Methanol via Dry Reforming of CH4 and CO2, and Catalylic Dry Reforming of CH4 and CO2
1. Introduction
Although the traditional paths to making methanol require gasification of natural gas and steam methane reforming (SMR), followed by catalytic methanol formation from the resulting syngas (H2 and CO), we want to discuss the alternative called Dry Methane Reforming because it does not emit any CO2.
1.1. Steam Methane Reforming (SMR)
SMR is achieved in a processing device called a reformer which reacts steam at high temperature with the fossil fuel. The steam methane reformer is widely used in industry to make hydrogen. At high temperatures (700 – 1100 °C) and in the presence of a metal-based catalyst (nickel), steam reacts with methane to yield carbon monoxide and hydrogen. These two reactions are reversible in nature.
CH4 + H2O ⇌ CO + 3 H2
Additional hydrogen can be recovered by a lower-temperature gas-shift reaction with the carbon monoxide produced. The reaction is summarized by:
CO + H2O → CO2 + H2
The first reaction is strongly endothermic (consumes heat), the second reaction is mildly exothermic (produces heat).
SMR is mainly used for synthetic gas (CO/H2) production in the industry because it yields lower H2/CO ratios. Synthetic gas is used for downstream processing including technologies like FischerTropsch catalysis with iron-based catalysts or certain oxo-processes. Many investigations over catalytic methane dry reforming have been reported. Nickel-based catalysts as well as noble metals have been used for the reaction as they are relatively cheap and stable, respectively.
1.2. Dry reforming
If the temperature in the reformer is > 1200 °C the combination of CH4 and CO2 will go to syngas without a catalysts as follows:
CO2 + CH4 → 2H2 + 2CO
The H2/CO is 1
1.3. Catalylic Dry Reforming
Catalytic CH4-CO2 reforming has been of interest for a long time. It similarly combines CH4, the principal component of natural gas used as source of energy, and CO2, a mayor problematic greenhouse gas, whereby a contribution can be made to limit global warming. Once again the reaction is particularly interesting because both CH4 and CO2 are relatively inexpensive feedstocks due to their natural abundance. Therefore it is a good alternative to steam reforming, especially if a methanol catalysts can be found that favors its H2/CO ratio of close to one.
However when the syngas is made from CH4 and steam the H2/CO ratio is ~2. There are catalysts that have been optimized for the syngas ratio.
).