Methanol to olefins is another way to obtain ethylene and propylene using an let's say unconventional feed, like MeOH.

In a simple way MeOH reacts under catalyst to form an equilibrium mixture of MeOH and DME (dimethyl ether) further to ethylene and propylene.

Depending by reaction conditions C2= or C3= is favorized.

Usually reaction product is:
1. 75% C2= / C3=
2. 13-15% C4+ olefins
3. 3-5% paraffins
4. 1-2% oxygenates compounds
5. 3-6% coke

Off course the reaction is exothermic aprox. 6 kcal/mol.

The reaction section is very similar with an classical FCC unit, the reactor product is quench in a quench tower, from the product DME is recovery and recycle to reaction section by mixing with MeOH and the olefins are separated in desire ethylene / propylene.

Conversion shall be increase by providing additional heavy cracking unit to increase production of ethylene and propylene.

Simple process description: MeOH need to be vaporized and slightly superheated before to feed the reactor; if caustic is present in MeOH need to removed because is a permanent poison for catalyst. The reactor product at higher temperature is sent to quench tower to lower the temperature by various pumparounds using water. Caustic is injected in quench tower to neutralize the formed acids. The top vapor is wash and is feeding product separator where the vapors are further cooled down and the vapor stream of product separator is compressed and sent to recovery section where DME is recovered and recycle to reactor. Ethylene and propylene are separated as main products. Worth to mention that there is also an oxygenate stripper that recovers dissolved oxygenates compounds recycle them to reactor section and a water stripper to treat the product separator bottom water stream.

Process variables:

1. Temperature is very important because the ethylene / propylene ratio is affected (from 1.8 to 1.1) and also the light olefin yield - increase temperature increase E/P ratio and conversion

2. Pressure: usually the unit pressure is hard to be changed due to design but is pressure is decrease the E/P ration and selectivity increase, but conversion decrease

3. Coke: if coke level in increasing the conversion is decreasing and selectivity is increasing.

4. Space velocity: by increasing the SV the conversion shall decrease.

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