Process for manufacturing ethylene

Ethylene is produced by catalytic conversion of a methanol feed in the presence of steam or water diluent. The catalyst employed is exemplified by HZSM-5, a crystalline aluminosilicate zeolite, and the conversion is conducted at relatively low temperature, i.e. from about 600.degree. F to about 750.degree. F. The hydrocarbon conversion product contains at least 18 wt.% ethylene.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention is concerned with the manufacture of ethylene from a 
methanol feed. It is particularly concerned with the catalytic conversion 
of a methanol feed to a hydrocarbon mixture of high ethylene content. 
2. Description of the Prior Art 
A remarkable growth in the production of synthetic fibers, plastics and 
petrochemicals has taken place in recent decades. This growth, to a very 
large extent, has been supported and encouraged by an expanding supply of 
inexpensive petrochemical raw materials such as ethylene, propylene, and 
other lower olefins. The principal raw material for ethylene at the 
present time is petroleum naphtha, which is steam cracked to produce a 
mixture of products from which ethylene is recovered. A large fraction of 
this ethylene is used in the manufacture of polyethylene and styrene 
monomer. 
The burgeoning demand for olefins has of course led to periods of shortage, 
due either to short supply of suitable petroleum feedstocks or to limited 
processing capacity. It is obviously desirable to provide efficient means 
for manufacturing ethylene from raw materials other then petroleum. 
U.S. Pat. No. 4,025,575, Ser. No. 566,166 filed Apr. 8, 1975 describes a 
process by which lower alcohols and/or their ethers are converted to a 
mixture of C.sub.2 to C.sub.5 olefins by contact at subatmospheric inlet 
partial pressure with a crystalline aluminosilicate zeolite catalyst 
having a constraint index of 1 to 12 and a silica to alumina ratio of at 
least 12. 
The production of olefins from aliphatic ethers by catalytic conversion 
with, e.g., a HZSM-5 zeolite catalyst is described in U.S. Pat. No. 
3,894,106 issued July 8, 1975. 
The use of diluents to dissipate exothermic heat in a two stage conversion 
of methanol to gasoline is described in U.S. Pat. No. 3,931,349 issued 
Jan. 6, 1976. 
A two stage conversion of a lower alcohol to olefins or to gasoline, which 
process employs a tubular reactor for the second stage is described in 
U.S. Pat. No. 4,058,576, Ser. No. 720,870 filed Sept. 7, 1976. 
BRIEF SUMMARY OF THE INVENTION 
It has now been discovered that a methanol feed is directly converted to a 
hydrocarbon mixture of high ethylene content by catalytic contact of the 
feed in the presence of 2 to 20 mols of steam diluent per mol of feed, 
said contact being effected at a temperature from about 600.degree. F to 
about 750.degree. F, with a zeolite catalyst such as HZSM-5, said zeolite 
catalyst being more fully described hereinbelow. As will be seen, the 
presence of the steam diluent induces sustained high catalytic activity 
with high selectivity for the formation of ethylene even at high 
conversion levels. 
The process of this invention, more fully described hereinbelow, produces 
as the primary product a mixture comprising hydrocarbons, and in its 
preferred form, the ethylene content of the hydrocarbon is at least about 
18 wt.%. Since the methanol feed may be manufactured from synthesis gas, 
i.e. a mixture of CO and H.sub.2 made from coal or from natural gas, this 
invention provides a process for making ethylene which is independent of 
petroleum feedstocks. 
It is to be noted that by the process of this invention the methanol feed, 
which is a one carbon alcohol, produces olefins which contain at least 2 
carbon atoms. Thus, the conversion of this invention clearly differs from 
the classical dehydration of alcohols in which the olefin produced has the 
same number of carbon atoms as the alcohol which is charged.

The following examples are given only for the purpose of illustration, and 
are not to be construed as limiting in any way. 
EXAMPLES 1 - 3 
HZSM-5 crystalline aluminosilicate zeolite catalyst with a crystallite size 
less than 0.5 microns was mixed with alumina binder and extruded to form 
cylindrical pellets. The catalyst was charged to a reactor and pure 
methanol was fed over it together with substantially inert diluent or 
steam, as specified. The results of comparing substantially anhydrous with 
steam diluent are shown in Table I. 
TABLE I 
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Example No. 
1 2 3 
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Temperature, .degree. F 
633 633 644 
Diluent, (mol ratio) 
(10:1)helium 
(10:1)steam 
(10:1)steam 
WHSV (methanol) 
1.0 1.0 1.0 
Conversion, % 
100 64.9 70.6 
Wt.% ethylene in 
7.2 24.5 22.7 
hydrocarbons 
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U.S. Patent Application 800,753 filed on even date herewith describes the 
use of substantially anhydrous diluent in a process for making ethylene 
from methanol.