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This thesis presents a catalytic membrane reactor configuration (CMMR), which is intended for efficient conduction of the fluorination of toluene with respect to industrial production of mono-fluorinated products. The underlying paradigms for the development of this device are process intensification, simplification and synthesis. In this manner a reactor is created which addresses the problematic features of the direct fluorination of toluene reaction and also aims on high overall efficiency, e.g. by reducing downstream processing. Microreactors inherently facilitate high gradients of concentrations and temperatures due to small measures, which results in high material and energy fluxes. Additionally, a multifunctional catalytic membrane is used to supports the electrophilic attack of fluorine on organic compounds and improve heat management and process safety. A mathematical model of this process is developed, based on heat, mass and momentum conservation equations, and equations describing the reaction chemistry. The model is too complex to be solved analytically because of the fact that momentum, heat and mass conservation equations including alchemical reactions have to be solved simultaneously in a 3-dimensional modelling domain. The finite element method was found to be suitable to solve this specific problem, because its intrinsic structure facilitates efficient handling of boundary value problems and complex modelling domain geometries. A commercial package is employed which allows 3-dimensional simulations and features powerful post-processing tools. Results obtained Jähnisch et al.(2000) with the direct fluorination of toluene in a failing film microreactor (FFMR) are used to determine some model parameters and to verify the model. In a simulation study the process model is used to analyse heat and mass transfer processes and to determine the achievable performance of the CMMR with regard to the selectivity, the production rate, the conversion of toluene and process safety. As a benchmark for the effectiveness of the membrane, results obtained with the FFMR employed by Jähnisch et al. (2000) are used. In this connection the most important feature of the membrane under investigation are: support of the electrophilic reaction (with rate constant k₁), decoupling of the momentum of the gas and the liquid flow, high heat conductivity and diffusion resistance imposed on reactants and intermediate products. Heat management with the CMMR is analysed in connection with the design of the integrated heat exchanger with the goal of minimising the temperature variations in the reactor cross-section and along the reactor as well as avoiding heat back-mixing which can potentially result in thermal run-away and unsafe operation. The results present a good basis for the design and experimental work with a pilot plant and optimisation of this process as well as scale-up in the course of plant design for the industrial production of mono-fluorinated toluene.

This thesis describes a process design procedure incorporating early consideration of extra design criteria. Traditionally cost is used as the main criterion to select a design alternative, but the design specification frequently has approximations and uncertainties associated with it. Further criteria for evaluating processes can be used to help the designer differentiate between alternatives. Synthesis is carried out on a cost basis selecting the <i>n </i>best processes based upon cost. The synthesis output is reassessed on the grounds of safety, environmental impact, flexibility etc. The methods are applicable to conceptual design and form the basis of further analysis. Where transparency and flexibility is required in the analysis, external packages are used. A post synthesis environment is described which stores the extra data required to perform the procedure and enables a collection of processes to be examined. Relationship assessments and value based assessments are applied to conflicting criteria so that a process ranking can be made. The procedure has been applied to two case studies in the manufacture of hydrogen cyanide and ethylene. The studies show how the method can be applied and demonstrates that the design selected upon a cost basis alone may not be the optimal design. The procedure demonstrates the requirement that the assessment package and synthesis package are linked to ensure consistency of the data set, and a record of all previous data sets are maintained. The cost of incorporating inherent features into a design can be evaluated and inferior designs can be removed from further consideration. By assessing the process alternatives early on in the design, development time can be reduced and the designers attention can focus upon the best process alternatives.

This thesis describes research undertaken in the synthesis of process design and the effect of uncertainty on process design, aspects of computer aided design which have received comparatively little attention. Heat exchange networks form the basis of the studies. Investigation of methods previously proposed for the synthesis of heat exchange networks are reported. Due to the immense size of the synthesis problem, these methods, mainly exhaustive search procedures, are limited to the solution of small problems. Following this study, a very fast, simple technique, based on the use of a single heuristic, is described; this technique overcomes most of the limitations of previous methods. The new method is applied to an industrial sized problem, the heat recovery section of a crude oil distillation unit, and networks up to 10% cheaper than those designed by conventional techniques result. Simulation studies of these synthesised networks suggest that they are sufficiently flexible to operate well under non-design conditions. The generation of synthesis trees indicates that the costs of these networks are consistently very close to the optimal. There are inevitable uncertainties associated with the design of equipment. Using published correlations, and data available for several exchangers, the statistical distribution of the uncertainty in overall heat transfer coefficient is investigated. Use of this distribution leads to higher overdesign factors than often quoted, and a method of finding optimum overdesign factors is presented. During preliminary investigations into uncertainty in networks of exchangers, a linearised model, based on a Taylor series expansion, which permits the calculation of system variances and covariances is developed. A scheme for the incorporation of this model into a modular simulator is outlined.

The design of a heat transfer sieve tray and its operation in an adiabatic 150 mm diameter distillation column is described. The capability to transfer a significant amount of heat is pivotal; hence, altering the vapour and liquid composition in a traceable way. The design philosophy of the heat transfer sieve tray and appropriate sampling devices are explained in detail. A review of heat integration technology is included. Numerous experiments with a binary mixture of methanol-water have been conducted in the cooling and heating mode respectively. The influence on Murphree tray efficiency of key variables like vapour flow rate, reflux ratio and heat flux were investigated. Simultaneously, overall heat transfer coefficients and plate-to-forth heat transfer coefficients were measured. Prediction methods for Murphree tray efficiency and stage models are reviewed. Based on the review, a model for stimulating a diabatic tray is proposed. The model is a modified nonequilibrium model including material and energy balances, rate equations and equilibrium relations. A set of equations for modelling a binary mixture is presented. Prediction methods for the overall and plate-to-forth heat transfer coefficients are presented. The prediction methods utilised heat flux, plate temperature, heat transfer medium temperature and froth temperature profile data. The experimental heat transfer coefficients were correlated with the plate-to-froth temperature difference in the heating mode, in which nucleate boiling is promoted and with the vapour velocity in the cooling mode, where convective cooling/condensation takes place along the vapour path. The experimentally obtained heat transfer coefficients and heat transfer correlations might be useful as contributor of real data in the modelling of diabatic distillation trays.

This thesis presents a method for the synthesis of multicomponent product separation systems which does not require an explicit superstructure. Separator functions are not predetermined and systematic stream splitting and blending are included. The synthesis algorithm employs a depth-first tree search in order to locate solutions and unit design variable discretisation to reduce the search space. The algorithm generates a set of good, feasible solutions which may be further optimised by continuous means. The method is applied to two different types of problems. The first is a petroleum industry problem involving the separation of a two-phase oil stream into specified gas and liquid products. An effect product specification in the form of vapour pressure bounds, is placed on the liquid product. Flash vessels are the separation technology considered and all solutions returned make use of stream blending. The second case study deals with nonideal separation problems. The recycles required to make these processes optimal can be multicomponent streams, for which both fuzzy and effect product specifications are defined. The MCP synthesis method is applied to nonideal problems by adding the means to handle recycles and a procedure for identifying feasible separations. Solutions containing entrainer-rich and azeotrope-rich recycles and boundary-crossing separations are returned for ternary nonideal separation problems.

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No description available.

No description available.

No description available.