CO hydrogenation combined with water-gas-shift reaction for synthetic natural gas production: a thermodynamic and experimental study

Fanhui Meng,Xiaoyang Lv,Xin Li,Zhong Li

doi:10.1007/s40789-017-0177-y

Fanhui Meng, Xiaoyang Lv + Show 2 more

Open Access

https://doi.org/10.1007/s40789-017-0177-y

Copy DOI

Abstract

The hydrogenation of CO to synthetic natural gas (SNG) needs a high molar ratio of H2/CO (usually large than 3.0 in industry), which consumes a large abundant of hydrogen. The reverse dry reforming reaction (RDR, 2H2 + 2CO ↔ CH4 + CO2), combining CO methanation with water-gas-shift reaction, can significantly decrease the H2/CO molar ratio to 1 for SNG production. A detailed thermodynamic analysis of RDR reaction was carried out based on the Gibbs free energy minimization method. The effect of temperature, pressure, H2/CO ratio and the addition of H2O, CH4, CO2, O2 and C2H4 into the feed gas on CO conversion, CH4 and CO2 selectivity, as well as CH4 and carbon yield, are discussed. Experimental results obtained on homemade impregnated Ni/Al2O3 catalyst are compared with the calculations. The results demonstrate that low temperature (200–500 °C), high pressure (1–5 MPa) and high H2/CO ratio (at least 1) promote CO conversion and CH4 selectivity and decrease carbon yield. Steam and CO2 in the feed gas decrease the CH4 selectivity and carbon yield, and enhance the CO2 content. Extra CH4 elevates the CH4 content in the products, but leads to more carbon formation at high temperatures. O2 significantly decreases the CH4 selectivity and C2H4 results in the generation of carbon.

Highlights

Natural gas is a highly efficient and clean fossil fuel due to its high calorific value, low sooting tendency and slag free products, leading to its increasing consumption year by year (Gao et al 2015; Meng et al 2015a; Ronsch et al 2016)
The results demonstrate that low temperature (200–500 °C), high pressure (1–5 MPa) and high H2/CO ratio promote CO conversion and CH4 selectivity and decrease carbon yield
The calculation results demonstrate that low temperature and high pressure are beneficial for the CO conversion and CH4 yield, and high H2/CO ratio promotes CH4 yield and decreases carbon yield

Summary

Introduction

Natural gas is a highly efficient and clean fossil fuel due to its high calorific value, low sooting tendency and slag free products, leading to its increasing consumption year by year (Gao et al 2015; Meng et al 2015a; Ronsch et al 2016). Among the coal-to-SNG production processes, SNG is produced through the four major steps, i.e., coal gasification, water-gas-shift (WGS) reaction The CO methanation reaction is a key process for increasing SNG production (Meng et al 2015b; Gotz et al 2016; Gao et al 2016). The high content of carbon in coal results in low H2/CO molar ratios, usually less than one, of produced gas from coal gasification (Messerle et al 2016). The produced gas of the British Gas-Lurgi (BGL) coal gasification process is composed of 60%–70% CO, 27%–30% H2, 0%–7% CH4, 1%–4% CO2, and trace amounts of O2 and light hydrocarbons (Yu and Wang 2010). More amount of CO needs to be converted to produce H2 by WGS reaction in order to get a high H2/CO ratio, which results in the high operating cost and energy consumption

Objectives

Methods

Results

Conclusion