HF Alkylation process utilizing compressed isoparaffin vapor in indirect heat exchanges

In an HF alkylation of an isoparaffin, e.g., isobutane, with olefins, the hydrocarbon phase from the HF reactor effluent settler is charged to an HF separation zone. HF-free bottoms from the HF separation zone are charged to an isobutane stripper thereby producing HF-free isobutane vapor as overhead. The heat available in the isobutane vapor overhead is then utilized by compressing the vapor and using it as additional heat exchange fluid prior to being recycled to the HF alkylation. The compressed vapor can, for example, be used to reboil the HF separation zone, e.g., an HF stripper, heat the inner-heater on the isobutane stripper, and heat the depropanizer inner heater.

BACKGROUND OF THE INVENTION 
This invention relates to a process for the production of higher boiling 
hydrocarbons from lower boiling hydrocarbons in the presence of catalytic 
agents. Another aspect of the present invention relates to a process for 
the alkylation of isoparaffins such as isobutane with olefins in the 
presence of a hydrofluoric acid catalyst. Another aspect of this invention 
relates to the processing of HF alkylation hydrocarbon effluent initially 
with HF stripping so that subsequently recovered isobutane stripper 
overhead vapors will be HF-free and can then be compressed and used as 
additional heat exchange fluid prior to being recycled to the HF 
alkylation. This invention also relates to the use of HF-free, compressed 
isobutane stripper overhead vapors to reboil an HF separation zone such as 
an HF stripper. In another aspect, this invention relates to an alkylation 
process wherein compressed HF-free isobutane stripper overhead vapors are 
used to (1) reboil the HF stripper, (2) heat the inner heater on the 
isobutane stripper and (3) heat the depropanizer inner heater. 
As is well known, hydrocarbon products may be produced by alkylation 
reactions involving the combination or condensation of two dissimilar 
hydrocarbon reactants in the presence of suitable catalytic agents. While 
various types of alkylate products may be obtained by employing various 
types of reactants, the alkylation of low boiling isoparaffins, such as 
isobutane and isopentane, with low boiling olefins, such as ethylene, 
propylene, the isomeric butenes, and the isomeric pentenes, for the 
production of various fuels has become of particular importance. Liquid 
hydrogen fluoride (hydrofluoric acid) has found favor as a catalyst in 
this type of reaction. 
The alkylation of isobutane with olefins is representative of this type of 
reaction and has been commonly carried out by feeding isobutane and olefin 
feed stocks in the liquid state along with hydrofluoric acid to an 
alkylation reactor such as a riser reactor. The reaction product stream is 
then passed to various separation zones such as an HF stripper, an 
isobutane stripper and a propane stripper in order to recover the various 
components of the stream. The energy requirements for heating the various 
separation zones and streams are great and it would be desirable, due to 
the high cost of energy, to use an energy conserving alkylation process. 
It is an object of this invention, therefore, to provide an improved 
alkylation process. 
Another object of this invention is to utilize the available heat in an HF 
alkylation plant in a more efficient manner. 
It is another object of this invention to cut down on the energy costs of 
an alkylation process. 
Other aspects, objects, and advantages of the present invention will become 
apparent from a study of the disclosure, the appended claims, and the 
drawings. 
SUMMARY OF THE INVENTION 
In accordance with the invention, the above objects are achieved by a 
process wherein the isoparaffin stripper overhead vapor stream is 
compressed and used as additional heat exchange fluid prior to being 
recycled to the HF alkylation reaction zone. The isoparaffin, olefin and 
hydrofluoric acid catalysts are reacted in a reaction zone such as a riser 
reactor to form an alkylate. Upon the separation of the hydrofluoric acid 
from the hydrocarbon constituents of the reaction mixture to yield a 
substantially hydrofluoric acid free hydrocarbon stream, the hydrocarbon 
stream is introduced into an isoparaffin stripping zone, which is HF-free 
isoparaffin stripper and the propane stripper (depropanizer). The 
compressed isoparaffin vapor can also be used in an indirect heat exchange 
relationship with feed streams to various separation zones such as the 
feed to the HF stripper. 
After the isoparaffin vapor is used in its heat exchange fluid capacity, 
the isoparaffin is then recycled to the HF alkylation reaction zone. The 
isoparaffin to which this invention is most applicable is that of 
isobutane.

DETAILED DESCRIPTION OF THE INVENTION 
This invention relates to an alkylation process in which energy is used 
efficiently and effectively, thereby cutting down on high energy costs, 
through the use of the heat of vaporization of HF-free isoparaffin vapor. 
The isoparaffin vapor is used in a number of indirect heat exchanges. The 
importance and desirability of this invention increases as the cost of 
energy increases and the need for conservation of energy continues. 
The process of this invention comprises a reaction of an isoparaffin, of 
which isobutane is the most preferred and in which context this invention 
will be described, and olefins such as propylene and/or the butylenes, 
isobutylene, butene-1, cis- and trans-butene-2, in the presence of 
hydrofluoric acid in an HF alkylation reaction zone. The type of reaction 
zone is not of significant importance and one that is commonly used for 
this type of reaction is a riser reactor. The reaction mixture is then 
passed to an acid settler from which the liquid hydrocarbon phase thereof 
is passed to an HF separation zone, e.g. HF stripper. The particular type 
of HF separation zone is not important as long as the separation zone 
removes substantially all of the hydrofluoric acid to yield a 
substantially HF-free hydrocarbon stream. 
A substantially HF-free hydrocarbon stream is then split into two streams 
with one stream sent to a propane stripper or depropanizer in an amount to 
rid the system of charged propane and produced propane, and the other 
stream sent to an isobutane stripper (isostripper). 
Several advantages of the process of this invention are herein apparent in 
that since the charge to the depropanizer is HF-free, the depropanizer can 
be operated at a lower pressure than in conventional alkylation processes. 
The pressures employed can be advantageously about 90 psi lower than 
conventional pressures. 
The fact that the charge to the isobutane stripper or isostripper is 
HF-free results in a substantially HF-free isobutane vapor overhead which 
can then be safely compressed in a conventional compressor with no danger 
of corrosion. Due to the low concentration or trace of HF, the isobutane 
vapor can be compressed by conventional equipment and therefore will 
result in a definite economic advantage in compressor design. It is the 
low concentration of HF in the isobutane vapor which allows the vapor to 
be compressed economically and thereby allow the sensible heat and the 
contained heat of vaporization of the substantially HF-free isobutane 
vapor to be utilized effectively as the compressed isobutane vapor can 
then be used as a heat exchange fluid before being recycled as liquid to 
the alkylation reaction zone. Compressed vapor can be placed in indirect 
heat exchange relationship with the HF stripper, the depropanizer, the 
isostripper, and even the feed stream to the HF stripper. Through the use 
of the compressed isobutane vapor in areas of heating which would normally 
use an independently heated heat exchange fluid, energy savings are 
realized in the alkylation process of the present invention. 
Further details of this invention will become apparent from the following 
detailed description of the drawings and the examples. The following 
embodiments are not intended to limit the invention in any way and are 
given only for illustration. Although the descriptions are given in terms 
of isobutane, the invention is applicable to any appropriate isoparaffin. 
Referring now to FIG. 1 of the drawings, olefins and isobutane feed (1) 
along with recycle isobutane (19) are contacted with cooled recycle HF 
catalyst (20) and is charged to HF alkylation reaction zone (21). The 
hydrocarbon phase (2) from the phase separation (reactor settler) A is 
preheated indirectly at (22) by isostripper bottoms (5) and charged to the 
HF stripper B. The isostripper bottoms (5) is then cooled by heat exchange 
(23) and then taken away for storage or further use. 
HF stripper B is reboiled indirectly at (24) by a portion of the 
compressed, HF-free isobutane stripper overhead vapors (9). The HF 
stripper overhead (16) is cooled and condensed (25) and pumped to a 
liquid-liquid separator C. Recovered acid phase is then returned via (17) 
to the reactor settler A. The hydrocarbon phase (18) is then recycled via 
(19) to the alkylation zone. 
The HF stripper bottoms (3) is divided into two streams with one stream 
(10) to remove charged and produced propane being pumped before indirect 
heating at (26) and (27) with the liquid isobutane-rich side-draw (13) and 
with the reboiled bottoms (12) from the depropanizer D. The bottoms (12) 
from the depropanizer D, which contains alkylate, is then charged to 
isostripper or the deisobutanizer E at (28). The second portion (4) of the 
HF stripper bottoms (3) is pumped into the top locus of the isobutane 
stripper E. Bottoms (5) of isobutane stripper E is used in an indirect 
heat exchange relationship at (22). HF-free, hot isobutane vapor overhead 
(6) is compressed at (29) and split into three streams, (7), (8) and (9). 
Stream (9) is used to indirectly reboil HF stripper B at (24). The 
isobutane vapor of stream (9) is then recycled to the alkylation reaction 
zone via (15), cooler (30), and conduit (19). 
Stream (8) is used to indirectly heat the inner heater (40) on the 
isostripper and is then recycled to the alkylation reaction zone via (15), 
cooler (30), and conduit (19). 
Stream (7) is used to indirectly heat the inner heater (41) on the 
depropanizer D and is then combined with the liquid isobutane-rich 
side-draw stream (13). The combined stream is then recycled to the 
alkylation reaction zone via (15), cooler (30), and conduit (19). 
Normal butane vapor is removed from isostripper E, condensed, and recovered 
at (42). HF-free propane is recovered at (43). 
Referring now to FIG. 2, a diagrammatic view of a system for producing an 
alkylate product stream is shown wherein the HF-free overhead isobutane 
vapors (6) from the isostripper E are compressed at (29) and used solely 
to reboil the HF stripper B at (24). The isobutane overhead is then 
recycled to the alkylation reaction zone (21) via (9), (15), cooler (30), 
and conduit (19). The bottoms (5) from isostripper E is passed via (32) to 
heat inner heater (40). Steam is used to preheat stream (2) in (22), and 
steam is used to inner heater (41). The remaining elements are the same as 
in the system shown in FIG. 1. 
A calculated example of the process of this invention carried out in a 
system as shown in FIG. 2 is as follows. Vessel conditions, as well as 
stream compositions and quantities (moles per hour), are set out. 
______________________________________ 
CALCULATED EXAMPLE 
______________________________________ 
Operating Conditions: 
______________________________________ 
Vessel (E) Isostripper (55 Trays): 
Pressure, psia., 
Top, 100 
Bottom, 105 
Temperature, .degree. F., 
Top, 135 
Bottom, 325 
Reboiler Duty, Btu/hr., 81,000,000 
Vessel (D) Depropanizer (50 Trays): 
Pressure, psia., 
Top, 245 
Bottom, 249 
Temperature, .degree. F., 
Top, 121 
Bottom, 242 
Reboiler Duty, Btu/hr., 56,000,000 
Condenser Duty, Btu/hr., 44,300,000 
Vessel (B) HF Acid Stripper (25 Trays): 
Pressure, psia., 
Top, 150 
Bottom, 157 
Temperature, .degree. F., 
Top, 144 
Bottom, 166 
Reboiler Duty, Btu/hr., 75,800,000 
Condenser Duty, Btu/hr., 45,700,000 
HF Alkylation and Settler (A) Unit: 
Pressure, psia., 160 
Temperature, .degree. F., 
90 
Total Isobutane/Olefin Mol Ratio, 
12 
HF/Total Hydrocarbon, vol., 
ratio 4:1 
______________________________________ 
__________________________________________________________________________ 
Stream Compositions and Quantities (Mols/hr.) 
__________________________________________________________________________ 
Components 
(2) (3) (4) 
(5) 
(6) (9) (10) 
(12) 
(13) 
(43) 
(15) 
(16) 
(17) 
(18) 
(19) 
__________________________________________________________________________ 
HF 697 (a) (b) 
-- (b) (b) (b) 
-- -- (b) (b) 697 
532 
165 
165 
Propane 1,600 
800 400 
-- 400 400 400 
-- 200 
200 600 800 
3 797 
1,397 
Isobutane 17,625 
13,834 
6,917 
2 8,634 
8,634 
6,917 
1,729 
5,185 
3 13,819 
3,791 
7 3,784 
17,603 
Normal Butane 
1,915 
1,670 
835 
98 939 939 835 
342 
493 
-- 1,432 
245 
-- 245 
1,677 
IC.sub.5 Plus 
1,933 
1,900 
950 
1,730 
112 112 950 
903 
47 -- 159 33 -- 33 192 
Total 23,770 
18,204 
9,102 
1,830 
10,085 
10,085 
9,102 
2,974 
5,925 
203 16,010 
5,566 
542 
5,024 
21,034 
Temperature, .degree. F., 
118 160 160 
325 
135 206 180 
242 
196 
121 202 144 
100 
100 
90 
Pressure, psia., 
-- -- -- -- 100 250 -- -- -- -- -- -- -- -- -- 
__________________________________________________________________________ 
Notes: 
(a) = 0.24 .times. 10.sup.-11 Mol/hr. HF 
(b) = 0.12 .times. 10.sup.-11 Mol/hr. HF 
The total utilities gain to the use of the process of the present invention 
is estimated at approximately $3,229 per day. The overhead vapors (6), 
which are substantially HF-free and can be safely compressed in a 
conventional compressor with no danger of corrosion, are at 100 psia and 
135.degree. F. before compression. The overhead vapors are then compressed 
to 250 psia and are at 206.degree. F. after compression. The compressed 
stream is referred to as stream (9) in FIG. 2. Stream (9) then indirectly 
heats the heat exchanger (24) of the HF stripper B, after which the used 
vapors are at 240 psia and 175.degree. F. This amounts to 73,000,000 
Btu/hr. for heating. If one approximates the cost of heat at $2.50 per 
million Btu's, the value of this heat is $4,380/day. Compression costs, 
however, are $1,247 per day if one estimates at 3,150 kilowatts per hour 
are used by the compresser and the cost of a kilowatt is $1.65. By using 
compression, various pumping costs are decreased, e.g. on recycled 
isobutane (15) charged to the alkylation reaction zone, which amount to 
244 kilowatts per hour or $96/day. The total utilities gain by the 
invention, therefore, is $3,229/day. With the cost of natural gas 
approximated at $2.50 per 1,000 standard cubic feet and 1,000,000 Btu's 
are obtained for every 1,000 standard cubic feet of natural gas, this is 
an equivalent savings of 1,290,000 standard cubic feet of natural gas per 
day. 
FIG. 2 further depicts another embodiment of the present invention in which 
the compressed overhead isobutane vapor is not only used to reboil the HF 
stripper B, but is also used to heat the innerheater (41), of the 
depropanizer D and innerheater (49) of the isobutane stripper E as well as 
to heat the stream (2) charged to the HF stripper B. This embodiment is 
depicted by the dashed lines. 
The overhead isobutane vapor (6) from the isostripper E is compressed at 
(29) and split into three separate streams. The first stream (7) is used 
to heat the innerheater (41) of the depropanizer D and is then combined 
with stream (13) to be recycled to the alkylation reaction zone (21) via 
conduit (15), cooler (30), and conduit (19). 
Stream 8 is used to heat the innerheater (40) on the isobutane stripper E 
and then via (31) to heat the stream 2 to be charged to the HF stripper B 
at (22). The used isobutane vapor of stream, now numbered (33), to conduit 
(15) from which it is recycled to the alkylation reaction zone (21). 
Stream 9 is used to reboil the HF stripper B at (24) and then recycled to 
the alkylation reaction zone as disclosed previously. 
Also bottoms stream (5) can be used to first heat innerheater (40) and then 
to preheat stream (2) at (22). The flow is from (5), (32), innerheater 
(40), (31), exchanger (22), (31) and exchanger (32), and conduit (5). 
Reasonable variations and modifications are possible within the scope of 
the foregoing disclosure and the appended claims to the invention.