used to determine the effects of nitrogen concentration and the flow rate of oxygen and air on the production of citric acid. Maximum citric acid production was attained with medium containing 0.01 g/L of NH₄NO₃. The rate of citric acid production in the nitrogenous medium was 33% higher when oxygen was used instead of air during the production phase. This corresponds to an increase of 85% when compared to production when neither oxygen nor air was fed into the system. In the nonnitrogenous medium citric acid concentration remained similar regardless of the use of air or oxygen. However, in the nonnitrogenous production medium, citric acid production was not influenced considerably when oxygen was used instead of air. The advantage of using immobilized cells is that production is achieved easily in the continuous system. Therefore, citric acid production was also tested using a packed-bed bioreactor, and an increase in productivity by a factor of 22 was achieved compared to the batch system.     

Modelling of a tubular solid oxide fuel cell with different designs of indirect internal reformer

The cell performance and temperature gradient of a tubular solid oxide fuel cell with indirect internal reformer(IIR-SOFC) fuelled by natural gas, containing a typical catalytic packed-bed reformer, a catalytic coated wall reformer, a catalytic annular reformer, and a novel catalytic annular-coated wall reformer were investigated with an aim to determine the most efficient internal reformer system. Among the four reformer designs, IIR-SOFC containing an annular-coated wall reformer exhibited the highest performance in terms of cell power density(0.67 W cm-2)and electrical efficiency(68%) with an acceptable temperature gradient and a moderate pressure drop across the reformer(3.53×10-5kPa).IIR-SOFC with an annular-coated wall reformer was then studied over a range of operating conditions: inlet fuel temperature, operating pressure, steam to carbon(S : C) ratio, gas flow pattern(co-flow and counter-flow pattern), and natural gas compositions. The simulation results showed that the temperature gradient across the reformer could not be decreased using a lower fuel inlet temperature(1223 K–1173 K)and both the power density and electrical efficiency of the cell also decreased by lowering fuel inlet temperature. Operating in higher pressure mode(1-10 bar) improved the temperature gradient and cell performance. Increasing the S : C ratio from 2 : 1 to 4 : 1 could decrease the temperature drop across the reformer but also decrease the cell performance. The average temperature gradient was higher and smoother in IIR-SOFC under a co-flow pattern than that under a counter-flow pattern, leading to lower overpotential and higher cell performance. Natural gas compositions significantly affected the cell performance and temperature gradient. Natural gas containing lower methane content provided smoother temperature gradient in the system but showed lower power density and electrical efficiency.     

Continuous production of extracellular l-glutaminase by ca-alginate-immobilized marine Beauveria bassiana BTMF S-10 in packed-bed reactor

l-Glutamine amidohydrolase (l-glutaminase, EC 3.5.1.2) is a therapeutically and industrially important enzyme. Because it is a potent antileukemic agent and a flavor-enhancing agent used in the food industry, many researchers have focused their attention on l-glutaminase. In this article, we report the continuous production of extracellular l-glutaminase by the marine fungus Beauveria bassiana BTMF S-10 in a packed-bed reactor. Parameters influencing bead production and performance under batch mode were optimized in the order-support (Na-alginate) concentration, concentration of CaCl₂ for bead preparation, curing time of beads, spore inoculum concentration, activation time, initial pH of enzyme production medium, temperature of incubation, and retention time. Parameters optimized under batch mode for l-glutaminase production were incorporated into the continuous production studies. Beads with 12×10⁸ spores/g of beads were activated in a solution of 1% glutamine in seawater for 15 h, and the activated beads were packed into a packed-bed reactor. Enzyme production medium (pH 9.0) was pumped through the bed, and the effluent was collected from the top of the column. The effect of flow rate of the medium, substrate concentration, aeration, and bed height on continuous production of l-glutaminase was studied. Production was monitored for 5 h in each case, and the volumetric productivity was calculated. Under the optimized conditions for continuous production, the reactor gave a volumetric productivity of 4.048 U/(mL·h), which indicates that continuous production of the enzyme by Ca-alginate-immobilized spores is well suited for B. bassiana and results in a higher yield of enzyme within a shorter time. The results indicate the scope of utilizing immobilized B. bassiana for continuous commercial production of l-glutaminase.     

Hydrogen production capacity of membrane reformer for methane steam reforming near practical working conditions

Currently, H₂ production techniques for application to proton exchange membrane fuel cells (PEMFC) are intensively investigated, aiming to realize a clean hydrogen society. Due to the limitation by the thermodynamics of methane steam reforming (MSR), multi-reactions and multi-steps should be performed before the generated H₂-rich gas could be delivered to PEMFC, which inevitably increases the cost of H₂. However, using a thermodynamic shifting membrane reformer, H₂ could be produced compactly from MSR, provided that the catalyst showed high performance for MSR reaction and membrane efficiently removed H₂ from the reaction zone. We presented here a Pd-based membrane reformer for MSR reaction. In contrast with previous reports, nickel-based catalyst pre-reduced at high temperature was applied in this work, as well as high performance Pd-based membrane. The performances of the membrane reformer in terms of H₂ production capacity were also widely investigated. It was found that combination of an active catalyst for MSR and a H₂ ultra-permeable Pd membrane obtained high flux of H₂ across the membrane and recovery rate of H₂ in the membrane reformer. For instance, 98.8% methane conversion, over 97.0% selectivity to CO₂ and over 95.0% recovery rate of H₂ were obtained under mild working conditions. Simultaneously, the hydrogen flux across the membrane reached 18.6 m³/(m² h), and Pd-based pure H₂ production capacity significantly increased and reached around 387.5 m³/(kg_Pd h) in membrane reformer. Further work on stability investigation may develop an efficient on-site route of H₂ production process for application to on-site power generation using PEMFC.     

熔融碳酸盐燃料电池系统中重整器性能分析

本文通过对热交换型重整器过程分析，建立了反映其性能的动态数学模型，并进行了稳态与动态模拟计算．结果表明，重整产物气能满足熔融碳酸盐燃料电池需要，同时也得到了水蒸气与天然气之比对重整产物成分的影响；研究了过程气入口流量、温度改变时重整器动态响应性能，为控制回路的制定提供了理论依据．     

现代蒸汽转化工艺

介绍了蒸汽转化工艺的最新进展。绝热预转化、换热式转化器及自热转化炉等现代转化工艺的开发和应用旨在改善一段转化炉的操作条件,节省转化段的燃料需求,降低整个氨厂的能耗。在转化段引入一种新型高温高压气体预热工艺(里格特工艺),收效也很显著.新型炉管合金和转化催化剂的开发是现代转化工艺的物质基础.参考文献14篇.     

板式反应器中甲醇自热重整制氢的研究

自行研制了一种高效的板式反应器，集预热、气化、重整、催化燃烧反应于一体。在该反应器中进行了一系列甲醇自热重整制氢实验，考察了反应器床层的温度分布及氧醇比、水醇比对甲醇重整制氢过程的影响。实验中重整温度保持在450 ℃～650 ℃，当甲醇的气体空速为4 000 h－1时，产生重整气3 m3/h～5 m3/h(重整气中氢气浓度44.0%～50.0%，CO浓度为10.0%～12.0%，产氢率为1.5m3／kg(CH3OH)，系统处于常压。     

Co—Mo／Al2O3型重整预加氢催化剂的研制

考察了不同方法制备的Ｃｏ－Ｍｏ／Ａｌ２Ｏ３型重整预加氢催化剂对石油加氢脱硫活性的影响，选出了一种工业生产步骤简单，金属含量容易控制，并且不腐蚀设备的碱必等量共浸法制备的ＤＳ－９４８催化剂。该催化剂在温度３５０℃，压力３．０ＭＰａ，液体空速６．０ｈ＾－１，体积氢油比７０的条件下，满足了双金属重整催化剂对精制石油脑油杂质含量的要求。     

Transient Heat Transport in Gas Flow Through Granular Porous Media

Models are developed to describe the time-evolution of gas and solid temperature profiles in a class of granular porous media; this time-dependence being the result of a heat source supplying energy uniformly to the gas as it flows into the medium. The solid-phase is treated as a fixed, axi-symmetric bed of randomly packed spheres of uniform size and material properties. An analytic expression for the locally averaged surface temperature of the solid phase is formulated in terms of the time history of the corresponding local gas temperature. This approach avoids the need to assume locally uniform temperatures within the solid phase, and provides a coupled model for the thermal energy transport in the system. A numerical scheme for treating the resulting transport equations is outlined, and results presented. A quasi-steady approximation is proposed, and this approximation is assessed by reference to numerical results obtained from the numerical scheme. One application of the work is to fixed-bed catalytic reactors and absorbers, and results are presented indicating how the regeneration times of such systems depend on operating parameters.