Reactivity of calcined limestone and dolomite with sulfur dioxide

Under the conditions prevailing in in-situ desulfurization of fluidized bed combustion two types of limestone and two types of dolomite were tested for their reactivity with sulfur dioxide. Experimental variables were sorbent size, sulfur dioxide concentration and reaction temperature. In general reactivity increased with temperature with activation energy ranging 15.9 to 19.5 kcal/mol for initial reaction rate. Reaction order with respect to sulfur dioxide was close to one and reactivity decreased with increase of sorbent size. With continuous feeding of coal and sorbent sulfur dioxide concentration in the effluent gas decreased with increase of Ca/S ratio.     

Reaction of SO2 and NO2 with polymers

A number of polymers have been exposed to SO₂ and NO₂ gas under various conditions. Chain scission, crosslinking reactions, and changes in infrared spectra have been noted. All polymers suffer some deterioration, which may be considerable with exposure over long periods of time. Elastomers form a separate group, being appreciably more susceptible to these gases than saturated polymers; however, they are still more sensitive to ozone.     

Numerical analysis of a finite cylindrical pellet model in solid-gas reactions

A two-dimensional grain model has been developed to describe solid-gas reactions in a cylindrical pellet of finite length. The grains are assumed to be spherical. Numerical solutions of the model have been compared to infinite cylinder solutions, infinite slab solutions, and the approximate infinite cylinder and infinite slab solutions developed by Szekely et al. (Szekely J., Evans J. W. and Sohn H. Y., Gas—Solid Reactions. Academic Press, New York 1976). Pellet sizes and reactor conditions under which one or more of these solutions is valid have been indicated. The accuracy of the other models depends on whether they are to be used to determine rate constants from initial rate data or whether they are to be used to relate conversion to time.When the Theile-type reaction modulus σ_L = L[3(1 - ε₀)K/D_ear_g]^{$\text{1}\text{2}$}, has a value 2.2 with a cylinder half-length of L = 0.2 cm and a cylinder radius of R_p = 0.8 cm the conversion levels after about 8 min are 40% by an infinite slab model, 50% by the 2-D model and 65% by the approximate infinite slab solution. If one determines a rate constant from the initial slope of the rate curve, then the infinite slab model gives a value 14% high. The approximate infinite slab solution is inappropriate for the latter purpose. Similar results are obtained when the cylinder radius is much smaller than the half-length.Pellets with R_p/L > 4 or <0.25 can be described by infinite slab or infinite cylinder models, respectively, if the diffusional resistance is not large.     

Analysis of reaction zone thickness in non-catalytic solid-gas reactions

An expression for determining the reaction zone thickness in a slab type solid pellet is derived based on the grain model for first order and isothermal reaction. It is shown that during reaction, the zone thickness remains constant for slab type pellets and varies for cylindrical and spherical shaped pellets. An approximate criterion is obtained from the expression for the applicability of the widely used shrinking core and homogeneous models. The expression is also useful for determining the rate parameters. The expression is found to be very satisfactory in predicting the experimental reaction zone thickness values and the activation energy value for the zinc sulphide oxidation reaction.     

硫酸钾催化环氧氯丙烷与三乙胺的反应研究

首次将硫酸钾作为催化剂,引入到环氧丙基三乙基氯化铵中间体的合成反应中。与无催化剂体系相比,催化下的反应速率大幅度提高,反应时间显著缩短。以环氧氯丙烷的转化率和产物中环氧基保留率的乘积作为中间体性能的评价指标,通过正交实验优化出最佳条件:甲醇水溶液为溶剂,反应温度50℃、n(硫酸钾)∶n(环氧氯丙烷)=0.010、n(三乙胺)∶n(环氧氯丙烷)=1.0、反应时间为1.5 h。该条件下,环氧氯丙烷的转化率可达92.02%,产物中环氧基保留率达到70.67%。可见硫酸钾用于催化环氧丙基三乙基氯化铵的合成反应是适宜的。     

Analytical prediction of conversion-time behaviour of gas-solid noncatalytic reactions

A procedure has been suggested for analytical prediction of conversion-time behaviour of gas-solid non-catalytic reactions which are first order with respect to the gaseous reactant but of any general form with respect to the solid species. Based on this method analytical solutions have been presente for some of the commonly encountered rate forms including the grain model. These solutions predict the behaviour of the system extremely well upto abou 50–70% conversion of the solid.     

Application of the zone model to multiple noncatalytic fluid-solid reactions

The effect of intraparticle diffusion on the multiple gas-solid reactions occurring in a porous solid reactant is analyzed by the zone reaction model. In parallel reactions for gases and a consecutive reaction for the solid, the solutions of transient concentration profiles of two solid reactants are given by classifying three zones, viz. Reaction zone and reaction-diffusion zone and diffusion zone in the course of the reaction progression. As an example, the simultaneous reduction-sulfidation of porous iron oxide sorbent in the desuifurization from low BTU coal gases is analyzed by the present model. The Thiele modulus of the reaction governs the behavior of the moving boundary between the reaction zone and the diffusion zone. When the Thiele modulus tends to be infinite, the present model is consistent with the solutions based on the unreacted shrinking core model.     

双系列高固气比预热系统热力学理论计算与分析

利用悬浮预热系统中质量和热量平衡的关系,从理论上推算出双系列高固气比五级悬浮预热系统热效率表达式,并利用Matlab编程计算,分析了固气比、各级预热器单体分离效率和预热器级数对悬浮预热系统热效率的影响,得到了优化的设计参数。结果表明:随固气比的增大,系统热效率出现峰值;热效率随各级旋风筒分离效率的增大而增大,C1分离效率对热效率的影响最明显;系统级数越多,越有利于提高热效率,但随级数的增多,提高幅度越来越小。     

Kinetic analysis of N2O decomposition over calcined hydrotalcites

Kinetics of N₂O decomposition over catalyst prepared by calcination of Co–Mn hydrotalcite was examined in integral fixed-bed reactor () at various N₂O and O₂ initial partial pressure at temperature range of 330–450 °C. Kinetic data were evaluated by linear and non-linear regression method, 15 kinetic expressions were tested. Based on the obtained results a redox model of N₂O decomposition was proposed. At low pressures of O₂, adsorbed oxygen is formed by the N₂O decomposition; the N₂O chemisorption is considered as the rate-determining step. On the contrary, at high O₂ pressure it could be assumed that adsorbed oxygen species appear as a result of O₂ adsorption and the Eley–Rideal mechanism is the rate determining. N₂O decomposition is well described by the 1st rate law at N₂O and O₂ concentrations typical for waste gases.     

Reaction of pyritic sulphur in coal with lime and calcined dolomite during the coking process

Various reactions occur between pyrite (FeS₂) in coal and CaO to form CaS when a finely pulverized intimate mixture of coal and CaO is coked at 900 °C in an inert atmosphere. The effectiveness of lime and calcined dolomite (CaO.MgO) in promoting this reaction has been evaluated; calcined dolomite is somewhat more effective than lime over coal/ oxide weight ratios from 2.8 to 14. The degree of conversion of pyrite to calcium sulphide at a coal/calcined dolomite weight ratio of 7 has been determined as a function of time at 900 °C; coking time in excess of 2.5 h does not have a significant effect. It has been shown that the total sulphur lost on coking coal/lime mixtures decreases and the percentage of FeS, originating from the dissociation of pyrite, converted to CaS increases as the amount of lime added increases. But although the total sulphur content of coke produced in the presence of CaO is then higher than when the coal is coked without lime, the pyritic sulphur has been converted to CaS which is more amenable to chemical conversion to H₂S. A method is outlined for determining CaS in the coked mixture in the presence of FeS.     

SO2-Na2S-H2O体系热力学分析

利用Na<,2>S溶液吸收SO<,2>是湿法烟气脱硫中具有良好应用前景的新方法.为了能更好地利用Na<,2>S溶液进行烟气深度脱硫,文中通过热力学计算,对Na<,2>S溶液吸收SO<,2>烟气所构成的SO<,2>-Na<,2>S-H<,2>O体系中气液固三相组成与pH值的关系进行了分析.结果表明,pH值大于6时,SO<...     

固体超强酸ZrO2/SO4=和Fe2O3/SO4=催化苯乙烯烷基化甲苯反应的研究

固体超强酸ＺｒＯ２／ＳＯ４＝和Ｆｅ２Ｏ３／ＳＯ４＝在室温下即可高活性地催化苯乙烯烷基化甲苯的反应。于２０分钟时苯乙烯转化率可在４０％￣５０％。在连续使用三次时,催化剂活性未见下降。     

In situ monitoring of the kinetics of solid-gas SHS reactions: Application to the Zr-O<Subscript>2</Subscript> system

The combustion of a powder mixture of zirconium and zirconia in a pure oxygen atmosphere was chosen to present a new approach of the solid-gas-type SHS process. Indeed, this study is the first attempt to monitor the reaction rate in situ by pressure measurements of the reactive gas Two kinetic modes have thus been defined: (1) a surface reaction which corresponds to the combustion wave propagation and (2) a parabolic consumption of oxygen which occurs during the after-burn reaction. Some specific phenomena such as the trigger mechanism of the self-sustaining combustion have also been highlighted by this method. The latter, easy to implement, should provide a better insight into reaction mechanisms of any solid-gas reaction.      

SO2催化氧化反应的平衡温度与最佳温度探讨

阐述硫酸生产过程中SO2催化氧化反应的平衡温度与最佳温度的确定,应考虑催化剂的内表面利用率和综合校正系数对反应过程的影响,针对其反应过程推导出不同催化剂的平衡温度与最佳温度的计算式。     

液相中H2S与SO2反应动力学研究

在鼓泡反应器中研究了二氧化硫和硫化氢在三种不同pH值溶液,即水溶液、盐酸-柠檬酸钠缓冲溶液和碳酸钠-碳酸氢钠缓冲溶液中的反应行为.结果表明,液相中两者的反应主要是发生在硫化氢分子和亚硫酸氢根离子之间.在对实验数据分析的基础上,得出了三种液相溶液中的统一反应速率方程为r=kcH2SC0.5HSO3-,k=1.531×104exp(-2139—T)其中,反应活化能为17.78kJ·mol-1.     

Solution of moving boundary problems for gas—solid noncatalytic reactions by orthogonal collocation

An integral transformation, a coordinate transformation for immobilization of the moving boundary, and orthogonal collocation are used to reduce a nonlinear initial-boundary value problem in time and space to a set of ordinary differential equations in time with given initial conditions. The method is developed for solution of models for gas—solid noncatalytic reactions and is especially useful for moving boundary, two-stage reaction problems. The method represents an advantage and an alternative to the available finite difference techniques. Results of various gas—solid reaction models are analyzed.     

Solution of models for gassolid noncatalytic reactions by orthogonal collocation on finite elements with moving boundary

A variable size grain model is used to describe gassolid non-catalytic reactions which are accompanied by change in solid structure. A finite element collocation method with a moving boundary is developed to describe gas and solid concentration profiles in the reacting pellet and to compute conversion-time relationships. Such a method is necessary in case of structural changes which lead to complete pore mouth blockage and gives good results until such blockage occurs. A modified shrinking core model is used as an approximation after the time at which complete pore mouth closure occurs. The developed computational algorithms show that the effect of structural changes on time-conversion relationship is significant.