Otimização de um reator de leito de jorro modificado para produção de etileno a partir de metano

Author(s)

Daison Manuel Yancy Caballero

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Química
• Defense date: 2016-06-15

Examining board members

Reginaldo Guirardello; Rubens Maciel Filho; Maria Teresa Moreira Rodrigues; Reinaldo Giudici; Rita Maria de Brito Alves

• Advisor: Lorenz T Biegler; Reginaldo Guirardello

Abstract

Optimization is a fundamental tool that helps with decision making in chemical processes using computer-aided approaches. Today, ethylene is an essential input used in chemical and petrochemical industry to produce a wide variety of more high value-added industrial products. Ethylene is commercially produced by thermal cracking of feedstocks derived from hydrocarbons, but alternative processes for ethylene production from cheaper sources are encouraged in recent decades. One of the promising alternative routes to produce ethylene is the oxidative coupling of methane. However, this is a challenging route because it presents limitations associated with the yield. Optimization techniques are valuable tools to improve the operating conditions of the oxidative coupling of methane, and to overcome the drawback associated with the yield of the process. In this context, the current Ph.D. thesis explores a theoretical analysis of ethylene production from oxidative coupling of methane in a spouted bed reactor. On the other hand, accurate mathematical models are essentials for both process simulation and optimization. Today, very complex and large problems in chemical engineering can be solved efficiently and accurately due to the development of powerful computers and improved numerical solvers. Still it is common to use simpler models in optimization since rigorous models lead to a significant CPU time consuming making impractical the implementation of this kind of models in any optimization nowadays. This fact indicates that there is still a trade-off between rigorous and slower models when compared with simplified and less accurate models. The main goal of this work is to apply optimization techniques to a simplified model of a modified spouted bed catalytic reactor to maximize the ethylene yield via oxidative coupling of methane. The project is theoretical and computational, using specialized optimization software (GAMS). In this way, a comprehensive model-based DAE-constrained optimization strategy is proposed, which was applied to three case studies of reacting systems to illustrate the computational capability of the proposed formulation. The models for the first two case studies were taken from literature while the model for the third case was developed applying conservation laws. The first case is an ammonia reactor, which requires obtaining the optimal reactor length with maximum economic return. The second case is a cracking reactor of ethane to make ethylene and hydrogen. The third case study deals with the main proposal of this thesis, a spouted bed reactor to carry out the oxidative coupling of methane. The model developed for this last reactor is a one-dimensional model composed of material, energy, and momentum balances. All of these reactor models along with the kinetic models of each case constitute non-linear and differential-algebraic systems. These complex differential-algebraic equations are discretized using orthogonal collocation on finite elements with continuous profiles approximated by Lagrange polynomials. The resulting algebraic collocation equations are written as equality constraints in the optimization problem. The optimization problem is solved by implementing the IPOPT solver within the GAMS optimization-modeling platform. A systematic initialization routine based on model simulations was carried out as a practical alternative to guarantee the global convergence in optimizations. Complementarity constraints were also used to model switches in some piecewise-defined functions such as the function found in the drag model for the spouted bed (AU)

• FAPESP's process: 11/22800-3 - OPTIMIZATION OF A MODIFIED SPOUTED BED REACTOR FOR ETHYLENE PRODUCTION FROM METHANE
• Grantee: Daison Manuel Yancy Caballero
• Support Opportunities: Scholarships in Brazil - Doctorate