CO₂ Recycling to Dimethyl Ether: State-of-the-Art and Perspectives

Abstract

This review reports recent achievements in dimethyl ether (DME) synthesis via CO₂ hydrogenation. This gas-phase process could be considered as a promising alternative for carbon dioxide recycling toward a (bio)fuel as DME. In this view, the production of DME from catalytic hydrogenation of CO₂ appears as a technology able to face also the ever-increasing demand for alternative, environmentally-friendly fuels and energy carriers. Basic considerations on thermodynamic aspects controlling DME production from CO₂ are presented along with a survey of the most innovative catalytic systems developed in this field. During the last years, special attention has been paid to the role of zeolite-based catalysts, either in the methanol-to-DME dehydration step or in the one-pot CO₂-to-DME hydrogenation. Overall, the productivity of DME was shown to be dependent on several catalyst features, related not only to the metal-oxide phase-responsible for CO₂ activation/hydrogenation-but also to specific properties of the zeolites (i.e., topology, porosity, specific surface area, acidity, interaction with active metals, distributions of metal particles, …) influencing activity and stability of hybridized bifunctional heterogeneous catalysts. All these aspects are discussed in details, summarizing recent achievements in this research field.

Keywords: CO2 hydrogenation; catalysis; dimethyl ether; low-carbon processes; thermodynamics; zeolites.

Figure 1

Proposed carbon cycle loop involving CO₂ as energy vector.

Figure 2

Effect of reaction temperature and pressure on CO₂ equilibrium conversion. H₂/CO₂ (mol/mol) = 3.

Figure 3

Effect of reaction temperature and pressure on DME equilibrium selectivity. Initial H₂/CO₂ molar ratio equals to 3.

Figure 4

Effect of reaction temperature and pressure on CO equilibrium selectivity. Initial H₂/CO₂ molar ratio equals to 3.

Figure 5

Effect of reaction temperature and pressure on methanol equilibrium selectivity. Initial H₂/CO₂ molar ratio equal to 3.

Figure 6

Effect of initial H₂/CO₂ molar ratio on CO₂ equilibrium conversion and DME, CO and methanol equilibrium selectivity. Reaction temperature and pressure: 240 °C and 30 bar, respectively.

Figure 7

CO₂ equilibrium conversion of CO₂-to-DME (a) and CO₂-to-MeOH (b) process as a function of reaction temperature (left) and pressure (right).

Figure 8

CO₂ conversion percentage gain (CPG) as a function of reaction temperature and pressure.

Figure 9

Scheme of the direct synthesis of DME through CO₂ hydrogenation.