Uniformity in a thin-zone multi-pulse TAP experiment: numerical analysis

The thin-zone TAP reactor (TZTR) model of a multi-pulse experiment is computationally validated based on a more general three-zone reactor model. The analysis is focused on the uniformity of gaseous and surface concentrations in the catalyst zone, which is a key property of TZTR model. It is shown that if the TZTR model is valid for the first pulse in a multi-pulse experiment then it is valid for all subsequent pulses. For a typical reactor packing (the ratio of the thin-zone thickness to the length of reactor is 1/30) and with the first pulse conversion up to 97%, the gaseous and surface concentration profiles can be considered uniform and characterized by their spatial average values only. The reaction rate in the catalyst zone may also be characterized by its spatial average value and directly related to the spatial average gaseous and surface concentrations, in the same way as an elementary rate is related to concentrations. As a result of these unique characteristics, the TZTR may be considered a “perfectly-mixed” reactor even at high conversion.     

“State defining” experiment in chemical kinetics—primary characterization of catalyst activity in a TAP experiment

This paper presents a new strategy, “state-by-state transient screening”, for kinetic characterization of states of a multicomponent catalyst as applied to TAP pulse-response experiments. The key idea is to perform an insignificant chemical perturbation of the catalytic system so that the known essential characteristics of the catalyst (e.g. oxidation degree) do not change during the experiment. Two types of catalytic substances can be distinguished: catalyst state substances, which determine the catalyst state, and catalyst dynamic substances, which are created by the perturbation. The general methodological and theoretical framework for multi-pulse TAP experiments is developed, and the general model for a one-pulse TAP experiment is solved. The primary kinetic characteristics, basic kinetic coefficients, are extracted from diffusion-reaction data and calculated as functions of experimentally measured exit-flow moments without assumptions regarding the detailed kinetic mechanism. The new strategy presented in this paper provides essential information, which can be a basis for developing a detailed reaction mechanism. The theoretical results are illustrated using furan oxidation over a VPO catalyst.     

A general formula for reactant conversion over a single catalyst particle in TAP pulse experiments

We obtain a general formula for reactant conversion in diffusion-reaction TAP systems over single non-porous catalyst particles as a product of two terms: α=P_H×K.The first term, P_H, is a purely geometric factor dependent only on the shape of the reactor and the shape and position of the catalyst particle, interpreted as the probability that an individual molecule of reactant will hit the catalyst before leaving the reactor. The second term, K=kτ_H/(1+kτ_H), is a geometrical/chemical term involving the kinetic constant k and a transport characteristic (residence time in the catalyst zone, τ_H). Both P_H and τ_H can be effectively calculated for any given reactor-particle configuration. Our formula greatly extends the validity of a formula given in Shekhtman et al. [1999. Thin-zone TAP-reactor—theory and application. Chem. Eng. Sci. 54, 4371-4378] for thin-zone TAP-systems. It is derived by a probabilistic analysis of the residence time of individual molecular trajectories in chemically active regions. Our results are based on the theory previously developed in our paper [Feres, R., Yablonsky, G.S., Mueller, A., Baernstein, A., Zheng, X., Gleaves, J., 2009. Probabilistic analysis of transport-reaction processes over catalytic particles: theory and experimental testing. Chem. Eng. Sci. 64, 568-581].     

Modeling of fast pulse responses in the Multitrack: an advanced TAP reactor

A detailed transport model for the Multitrack setup, a TAP-like system, has been developed, which allows further analysis of adsorption, diffusion and catalysis phenomena. This includes the transport in the void part between the pulse valve and the reactor inlet. The effects of viscous flow and thermal transpiration, aspects that have not been studied in detail before for this type of setup, have been analyzed. A new expression for the modeling of the output signal is proposed depending on the positioning of the MS detector used in the study. The transport parameters of the model have been estimated by the analysis of the experimental pulse responses of the empty reactor system and the reactor charged with an inert packed bed. The proposed model reproduces the experimental pulse responses very well, and therefore can be extended to study systems with reacting or adsorbing beds by including the corresponding rate equations for the processes occurring in the bed of particles.     

Determination of pitting initiation of duplex stainless steel using potentiostatic pulse technique

Duplex stainless steel simultaneously comprises various phases, inclusions, precipitates and grain boundaries. It is full of academic and valuable significance for materials designing and processing optimization to ascertain the corrosion resistance of corresponding phases and various microstructures. However, up to date, efficient evaluation technique is still scare mainly due to difficulty in controlling of micropits. In this work, for the first time, optimized potentiostatic pulse technique (PPT) was established and applied to study the rule of initiation of pits of solution annealed and aged DSS in 1.0 mol/L NaCl solution. The results showed that the size of pits can be well-controlled by adjusting the condition of potential pulse. Combined with SEM/EDS system observation, it was found that for solution-annealed specimens, sulphide and oxide mixed inclusions were the preferential pit initiation sites, while for aged specimens, majority pits occurred at inclusions in area impoverished in Cr/Mo, which is vicinal to σ phase. The phenomena that growing pits is retarded by precipitation rich in Cr/Mo, i.e. σ phase, was testified and explained.     

Effect of catalyst activity in SMR-SERP for hydrogen production: Commercial vs. large-pore catalyst

In this work, we have evaluated the performance of an SMR-SERP unit (steam methane reforming sorption enhanced reaction process), using two different Ni/Al₂O₃ catalysts: commercial “Octolyst 2001” from Degussa and a large-pore catalyst (Catalyst A). The selective CO₂ sorbent was a potassium modified hydrotalcites. Several experiments were performed under different operating conditions to validate a mathematical model.Experimental results show that the Degussa catalyst is more active and more selective to CO₂ producing hydrogen with higher purity and less CO than the large-pore catalyst. Cyclic SMR-SERP experiments were also performed. The cycles comprise four different steps: reaction, depressurization, reactive regeneration and pressurization. In the cyclic experiments, conversion was 43% higher than in an SMR reactor, while H₂ purity was 75%, which is 25% higher than in normal SMR operation. Results indicate that more active catalysts also promote a better reactive regeneration optimizing the use of part of the product (H₂). The proposed mathematical model was validated in a wide range of operating conditions and in a cyclic experiment. The model was able to describe the SMR-SERP experiments without any fitting parameters.     

Synthesis of esters: Development of the rate expression for the Dowex 50 Wx8-400 catalyzed esterification of propionic acid with 1-propanol

The kinetics of the esterification reaction of propionic acid with 1-propanol over the ion-exchange resin Dowex 50Wx8-400 has been studied in this investigation. Kinetic experiments were conducted using a 1 L Lab-Max system at a stirrer speed of 900 rpm over a temperature range of 303.15 -333.15 K. The catalyst loading was varied from 10 to 60 g dry cat/L and acid to alcohol molar ratios of 1:1, 1:2, 1:4, 2:1 and 4:1 were employed. The equilibrium constants for this reaction were determined in separate experiments at 303.15, 313.15 and 323.15 K. The values were equal to 33.18, 30.62 and 28.37, respectively, with a standard enthalpy change of reaction of 6.4 kJ/mol. These values show the reaction to be mildly exothermic. It was found that both external and internal diffusion limitations did not affect the overall reaction rate. The conversion of propionic acid increased with increasing temperature and catalyst loading and decreased with increasing initial mole fraction of acid. The increase in chain length of acid or alcohol or branching had a retarding effect on the conversion. Several kinetic models were tested to correlate the kinetic data, the pseudo-homogeneous (P-H) model, the Eley-Rideal (E-R) model, the Langmuir-Hinshelwood (L-H) model, the modified Eley-Rideal (M-E-R) model and the modified Langmuir-Hinshelwood (M-L-H) model. In all models, the activity coefficients were estimated using UNIFAC to account for the non-ideal thermodynamic behavior of reactants and products. A correction factor for the resin affinity for water (α) was used in both M-E-R and M-L-H models. The above models predicted the kinetic behavior of the studied system with an overall error ranging from 1.65% to 13.32%. Water was found to be more strongly adsorbed than other species present in the system. The M-E-R model between adsorbed 1-propanol and non-adsorbed propionic acid which assumes surface reaction as the rate controlling step, with α equal to 2, was found to be the best model with the least overall error (1.65%). The activation energy for the esterification was estimated to be 67.3 kJ/mol by this model.     

Rate measurement by pulse technique for individual steps involved in CO hydrogenation and its application to catalyst design

By using pulse reaction technique, the rates were measured for the individual steps involved in CO hydrogenation over transition metal catalysts with and without promoters. On all the transition metals other than Rh, the rate constant for the dissociation of C-O bond (k ₁) was much smaller than that for the hydrogenation of surface carbon species (k ₂). The oxides of V, Nb, Mo, and W added to Ru/Al₂O₃ increasedk ₁ and decreasedk ₃. The Rh catalyst was unique in the sense that there was not much difference betweenk ₁ andk ₂. The characteristic feature observed was found to be useful in designing a catalyst for the production of liquid fuel or C₂-oxygenates from syngas.     

When the final catalyst activity profile depends only on the total amount of admitted substance: Theoretical proof

It is shown, based on pulse‐response experiments, that under special conditions the activity profile of a prepared catalytic system depends only on the total amount of admitted substance. This property, previously found computationally, is here established mathematically for porous and nonporous catalysts in different pulse reactors. This result can be used as a theoretical guidance for the design of systems or materials with an optimal activity profile, in particular a catalyst bed or a catalyst particle. Consequently, it can be used for understanding and developing the different diffusion‐reaction processes, e.g., wet impregnation, deactivation of active materials, and so forth. © 2014 American Institute of Chemical Engineers AIChE J, 61: 31–34, 2015     

新型固定床Raney Ni催化剂的制备、表征及苯加氢活性评价

将镍铝合金粉、拟薄水铝石和田菁粉捏合、成型,在空气中高温焙烧,然后用苛性碱溶液充分浸取,制备出可应用于固定床加氢的活性Raney Ni催化剂.实验结果表明,成型合金焙烧过程中,富铝合金相逐渐转化为贫铝相,同时小部分金属铝氧化生成α-Al₂O₃,可提高催化剂的颗粒强度.BET和SEM分析表明,催化剂表面具有较宽的缝隙和丰富的大孔结构.苯加氢活性评价表明,在一定反应条件下,该新型固定床Raney Ni催化剂活性高于传统负载型镍催化剂,也高于按照专利方法制备的同类型催化剂.     

响应面法优化月桂酸单甘油酯的酶催化合成工艺

以月桂酸三甘油酯和甘油为原料,脂肪酶催化甘油解反应合成月桂酸单甘油酯。在单因素试验的基础上,采用响应面分析法进行合成工艺优化。结果表明,含水量(相对于甘油的质量)对月桂酸单甘油酯产率的影响最为显著,且较优合成条件为:恒温振荡器转速100 r/min,酶添加质量分数(相对于底物)5%,n(甘油)∶n(月桂酸三甘油酯)=6∶1,底物质量分数(相对于整个反应体系)51.9%,温度65℃,含水量4.23%,反应时间5 h。在此条件下,月桂酸单甘油酯产率的预测值和实验值分别为81.68%和81.32%,说明二次多项回归模型具有良好的预测性。     

Pillared smectite modified with carbon and manganese as catalyst for SCR of NOx with NH3. Part I. General characterization and catalyst screening

Carbon- and manganese-modified zirconia-pillared smectites were prepared, characterized (XRD, BET and pore analysis, XPS) and tested in selective catalytic reduction of NO_x with NH₃. Both untreated and acidic pretreated smectites were used. The acid pretreatment increased NO conversion and influenced the extent of carbon introduction into the porous system. The carbon deposit improved selectivity of the catalytic reduction to N₂. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optimization of the activity of CaO/Al2O3 catalyst for biodiesel production using response surface methodology

In this work the response surface methodology (RSM) in conjunction with the central composite design (CCD) were used to optimize the activity of CaO/Al₂O₃ solid catalysts for the production of biodiesel. In order to measure the catalyst activity, we used palm oil as a representative raw material for the conversion to biodiesel. The biodiesel production was carried out in a batch laboratory scale reactor. The results showed that both the calcination temperature and the amount of calcium oxide loaded on the support had significant positive effects on the biodiesel yield. The maximum basicity and biodiesel yield obtained were about 194 μmol/g and 94%, respectively. Overall, the catalyst showed high performance at moderate operating conditions and its activity was maintained after two cycles.     

新型介孔有机硅高沸物裂解催化剂的合成、表征及活性

以十二胺（C₁₂）为模板剂, 3-氨丙基三乙氧基硅烷（APTES）与正硅酸四乙酯（TEOS）为原料,在中性条件下,利用共缩聚法合成了含胺MCM型介孔催化剂。采用X射线粉末衍射（XRD）、N₂吸附-脱附、红外（IR）及热重分析（TGA）等手段对催化剂进行表征,结果表明,氨丙基已引入介孔MCM,但过量氨丙基引入会破坏催化剂介孔结构,导致催化剂比表面积和比孔容降低。考察了氨丙基含量和催化剂用量对裂解反应的影响,最佳条件下,单体产率和高沸物转化率分别为63.3%和76.6%。     

Synthesis, characterization and catalytic activity of an ultrafine Pd/C catalyst for formic acid electrooxidation

An ultrafine Pd/C catalyst with a uniformly sized and highly dispersed nanostructure was synthesized by an improved liquid phase reduction method; in this process, a complexone (trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid, C_yDTA) was used as an alternative stabilizer for the first time. Physicochemical characterizations indicated that the resulting Pd nanoparticles possessed ideal structural characteristics, including an average diameter of 2.1 nm, narrow size distribution ranging from 0.5 to 4.0 nm, no visible agglomerations, and no residual C_yDTA. Electrochemical tests showed that the catalytic activity of the obtained Pd/C catalyst for formic acid electrooxidation was 2.2 times greater than that of Pd/C catalyst prepared in the absence of C_yDTA. This improvement in the electrocatalytic performance was attributed to the uniformly sized and highly dispersed nanostructure, which provided a larger overall electrochemical active surface area.     

响应面法优化Ni-P/APO-11非晶态催化剂催化松节油加氢反应

以二异丙胺、氢氧化铝为原料,采用水热合成法制得APO-11磷酸铝分子筛。采用化学还原法制备非晶态Ni-P/APO-11催化剂用于α-蒎烯加氢反应,考察了α-蒎烯加氢反应条件,通过响应面法实现进一步优化,而后采用XRD、BET、SEM、XPS、ICP等对该催化剂进行了表征。结果显示,在反应温度124.8℃,反应压力4.9 MPa,催化剂用量6.3%,反应时间90 min时,α-蒎烯转化率为99.45%,顺式蒎烷选择性97.35%。为进一步拓宽该催化剂使用范围及提高松节油体系的深加工利用水平,将该催化剂用于松节油其他组分的加氢反应中,展现出良好的催化活性,原料转化率均可达到99%以上,选择性65%以上。     

响应面法优化以重组大肠杆菌发酵生产类人胶原蛋白过程

In order to improve the production of human-like collagen Ⅲ (HLC Ⅲ) by fed-batch culture of recom-binant Escherichia coli BL21, the Plackett-Burman and Box-Behnken design were applied to optimize the fermen-tation process parameters.Three variables (induction time, inoculum age and pH), which have significant effects on HLC Ⅲ production, were selected from eight variables by Plackett-Burman design.With the regression coefficient analysis in the Box-Behnken design, a relationship between HLC Ⅲ production and three significant factors was obtained, and the optimum levels of the three variables were as follows: induction time 3.2h, inoculum age 12.6 h and pH 6.7.The 3D response surface plots and 2D contour plots created by the Box-Behnken design showed that the interaction between induction time and pH and that between innoculum age and pH were significant.An aver-age 9.68 g·L~(-1)HLC Ⅲ production was attained in the validation experiment under optimized condition, which was 80% higher than the yield of 5.36 g·L~(-1) before optimization.     

Optimization of synthesis and characterization of cassava starch‐graft‐poly(acrylonitrile) using response surface methodology

Graft copolymerization of poly(acrylonitrile) onto cassava starch was carried out with potassium persulphate (PPS) as the free radical initiator using a response surface Box–Behnken design. Different levels of monomer concentration, initiator concentration, and temperature were used, and regression models were generated in terms of these factors, which can be used to predict the grafting level and efficiency at a given level of the factors. The grafted starches were characterized by FTIR, XRD, and SEM analyses and determination of %grafting (%G), N‐content, thermal properties, water and saline solution retention, and rheological properties. Under the conditions used, %G was found to depend only on the temperature used for the reaction. The maximum %G of 120.1 was obtained for the sample synthesized under the following conditions: weight of AN = 0.753 mol/10 g starch, weight of PPS = 0.284 g and temperature = 55°C, and the grafting efficiency was 30.03%. The absorption bands at 2243 cm^?1 for the nitrile group (? CN) in the FTIR spectra of the products confirmed the grafting reaction. There was a decrease in crystallinity and disappearance of the granular structure after grafting of the starch. The melting temperatures of the graft copolymers determined by differential scanning calorimetry analysis were higher than that of the native starch. The grafted starches exhibited very high thermal stability as observed from the thermogravimetric analysis. The superabsorbent polymer prepared from the grafted starch by alkali saponification exhibited a maximum water absorbency of 636 g/g. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Kinetics and the difference for extraction of praseodymium and neodymium from nitrate aqueous solution by[A336] [NO3] using the single drop technique

The kinetics and the difference for Pr(Ⅲ) and Nd(Ⅲ) extraction from nitrate aqueous solution using trialkylmethylammonium nitrate([A336][NO_3]) as extractant were investigated by the single drop technique.The dependence of the extraction rate of Pr(Ⅲ) and Nd(Ⅲ) on the concentrations of free Pr(Ⅲ) and Nd(Ⅲ)ions, the concentrations of Na NO_3 and H~+in aqueous solutions, and the concentrations of [A336][NO_3] in kerosene solutions were discussed and the corresponding extraction rate equations for Pr(Ⅲ) and Nd(Ⅲ) were obtained. These equations demonstrated that the reaction rate constant of Pr(Ⅲ) with [A336][NO_3] was double than that of Nd(Ⅲ). The effect of the addition of diethylenetriaminepentaacetic acid(DTPA) on the difference in the extraction rate of Pr(Ⅲ) and Nd(Ⅲ) by [A336][NO_3] was also investigated. It was revealed that the difference in the complex formation rates of Pr(Ⅲ) and Nd(Ⅲ) with DTPA made a significant impact on the difference in the extraction rates of Pr(Ⅲ) and Nd(Ⅲ) with [A336][NO_3]. The ratio of extraction rates of Pr(Ⅲ) to Nd(Ⅲ) with[A336][NO_3] was in proportion to the ratio of complex formation rates of Pr(Ⅲ) to Nd(Ⅲ) with DTPA. The extraction rate difference for Pr(Ⅲ) and Nd(Ⅲ) with [A336][NO_3] increased due to a higher complex formation rate constant of DTPA with the free and un-complexed Nd(Ⅲ) ions in the aqueous nitrate solution than that with Pr(Ⅲ) ions. Therefore, the addition of DTPA in the aqueous nitrate solution is an effective method to intensify the separation of Pr(Ⅲ) and Nd(Ⅲ) in kinetics. The study on the extraction mechanism indicated that both the extraction of Pr(Ⅲ) and Nd(Ⅲ) by [A336][NO_3] were diffusion controlled, and the reactions obeyed SN2 mechanism. The present work highlights a possible approach to strengthen the kinetic separation of Pr(Ⅲ) and Nd(Ⅲ).