Reaktif Distilasyon Kolonunun Dinamik Modellemesi

Abstract

Kimya endüstrisinde ayırma işlemlerine karşı sürekli artan ve çok büyük bir ilgi bulunmaktadır. Bu endüstride kullanılan en yaygın ayırma işlemleri ise distilasyon, ekstraksiyon, evaporasyon ve kristallendirmedir. Artan ilgiyle birlikte son yıllarda bu teknolojiler arasında en çok kullanılan ve bilinen işlem distilasyon olmuştur. Ayırma işlemleri endüstrisinde, enerji verimini artırarak daha ekonomik ve de daha çevreci işlemler gerçekleştirecek ekipmanların kullanılacağı yaklaşımlara ihtiyaç duyulmaktadır. Bu amaçları gerçekleştirebilecek en makul yol ise endüstriyel operasyonlar için en uygun dinamik sistemin seçilmesidir. Reaktif distilasyon hem sıvı buhar ayrımının hem de bir veya daha fazla kimyasal reaksiyonun aynı anda gerçekleştiği bir prosestir. Böylece, sadece bir adet reaktif distilasyon kolonu kullanarak hem yatırım için hem de operasyon için kullanılan maliyetler azalmakta ve böylece kullanılma oranları artmaktadır. Bu projedeki temel amacımız reaktif distilasyon işlemini yeni bir sistematik dinamik modelleme yaklaşımıyla optimizasyon ve kontrol işlemlerinde kullanmaya hazır hale getirmektir. Bu model reaktif distilasyon uygulamasını anlamak için iyi bir fikir vermektedir; ama optimizasyon ve kontrol uygulamaları için bazı kısıtlamalar getirilmesi uygun olacaktır. Bu çalışmada dinamik kütle ve enerji dengesi, temel kinetik ve temel termodinamik (MESH eşitlikleri) denklemleri kurularak, denge modelimizin oluşturulmasında kullanılmıştır. Dinamik model ilk olarak 3 raflı bir kolonda, MATLAB kullanılarak test edilmiş, daha sonra yine aynı program 3, 5, 10 raflı kolonlar için denenmiş ve bu model, A + B ↔ C + D gibi bir reaksiyon için, 5 raflı reaktif bir distilasyon kolonuna genişletilmiştir. Bu model geliştirilirken, farklı raf sayılarında uygulanarak (3, 5, 10 raflı reaktif distilasyon kolonu) test edilmiştir. Bileşim profilleri ve bu raflardaki çözümleri adım adım gözlenmiştir. Çıktılarımızın olduğu kısımdaki grafiklerde görüleceği üzere besleme akımında ya da besleme bileşiminde herhangi bir değişim uyguladığımızda sistemimizin buna nasıl cevap vereceği de tespit edilmiştir. Ayrıca, çeşitli adi diferansiyel eşitlikler kullanarak (ODE 23, 23s, 15s, 45), sistemimiz için en uygun profili verecek adi diferansiyel eşitliğin ne olabileceği MATLAB’ da uygulanarak belirlenmiştir.

There is a great interest for seperation processes in chemical industry. Common separation technologies are distillation, extraction, pervaporation, crystallization, etc. Distillation is the most used and known process between all these technologies for last years. In the separation processing industry, there is the need to approach the operation of industrial equipment so they increase their energy efficiency, leading to more-economical and environmentally oriented processes. A feasible way to achieve these purposes lies in the optimal dynamic operation of industrial operations. Reactive distillation (RD) is the process in which vapor-liquid separation and one or more chemical reactions occur simultaneously. Separation of the product from the reaction mixture does not need a separate distillation step, which saves energy (for heating) and materials. In this way, only one piece of equipment (the RD column) is used, possibly reducing investment and operation costs. This technique is especially useful for equilibrium-limited reactions such as esterification and ester hydrolysis reactions. Conversion can be increased far beyond what is expected by the equilibrium due to the continuous removal of reaction products from the reactive zone. This helps reduce capital and investment costs and may be important for sustainable development due to a lower consumption of resources. Being a relatively new field, research on various aspects such as modeling and simulation, process synthesis, column hardware design, non-linear dynamics and control is in progress. The suitability of RD for a particular reaction depends on various factors such as volatilities of reactants and products along with the feasible reaction and distillation temperature. Hence, the use of RD for every reaction may not be feasible. Exploring the candidate reactions for RD, itself is an area that needs considerable attention to expand the domain of RD processes. Although invented in 1921, the industrial application of reactive distillation did not take place before the 1980s. The esterification of acetic acid with alcohols like n-butanol, ethanol, isobutyl alcohol and amyl alcohol fall in a typical class of reacting systems. Butyl acetate is an industrially important chemical with wide applications as a versatile solvent. n-Butyl acetate is manufactured by the esterification of acetic acid with n-butanol in the presence of suitable acid catalyst. The alcohol is sparingly soluble in water and the ester is almost insoluble. Another interesting feature of this system is that it is associated with the formation a minimum boiling ternary azeotrope of ester, alcohol and water, which is heterogeneous in nature. Hence, in a typical reactive distillation column that consists of both reactive and non-reactive zones, the heterogeneous azeotrope or a composition close to the azeotrope can be obtained as the distillate product. Moreover, the aqueous phase that forms after the condensation of the vapor is almost pure water. Depending on the requirement either of the phases can be withdrawn as a product and the other phase can be recycled back as reflux. The pure ester i.e. butyl acetate is the least volatile component in the system is realized as a bottom product. RD columns have a tendency to be difficult to control. To operate distillation columns, the design of the column will likely be based on a mathematical model of the process. Because there are strong nonlinearities (trough mass, energy and chemical kinetic couplings), the modeling and design problem could be difficult to handle, which means that simulation and design tasks will be rather complicated. The main goal of this project is to obtain new insights on systematic dynamic modeling of a reactive distillation with the aim to use it for optimization and control. This model gives a good idea to figure out the RD concept but it should be reduced dynamic model that can be used to optimize a grade transition a reactive distillation system. In this study, the dynamic mass and energy balances, basic kinetics and basic thermodynamics (MESH equations) have been set up using equilibrium model. The dynamic modeling begins with those equations implemented on MATLAB in a toy problem (3 stages distillation) until a model that works for a 5 stages reactive distillation column with a reaction such as A + B ↔ C + D. While being developed this model, it has been applied for different stages. Composition profiles and resolutions of these stages were observed step by step. It was shown on diagrams how we could gain step response while we were changing the feed flow and feed compositions. The best ODE function was selected for reactive distillation column. The issues covered include the liquid – vapor equilibrium, mass – energy balances, reaction rate equations, feed compositions, feed flows, step changes and step responses, ODE functions, linearization. It works with for A + B ↔ C + D. reaction in 5 stages RD.