(Solar) Mixed Reforming of Methane: Potential and Limits in Utilizing CO2 as Feedstock for Syngas Production—A Thermodynamic Analysis

Henrik Von Storch,Sonja Becker-Hardt,Christian Sattler

doi:10.3390/en11102537

Abstract

The reforming of natural gas with steam and CO2 is commonly referred to as mixed reforming and considered a promising route to utilize CO2 in the production of synthetic fuels and base chemicals such as methanol. In the present study, the mixed reforming reaction is assessed regarding its potential to effectively utilize CO2 in such processes based on simple thermodynamic models. Requirements for the mixed reforming reactions based on process considerations are defined. These are the avoidance of carbon formation in the reactor, high conversion of the valuable inlet streams CH4 and CO2 as well as a suitable syngas composition for subsequent synthesis. The syngas composition is evaluated based on the module M = ( z H 2 − z CO 2 ) / ( z CO 2 + z CO ) , which should assume a value close to 2. A large number of different configurations regarding CO2/H2O/CH4 at the reactor inlet, operating pressure and outlet temperature are simulated and evaluated according to the defined requirements. The results show that the actual potential of the mixed reforming reaction to utilize CO2 as feedstock for fuels and methanol is limited to approximately 0.35 CO2/CH4, which is significantly lower than suggested in literature. At 900 °C and 7 bar at the reactor outlet, which is seen suitable for solar reforming, a ratio of H2O/CH4 of 1.4 can be set and the resulting value of M is 1.92 (CO2/CO/H2 = 0.07/0.4/1).

Highlights

Reforming of natural gas has been a well-established and widely practiced industrial process for the production of synthesis gas and hydrogen for several decades [1,2,3]
Based on the above recommendations for determining suitable conditions for a mixed reforming process, the central result to be presented are the maximum values for CO2 /CH4, which are possible for each temperature and pressure
The concept of mixed reforming of natural gas, i.e., utilization of steam and CO2 as reactants was investigated with the focus on generating a suitable syngas for subsequent processing

Summary

Introduction

Reforming of natural gas has been a well-established and widely practiced industrial process for the production of synthesis gas (syngas) and hydrogen for several decades [1,2,3]. The reaction is commonly carried out with steam as oxidizing agent, i.e., steam reforming according to Equation (1). Depending on the foreseen application of the syngas, oxygen may be added to carry out partial oxidation of methane or autothermal reforming to omit the external heating [2]. Accompanying the discussions on the reduction of greenhouse gas emissions, the dry reforming reaction (cf Equation (2)) has increasingly attracted attention as an option to convert carbon dioxide into a useful product [4,5]: CH4 + H2 O

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