Microwave Enhanced Reactive Distillation

Abstract

The application of electromagnetic irradiation in form of microwaves (MW) has gathered the attention of the scientific community in recent years. MW used as an alternative energy source for chemical syntheses (microwave chemistry) can provide clear advantages over conventional heating methods in terms of reaction time, yield and selectivity. Several applications using this technology have been proven effective in diverse scientific fields. In this thesis, the scope of microwave chemistry was further expanded to a reactive distillation (RD) process with the primary objective to evaluate its use in view of possible process intensification (PI). The ultimate goal was to conceptually address the novel concept of a MW enhanced RD process (MWeRD) based on demonstrated effects in partial processes namely; molecular separation and chemical reaction. The thesis is divided in four main parts, each of them covering different aspects of the research. Part I, comprises Chapters 1, 2 and 3, giving the introductory guideline and the basic data neededTo proof the concept, the synthesis of n-propyl propionate was chosen as case system. The thermo-physical data required to accurately address RD design and operation, and the dielectric properties relevant for MW dielectric heating were experimentally determined. The thermodynamic behavior of the system was accurately predicted using a fitted UNIQUAC-HOC model, while experimental reaction kinetics data were used to fit parameters of a pseudo-homogenous model. Both models were used to build the residue curve maps, needed to determine process feasibility. Experiments performed in a conventionally heated pilot-scale column (DN-50) equipped with two types of structured packings (Sulzer BX and Katapak-SP 11) are reported. In addition, a non-equilibrium stage model (NEQ model) for the column was implemented. Model predictions were compared to experimental results showing good accuracy. Theoretical investigations of the most important operating parameters (total feed, molar feed ratio, reflux ratio and heat duty) and their effect on the overall process performance are presented. The fundamental research performed with MW was divided in two parts. First, the influence of MW on molecular separation of the binary mixtures composing the quaternary case system is discussed based on experimental results. Four binary pairs were studied showing, in some cases, an enhanced separation of the components. Then, the effects of MW radiation on the case reaction were studied comparing reaction conditions under MW and conventional heating using different homogenous and heterogeneous catalysts. From all the catalysts tested, Zn triflate proved to be more effective under microwave heating producing 40% more ester compared to the conventionally heated experiment. Finally, the general benefits and barriers of the technology integration are discussed based on the results of the MW enhanced reaction and separation. The novel concept of a MWeRD process is presented, giving recommendations for further research in terms of hardware, operating conditions and up-scalability of the process.