Production of oxygenated fuel components

A low value C.sub.5 feedstock is efficiently upgraded by a series of process steps involving reacting branched tertiary olefins in the feed and from subsequent isomerization with methanol and/or water to form TAME and/or TAA, separating isopentene by distillation from the reaction mixture, separating product TAME and/or TAA by distillation from linear C.sub.5 hydrocarbons, and converting the linear C.sub.5 hydrocarbons by skeletal isomerization to branched C.sub.5 hydrocarbons which are recycled to said reaction with methanol and/or water.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the improved production or yield of 
tertiary amyl methyl ether (TAME) and/or tertiary amyl alcohol (TAA) from 
predominantly C.sub.5 hydrocarbon feed streams containing mixed C.sub.5 
olefins which are of relatively low value. 
2.Description of Prior Art 
Various methods are known in the art for the conversion of branched olefins 
to the corresponding ether and/or alcohol. See U.S. Pat. Nos. 4,605,787, 
4,575,566, 4,925,455, 4,957,709, 4,962,239, 4,967,020, 4,969,987, 
4,830,685, 4,835,329, 4,827,045, 4,826,507, 4,814,519, 5,001,292, 
5,003,112 and the like. 
Likewise, methods are known whereby linear olefins can be converted by 
skeletal isomerization to branched olefins See, for example, U.S. Pat. 
Nos. 4,037,029, 4,793,984, 4,683,217, 4,973,785, 4,882,038, 4,758,419, 
4,500,651, 4,973,460 and the like. 
Various integrated processes for the conversion of hydrocarbons to gasoline 
components which involve etherification of branched tertiary C.sub.4 
and/or C5 olefins are also known. See, for example, U.S. Pat. Nos. 
4,988,366, 4,925,455, 4,957,709, 4,969,987, 4,830,635, 4,835,329, 
4,827,045, 4,826,507, 4,854,939, 5,001,292, 4,857,667, 5,009,859, 
5,015,782, 5,013,329 and the like. 
European publication 0 026,041 describes a process for producing olefins 
and/or ethers of high octane number from a wide C.sub.2 to C.sub.10 
olefinic stream .The wide olefinic feedstock is restructured over a 
zeolite catalyst to form primarily C.sub.4 to C.sub.7 olefins, the C.sub.4 
to C.sub.7 iso-olefins are reacted with methanol to form high octane 
ethers and unreacted olefins and methanol are separated from the ether 
product and recycled to the restructuring operation. 
U.S. Pat. No. 4,814,519 shows a two-stage process for the production of 
ethers from olefin-containing feedstock such as from an FCC unit whereby 
the feedstock is reacted under conditions to maximize production of 
C.sub.4 -C.sub.5 iso-olefins, particularly tertiary iso-olefins. The 
resulting iso-olefin rich product is then subjected to a catalytic 
etherification reaction to produce ethers such as TAME. 
The above art teaches that the amount of ether which can be produced from a 
mixed olefin stream is limited to the contained branched olefins and that 
the amount of contained branched olefins in the stream is limited by the 
thermodynamic equilibrium condition of this source olefin stream. 
The current invention provides a process whereby substantially all of the 
contained olefin in the feed stream can be upgraded to TAME. 
BRIEF DESCRIPTION OF THE INVENTION 
In accordance with the present invention, a hydrocarbon stream comprised 
predominantly of C.sub.5 hydrocarbons including both olefins and paraffins 
such as is produced by FCC procedures is reacted in a first step with 
lower alcohol and/or water under conditions such that the branched 
tertiary C.sub.5 olefins contained in the feed selectively react to form 
the ether and/or alcohol, e.g. TAME and/or TAA. The resulting reaction 
mixture is fractionally distilled in order to separate a lower boiling 
isopentane fraction from a mixture of linear C.sub.5 olefins and paraffin 
and TAME and/or TAA, the isopentane fraction being separated and 
representing a valuable gasoline blending fraction. The mixture of linear 
C.sub.5 's and TAME and/or TAA is separated by fractional distillation and 
a product fraction of TAME and/or TAA is recovered. The linear C.sub.5 
stream is passed to an isomerization reactor wherein skeletal 
isomerization takes place, converting normal C.sub.5 olefins to branched 
tertiary C.sub.5 olefins and converting pentane to isopentane. The 
isomerizate product stream is then recycled to the first reaction zone and 
the branched tertiary olefins from the isomerization step together with 
net feed branched C.sub.5 olefins are converted to TAME and/or TAA. 
Subsequently, isopentane from the isomerization is separated together with 
the net isopentane feed.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the accompanying drawing, a mixed C.sub.5 hydrocarbon feed 
stream such as that from an FCC unit and containing C.sub.5 olefins and 
paraffins is introduced via line 1 into zone 2. The hydrocarbon feed 
stream comprises at least 90% by volume C.sub.5 hydrocarbons of which at 
least 40% by volume are olefins. Of the olefins, at least 40% are tertiary 
olefins. A recycle stream from the isomerization step is also introduced 
into zone 2 via line 3. Lower alcohol such as methanol and/or water is 
introduced into zone 2 via line 4. 
In zone 2, branched tertiary C.sub.5 olefins are selectively reacted with 
the lower alkanol and/or water in accordance with known procedures to form 
ether such as TAME and/or TAA. 
The reaction mixture passes via line 5 from zone 2 to distillation zone 6 
wherein an isopentane stream is separated overhead via line 7 as a low 
boiling fraction which is useful as a gasoline blending material. This 
separation is conveniently accomplished at this point in the process since 
the branched olefins which normally are extremely difficult to separate 
from isopentane because of the closeness of the boiling points, have been 
converted to the much higher boiling ether and/or alcohol. 
From zone 6 the higher boiling liquid fraction comprised of the ether 
and/or alcohol formed in zone 2 and linear C.sub.5 olefins and paraffin 
pass via line 8 to distillation zone 9. In zone 9 the linear olefins and 
paraffins are separated as a light overhead fraction via line 10 and pass 
to isomerization zone 11. 
The product TAME and/or TAA stream passes from zone 9 via line 12 and 
comprises a useful and valuable product of the invention which can be 
used, for example, as an octane enhancing gasoline component. 
In isomerization zone 11, the linear C.sub.5 olefins and paraffin are 
converted by known skeletal isomerization fixed reactor bed procedures to 
branched tertiary C.sub.5 olefins and isopentane. Generally, the 
conversion in zone 11 is carried out such that close to the thermodynamic 
equilibrium mixture is obtained at the selected reaction conditions. Under 
the isomerization conditions, considerable isomerization of the linear 
C.sub.5 paraffin to the higher octane value branched C.sub.5 paraffins 
takes place which is an additional advantage of the invention. 
The isomerization reaction mixture from zone 11 passes via line 3 to zone 2 
wherein the branched C.sub.5 olefins formed in zone 11 are selectively 
converted to the ether and/or alcohol as previously described. 
Practice of the invention has the outstanding advantage that a low value 
material such as the C.sub.5 olefin and paraffin mixture from an FCC unit 
can be employed as feedstock. The olefin content of the feed material can 
be essentially completely converted to the valuable ether and/or alcohol 
gasoline blending components. In addition, the separation of C.sub.5 
branched paraffins is readily accomplished after the branched olefins 
first are converted to ether and/or alcohol. An added benefit is the 
conversion of linear C.sub.5 paraffins to higher octane branched C.sub.5 
paraffins. 
Statutory regulations are expected to require in the near future a lowering 
of both the olefin content of gasoline and the amount of components 
boiling over 200.degree. F. In accordance with the invention, relatively 
low value olefins are converted to TAME thus facilitating compliance with 
such regulations while producing a higher quality end product. 
Both the etherification reaction in zone 2 and the skeletal isomerization 
in zone 11 are carried out in accordance with known procedures as taught, 
for example, in the patents listed above. 
Particular preferred catalysts for use in the skeletal isomerization are 
the medium pore-sized molecular sieves such as SAPO-11 and SAPO-31 and 
molecular sieves having the same general pore configuration. Especially 
preferred are the molecular sieves which are described in U.S. Pat. Nos. 
4,973,785 and 4,793,984 and which contain in addition to the framework 
oxide units of AlO.sub.2, SiO.sub.2 and PO.sub.2 an oxide of a metal from 
the group consisting of arsenic, barium, boron, chromium, cobalt, gallium, 
germanium, iron, lithium, magnesium, manganese, titanium, vanadium and 
zinc. Suitable catalysts employed are the MgAPSO-11 and 31 sieves 
described in U.S. Pat. No. 4,882,038 and 4,758,419. 
The skeletal isomerization is carried out at elevated temperatures, i.e., 
above 300.degree. C. 
It is preferred that the vapor phase isomerization reaction temperature be 
maintained in excess of 900.degree. F., and preferably in excess of 
925.degree. F. Generally, the temperature should not exceed 1350.degree. 
F. Normal isomerization pressures ranging from about atmospheric to 1,000 
psig are conveniently employed. Isomerization space velocities of the 
order of about 1 to about 10,000 hr..sup.-1 WHSV are employed, preferably 
10 to 1000 hr..sup.-1 WHSV. 
The isomerization vapor feed can contain, in addition to the hydrocarbon to 
be isomerized, inert gas and/or steam, although the use of these materials 
is not necessary or preferred. 
The reaction of methanol with isoamylenes at moderate conditions with a 
resin catalyst is known technology, as provided by R. W. Reynolds, et al., 
The Oil and Gas Journal, Jun. 16, 1975, and S. Pecci and T. Floris, 
Hydrocarbon Processing, Dec. 1977. An article entitled "MTBE and TAME--A 
Good Octane Boosting Combo," by J. D. Chase, et al., The Oil and Gas 
Journal, Apr. 9, 1979, pages 149-152, discusses the technology. A 
preferred catalyst is a polymeric sulfonic acid exchange resin such as 
Amberlyst 15. 
In the etherification process it is known that alkanol and iso-olefins may 
be reacted in equimolar quantities or either reactant may be in molar 
excess to influence the complete conversion of the other reactant. Because 
etherification is an incomplete reaction, the etherification effluent 
comprises unreacted alkanol and unreacted hydrocarbons. On a 
stoichiometric equivalencies basis, equimolar quantities of methanol and 
iso-olefins are advantageous, but an excess between 2 and 200% of either 
component can be passed to the etherification reaction unit. In the 
present invention, the molar ratio of alkanol to iso-olefin can be between 
0.7 and 2. 
The following example illustrates the invention. 
A C.sub.5 hydrocarbon feed mixture from an FCC unit was fed at the rate of 
100 M lbs./hr. to reaction zone 2 via line 1. The feed mixture had the 
following composition by volume: 
______________________________________ 
3-methyl butene-1 
1.3% 
isopentane 50.0% 
Pentene-1 3.5% 
2-methyl butene-1 
8.8% 
n-pentane 6.0% 
trans pentene-2 9.7% 
cis pentene-2 4.8% 
2-methyl butene-2 
15.9% 
______________________________________ 
A recycle stream from isomerization zone 11 was returned via line 3 at the 
rate of 55 M lbs./hr and was introduced into zone 2 along with the fresh 
feed. The recycle stream had the following composition by volume: 
______________________________________ 
Isopentane 17.0% 
Pentene-1 0.8% 
2-methyl butene-1 
18.5% 
n-pentane 9.2% 
trans-pentene-2 6.6% 
cis-pentene-2 3.7% 
2-methyl butene-2 
44.3% 
______________________________________ 
Methanol in amount of 19.5 M lbs./hr. was introduced into zone 2 by means 
of line 4. 
In zone 2, the reaction of methanol with branched tertiary C.sub.5 olefins 
was carried out at 70.degree. C. and 60 psig using a sulfonic acid ion 
exchange catalyst. Conversion of the tertiary C.sub.5 olefins to TAME was 
70%. The reaction mixture from zone 2 was passed via line 5 and 
fractionally distilled in distillation zone 6. The reaction mixture from 
zone 2 had the following composition by volume: 
______________________________________ 
Isopentane 34.0% 
Pentene-1 2.2% 
2-methyl butene-1 2.1% 
n-pentane 6.3% 
trans-pentene-2 7.7% 
cis-pentene-2 3.9% 
2-methyl butene-2 8.3% 
tertiary amyl methyl ether 
35.5% 
______________________________________ 
Distillation zone 6 comprised 25 theoretical stages and an overhead 
isopentane stream was removed via line 7 at the rate of 57.7 m lbs./hr. 
The isopentane stream had the following composition by volume: 
______________________________________ 
Isopentane 
97.1% 
Pentene-1 
2.9% 
______________________________________ 
Conditions of distillation were an overhead temperature of 50.degree. C. 
and pressure of 20 psig. 
A bottoms stream at 65.degree. C. was removed from zone 6 and passed via 
line 8 to fractional distillation zone 9 which comprised 20 theoretical 
stages. An overhead fraction was removed at 60.degree. C. and 20 psig via 
line 10 and was passed to isomerization zone 11. This overhead fraction 
had the following composition by volume: 
______________________________________ 
Isopentane 6.1% 
Pentene-1 4.1% 
2-methyl butene-1 
6.6% 
n-pentane 20.1% 
trans-pentene-2 24.3% 
cis-pentene-2 12.4% 
2-methyl butene-2 
26.4% 
______________________________________ 
A product TAME stream was removed from zone 9 at 105.degree. C. at the rate 
of 61.8 M lbs./hr and was recovered as a valuable oxygenated gasoline 
component product. 
The overhead stream from distillation column 9 was subjected to skeletal 
isomerization in isomerization zone 11; the conditions of isomerization 
were a space velocity of 2.sup.-hr., a temperature of 210.degree. C. and a 
pressure of 600 psig. A catalyst comprised of 3% P in ZSM-5 was used to 
accomplish the skeletal isomerization. From zone 11, the isomerization 
product mixture passed at the rate of 55 M lbs./hr. via line 3 to reaction 
zone 2.