Optimization of Methanol Synthesis under Forced Periodic Operation

Carsten Seidel,Achim Kienle,Daliborka Nikolić,Andreas Seidel-Morgenstern,Menka Petkovska,Matthias Felischak

doi:10.3390/pr9050872

Abstract

Traditionally, methanol is produced in large amounts from synthesis gas with heterogeneous Cu/ZnO/Al2O3 catalysts under steady state conditions. In this paper, the potential of alternative forced periodic operation modes is studied using numerical optimization. The focus is a well-mixed isothermal reactor with two periodic inputs, namely, CO concentration in the feed and total feed flow rate. Exploiting a detailed kinetic model which also describes the dynamics of the catalyst, a sequential NLP optimization approach is applied to compare optimal steady state solutions with optimal periodic regimes. Periodic solutions are calculated using dynamic optimization with a periodicity constraint. The NLP optimization is embedded in a multi-objective optimization framework to optimize the process with respect to two objective functions and generate the corresponding Pareto fronts. The first objective is the methanol outlet flow rate. The second objective is the methanol yield based on the total carbon in the feed. Additional constraints arising from the complex methanol reaction and the practical limitations are introduced step by step. The results show that significant improvements for both objective functions are possible through periodic forcing of the two inputs considered here.

Highlights

Methanol is one of the most important raw materials of the chemical industry
The focus of this paper is on improving reactor performance compared to conventional steady state operation by forced periodic operation, which is a specific type of dynamic reactor operation
We have shown theoretically that the performance of methanol synthesis from synthesis gas with a commercial Cu/ZnO/Al2 O3 catalyst can be improved significantly by periodic forcing of the CO feed concentration and the phase-shifted feed flow rate compared to optimal steady state operation

Summary

Introduction

Methanol is one of the most important raw materials of the chemical industry. It is used to produce paraffins, olefins, other organic chemicals, and fuels [1]. There has been a growing interest in dynamic methanol reactor operation in the context of energy storage and power to methanol processes [2]. In these types of processes, green hydrogen is produced from excess wind or solar energy via electrolysis. It reacts with CO/CO2 from biogas or waste streams to methanol [3,4,5]. The idea is not new and has been discussed since the

Methods

Results

Conclusion