Method for regenerating HF/sulfolane alkylation catalyst

This invention provides a method for separating ASO from a mixture containing ASO, HF and sulfolane comprising the steps of: PA1 (a) contacting said mixture with a sorbent to selectively sorb HF and water from said mixture to evolve an intermediate product containing less than 5 weight percent HF; PA1 (b) charging said intermediate product to a gravitational separation zone; PA1 (c) holding said intermediate product in said gravitational separation zone for time sufficient to evolve two at least partially immiscible liquid phases in said gravitational separation zone; and PA1 (d) withdrawing a less-dense phase enriched in ASO and a more-dense phase enriched in sulfolane from said gravitational separation zone.

This application is related by disclosure of similar subject matter to Ser. 
No. 07/991,918. filed Dec. 17, 1992, Ser. No. 07/991,919, filed Dec. 17, 
1992, Ser. No. 07/991,921, filed Dec. 17, 1992, and Ser. No. 07/991,922, 
filed Dec. 17, 1992, filed on even date herewith now all allowed. 
FIELD OF THE INVENTION 
The present invention relates to the art of catalytic alkylation. More 
specifically, the invention relates to a method for regenerating a liquid 
alkylation catalyst. Particularly, the invention provides a method for 
removing conjunct polymeric byproducts from a mixture of HF and sulfolane. 
BACKGROUND OF THE INVENTION 
Recent regulatory developments have led refiners to seek methods for 
reformulating motor gasolines to meet increasingly stringent air quality 
requirements. These techniques include reducing the olefin and aromatic 
content of the motor gasoline while maintaining the desired octane rating 
by increasing the relative content of isooctane (trimethylpentane) and 
other octane-enhancing additives such as oxygenates. 
Commercial isobutane-butene alkylation, catalyzed by a strong mineral acid 
such as HF or H.sub.2 SO.sub.4, produces a highly desirable motor gasoline 
blending component which is enriched in high-octane trimethylpentane. Thus 
with the advent of more restrictive air quality regulations, the known 
commercial isobutane-butene alkylation processes present a seemingly ideal 
solution to the problem of reformulating motor gasoline to minimize both 
evaporative losses from storage as well as pollutants emissions from 
gasoline engine operations. 
Alkylation is a reaction in which an alkyl group is added to an organic 
molecule. Thus an isoparaffin can be reacted with an olefin to provide an 
isoparaffin of higher molecular weight. Industrially, the concept depends 
on the reaction of a C.sub.2 to C.sub.5 olefin with isobutane in the 
presence of an acidic catalyst producing a so-called alkylate. This 
alkylate is a valuable blending component in the manufacture of gasolines 
due not only to its high octane rating but also to its sensitivity to 
octane-enhancing additives. 
Industrial alkylation processes have historically used large volumes of 
liquid Bronsted acid catalysts such as hydrofluoric or sulfuric acid under 
relatively low temperature conditions. Acid strength is preferably 
maintained at 88 to 94 weight percent by the continuous addition of fresh 
acid and the continuous withdrawal of spent acid. Liquid acid catalyzed 
isoparaffin-olefin alkylation processes share inherent drawbacks including 
environmental and safety concerns, acid consumption, and sludge disposal. 
For a general discussion of sulfuric acid alkylation, see the series of 
three articles by L.F. Albright et al., "Alkylation of Isobutane with 
C.sub.4 Olefins," 27 Ind. Eng. Chem. Res., 381-397, (1988). For a survey 
of hydrofluoric acid catalyzed alkylation, see 1 Handbook of Petroleum 
Refining Processes 23-28 (R.A. Meyers, ed., 1986). 
Both sulfuric acid and hydrofluoric acid alkylation share inherent 
drawbacks including environmental and safety concerns, acid consumption, 
and sludge disposal. Research efforts have been directed to developing 
alkylation catalysts which are equally as effective as sulfuric or 
hydrofluoric acids but which avoid many of the problems associated with 
these two acids, and alternatives such as Lewis acids, e.g., BF.sub.3, 
have been explored. While Lewis acids generally pose fewer and less severe 
safety and environmental concerns than strong liquid acids such as HF and 
H.sub.2 SO.sub.4, it would be desirable to produce paraffin-rich product 
streams useful as gasoline blending components without the use of noxious 
and/or corrosive liquid catalyst systems. 
Allowed U.S. application Ser. No. 07/883,684, filed Feb. 11, 1992 now U.S. 
Pat. No. 5,191,150 discloses a method for decreasing the cloud-forming 
tendency of HF comprising adding a controlled amount of sulfolane to the 
HF. The application further discloses that conjunct polymeric byproducts 
(also referred to as acid soluble oil or ASO) accumulate in the liquid 
acid catalyst mixture and must be removed. The ASO, a complex mixture of 
polymers, is difficult to separate from mixtures of sulfolane and HF 
because the ASO contains components having boiling points which bracket 
the boiling point of sulfolane. The process solves this purification 
problem by removing (stripping) HF from the mixture to provide an 
intermediate stream containing less than about 30 weight percent HF. Below 
about 30 weight percent HF, the sulfolane/ASO mixture readily separates 
into a less-dense ASO-enriched liquid phase and a more-dense 
sulfolane-enriched phase. The gravitational separation step depends upon 
effective upstream HF removal. Because the known processes for removing HF 
from the ASO/sulfolane mixture (e.g., stripping and fractional 
distillation) are subject to process upsets, it would be beneficial to 
provide a separation method which in independent of upstream operating 
variations. Further, it would be desirable to generate a purified 
sulfolane stream which can be recycled directly to an operating alkylation 
reactor without further processing. 
SUMMARY OF THE INVENTION 
This invention provides a method for separating conjunct polymers (ASO) 
from a mixture containing conjunct polymers (ASO), HF and sulfolane which 
method is independent of upstream process steps for removing HF. The 
present method operationally isolates the gravitational separation step 
from conventional upstream HF removal steps to improve reliability. Prior 
to the advent of the present invention, an upstream process upset could 
compromise the effectiveness of the two-phase gravitational separation 
step by raising the HF concentration in the gravitational separator above 
the level necessary to effect phase separation, thus converting the two 
immiscible liquid phases in the gravitational separator to a single liquid 
phase and disrupting catalyst regeneration. The method of this invention 
first guards the gravitational separator against excursions in HF 
concentration. Second, the method of the invention partitions ASO and 
sulfolane between a less-dense liquid phase and a more-dense liquid phase 
to an extent sufficient that no further sulfolane purification is 
typically required before recycling the sulfolane to the reactor of an 
HF/sulfolane-catalyzed isoparaffin-olefin alkylation process. Third, the 
method of the invention improves operator control over the water content 
of an HF/sulfolane catalyst for continuous isoparaffin-olefin alkylation. 
The method of the invention comprises the steps of: 
(a) contacting a mixture of conjunct polymers, sulfolane, and HF with a 
sorbent to selectively sorb HF and water from said mixture to evolve an 
intermediate product containing less than about 5 weight percent HF; 
(b) charging said intermediate product to a gravitational separation zone; 
(c) holding said intermediate product in said gravitational separation zone 
for time sufficient to evolve two at least partially immiscible liquid 
phases in said gravitational separation zone; and 
(d) withdrawing a less-dense phase enriched in conjunct polymers and a 
more-dense phase enriched in sulfolane from said gravitational separation 
zone. 
The method of the invention preferably further comprises removing at least 
a portion of the HF from the mixture of conjunct polymers, sulfolane, and 
HF before charging the stream to the sorption step. In this preferred 
embodiment, the HF is preferably removed by stripping the mixture with a 
gas. Useful stripping gases include isoparaffins and normal paraffins 
which are gaseous under ambient conditions, as well as vaporized alkylate. 
The selective sorbents useful in the method of the invention are preferably 
regenerable, that is, the materials preferably sorb HF and water under 
sorption conditions and then release the HF and water under regeneration 
conditions so that the sorbent can be reused. From a process standpoint, 
the sorbent need not be regenerable to be useful, but regenerable sorbents 
are preferred to minimize waste disposal costs. 
The preferred sorbents for the present invention contain no alumina or 
silica, which may react with HF under certain sorption conditions. 
Similarly, the selective sorbents useful in the method of the invention 
are preferably essentially free of ions which are exchangeable in the 
presence of HF. Sorbents containing exchangeable ions tend to consume HF 
to produce stable fluoride salts. Thus activated carbon, poly-sulfone 
resins, and poly-vinyl alcohols are the more preferred sorbents. 
Poly-vinyl alcohols are particularly preferred due to their ability to 
effectively sorb both HF and water. 
The sorption step of the invention produces a product stream containing a 
lower concentration of HF and water than the feed. The sorption zone can, 
in theory, be sized to remove any amount of HF and water from the feed, 
but, from a practical standpoint, is typically sized to decrease the feed 
HF concentration by about 50 weight percent. Greater reductions in HF 
concentration produce higher purity ASO and sulfolane phases in the 
downstream gravitational separation zone, and for this reason, reductions 
in HF concentration of as much as 70 or 90 weight percent may be 
preferred. If a stripping step precedes the sorption step, the stripped 
feed preferably contains less than about 5 weight percent HF, more 
preferably less than about 1 weight percent HF. Typical weight hourly 
space velocities in the sorption zone (based upon HF and water in the 
feed) range from about 0.001 to about 1 hr.sup.-1. Temperature in the 
sorption zone is not critical, but typically falls within the range of 
from about 27.degree. C. (80.degree. F.) to about 100.degree. C. 
(212.degree. F.), more typically from about 32.degree. C. (90.degree. F.) 
to about 43.degree. C. (110.degree. F.). 
While many forms of activated carbons are useful sorbents in the present 
invention, the activated carbons referred to as gas- or vapor-phase 
activated carbons are preferred. The gas-phase activated carbons, 
characterized by surface areas of from about 800 to about 1200m.sup.2 /g, 
are preferred because they are readily regenerable and are typically 
available as hard granules or formed pellets (for ease of handling and 
mechanical durability). The pore size of the gas-phase activated carbons 
is typically less than about 3.0 nm, and the surface area is typically 
about 1000 m.sup.2 /g. See generally Handbook of Separation Process 
Technology 651 (R. W. Rousseau ed. 1987), which is incorporated by 
reference as if set forth at length herein. 
If a regenerable sorbent material is used, the sorbent is typically 
regenerated by first rinsing with a solvent to remove residual ASO and 
sulfolane, and then flowing a carrier gas through the sorption bed at 
elevated temperature to desorb hydrodrofluoric acid and water. While any 
suitable hydrocarbon solvent may be used, alkylate is readily available, 
and is therefore preferred. Regeneration temperatures for most useful 
sorbents fall within the range of from about 150.degree. C. 
(.apprxeq.300.degree. F.) to about 315.degree. C. (.apprxeq.600.degree. 
F.), and the carrier gas flow is typically maintained through the sorption 
bed until the effluent gas gas is essentially free of HF.

EMBODIMENT 
Referring now to the Figure, a slipstream of spent alkylation catalyst 10 
flows from an operating HF/sulfolane catalyzed isoparaffin-olefin 
alkylation process unit (not shown) and enters primary 
distillation/stripping tower 20. Stripping gas, for example, isobutane, 
enters distillation/stripping tower 20 through line 22, carries stripped 
HF upwardly through the tower, and exits the primary 
distillation/stripping tower 20 via overhead line 26, and optionally 
flowing to an overhead cooler and accumulator (not shown). 
The bottoms product withdrawn from the primary distillation/stripping tower 
is withdrawn from the tower through line 28 at tower temperature of about 
300.degree. F. The bottom stream may optionally be cooled to a temperature 
as low as about 100.degree. F. before entering sorption unit 30. 
Sorption unit 30 comprises at least two sorption beds contained in separate 
vessels (not shown). The vessels are piped and valved for parallel/swing 
operation so that at least one sorption bed can be on stream while at 
least one sorption bed is being regenerated. The sorption unit preferably 
contains three sorption beds so that one bed can be operational while a 
second bed is being regenerated and the third bed is on standby to avoid 
any interruption in operation when the process flow shifts for 
regeneration. To regenerate a sorption bed, the process flow (from line 
28) is shifted to a second sorption bed and the first sorption bed is 
rinsed with a suitable solvent, e.g., alkylate. A dry, inert gas at a 
temperature of about 205.degree. C. (400.degree. F.) is then charged to 
the sorption bed until the effluent gas from the sorption bed is 
essentially free of HF. Nitrogen or isobutane are typically used, and 
isobutane is preferred because the HF-enriched isobutane can then be 
recycled to the alkylation reaction zone (not shown). 
COMATIVE EXAMPLE 
A mixture of hydrofluoric acid, sulfolane, and conjunct polymeric 
byproducts (which conjunct polymeric byproducts are evolved from the 
catalytic alkylation of isobutane with butene, referred to hereinafter as 
acid soluble oil or ASO) containing about 65 weight percent hydrofluoric 
acid, 30 weight percent sulfolane and about 5 weight percent ASO, is 
charged to a decantation vessel at ambient temperature and pressure 
sufficient to maintain the mixture in the liquid phase. The mixture is 
allowed to stand for approximately 24 hours. No phase separation is 
observed. 
EXAMPLE 1 
A mixture of hydrofluoric acid, sulfolane, and ASO (having the same 
composition as the mixture of the Comparative Example, above) is charged 
to a stripping tower having three theoretical stages. Isobutane is 
introduced into the tower at a level below the height of the liquid 
(HF/sulfolane/ASO) charge point, and the isobutane and mixture charge 
rates are controlled to maximize stripping of HF while operating below the 
flooding point of the tower. A stripped liquid is withdrawn from the 
bottom of the tower and a HF-enriched isobutane stream is withdrawn from 
the top of the tower. The stripped liquid contains less than about 30 
percent by weight of hydrofluoric acid. 
The stripped liquid is then charged to a decantation vessel and allowed to 
stand for approximately 24 hours. The mixture separates into two distinct 
phases, an upper, less dense ASO-enriched phase, and a lower, more dense, 
sulfolane-enriched phase. 
EXAMPLE 2-4 
Additional samples of the mixture of hydrofluoric acid, sulfolane, and ASO 
(having the same composition as the mixture of the Comparative Example) 
are stripped with isobutane to hydrofluoric acid contents of 25 weight 
percent, 10 weight percent, and 5 weight percent, respectively. The 
stripped mixture containing about 5 weight percent HF (Example 4) 
separates into two distinct liquid phases more completely, forming higher 
purity phases than the stripped mixtures containing 10 weight percent HF 
(Example 3) and 25 weight percent HF (Example 2). Each of the more-dense 
sulfolane-enriched phases generated in Examples 2-4 may, in some cases, 
require further purification to maintain alkylate product quality while 
continuously recycling the sulfolane-enriched phase to an operating HF 
alkylation reactor. 
EXAMPLE 5 
The HF/sulfolane/ASO sample of Example 5 has the following composition: 
HF 62 wt. % 
Sulfolane 27 wt. % 
Isobutane 4 wt. % 
Water 1-2 wt. % 
ASO 3 wt. % 
Balance to 100% other hydrocarbons. This mixture is a single liquid phase 
at 90.degree. F. and 120 psig. 
The sample is brought to atmospheric pressure and room temperature and most 
of the light hydrocarbons and part of the HF are vented off. Under these 
conditions, the sample is a single liquid phase containing about 50 wt. % 
HF. 
Nitrogen is then bubbled through the mixture at room temperature and 
atmospheric pressure to strip HF off the mixture. As the mixture is 
depleted in HF, the mixture separates into two phases. In Example 5, the 
two phases appear within several minutes of the HF concentration reaching 
about 2 wt. %. 
Both phases are analyzed, and the dense phase (specific gravity about 1.26) 
contains 83.2 wt. % sulfolane, 2.2 wt. % ASO, and the balance water, 
salts, and a sludge. The lighter phase, having a density of less than 
about 1, contains 82.8 wt. % ASO, 13.3 wt. % sulfolane, and the balance of 
salts. 
EXAMPLE 6 
The HF/sulfolane/ASO sample of Example 5 is charged to an upper section of 
a packed stripper tower having five theoretical stages. Dry isobutane, 
entering near the bottom of the tower, flows upwardly through the packed 
section, stripping HF from the HF/sulfolane/ASO mixture. The stripped 
HF/sulfolane/ASO mixture (the stripper bottoms product) contains the 
following: 
HF 9.3 wt. % 
Sulfolane 72 wt. % 
ASO 18.7 wt. %. 
The stripped HF/sulfolane/ASO mixture is then charged to a sorption vessel 
containing granular activated carbon having a surface area of about 1000 
m.sup.2 /g at a weight hourly space velocity of about 0.01 hr.sup.-1 
(based upon HF and water in the feed) and a temperature of about 
38.degree. C. (100.degree. F.). The effluent stream from the sorption 
vessel (containing less than about 1 weight percent HF) flows to a 
gravitational separator where it separates into two distinct liquid 
phases. The more-dense sulfolane-enriched phase contains about 8 weight 
percent ASO. 
EXAMPLE 7 AND 8 
The apparatus of Example 6 is modified with the addition of a bypass line 
and valving so that the stripper bottoms product may be selectively 
charged to the sorption zone or directly to the gravitational separation 
zone. Examples 7 and 8 first repeat the procedure of Example 6, allowing 
the process to reach steady state. Periodic sampling during continuous 
operation shows the the more-dense sulfolane-enriched phase withdrawn from 
the gravitational separator to consistently contain about 6-8 weight 
percent ASO. 
EXAMPLE 7 
Example 7 illustrates the potential effects of a stripper upset in the 
absence of the sorption zone. 
After steady state has been reached with the sorption zone in-line, valves 
in the bypass line are opened to shunt the total stripper bottoms product 
through the bypass line. The gravitational separator continues to form two 
distinct liquid phases, although the purity of both phases gradually 
decreases. The isobutane flow to the stripper tower is shut off and the 
stripper bottoms composition is periodically sampled and analyzed. HF 
concentration rises markedly in the stripper bottoms product; periodic 
analysis of the less-dense and more-dense phases shows that ASO and 
sulfolane partition less effectively between the two phases as the HF feed 
concentration rises. 
EXAMPLE 8 
The procedure of Example 7 is repeated. With no isobutane flowing to the 
stripper tower and no liquid visible interface present in the 
gravitational separator, the valves in the sorption zone bypass are 
closed, charging the total stripper bottoms stream through the sorption 
zone at a weight hourly space velocity of less than about 0.1 based upon 
HF and water in the feed. After about one (1) gravitational separator 
volume flows through the sorption zone, a liquid-liquid interface appears 
in the gravitational separator and partitioning of ASO and sulfolane 
improves with time as steady state operation is achieved. 
EXAMPLES 9-11 
Examples 9-11 demonstrate the effectiveness of three sorbents for removing 
HF and water from feedstreams containing HF, sulfolane, and water. Each 
solid is added to a mixture of HF, sulfolane and water and then each 
mixture is sampled after 48 hours. The results are shown in the Table 
below. 
TABLE 
______________________________________ 
Example Number 9 10 11 
______________________________________ 
HF/Water (48/52 wt/wt), 
1.00 1.00 1.3 
parts by wt 
Sulfolane, parts by wt 
10.00 10.15 13.05 
Poly-sulfone resin, parts by wt 
2.01 
Poly-vinyl alcohol, parts by wt 
1.95 
Activated carbon, parts by wt 2.55 
Original Percentages (weight) 
HF 4.36 4.30 4.35 
Water 4.73 4.66 4.71 
Final Percentages (weight) 
HF 4.03 3.59 3.79 
Water 4.80 3.29 5.65 
______________________________________ 
The poly-vinyl alcohol sorbent is most preferred because of its ability to 
sorb both water and HF. Water content in HF/sulfolane alkylation catalysts 
has been found to be an important operating variable, and the poly-vinyl 
alcohol not only sorbs HF to enhance sulfolane/ASO gravitational 
separation, but improves operational flexibility by effectively sorbing 
water as well. 
Changes and modifications in the specifically described embodiments can be 
carried out without departing from the scope of the invention which is 
intended to be limited only by the scope of the appended claims.