Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By addition of extraneous agent – e.g. – solvent – etc.
Reexamination Certificate
1996-08-16
2002-05-28
Tran, Hien (Department: 1764)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By addition of extraneous agent, e.g., solvent, etc.
C585S845000, C585S848000, C585S809000
Reexamination Certificate
active
06395952
ABSTRACT:
The present invention relates to a process for the recovery of olefins from cracked gases employing a chemical absorption process.
BACKGROUND OF THE INVENTION
The processes for converting hydrocarbons at high temperature, such as for example, steam-cracking, catalytic cracking or deep catalytic cracking to produce relatively high yields of unsaturated hydrocarbons, such as, for example, ethylene, propylene, and the butenes are well known in the art. See, for example, Hallee et al., U.S. Pat. No. 3,407,789; Woebcke, U.S. Pat. No. 3,820,955, DiNicolantonio, U.S. Pat. No. 4,499,055; Gartside et al., U.S. Pat. No. 4,814,067; Cormier, Jr. et al., U.S. Pat. No. 4,828,679; Rabo et al., U.S. Pat. No. 3,647,682; Rosinski et al., U.S. Pat. No. 3,758,403; Gartside et al., U.S. Pat. No. 4,814,067; Li et al., U.S. Pat. No. 4,980,053; and Yongqing et al., U.S. Pat. No. 5,326,465.
It is also well known in the art that these mono-olefinic compounds are extremely useful in the formation of a wide variety of petrochemicals. For example, these compounds can be used in the formation of polyethylene, polypropylenes, polyisobutylene and other polymers, alcohols, vinyl chloride monomer, acrylonitrile, methyl tertiary butyl ether and other petrochemicals, and a variety of rubbers such as butyl rubber.
Because the mono-olefins contained in the cracked gases typically contain a large amount of other components, such as diolefins, acetylenes, hydrogen, carbon monoxide and paraffins, it is highly desirable to separate the mono-olefins into relatively high purity streams of the individual mono-olefinic components. To this end a number of processes have been developed to make the necessary separations to achieve the high purity mono-olefinic components.
Multi-stage rectification and cryogenic chilling trains have been disclosed in many publications. See, for example Perry's Chemical Engineering Handbook (5th Edition) and other treatises on distillation techniques. Recent commercial applications have employed technology utilizing dephlegmator-type rectification units in chilling trains and a reflux condenser means in demethanization of gas mixtures. Typical rectification units are described in Roberts, U.S. Pat. No. 2,582,068; Rowles et al., U.S. Pat. No. 4,002,042, Rowles et al., U.S. Pat. No. 4,270,940, Rowles et al., U.S. Pat. No. 4,519,825; Rowles et al., U.S. Pat. No. 4,732,598; and Gazzi, U.S. Pat. No. 4,657,571. Especially successful cryogenic operations are disclosed in McCue, Jr. et al., U.S. Pat. No. 4,900,347; McCue, Jr., U.S. Pat. No. 5,035,732; and McCue et al., U.S. Pat. No. 5,414,170.
In a typical conventional cryogenic separation process, as shown in
FIG. 1
, the cracked gas in a line
2
is compressed in a compressor
4
. The compressed gas in a line
6
is then caustic washed in a washer
8
and fed via a line
10
to a dryer
12
. The dried gas in a line
14
is then fed to the chilling train
16
. Hydrogen and methane are separated from the cracked gas by partially liquefying the methane and liquefying the heavier components in the chilling train
16
. Hydrogen is removed from the chilling train
16
in a line
18
and methane is removed via a line
20
, compressed in a compressor
24
and recovered in a line
26
.
The liquids from the chilling train
16
are removed via a line
22
and fed to a demethanizer tower
28
. The methane is removed from the top of the demethanizer tower
28
in a line
30
, expanded in a turboexpander
32
and sent to the chilling train
16
as a refrigerant via a line
34
. The C
2+
components are removed from the bottom of the demethanizer tower
28
in a line
36
and fed to a deethanizer tower
38
. The C
2
components are removed from the top of the deethanizer tower
38
in a line
40
and passed to an acetylene hydrogenation unit
42
for selective hydrogenation of acetylene. The effluent from the C
2
hydrogenation unit
42
is then fed via a line
44
to a C
2
splitter
46
for separation of the ethylene, removed near the top of splitter
46
in a line
48
, and ethane, removed from the bottom of splitter
46
in a line
50
. Lighter gases are vented from the top of the splitter
46
in a line
49
.
The C
3+
components removed from the bottom of the deethanizer tower
38
in a line
52
are directed to a depropanizer tower
54
. The C
3
components are removed from the top of the depropanizer tower
54
in a line
56
and fed to a C
3
hydrogenation reactor
58
to selectively hydrogenate methyl acetylene and propadiene. The effluent from the C
3
hydrogenation unit
58
in a line
60
is fed to a C
3
splitter
62
wherein the propylene and propane are separated. The propylene is removed from the top of the C
3
splitter
62
in a line
64
and the propane is removed from the bottom of the C
3
splitter
62
in a line
66
.
The C
4+
components removed from the bottom of the depropanizer tower
54
in a line
68
are directed to a debutanizer
70
for separation into C
4
components and C
5+
gasoline. The C
4
components are removed from the top of the debutanizer
70
in a line
72
and the C
5+
gasoline is removed from the bottom of the debutanizer
70
in a line
74
.
However, cryogenic separation systems of the prior art, such as shown in
FIG. 1
, while meeting with a relatively good amount of commercial success, have suffered from various drawbacks. In conventional cryogenic recovery systems, the cracked gas is typically required to be compressed to about 450-500 psig, thereby requiring 4-5 stages of compression. Additionally, in conventional cryogenic recovery systems, five towers are required to separate the C
2
and C
3
olefins from the paraffins: a demethanizer, a deethanizer, a C
2
splitter, a depropanizer and a C
3
splitter. Because the separations of ethane from ethylene and propane from propylene, involve close boiling compounds, the splitters generally require very high reflux ratios and a large number of trays, such as on the order of 120 to 250 trays each. The conventional cryogenic technology also requires multi-level propylene and ethylene refrigeration systems, as well as complicated methane turboexpanders and recompressors or a methane refrigeration system, adding to the cost and complexity of the conventional technology. Moreover, in conventional cryogenic technology the driers are required to dry the entire cracked gas stream thereby increasing their duty.
It has also been studied in the prior art to employ metallic salt solutions, such as silver and copper salt solutions, to recover olefins, but none of the studied processes have been commercialized to date. A note is made that a commercial Hoechst plant recovering olefins from cracked gases was operated at their Gendorf works in Germany during the 1950's and early 1960's which used cuprous nitrate and an ethanolamine ligand.
For example, early teachings regarding the use of copper salts included Uebele et al., U.S. Pat. No. 3,514,488 and Tyler et al., U.S. Pat. No. 3,776,972. Uebele et al. '488 taught the separation of olefinic hydrocarbons such as ethylene from mixtures of other materials using absorption on and desorption from a copper complex resulting from the reaction of (1) a copper(II) salt of a weak ligand such as copper(II) fluoroborate, (2) a carboxylic acid such as acetic acid and (3) a reducing agent such as metallic copper. Tyler et al. '972 taught the use of trialkyl phosphines to improve the stability of CuAlCl
4
aromatic systems used in olefin complexing processes.
The use of silver salts was taught in Marcinkowsky et al., U.S. Pat. No. 4,174,353 wherein an aqueous silver salt stream was employed in a process for separating olefins from hydrocarbon gas streams. Likewise, Alter et al., U.S. Pat. No. 4,328,382 taught the use of a silver salt solution such as silver trifluoroacetate in an olefin absorption process.
More recently, Brown et al., U.S. Pat. No. 5,202,521 taught the selective absorption of C
2
-C
4
alkenes from C
1
-C
5
alkanes with a liquid extractant comprising dissolved copper(I) compou
Dang Thuan D.
Hedman & Costigan ,P.C.
Stone & Webster Process Technology Inc.
Tran Hien
LandOfFree
Chemical absorption process for recovering olefins from... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Chemical absorption process for recovering olefins from..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Chemical absorption process for recovering olefins from... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2895615