Optimization of nylon 6 reactors with end-point constraints

Optimal temperature profiles for nylon 6 polymerization in plug–flow reactors have been obtained with end-point constraints involving the degree of polymerization and the cyclic dimer concentration, using the most recent kinetic information. Computations suggest that the temperature at the feed end of the reactor must be maintained close to the highest permissible level (determined by the boiling point of the ?-caprolactam). The temperatures in this region control the degree of polymerization more than other variables. Thereafter, the temperature should be reduced. This second zone controls the undesirable cyclic dimer concentration. The effect of a systematic change of values of the various design variables is studied. The profiles obtained herein are qualitatively similar to those obtained by earlier workers using similar formulations. However, they differ significantly from the profiles obtained by us earlier, using different objective functions which are more relevant to the design of new reactors. Attempts have also been made to obtain a global optimal scheme to produce polymer of a desired degree of polymerization and cyclic dimer content, using as short a reactor as possible, and using the water content and the modifier concentration in the feed as the independent variables.     

旋转微气泡反应器强化臭氧降解水中对硝基苯酚

臭氧氧化技术在水处理系统中具有良好的应用前景,但实际应用中受到臭氧传质及氧化选择性的限制。故本研究以对硝基苯酚废水为研究对象,采用一种新型旋转微气泡反应器,通过多孔陶瓷填料的旋转将臭氧气泡尺寸破碎至微米级别,实现对废水降解过程的强化,同时本研究还进一步考察了操作条件对臭氧传质过程和臭氧分解产生羟基自由基过程的影响规律。实验结果表明,提高反应器转速和气体流量可以加快臭氧传质和羟基自由基产率,同时提高溶液pH也可以提高羟基自由基产率进而提高对硝基苯酚的去除率。与其他操作变量相比,反应器转速的影响最为明显,说明改善臭氧气泡流体力学行为能有效地提高对硝基苯酚的去除效果,体现反应器强化臭氧体系的可行性。此外,二甲亚砜的加入抑制了对硝基苯酚的去除,说明臭氧的间接氧化方式是降解对硝基苯酚的一种重要途径。本研究结果为旋转微气泡反应器在臭氧氧化降解过程中开发及应用提供合理指导。     

Kinetics of acetic acid esterification over ion exchange catalysts

Computer simulation showed that catalytic distillation is an attractive process for the removal of dilute acetic acid from wastewater. Selection of catalysts and kinetic data have been obtained for the design of the catalytic distillation column. Kinetic measurements were conducted in a batch reactor. Methanol was added to the dilute acetic acid solutions and reacted with the acid in water to form methyl acetate and water. The reaction can be catalyzed by solid acid catalysts. It was found that Amberlyst 15 was an effective catalyst for this reaction. The effects of stirrer speed, reaction temperature, reactant concentration and catalyst loading on reaction rate were investigated. A complete kinetic equation for describing the reaction catalyzed by Amberlyst 15 was developed. This equation can be used in the simulation and design of the catalytic distillation column for removing acetic acid from wastewater.     

采用硫化碱处理克劳斯装置尾气的中试开发研究

本文报道了一种采用硫化碱对克劳斯尾气进行脱硫净化的技术开发过程。在实验室半连续装置上研究采用硫化碱脱除SO2 同时制取H2 S的适宜条件 ,SO2 吸收动力学及CO2 的存在对脱除SO2 同时制取H2 S的影响。进而在实验室小型连续装置上进行了验证 ,并确定了一个最佳SO2 /Na2 S进料摩尔比 ;依据实验研究结果 ,进行了 2 0 0m3 /h的中试装置放大设计 ,经 3个月的连续运行 ,试验表明中试装置工艺设计合理 ,采用Na2 S脱除SO2 同时制取H2 S在技术上可行。经济分析显示 ,采用本法每处理 1m3 尾气仅耗费 0 0 39元人民币 ,显示出有很好的社会经济综合效益     

甲醇合成水冷反应器的优化设计

采用合适的反应器结构来保证催化剂床层温度的相对恒定,是合成过程高效、稳定运行的关键.简述了首台甲醇合成水冷反应器与以往类似设备在设计的选材及设计过程中的结构优化,使甲醇合成反应取得较高的反应物单程转化率和较低的副产物产率,提高了相同直径甲醇合成水冷反应器的甲醇产量,并去掉了不必要的大接管,减少了对筒体强度的影响,降低了...     

CONSTRUCTION OF ADMISSIBLE OPERATION CONDITION DOMAIN FOR WELL-STIRRED REACTORS DURING THEIR DESIGN AND CONTROL STAGES

The work examines the problem of constructing an admissible operation condition domain for a well-stirred reactor which would satisfy restrictions in conversion, selectivity, heat removal and stability. The domain is very important and must be known during the reactor design and control stages because it yields visual information for analyzing the reactor operations and makes it possible to find the variation intervals of decision variables, necessary to calculate and optimize the reactor. Being known, the admissible operation condition domain makes it possible to estimate the limiting restrictions and to choose the necessary reserves. The domain has completely been studied analytically for chemical processes with arbitrary kinetics.     

Application of water vapor and hydrogen-permselective membranes in an industrial fixed-bed reactor for large scale methanol production

Coupling reaction and separation in a membrane reactor improves the reactor efficiency and reduces purification cost in the next stages. In this work a novel reactor consisting two membrane layers has been proposed for simultaneous hydrogen permeation to reaction zone and water vapor removal from reaction zone in the methanol synthesis reactor. In this configuration conventional methanol reactor is supported by a Pd/Ag membrane layer for hydrogen permeation and alumina-silica composite membrane layer for water vapor removal from reaction zone. In this reactor syngas is fed to the reaction zone that is surrounded with hydrogen-permselective membrane tube. The water vapor-permselective membrane tube is placed in the reaction zone. A steady state heterogeneous one-dimensional mathematical model is developed for simulation of the proposed reactor. To verify the accuracy of the model, simulation results of the conventional reactor is compared with the available plant data. The membrane fixed bed reactor benefits are higher methanol production rate, higher quality of outlet product and consequently lower cost in product purification stage. This configuration has enhanced the methanol yield by 10.02% compared with industrial reactor. Experimental proof-of-concept is needed to establish the safe operation of the proposed configuration.     

炭循环微电解反应器处理腈纶废水的Design-Expert设计优化

利用Design-Expert 7.1试验设计系统对炭循环微电解反应器处理腈纶废水的试验进行了试验设计和试验结果分析;通过试验设计分析得出了腈纶废水COD去除率与试验影响因素之间的定量关系模型,并得到了腈纶废水COD去除率的残差分布以及在不同影响因素变量之间的COD去除率等值线和三维关系。优化结果表明:利用Design-Expert 7.1对炭循环微电解反应器处理腈纶废水试验条件进行优化,得到了最佳COD去除率的操作条件。     

Feasibility Study of a Solar Reactor for Phenol Treatment by the Photo‐Fenton process in Aqueous Solution

Solar reactors can be attractive in photodegradation processes due to lower electrical energy demand. The performance of a solar reactor for two flow configurations, i.e., plug flow and mixed flow, is compared based on experimental results with a pilot‐scale solar reactor. Aqueous solutions of phenol were used as a model for industrial wastewater containing organic contaminants. Batch experiments were carried out under clear sky, resulting in removal rates in the range of 96–100 %. The dissolved organic carbon removal rate was simulated by an empirical model based on neural networks, which was adjusted to the experimental data, resulting in a correlation coefficient of 0.9856. This approach enabled to estimate effects of process variables which could not be evaluated from the experiments. Simulations with different reactor configurations indicated relevant aspects for the design of solar reactors.     

Preliminary Design of a Loop Reactor for Bulk Propylene Polymerization

Some typical problems in the early design stages of a tubular loop reactor for bulk propylene polymerization are analyzed. Characteristic variables are identified, and a shortcut method for the preliminary estimation of the reactor dimensions is developed. the influences of process variables such as catalytic activity, suspended solid fraction, and average particle size are studied. In particular, a relationship between the average particle size in the reactor and the particle size at both the inlet and the outlet is obtained. the behavior of the reactor under different operating conditions is studied, and critical parameters are identified. Most relevant results are related to the importance of the particle size inside the reactor. the two goals of maximum yield and maximum productivity for a given loop reactor configuration cannot be achieved simultaneously: While catalyst yield increases with the third power of the average particle size in the reactor, the smaller the average particle size in the reactor, the greater the productivity. the steps to be followed for a preliminary design of a propylene polymerization, loop reactor are discussed. A priority list for the sequence of parameters to be adopted is proposed, according to the relative importance of the variables involved.     

Designing and operating a pilot plant for purification of industrial wastewater from toxic organic compounds by utilizing solar energy

The aim of the present project was to design and operate a solar reactor system and to analyze its performance for the removal of different types of toxic organic pollutants (e.g., synthetic methyl violet dye and phenol) from water with titanium dioxide as the photocatalyst. Various operating parameters were studied to investigate the behavior of the designed reactor like initial substrate concentration, loading of catalyst, pH of solution, and H₂O₂ concentration. The operating parameters were optimized to give higher efficiency to the reactor performance. Results showed that a photocatalysis system, operating at optimum conditions, offered within one hour of operation degradation up to 95.27% for synthetic dye, while a conversion of 99.95% was obtained in three hours. With phenol, degradation was up to 80.0% and 98.0%, respectively. The removal of TOC for the two toxic materials was also at high levels. This confirmed the feasibility of the designed solar system. The kinetics of dye degradation was first order with respect to dye concentration and could be well described by Langmuir-Hinshelwood model. A preliminary design of a solar photocatalysis system as an alternative treatment method for wastewater effluents from an Iraqi textile mill was introduced.     

用竖井管式絮凝器处理生活污水的研究

对竖井管式絮凝反应器作了大量实验研究,发现聚合氯化铝投加量为25~45 mg/L时,对城市生活污水有较好的处理效果,COD去除率可以达到65%左右,总磷去除率达55%~70%,浊度去除率达85%左右。运行时借助于水位落差和水力学作用,可以不需要其他搅拌设备,耗能少,占地小,有较强的推广价值。适合对城市污水的预处理,也适合于与生物法相结合,提高脱磷效果。     

The application of simulation vessel flow studies to an industrial chemical reactor mixing problem

A general technique for treating industrial chemical reactor mixing problems is presented. This technique involves mathematical analysis to predict reactor performance in terms of the parameters of a realistic flow model. The variables of the system model are then coupled with the parameters of agitator design and operation through a simulation vessel mixing study. In this way, reactor performance can be expressed in terms of agitator design. The application of this approach to the solution of an industrial chemical reactor design problem is discussed.     

Simulation of a multi-annular photocatalytic reactor for degradation of perchloroethylene in air: Parametric analysis of radiative energy efficiencies

A multi-annular photocatalytic reactor was designed, that shows good effectiveness for perchloroethylene (PCE) removal from contaminated air streams. In a previous work, a rigorous physical and mathematical model of the photocatalytic reactor was developed and experimentally verified. In this work, this mathematical model was used to study the radiative energy efficiency of the multi-annular photoreactor. The total quantum efficiency is defined as the ratio of the number of molecules of PCE reacted to the number of photons emitted by the lamp, and it is expressed as the product of the following factors: the reactor radiation incidence efficiency, the catalyst radiation absorption efficiency, and the overall reaction quantum efficiency. For the employed reactor, the numerical values of each one were 83%, 92%, and <2.5%, respectively. Particularly, the dependence of the overall reaction quantum efficiency upon operating variables such as the PCE feed concentration, gas flow rate, irradiation level and relative air humidity was analyzed. These results are useful to optimize the operating conditions and design parameters of the photocatalytic reactor.     

Esterification in a structured catalytic reactor with counter-current water removal

In this research the liquid phase esterification of hexanoic acid and 1-octanol was studied. Very high activities were obtained for zeolite BEA and Nafion/silica composite with 13% of Nafion. The advantage of water removal in this system was demonstrated. In a closed system an equilibrium conversion of 35% was reached, while in a system with water removal all the reactants were converted in a shorter period. The initial reaction rate decreases when increasing the initial water concentration, following a Langmuir–Hinshelwood type of rate expression. An active zeolite coated structured monolithic reactor configuration was prepared. Enhancement by the counter-current water stripping of the performance of the structured catalysts was demonstrated.     

不同温度条件下厌氧处理食品废水的试验研究

本试验采用UASB厌氧反应器对某工业园区食品加工废水进行处理。比较了在中温(37±2℃)和模拟原水水温(26～30℃)的条件下,不同负荷对COD去除率的影响。实验结果显示,当水力停留时间为8 h/d时,厌氧反应器容积负荷为6 kgCOD/(m3.d),在模拟原水水温条件下,COD去除率可达到75%左右;在中温条件下,COD去除率可达到80%左右,均有较好的效果;相对于中温而言,原水水温厌氧在工程应用上节省了投资,该实验结果可为该类食品废水厌氧生物处理提供设计运行依据。     

Design of a novel sequencing batch internal micro-electrolysis reactor for treating mature landfill leachate

A novel sequencing batch internal micro-electrolysis reactor (SIME) was specifically designed to treat mature landfill leachate. The idea of simulating the biological process of a sequencing batch activated sludge reactor (SBR) was employed in the design of the new reactor. The innovative concepts behind this design are the combination of the processes of reductive internal micro-electrolysis (IME) without aeration and oxidative IME with aeration, and the integration of electro-aggregation and electro-coagulation. The automated operating system in this reactor is centralized automation which rewards for safe control, convenient operation and the possibility of commercial application. The SIME reactor exhibited a COD removal efficiency of 86.1% for mature landfill leachate in this study, which is much higher than that of conventional treatments, such as electrolysis, coagulation–sedimentation, and the Fenton process. A pilot-scale experiment showed that the reactor was also particularly efficient in the removal of color, humic acids, and metal ions. The BOD₅/COD ratio of the leachate was significantly improved after the treatment. All of these results show that the SIME reactor is a promising new technology because it is efficient and automated, and has the potential to be applied to the practical treatment of mature landfill leachate.     

Optimization of the Iron Electro-Coagulation Process of Cr,Ni, Cu,and Zn Galvanization By-Products by Using Response Surface Methodology

An electrocoagulation laboratory scale system was studied for the removal of inorganic pollutants from a mixture of galvanic process-based by-products. Response surface methodology based on a five-level, four-variable central composite rotatable design was employed for optimization with respect to four important variables—reaction time, agitation velocity, current density, and pH. The electrocoagulation process response was evaluated on the basis of chemical oxygen demand (COD), turbidity, total suspended solid, and element concentration values. Interaction effects between reactor operating variables and response variables were evaluated by using 3-D response surface analysis Second-order models were validated by ANOVA. Predicted yields were in a good agreement with the experimental ones. The reactor optimal performance was achieved at 35 min reaction time, 170 rpm agitation velocity, 97.7 Am^?2 current density, and 6.5 initial pH. Under these conditions 100% color and turbidity, 90% COD and total suspended solids, 100% chromium and nickel, and almost 99% zinc and copper were removed. A pseudo-first-order rate model was applied to describe the metal removal kinetics. The EC treatment of heavy metal solutions proved to be more cost-effective than the conventional one, indicating clearly that the method of electro-coagulation is a very promising alternative for industrial applications.     

Effects of structural parameters on water film properties of transpiring wall reactor

Corrosion and salt deposition problems severely restrict the industrialization of supercritical water oxidation. Transpiring wall reactor can effectively weaken these two problems by a protective water film. In this work, methanol was selected as organic matter, and the influences of vital structural parameters on water film properties and organic matter removal were studied via numerical simulation. The results indicate that higher than 99% of methanol conversion could be obtained and hardly affected by transpiration water layer, transpiring wall porosity and inner diameter. Increasing layer and porosity reduced reactor center temperature, but inner diameter's influence was lower relatively. Water film temperature reduced but coverage rate raised as layer, porosity, and inner diameter increased. Notably, the whole reactor was in supercritical state and coverage rate was only approximately 85% in the case of one layer. Increasing reactor length affected slightly the volume of the upper supercritical zone but enlarged the subcritical zone.     

Effects of carboxylic additives on the polymerization characteristics of nylon‐6 reactors with diffusional water removal

The effects of carboxylic acid on the polymerization characteristics of nylon‐6 were investigated in reactor models that consist of a continuous‐flow stirred tank reactor (CSTR) and a tubular reactor with a diffusional water‐removal system, which are connected in series. Mathematical models for the CSTR and the tubular reactor were established and solved by numerical methods. In the CSTR, with an increase of the feed acetic acid content, the monomer conversion, and the molecular weights are increased. In the tubular reactor, the acid behaves like a catalyst and a modifier at the same time in the polymerization of nylon 6. The effects of the feed acetic acid content and the diffusional water removal on the zeroth, first, and second moments and the polydispersity index of the polymer were investigated. The polydispersity index is greatly affected by the feed content of carboxylic acid in the CSTR, but it finally approaches to values of ～ 2 in the tubular reactor. The diffusional water removal is found to have little effect on the polydispersity index of the polymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1226–1237, 2001