Page 161 - Advances in bioenergy (2016)

or higher alcohols. 17

The catalyst deactivates primarily because of loss of active copper due to physical blockage of
the active sites by large by-product molecules; poisoning by halogens or sulfur in the synthesis
gas, which irreversibly form inactive copper salts; and sintering of the copper crystallites into
larger crystals, which then have a lower surface to volume ratio.

Conventionally, methanol is produced in two-phase systems: the reactants and products
forming the gas phase and the catalyst being the solid phase. The production of methanol from
synthesis gas was first developed by the company BASF in Germany already in 1992. This
process used a zinc oxide/chromium oxide catalyst with poor selectivity, and required

extremely vigorous conditions—pressures ranging from 300 to 1000 bar, and temperatures of
about 400°C. In the 1960s and 1970s, the more active Cu/Zn/Al catalyst was developed
allowing more energy-efficient and cost-effective plants, and larger scales. Processes under
development at present focus on shifting the equilibrium to the product side to achieve higher
conversion per pass than the currently achieved 20–30% in tubular- or quench-type reactors.
Examples are the gas/solid/solid trickle flow reactor, with a fine adsorbent powder flowing
down a catalyst bed and picking up the produced methanol; and liquid phase methanol
processes where reactants, product, and catalyst are suspended in a liquid. Fundamentally
different could be the direct conversion of methane to methanol, but despite a century of
research this method has not yet proved its advantages.

Methanol to Diesel

The methanol to diesel (MtD) process first converts methanol into propylene, this is followed
by olefin oligomerization (conversion to distillates), then product separation-plus-

hydrogenation. 18

The process would yield mostly kerosene and diesel, along with a small yield of gasoline and
light ends. The near-zero sulfur/polyaromatics diesel fuel resulting from this process would
differ from more conventional FT diesel only in cetane number (>52 via ‘Methanol-to-Synfuel’
vs >70 cetane for FT diesel). The incidental gasoline stream not only would be near-zero
sulfur but also have commercial octane ratings (92 RON, 80 MON) and maximally 11%
aromatics.

Methanol to Gasoline

In the 1970s, Mobil developed and commercialized a methanol to gasoline (MtG) process. A
plant was built in Montunui, New Zealand in 1985 and sold to Methanex. It produced gasoline
until 1997 when the plant was permanently idled. If the gasoline is to be sold without

additional blending, then further treating is necessary to reduce the amount of benzenes. 19

Methanol to Olefins

Methanol to olefin (MtO) synthesis is a commercially attractive process because of the high
demand of propylene and ethylene in the market. Nowadays, these compounds are produced