Production of ethylene using high temperature demethanization

Details Production of ethylene using high temperature demethanization Production of ethylene using high temperature demethanization

1999-06-23

2001-04-10

Capossela, Ronald (Department: 3744)

Refrigeration

Cryogenic treatment of gas or gas mixture

Separation of gas mixture

C062S925000

Reexamination Certificate

active

06212905

ABSTRACT:

FIELD OF INVENTION
This invention comprises a process for using pressurized charge gas mixtures of olefins, aliphatics, hydrogen, carbon monoxide, and other components, from a range of olefin generation/preparation techniques, to produce ethylene rich product streams suitable for use in the manufacture of ethylene bearing derivative products.
BACKGROUND OF THE INVENTION
Ethylene is the leading petrochemical in terms of production volume, sales value and number of derivatives. Total worldwide ethylene production in 1995 was estimated at 76 million tonne per year, expectations are for a growth rate of about 3% per year, and meeting this growth will require significant capital investment in new production facilities. Sales prices average on the order $440/tonne, translating to a worldwide cash volume for the ethylene business of over $30 billion per year. End and intermediate uses of ethylene include production of plastics, resins and fibers, and a host of other products.
Before ethylene can be sold or used, it is necessary to employ a process which recovers the ethylene component in a desireable, ethylene rich product stream by separating it from a myriad of other components, including methane, ethane, hydrogen and carbon monoxide, among others, all of which components are found together in a single stream obtained from another, different olefin generation/preparation process. Currently, a desireable, ethylene rich product stream is generally defined by those skilled in the art as one having greater than about 95 wt. % ethylene, containing substantially inert components such as methane and ethane in proportions less than about 2000 molar ppm each and potentially reactive components such as hydrogen, carbon monoxide, carbon dioxide, propylene and others in proportions less than about 20 molar ppm each. This definition arises from the nature of the derivative processes that use the ethylene rich product stream, each suffering varying degrees of adverse process performance and economic impact associated with the levels of the various non-ethylene components in the stream. Such material shall hereinafter be referred to as a primary ethylene rich product stream.
The recovery and separation process which produces a primary ethylene rich product stream from components received from an olefin generation/preparation process represents the majority of total capital investment and energy usage required for ethylene manufacture. This reflects the difficulty associated with techniques required to manage the low normal boiling points and low relative volatilities of ethylene and the other components received from an olefin generation/preparation process. Furthermore, as recognized by those skilled in the art, capital recovery and energy usage are generally the two largest cost elements, respectively, in the total cost of ethylene manufacture. Thus, the process by which one effects recovery and separation to produce a primary ethylene rich product stream is a substantial factor in the economic feasibility of ethylene manufacture.
Methods for the recovery and separation of ethylene found in multi-component streams have been under consideration since the 1940's, when the first practical, large scale olefin generation technique of hydrocarbon pyrolysis, also called steam cracking, was developed and applied commercially. This olefin generation technique, now a substantially mature art, currently dominates the industry, utilizing a number of different hydrocarbon feedstocks. Also, alternative processes of potential commercial significance for the generation of olefins are emerging, such as the methanol to olefins process, taught in Kaiser, U.S. Pat. No. 4,499,327, and now being offered for commercial license by UOP. As shown in Table 1, olefin generation techniques of commercial importance, in general, create differing quantities of various byproduct components in a mixture with the desired ethylene component.
TABLE 1
Typical Component Distribution From Various Olefin
Generation Techniques
Process
Steam Cracking(1)
Atmospheric
Methanol
Feedstock
Light Naphtha
Gas Oil
To Olefins(2)
(excluding
Ethane
(boiling range
(boiling range
Methanol
water)
(C
2
H
6)
95-300° F.)
365-635° F.)
(CH
3
OH)
Yields,
wt. %
(excluding
water)
H
2
3.9
1.00
0.6
0.03
CO
trace
trace
trace
0.49
CO
2
trace
trace
trace
2.46
CH
4
3.8
18.00
11.2
1.45
C
2
H
2
0.4
0.95
0.4
0.00
C
2
H
4
53.0
34.30
26.5
53.73
C
2
H
6
35.0
3.80
3.4
1.67
C
3
H
4
0.0
1.02
0.8
0.00
C
3
H
6
0.8
14.10
13.4
26.37
C
3
H
8
0.1
0.35
0.2
1.53
C
4
H
6
1.1
4.45
5.0
0.00
C
4
H
8
0.1
3.70
3.7
6.64
C
4
H
10
0.2
0.10
0.1
1.21
C
5
0.2
2.75
2.7
3.37
C
6
-C
8
0.3
1.20
1.2
0.88
benzene
0.3
6.90
6.9
0.00
toluene
0.0
3.20
3.2
0.00
xylene +
0.0
1.30
1.3
0.00
ethylbenzene
styrene
0.0
0.79
0.7
0.00
C
9
- 400° F.
0.0
2.96
2.9
0.00
fuel oil
0.0
15.45
15.4
0.00
carbon
trace
trace
trace
0.17
Total
100.0
100.0
100.0
100.00
Note:
(1)per Howe-Grant, M. - Ed., Encyclopedia of Chemical Technology, fourth edition, Volume 9, page 880 (1994)
(2)per Nirula, S. C., Ethylene from Methane, Stanford Research Institute International Process Economics Program Report No. 208, page 4-2 (1994)
This mixture is generally unsuitable for further commercial use, hence the need for a distinct recovery and separation process. It should be stated that this is the case for many other olefin generation techniques not shown in Table 1, and for blends of mixtures from those techniques, one commercially important example being off-gas mixtures generated in various refinery processes blended with mixtures created in steam cracking. Further, such mixture may be a blend of those created by the olefin generation process and recycle streams from other parts of an ethylene manufacturing or ethylene derivative manufacturing facility, and may contain components other than those listed in Table 1.
The prevailing conventional wisdom relating to ethylene manufacture directs one, in addition to creating ethylene and byproduct components in a mixed stream via an olefin generation technique or blend of techniques, to further prepare that stream for introduction to the subsequent recovery and separation process. This may include, in various embodiments and sequences, the actions of cooling the stream from conditions at which the olefin generation reaction is effected to near ambient conditions, compressing the normally gaseous mixed stream to pressures usually between 200 and 600 psia, removing almost all of the water, carbon dioxide and sulfur compounds used or produced in the olefin generation step, and removing various normally liquid components at various pressures from the mixed stream. Hence the combination of steps described above, namely those of olefin generation and olefin preparation, embody what is referred to herein as the olefin generation/preparation process. Those skilled in the art recognize the result of employing an olefin generation/preparation process is production of a stream known as “charge gas,” so named because it is both the mixed component gaseous charge to and from large and expensive compressors within the process, and the mixed component gaseous charge to the subsequent recovery and separation process. This latter stream will hereinafter be referred to as pressurized mixed olefin bearing charge gas.
Though methods for the recovery and separation of ethylene from a pressurized mixed olefin bearing charge gas are known, the low normal boiling points of ethylene and other components require the use of very low temperature vapor-liquid flash and fractional distillation techniques, in order to have a high recovery of the ethylene molecules present in a primary ethylene rich product stream, and thereby render ethylene manufacture sufficiently efficient for economic viability. Of particular expense in these processes are equipment items which serve to separate ethylene from lower boiling components such as hydrogen, carbon monoxide and methane. In current state of the art ethylene recovery and separation processes which dominate the industry, temperatures on the order of −60 to &mi

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