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PROCESS & TECHNOLOGY FOR METHANOL AND DME

is partial oxidation. This route is particularly suitable for production of methanol due to two
reasons, namely,

a. Less external energy is required to be supplied, and
b. The ratio of hydrogen and carbon monoxide is of the order of 2, which is the
stoichiometric ratio for methanol synthesis.
The main difference here is that oxygen is added in place of steam and normally no catalysts
are used. The main reactions are shown below:
2 CH + O → 2 CO + 4 H ΔH = -38kJ/mol
4 2 2
It may be noted that even if the carbon monoxide is converted to hydrogen by shift reaction,
only two molecules of additional hydrogen will be available, making 6 molecules of hydrogen
from 2 molecules of methane as compared to 8 by methane reforming as shown below:
2 CH + O + 2 H O → 2 CO + 6 H (POX)
4 2 2 2 2
2 CH + 4 H O → 2 CO + 8 H (steam reforming)
4 2 2 2
Although the energy requirement is much higher for steam reforming compared to POX, this
is often preferred, at least for small scale hydrogen production. On the other hand, POX is the
preferred route for large scale syngas production for methanol.
There are two major strategies for POX as regards the use of an oxidizing agent. The oxygen
could be added either as air or as pure oxygen. Both options have pros and cons. Although
oxygen separation facility preceding the POX unit adds to the investment, it offers several
benefits. Addition of oxygen in place of air is favoured for syngas production since this route
saves cost in post purification of syngas before sending to methanol reactor. In addition to this,
pre separation of air is particularly attractive when carbon dioxide sequestering and / or NOx
control is desired, since the carbon dioxide from oxygen fired gasifiers is more concentrated
than that of air fired gasifiers. It is easier and cost effective to capture carbon dioxide from
concentrated flue gas [2].
There are several types of gasifier systems with combinations of steam reforming, shift reaction
and partial oxidation. Some of the available technologies are summarized in the subsequent
sections.

2.1.1.3

AUTO THERMAL REFORMING
Auto thermal reforming is a combination of both non-catalytic partial oxidation and reforming in
a single reactor system. The combination of these two exothermic and endothermic reactions
in sequence permits the operation without any addition of energy from external sources.
Recently this technology is gaining popularity due to availability of proven technologies from
reputed licensors as well as inherent advantages of this technology.
By proper adjustment of hydrocarbon to oxygen ratio in the partial combustion zone and
addition of steam in the catalytic reforming zone, it is possible to achieve equilibrium. The H /
2
CO ratio is between 1.5 and 3, which is most suitable for methanol production.
Although at present there are relatively few such units in operation world-wide, several large
scale units are operating. The potential for this technology is very high for conversion of natural
gas to syngas for methanol or DME production.

28 Methanol and DME Production: Survey and Roadmap | 2017