Pore network model of deactivation of immobilized glucose isomerase in packed-bed reactors. Part III: Multiscale modelling

A widely used method for converting glucose to fructose is by enzymatic isomerization. This process, which uses immobilized glucose isomerase, takes place in a packed-bed reactor that consists of microporous particles with a range of pore sizes, characterized by a pore size distribution. The micropores are also interconnected, giving rise to a three-dimensional (3D) network of pores with distributed sizes and connectivities. The particles themselves generate a 3D pore network at the reactor level with distributed pore sizes, but with a fixed connectivity. In this paper, Part III of a series, we develop a multiscale modelling approach to this problem, beginning with the relevant phenomena at the scale of the micropores, and integrating them into the particle and reactor length scales. As the efficiency of the process is significantly affected by deactivation of the microporous particles, we take this phenomenon into account at all the relevant length scales. We use a real random packing of particles, originally constructed by Finney (Proc. R. Soc. Lond. A, 319 (1970) 479), and map its pore space onto an equivalent 3D Voronoi network in which the pores are represented by the edges of the Voronoi polyhedra. The flow field in the Voronoi network is determined, and the convection-diffusion-reaction equation is then solved in the Voronoi network, taking into account the gradual deactivation of the microporous particles. Several plausible mechanisms of deactivation of the microporous particles are considered, and their effect on the performance of the reactor is investigated. Good agreement is found between the results of the computer simulations and the relevant experimental data.     

Kinetic Modeling of Hydrocarbon Processing and the Effect of Catalyst Deactivation by Coke Formation

Previously derived fundamental rate equations for coke formation and catalyst deactivation are applied to the modeling of a number of commercial processes: steam reforming of natural gas, styrene production from ethylbenzene, catalytic cracking of heavy oil fractions, methanol-to-olefins on SAPO 34, and solid acid alkylation on a Y zeolite. The modeling accounts in great detail for the chemistry of the process, including the formation of the deactivating agent, commonly called coke. It is shown that the deactivating agent is not an inert substance but is involved in reactions, sometimes of the same type as those leading to the main products of the process.     

Deactivation of barium oxide-based NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> storage and reduction catalyst by hydrothermal treatment

The deactivation of a barium oxide-based NO _x storage and reduction (NSR) catalyst with hydrothermal treatment was studied by treating it with 10 vol% water vapor diluted in nitrogen at 850°C. XRD, XPS, SEM, IR of CO adsorption, and the N₂ adsorption was used to investigate the physical and chemical changes of the NSR catalyst caused by the hydrothermal treatment. The 12 h hydrothermal treatment decreased its NO₂ storage capacity by 20%. However, the hydrothermal treatment significantly decreased its ability to reduce the stored NO₂. The formation of an inactive phase consisting of platinum and aluminum is believed to be the cause of the severe deactivation of the NSR catalyst.     

乙炔氢氯化反应负载型金催化剂的失活及其再生的研究进展

综述了国内外对乙炔氢氯化反应负载型金催化剂失活及其再生的研究,分别介绍了在乙炔氢氯化反应中影响负载型金催化剂催化活性的因素以及负载型金催化剂失活的原因和使其再生的方法。展望了负载型金催化剂再生的发展前景。     

QZ-2000催化剂的工业再生及应用

对吉林石化公司双苯厂苯酚丙酮装置异丙苯单元中使用的QZ-2000分子筛催化剂的失活问题进行了研究。通过质谱仪(GC-MS)、热重分析(TG)、X射线衍射仪(XRD)、X荧光、比表面测试手段,确定了QZ-2000催化剂上的沉积物主要是多异丙基苯,掩盖了部分酸性中心,致使催化剂活性下降。通过烧碳再生处理后在工业装置上使用,二异丙苯转化率达到75%以上,满足了生产要求。     

Experimental and modeling analysis of the effect of catalyst aging on the performance of a short contact time adiabatic CH4-CPO reactor

Catalytic partial oxidation of methane at short contact time was studied in a lab-scale packed bed reactor over a 0.5 wt% Rh/A₂O₃ catalyst. Experiments were focused on the investigation of catalyst stability and durability upon repeated start-up/shut-down tests at different inlet temperatures and flow rates. Measurements of the axial temperature profiles evidenced a high sensitivity of the steady state thermal behavior of the reactor on catalyst activity: a decrease of the intrinsic catalytic activity was interpreted as the cause of a progressive over-heating of the bed which, in turn, moderated the loss of methane conversion and syngas productivity. At sufficiently high flow rate the observed temperature rise spread along the whole catalytic bed. Under such conditions both steady state and dynamic reactor performances were affected by the progressive decay of catalyst activity. A rationalization of the observed results was pursued by applying a one dimensional (1D) heterogeneous model of the reactor to the quantitative analysis of experimental results. Model predictions revealed the occurrence of operating surface temperatures up to 1100 °C and allowed to quantify the progressive worsening of reactor performances in terms of a loss of reforming activity localized in correspondence of the catalyst hot spot.     

Determination of kinetic parameters of the oxidehydrogenation of ethane with CO2 on nanosized calcium-doped ceria under fast deactivation processes

Kinetic parameters of the oxidehydrogenation of ethane with CO₂ on nanosized Ca-doped CeO₂ have been investigated. During reaction, interaction of the reactants with the oxide catalyst causes a fast deactivation process. Overlapping of this fast deactivation with catalytic reaction makes quite difficult the reliable determination of kinetic parameters. This handicap can be overcome by getting sufficient data in a short testing time, thus reducing the degree of deactivation. The kinetics of catalytic reaction and of catalyst deactivation have been studied by conducting a series of consecutive tests at increasing temperatures in steps of 20 °C and monitoring the evolution of the reaction for periods of 30 min on stream at each temperature, with full product analysis every 3 min. At temperatures above 680 °C, catalytic rates decreased linearly with run time at isothermal operation, while deactivation rates increased with increasing temperature. Analysis of the results allows to uncouple catalyst deactivation and catalytic reaction and to obtain the kinetic parameters of both processes (i.e., steady-state and deactivation rates, and their apparent activation energies). Deactivation rate of CO formation is one order of magnitude faster than of ethene formation but both processes show the same apparent activation energy, ca. 47 kcal/mol. The apparent activation energy values for the catalytic reaction are 32 ± 4 and 26 ± 2 kcal/mol for the rates of formation of ethene and CO, respectively.     

Optimal design of a radial-flow membrane reactor as a novel configuration for continuous catalytic regenerative naphtha reforming process considering a detailed kinetic model

The significance of the catalytic naphtha reforming process in the petroleum refining and petrochemical industry generates continuous evolution of the technology. These improvements would be observed in presenting more efficient reactor setups in order to improve production yield and operating conditions, as well as elucidating better kinetic and deactivation models with higher predicting ability. Both of these items have been considered in this work. An optimized radial-flow moving bed membrane reactor has been proposed as a novel configuration for naphtha reforming process. Optimization has been carried out by differential evolution (DE) method considering 40 decision variables. A detailed kinetic model has also been presented. The proposed kinetic model consists of 32 lumped pseudo-components and 84 reactions. Deactivation rate of catalyst has also been taken into account by considering coke deposition on both acidic and metallic sites. Plant data have been used to validate the modeling results. In order to assess the performance of the proposed configuration, the obtained modeling results have been compared with those of conventional configuration, which shows the superiority of the presented one.     

甲醇在ZnI2催化下转化为triptane工艺的优化及催化剂再生研究：制备一种优质的航空汽油调和组分

采用间歇釜式反应器研究了甲醇在ZnI₂催化作用下转化为2,2,3-三甲基丁烷（triptane)的反应。优化了反应工艺条件并研究讨论了催化剂的失活机理及再生工艺。采用XRD,TG及XRF方法表征分析了催化剂反应前后,及催化剂再生后的物理化学性质。实验结果表明在反应温度为200^oC,初始压力0.35MPa,反应时间2h,甲醇:ZnI₂摩尔比为2:1的条件下,triptane的收率为12.2%。随着循环反应次数的增加,催化剂的催化活性降低,在失活的催化剂中有少量的I₂及ZnO形成。I元素的流失及ZnO的形成导致了催化剂活性的降低,采用HI再生催化剂并同时向原料中加入少量叔丁醇能恢复催化反应活性。叔丁醇是反应的引发剂,通过ZnI₂催化剂的重构及起始反应的引发而实现反应活性的恢复。
       

The impact of EPI voxel size on SNR and BOLD sensitivity in the anterior medio-temporal lobe: a comparative group study of deactivation of the Default Mode

Objectives  To quantify the gain in time-series SNR that can be achieved in the amygdala by reducing EPI voxel size, and to assess the extent to which this advantage is carried through to statistical significance in a group fMRI study, using a cognitive task to trigger task-independent deactivation of anterior medial temporal structures. Materials and methods  Two groups of seven subjects were posed number-series tasks to induce deactivation of the Default Mode network. This is known from PET work to include the amygdala, which lies in a region of high magnetic field gradient. In 3 T imaging, one group was studied with high resolution EPI with 6 μl voxels, the other with lower resolution EPI with 17 μl voxels. Field maps were acquired to allow field gradients in relevant ROIs to be assessed. Results  Time-series SNR was 45% higher in the amygdala in the high resolution EPI data than in the low resolution data. In activation results, whilst there was good agreement between other areas, the involvement of the amygdala could only be demonstrated in the high resolution data. Conclusion  We find that reduction in signal dephasing afforded by high resolution EPI is realized as a substantial increase in SNR and BOLD sensitivity in group fMRI data. This has allowed the first demonstration of the involvement of the amygdala in the Default Mode in fMRI.