CA1062229A - Alkylation catalyst recovery process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A process for removal of fluoride compounds from spent alkylation catalyst containing fluorosulfonic acid and sulfuric acid wherein hydrogen fluoride and fluorosulfonic acid, in the presence of water, are removed by vacuum dis-tillation following which the remaining sulfuric acid rich fraction of the spent catalyst is treated with an alumina containing material to remove most of the remaining residual fluoride compounds and thereby provide a sulfuric acid ef-fluent free of substantial amounts of fluoride compounds.
The hydrogen fluoride recovered is reacted with sulfur trioxide to form fresh fluorosulfonic acid which is combined with sulfuric acid to provide fresh alkylation catalyst.

Description

106Z~Z9 BACKGROUND OF THE INVENTION
The present invention relates to a catalyst re-covery process. More particularly, the present invention relates to a process for ~he removal of fluoride compounds from spent alkylation catalysts comprised of fluorosulfonic acid and sulfuric acid, and to the regeneration of fresh alkylation catalyst.
Liquid phase alkylation processes wherein an iso-paraffin hydrocarbon, such as isobutane, isopentane, etc.
are alkylated with olefin hydrocarbons such as propylene, butylenes, etc. for the production of alkylate products com-prising highly branched C7-C8 range paraffin hydrocarbons having high octane value, are well known and widely practiced.
In such processes, the reactant hydrocarbons are usually con-tacted in the liquid phase, at elevated temperatures in the presence of acid alkylation catalysts and under conditions ~-of good mixing, reaction pressures usually being only suffi- ~ -cient to maintain the reactants in the liquid phase.
Although numerous acid catalysts may be employed in such alkylation processes, an effective catalyst com-prises a mixture of sulfuric acid and fluorosulfonic acid.
One such catalyst, particularly effective in the alkylation processes under consideration comprises fluorosulfonic acid and sulfuric acid in a weight ratio of from about 0.11/1 to about 0.32/1, repsectively, the catalyst having a titrat-able acidity in the range of 16.6 to 21 milli-equivalents per gram (meq/gm) and which may contain up to 3% by weight .-.~ .... "

10~i2Z29 water and up to 10% by weight acid oils, the acid oils com-prising relatively high molecular weight reaction products of sulfuric acid and hydrocarbons present in the process.
In an alkylation process employing sulfuric acid and fluoro-sulfonic acid as catalyst, a C4-C6 isoparaffin hydrocarbon such as isobutane is contacted with C3-C5 olefin hydrocarbon such as propylene, a butylene, or mixtures thereof, in a molar ratio of isoparaffin to olefin of from about 2/1 to 20/1, in the liquid phase, in the presence of the alkylation catalyst at a temperature in the range of from about 0F to about 100F. Reaction pressures employed may range from ambient to superatmospheric, the pressure employed generally : . .
being sufficient to maintain the hydrocarbon reactants in the ~ liquid phase. Since the reactants may be normally gaseous

2~ at alkylation reaction temperatures, reaction pressures -~ generally range from about 10 to about 150 psig. Preferably, ~ -the alkylation reaction mixture is sub]ected to good mixing .
to form a hydrocarbon in continuous acid phase emulsion which , -~ comprises from about 40 to about 70 volume % acid phase and -- 20 from about 60 to about 30 volume % hydrocarbon phase. Liquid volume ratios of isoparaffin hydrocarbons to olefin hydrocarbons ::;
of from about 2/1 to about 20/1 are generally employed in the process. Contact times for hydrocarbon reactants in the alkylation zone, in the presence of the alkylation catalyst, - may range from about 0.5 to about 60 minutes. Preferably, the contact time is sufficient to ensure essentially complete - conversion of olefin reactant in the alkylation zone. Such contact times are sufficient for providing an olefin space velocity in the range of about 0.1 to about 1.0 volumes olefin/hour/volume of catalyst. The process may be conducted :' ..`. ~, ,~ ,. . . ..

lO~Z;~29 batchwise or continuously. It has been found that use of the aforementioned catalyst in alkylating C4-C4 isoparaffin with a C3-C5 mono-olefin, produces an alkylate of increased octane value over that obtained by prior art catalysts.
When using the above-described fluorosulfonic-sulfuric acid alkylation catalyst, or for that matter, any sulfuric acid alkylation catalyst containing a similar fluoro acid, it is common practice to process the spent catalyst in such a fashion so as to regenerate fresh sulfuric acid, the major component of the catalyst. However, even though the fluorosulfonic acid is present as a minor component in the alkylation catalyst, because of its expense relative to that of sulfuric acid, it is desirable to recover, as well, the fluorosulfonic acid or any fluoro compounds which can be . .
easily converted to the fluorosulfonic acid.
~ One method for recovering the sulfuric acid from '7' the spent alkylation catalyst is to treat the spent catalyst ~- in what is known as a sludge conversion unit. In such a unit the spent catalyst containing water and organic materials is charged to a furnace for oxidative conversion of all the sulfur species present to sulfur dioxide. The sulfur dioxide, in admixture with air, is then passed over a catalyst, e.g.
V2O5 or some other such suitable oxidation catalyst, in a `` converter section of the unit to form SO3. The SO3 is then absorbed in a sulfuric acid solution to produce oleum which ~- is then diluted with water to produce sulfuric acid of the desired concentration, i.e. 97-99 weight %, for the alkyl-- ation catalyst. The furnaces used in such sludge conversion units employ refractories which are readily attacked by HF

_3_ .. i_,.................................................................... .

10~2Z29 or HF precursors such as fluorosulfonic acid. For example, to prevent damage to refractory furnace linings, fluoride concentrations (calculated as HF) of about lo ppmw or less are particularly desirable. At levels above about 10 ppmw, fluoride attack upon refractory lining is accelerated, thus shortening the operating lifetime of such materials in the sludge conversion unit.
Over and above the potential damage to the refractories in the furnace, any HF in the converter section would volatilize the vanadium from the V205 oxida-tion catalyst. Accordingly, a process which effectively recovers the fluoro-sulfonic acid or precursors thereof from the spent catalyst and also provides a feed to the sludge conversion unit substantially free of damaging fluoro compounds is highly desirable.
SllMMA~ OF THE INVENTION
According to one aspect of the present invent~on, there is provided a process for the removal of fluoro compounds from spent sulfuric-acid -fluorosulfonic acid alkylation catalyst, wherein said fluoro compounds com-prise about 15,000 - 30,000 ppmw, calculated as HF, of said spent catalyst;
which process comprises:
a) reacting, in a hydrolysis zone, said spent catalyst, at sub-atmospheric pressure, at a temperature in the range of from about 50 to about 120 C in the presence of at least about 3 weight percent water for a period in the range of about 1-8 hours, for production of a first vapor phase com-~- prising mainly hydrogen fluoride and a first liquid phase comprising sulfuric - acid, and containing about 800 ppmw or less fluoro compounds;
~ b) contacting, in an absorption zone, said first liquid phase with - a fluidizable silica-alumina cracking catalyst in an amount equivalent to ; about 0.3-5 weight percent of said first liquid phase for a period of time in - the range of about 1-8 hours, at a temperature in the range of 50-120 C for production of a second liquid phase comprising said sulfuric acid and a first solid phase comprising cracking catalyst containing fluoro compounds; and ~51--~ --4--~", lOf~Z~9 c) separating, in a solid-liquid separation zone, said second liquid phase from said first solid phase for production of an effluent acid containing the greater part of said sulfuric acid present in said spent cat-alyst and containing about 10 ppmw or less fluoro compounds.
In another aspect of the present invention, there is provided a process for the regeneration of spent sulfuric acid-fluorosulfonic acid alkylation catalyst containing about 15,000-30,000 ppmw, calculated as HF, , fluoro compounds, which process comprises:
-` a) reacting, said spent catalyst, in a hydrolysis zone, at subat-mospheric pressure, at a temperature in the range from about 80 to about 110 C in the presence of about 3-15 weight percent water for a period in the - range of about 4-8 hours, for production of a first vapor phase comprising mainly hydrogen fluoride and a first liquid phase comprising sulfuric acid and containing about 800 ppmw or less residual fluoro compounds, b) flowing said first vapor phase overhead from said hydrolysis ~ zone into a fluorosulfonic acid generation zone;
c) treating said first vapor phase with sulfur trioxide to form regenerated fluorosulfonic acid in said hydrogen fluoride present in said .:
first vapor phase;
20 d) flowing said first liquid phase from said hydrolysis zone into an absorption zone;
e) contacting in said absorption zone, said first liquid phase with a fluidizable silicia-alumina cracking catalyst in an amount equivalent to about 0.3-5.0 weight percent of said first liquid phase for period of time in the range of about 1-8 hours, at a temperature in the range of about 50-120 C sufficient to react a major portion of said residual fluoro compounds of said cracking catalyst;
f) separating in a solid-liquid separation zone, said ~feeo~d liquid phase from said cracking catalyst for production of an effluent acid _5_ . ' ' ' -10f~29 free of cracking catalyst, comprising sulfuric acid and containing about 10 ppmw or less fluoro compounds;
g) combusting said effluent acid to convert said sulfuric acid to : sulfur dioxide;
h) converting at least a portion of sulfur dioxide to sulfur tri-oxide;
i) absorbing a portion of said sulfur trioxide from step (h) into a sulfuric acid solution for production of regenerated sulfuric acid;
j) flowing a portion of said sulfur trioxide from step (h) to said fluorosulfonic acid regeneration zone of step (c) and k) combining said regenerated fluorosulfonic acid with said regen-~ erated sulfuric acid in a weight ratio of from about 0~11/1 to about 0.32/1 : respectively to produce fresh alkylation catalyst.
- BRIEF DESCRIPTION OF THE DRAWINGS
.: The single figure is a schematic flow diagram of the process of the present invention.
DESCRIPTION OF THE Ph~RRED EMBODIMENT
Reference is now made to the accompanying drawing for a-~more de-tailed description of the process of the , ' . - 5a - .

106Z~Z9 present invention.
Spent catalyst from alkylation unit 10 passes vla line 11 into distillation zone 12, the primary treatment stage of the process. The spent catalyst from alkylation unit 10 comprises primarily sulfuric acid (about 88 - 90%
by welght) and contains ln additlon, fluorosulfonic acld, (_ 15% by volume) water (3 - 4% by weight), acld oils, sul-fonated and ~luorinated organlc materlals and other side reaction products formed in the alkylation reaction. Gen-erally, the total fluoride content, measured as HF, is in the range of 15,000 to 30,000 ppmw (parts per million weight).
Distillatlon zone 12 is preferably operated at atmoæpheric pressure or below and elevated temperatures of from about 50 to about 120C. It is desirable that the distillation apparatus be of a type which can generate a large surface area of spent catalyst, one such type of preferred apparatus -` being a multi-stage agitated vacuum digester.
As noted above, the distillation is conducted ln the presence of at least the stoichometric amount of water ~, .
needed to hydrolyze the fluorosulfonic acid to hydrogen fluoride. Generally speaking, in spent alkylation catalyst the water content i8 from 3 to 4% by weight. Thus, in a typical spent alkylation catalyst, it is not necessary to ;. add water to effect hydrolysis of all of the fluorosulfonic acid in the spent catalyst. As will be seen hereafter, how-ever, conducting the distillation in the presence of a stoichometric excess of water, e.g. up to 15% by weight of the spent catalyst, greatly enhances fluoride removal in the :-;~ distillation zone. Accordingly, provision can be made for ` 30 adding water to distillation zone 12 via line 26.
.

, ~

106Z~29 A llght, substantially vapor fractlon comprislng primarily hydrogen fluoride, some fluorosul~onlc acld and a small amount Or S02 formed from oxidative slde reactlons flashes and is removed from distillation zone 12 via line 13.
The hydrogen fluoride in the fraction removed vla llne 13 results not only from the hydrogen fluorlde origlnally pres-ent in the spent catalyst and that formed by hydrolysis of the fluorosulfonic acld, but in addltlon, arlses from de-compositlon of alkyl fluorosulfonates and other organofluoro compounds formed ln the alkylatlon reaction.
A second, heavier fraction comprl~ing the resi-dual materlal ~rom zone 12 and contalnlng substantially all of the sulfuric acid present in the spent catalyst, plus residual fluoride compounds (preferably ' 100 ppmw as HF), acld oils, water and other impurities is removed from dls-tillation zone 12 vla llne 14 and transferred to adsorption zone 15. Adsorptlon zone 15 ls the secondary treatment .-- .
stage of the process and convenlently employs a vessel, pref-erably agltated, lnto which is introduced a partlculate alumlna containing material via llne 16. In adsorptlon zone 15, the residual fluoride compounds, e.g. HF present in the spent catalyst fraction removed ~rom distillation zone 12, chemlcally react wlth the alumina to form insoluble aluminum !,' fluoride or other fluorided alumina compounds, or undergo physlochemical lnteraction, such as chemisorptlon, with the alumlna, and are substantially separated from the spent ` catalyst. The alumlnum fluoride and other fluorided alumina containing material is removed from the adsorptlon zone 15 via line 17 and is elther sent to waste or, if posslble, is regenerated for reuse in adsorpt~on zone 15.

' . .

1062~29 An acid effl~ent stream containing substantially all Or the sulfuric acid present in the spent catalyst and preferably having a fluoride content, as HF, of ~ 10 ppmw is removed from adsorption zone 15 via llne 18 and fed to sludge conversion unit 19. In sludge conversion unlt 19, the spent catalyst, havlng a greatly reduced fluorlde con-tent, ls combusted ln a suitable furnace under conditions such that all the sulfur specles present in the catalyst are ` converted to sulfur dioxide. The sludge conversion unit further contains a converter section employing an oxidation catalyst such a~ V205 whlch, in the presence of air, converts the S02 into S03. Part of the S03 thus produced is absorbed ln a fresh sulfuric acld solution to form oleum which is then diluted wlth water to form 97 - 99 weight % sulfuric acid.
The sulfuric acld thus produced is removed via line 20 for ~
recycle to alkylation unit 10.
The light fraction removed from zone 12 via line -s 13 and comprising hydrogen fluoride, fluorosulfonic acid and S02, is introduced into fluorosulfonic acid regeneration unlt 27 and combined wlth S03, to convert the HF to additional fluorosulfonic acid. A portion of the S03 ln unit 27 may be obtained from unlt 19 via line 22. Any addltional S03 needed to convert the hydrogen fluoride to fluorosulfonlc acid can be obtained from S03 make-up stream 23. The regenerated fluorosulfonic acid stream exlts unlt 27 via line 28. The S2 present in the fluorosulfonic acld stream ls removed from line 28 via line 24 to provide a stream comprising sub-stantially fluorosulfonic acid. The fluorosulfonlc acid is then comblned with the sulfuric-acid from llne 20 ln the proper proportions to form fresh alkylatlon catalyst which ls fed to alkylatlon unit 10 vla llne 25.
While reference has been made to the use of a multl-stage stlrred vacuum dlgester in dlstillatlon zone 12, lt ls to be understood that other types of equlpment can be employed. The purpose of the prlmary treatment stage or distlllatlon zone ls to remove the relatively volatile hydrogen fluorlde from the spent catalyst. Thus, any means which wlll provide a large surface area of spent catalyst to allow efflcient flashing of the hydrogen ~luorlde can be used. For example, rotary film evaporators, packed trickle towers, spray towers, baffle towers, rotary dlsc contactors, etc. can be employed.
Preferably, the distillation æone, i.e. the pri-mary treatment stage, comprises distillation at atmospherlc pressure or below and at elevated temperatures. Pressures ln the distillatlon zone should be as low as economically prac-tical and preferably below about 1 psia. Temperatures will, of course, depend on the pressures, but generally will range from about 50 to about 120C., and preferably from about 80 to 110C. It has been found that if the spent alkylatlon catalyst is sub~ected to temperatures o~ 125C. or hlgher for extended periods o~ time, the catalyst tends to thicken to a semi~solid mass. Thus, the temperatures should be kept below about 125C. For a typical spent alkylation catalyst containing 20,000 to 30,000 ppmw fluoride as HF, it has been found that lf the distillation zone is maintained at a temperature of around 100C. and a pressure of about or below 1 psia, and under conditions af~ording increased surface area Or the spent catalyst, 90% recovery, by weight, of the fluoride (calculated as HF) can be achieved without _ g _ - . ' . ' ' .

adverse degradation side reactions whlch occur at higher temperatures.
The residence time ln the dlstillation zone will vary depending on pressure, temperature, fluoride content of the spent acid, water content, etc. Generally speaking, the residence time of the spent catalyst in the distillation zone should be sufficient to permit maximum hydrolysis of the fluorosulfonic acid to hydrogen fluoride and subsequent flashing of the hydrogen fluoride and/or remainlng fluoro-sulfonic acid from the distillation zone. Additionally, relatively long residence times in the distillation zone promote the decompositlon of organofluoro compounds in the spent catalyst into hydrogen fluoride and/or fluorosulfonic acid thereby maximizing the recovery of the fluorosulfonic acid for recycle to the alkylation unit and minimizing the fluoride removal needed in the second stage of the process.
However, while long residence times increase the fluoride recovery from the spent catalyst in the distilla-tion zone, there is also a concomitant increase in the amount .
of S02 recovered in the vapor fraction with the hydrogen fluoride. Since S02 losses represent loss of sulfur for ` regeneratlon into fresh sulfuric acld, minlmum digestion or .
- residence time in the distillation zone consistent with adequate fluoride removal should be used so as to minimize .
such losses. In general, it has been found that at a tem-.' 1 perature of about 100C. and a pressure of about l psia or lower, a residence time of 4 hours or greater wlll effect - removal of 90% by weight of the total fluoride, calculated as HF, from a typical spent catalyst, i.e. containing 20,000

3 0 - 30,000 ppmw fluoride. In such a typical spent catalyst, if the digestion time is increased to 6 hours or greater, as for example, from about 6 to about 8 hours, greater fluoride removal (about 97% by weight) can be obtained, e.g. from about 23,000 ppmw to about 700 - 800 ppmw. It has also been found that if the spent catalyst has a rela-tively low initial fluoride concentration, e.g. about 1000 - 1500 ppmw, calculated as HF, the fluoride level can be reduced to 74 ppmw after 2 hours and 33 ppmw after 8 hours.
With ample residence time and at a temperature of around 100C. and a pressure of 5 - 15 mm. Hg, the fluoride content (as HF) of a typical spent acid catalyst can be reduced to 100 ppmw or less.
While the distillation step of the process of the present invention can be conducted ln the presence of the amount of water needed to stoichometrically react with the fluorosulfonic acid to form hydrogen fluoride, it has been found that higher water content in the spent catalyst greatly improves fluoride recovery in the distillation zone.
As noted, typical spent catalyst contains 3 - 4% by weight water which is sufficient, as noted above, to effect good ; recovery of fluoride from spent catalyst in the distillation zone. However, when the water content of the spent catalyst contains up to 8% by weight water, and more preferably from about 8 to about 15% by weight water9 the volatility of the fluorides in the spent acid is greatly increased. Apparent-ly, the excess water is needed to (1) force the hydrolysis of the fluorosulfonic acid to HF which is more volatile, and/or (2) reduce the solubility of the HF in the spent acid catalyst. Indeed, the presence of approximately 15 weight % water in the spent catalyst will permit reduction of the fluoride content (calculated as HF) from around 24,000 ppmw, to about 50 ppmw after only 8 hours resldence time in the distillation zone.
It is also possible to employ inert gas purglng or stripping of the spent acid catalyst in the dlRtlllatlon zone. Thus, purge gases such as N2, argon, helium, etc.
could be used. Moreover, steam stripping could be employed, the steam serving the added purpose of supplying water to the system.
In the secondary treatment stage, i.e. the ad-sorption zone, of the process of the present invention, the residual fluoride compounds in the spent catalyst are con-tacted wlth an alumina containing material (adsorbent) in an amount and for a period of time sufficient to effect reaction between at least a portion of the fluoride compounds and the alumina. Virtually any material containing alumina can be used as the adsorbent. The term alumina, as used herein, refers to the compound A1203 in anhydrous or hy-. . .
drated form. The alumina containing material can be either substantially pure alumina, such as for example chromato-; graphic grade alumina, or a natural;ly occurrlng mineral prod-uct such as bauxite, corundum, etc. Also, alumina contain-ing materlals such as spent silica-alumina cracking catalysts which contain varying amounts of alumina can also be employed.
The actual amount of alumina which must be used in the adsorption zone to effect efficient removal of the residual fluoride compounds, e.g. HF, will depend upon the fluoride content of the spent catalyst fraction removed from the distillation zone, temperature conditions, contact times, etc. Thus, for example, an alumina containing material such ' .

- 12 - ~

.
.;.,, - . - , . . . , - .
. . ~ , . - ~ , .

.~06222g as the above-mentioned silica-alumina cracking catalyst containing as little as 10% by weight alumina has been found to be effectlve in the adsorption zone to remove the resi-dual fluoride compounds.
The total amount of alumina containing material used in the adsorptlon zone will vary depending upon the fluorlde content of the spent acid catalyst, the alumina content of the adsorbent~ temperature conditions, contact times, surface area of the alumina containing materlal, etc.
However, in general, when the alumina content of the adsorb-ent is 10 weight % or greater, the amount of alumina con-talning materlal used wlll range from about 0.3% by weight and higher of the spent catalyst fraction ln the adsorption zone. While higher concentrations of adsorbent, e.g~ up to 5% by weight, reduce the tlme required to effect removal :~ of the residual fluoride to a glven level, the reduction in the ultimate fluoride concentratlon ls not slgnificantly reduced. It has also been found that for substantially the ` same total amount of adsorbent used, multlple additions of the adsorbent are more effective than a slngle addition of the adsorbent. Thus, for example, a single charge of 1%
by weight adsorbent with a contact time of 4 hours and a temperature of 100C. is less effective than two additions of 0.5% by weight adsorbent at two hour intervals and a tem-perature of 100C. The use of a spent sllica-alumina cracking catalyst (36 weight % A1203, 70% 40-80 micron slze) in an amount of from about 1 to about 2% by weight of the ., , spent catalyst in the adsorption zone, at a temperature of around 100 for a contact time of from about 6 to about 8 hours will reduce the fluoride content (calculated as HF) ~ .

10~2229 of the spent acid in the adsorbent zone from about 1900 ppmw to lO ppmw or less.
It will be apparent that to effect efflclent removal of the residual hydrogen fluoride or other fluoro compounds ln the spent catalyst fraction in the adsorptlon zone, there must be suf~icient contact time between the spent catalyst and the adsorbent. The actual contact or residence time required will depend upon several varlables, such as for example, particle size of the adsorbent, the alumina content~ surface area and activity of the alumina, the ~luoride content of the catalyst, the temperature, etc.
Accordingly, no specific residence time can be stated. How-ever, it has generally been found that when the contacting is carrled out at an elevated temperature as, for example, approximately 100C., a residence time of one hour or greater, e.g. 2 to 4 hours, is required to obtain maximum reduction in the fluoride level.
The particle size of the alumina containlng material ls not critical. Alumina containing materlals such as, for example, spent silica-alumina cracking catalyst (partlcle slze 40-80 microns) having a relatively large surface area (approximately lO0 m2/g) provides much greater :i .
-i contact area for reaction Or the hydrogen fluorlde or other fluoro compounds with the alumlna than a material e.g.
;ij bauxlte, of much larger particle slze, e.g.~ 200 microns.
'h~ However, whlle an alumina contalning material Or relatlvely large particle size may requlre a longer residence tlme to - .
effect the desired reduction in the fluoride content, such material wlll work satisfactorlly. The use of an adsorbent ~-; 30 of relatlvely fine partlcle size ( ~ lO0 microns) generally ., .

,-1062~29 requires centrlfuging, filtering or some other such solld-liquld separation step to achieve removal of the fluorided alumina from the spent catalyst. The use of alumlna con-taining materials of relatively large partlcle size, e.g.
lO0 microns, permits separation by gravlty settling, thus minimizing process and equipment costs.
While the adsorption process can be conducted at amblent and even below ambient temperatures, the rate of reaction of the fluoro compounds, particularly hydrogen fluoride, with the alumina is greatly enhanced at elevated temperatures. Generally speaking, a temperature range of from about 50 to about 120C. promotes efficient reaction between the hydrogen fluoride or other fluoro compounds and the alumina, a temperature of around 100C. being particularly desirable.
The adsorption process can be conducted at pres-, sures ranglng from sub-atmospheric to super-atmospheric~
However, sub-atmospheric or super-atmospheric pressures appear to have no significant effect on the efficlency of the adsorption process and accordingly, from an economy stand-po~lnt, it ls convenient to carry the adsorption process out at atmospheric pressure.
As descrlbed above, the process of the present i invention also provldes a method for regeneration of fre~h `
alkylation catalysts. The hydrogen fluoride which ls re-moved in the primary treatment stage can be reacted with sulfur trioxide to form fluorosulfonic acid which together with the fluorosulfonic acid removed in the distillation zone can be employed as one of the components of fresh alkylation catalyst. Llkewise, the substantially fluoride free spent . . . .

,: ', ~ ' acid fed to the sludge conversion unit ls ultlmately used to generate fresh sulfuric acid, thus providing the other component of the alkylation catalyst. The sludge con~ersion unit can also provide at least a portion of the sulfur trioxide used to react with the hydrogen fluorlde recovered from the primary treatment stage to form the fluorosulfonic acid. In forming the fresh alkylation catalyst, the fluoro-sulfonic and sulfuric acids are combined in a welght ratio of from about 0.11/1 to about 0.32/1, respectively, to form an acid catalyst. The fresh catalyst may, in addition, contaln up to 3% by welght water.
The process of the present lnventlon not only provides an efflclent method for the recovery of the fluorosulfonic acld from the spent alkylatlon catalyst, but in addltlon, provides a feed for the sludge conversion unit which is substantially free of deleterious amounts of fluoride. As previously noted, the sludge conversion unit employs a refractory lined furnace which is readily attacked by hydrogen fluoride. Accordlngly, to avoid damage to the refractory, it is necessary that the hydrogen fluoride content of the feed be reduced as much as possible, lf not ellmlnated. Additlonally, removal of the fluoride from the spent acid ensures that the sulfur dioxide produced in the sludge conversion unit will be substantially free of :
- fluoride compounds which could volatilize the vanadium in the V20s oxidation catalyst used to convert the S02 to S03.
` To further illustrate the advantages of the `~ present lnvention, the following non-limiting examples are presented. All fluoride contents are by weight and calculated :
.' - .

\

as HF unless otherwise indicated.
Example I
A 200 ml. sample of spent alkylation acld cata-lyst containing 23,600 ppm fluoride was placed in a one-llter stirred reactor maintained at 100C. and 5 - 15 mm.
Hg absolute pressure for 8.5 hours, the evolving HF and HFS03 being collected. Periodic analysis of the spent acld cata-lyst showed 40% of the fluorlde had been removed after 4 hours, a fluoride content residual of 1530 ppm after 6.5 hours, and 780 ppm after 8.5 hours.
Example II
;` The procedure of Example I WQS followed except the spent alkylation catalyst was admixed with an amount of water equal to 5% by weight of the spent acid catalyst in the reactor which brought the total water content of the - spent acid catalyst to about 8 - 9~ by weight. It was found that after 8 hours of digestion (distillation), the spent acid catalyst had a residual fluoride content of 450 ppm.
Example III
The procedure of Example II was followed with the exception that an amount of water equal to 10 welght %
of the spent acid catalyst was added bringlng the total water content of the spent catalyst in the reactor to about 13 -14~. It was found that after 8 hours of dlgestion, the spent acld catalyst had a residual fluoride content of 50 ppm.
~xam~le IV
A 17.4 gram sample of the resldual spent acld from Example I havlng a fluoride content of ~ 800 ppm was mixe~ with 0.053grams of a spent sillca-alumina cracking catalyst (70% 40-80 micron slze, 36.1% A1203) and heated in .

.~

a polyethylene bottle at 100C. for two hours wlth occa-sional shaklng. An additional 0.102 grams of the spent alumina catalyst was added to make the total adsorbent content of the mixture 0.90% by weight and the mlxture heated at 100C. for an additional two hours. Upon cooling, the slurry was centrifuged to remove the fluorided adsorbent (aluminum fluoride). Analysis of the thus treated spent acid showed a fluoride concentration of 13 ppm.
Example V
A 17.4 gram sample of the residual spent acid from Example I was mixed with 0.0989 grams of the spent silica-alumina cracking catalyst descrlbed in Example II
and heated at 100C. for four hours as described in Example II. An additional 0.09609 grams of adsorbent was then added to make the total adsorbent content 1.1% by weight of the total mixturej and the heatin,g continued for an additional -.. . .
'~ four hours. Following centrifugation, the liquid phase was ~' ~ found to contain 10 ppm fluoride. ''! ' ',; Example VI
, 20 A 12.37 gram sample of spent alkylation catalyst -' which had been treated as per the general process of Example 'I was contacted for 8 hours at 100C. with 0.9 welght %
chromatographic grade acidic alumina (passes 80 mesh screen).
' -Analysis of the effluent acld showed that the fluorlde con- '-centratlon had been reduced from 780 to 475 ppm durlng the ~" adsorptlon treatment.
, Example VII
;~ A 200 ml. sample of spent alkylation acld catalyst ~ processed as per the general method of Example I and con- '--, 30 talnlng 62 ppm fluorlde was treated wlth 5 welght %

, ,~
~- ' ', '.

';
- , , 106~2Z9 chromatographic grade alumina (passes 80 mesh screen) at 100C. for 6 hours. Analysis of the effluent acid showed the fluoride level was reduced to 3 ppm.
EXAMPLE VIII
A 17.4 gram sample of spent alkylation acid catalyst treated as per the general method of Example I and containing 780 ppm fluoride was contacted with 1.18 weight % Porocel (activated bauxite) at 100C. for 8 hours. The effluent acid was found to contain 530 ppm. fluoride. A
similar run but employing 4.5 weight % activated bauxite (10-30 mesh) reduced the fluoride concentration to 246 ppm. ~-EXAMPLE_IX
A sample of residual spent acid catalyst obtained generally as per the procedure of Example I and containing approximately 1530 ppm fluoride was mixed with 0.6 weight % of the silica-alumina catalyst described in Example IV
and heated at 100C. with occasional shaking. It was found that the fluoride level was reduced to 50 ppm within one hour, the fluoride content being reduced to 11 ppm within 3 to 4 hours.
EXAMPLE X
Various alumina containing materials were used to treat spent alkylation acid catalysts which had been sub-jected to the primary distillation step. In all cases, con-tacting between the absorbent and the spent acid was conduct-ed at 100C at atmospheric pressure for a period of 8 hours.
The results are shown in Table 1 below.

,.................................... --19--.....

- ... : . .. .. .. ..

1062~Z9 Alum~na Wt.% Initial Final Run No. Code Adsorbent Ppm F ~pm F
1 1 0.67 780 78 2 1 1.12 780 10 3 2 0.90 780 475

4 2 4.86 62 3 ~ 6.80 33 9 6 3 0.56 780 ~25 ` 7 3 4.49 780 246 ~ lCode 1 - Spent silica-alumina cracking catalyst (70% 40-80 - micron size, 36.1 wt.% A1203).
Code 2 - Acidic alumina powder (Brockmann Activity Grade 1). ~ -` Code 3 - 10-30 mesh Activated Bauxite.
. EXAMPLE XI
Distillates obtained following the general pro-- cedure of Example I from two sample of spent acid were collected in a liquid N2 cooled trap, warmed to 0C., and mixed with liquid S03. The resulting solutions were dis-tilled at reduced pressure to purify the fluorosulfonic acid. The data for regeneration of the fluorosulfonic acid is given in Table II below.
~ ~r:

-. , ,'.-,( !.
" ~
; ' ~
, . . .

' , -20-' .
o o ~ ~ ~ r~ ~ ~ o u~
3 ^3 ~ o ~ J . U~
. O cr~ O 1~
~J ~ N ~ ~ ~ O S
E~ .

1 ~
~ W~ ~d .
@) ~
o ~ 0~
- ~C) ~)o o oo ~ O l~ ~1 ~: O ^J ~1 ~ C) . O t~ IS~~ O (~J O ~1~ P~

a~
~ J~
H O
~ ~3 E~ ~ .
~_ .
O bD
. .,_ .,',~ ~ J~
~ .
' ~ ~ O
i~ ' ~W o a~
C) ~_ - tq l,e 3 -I ~:
o a) ¢ ~
~ ~ N
.. ~e. J~ ~ ~ O ~Q
- ~e ~ .~
~ ~ ~ ~ ~ ~ C~
e c~ ~ + ~ ~ O ~D
o ~ ~ ~ ^ td ~1 bD e) O ~ C~ 0 ~ ~ ~d ~ O U~
td O ~ ~ O e~ O ^ ~ ~ Cd +
s C~ o ~ ~ O~ ~Oq b ~ ~ ae.m~ ,d a~ cq~4 ~
c~ ¢ ,1 ~ O h R, ~1--~ m o~
O ~ ~ ~ 1 .' Z J~ 00 ~ d ~
h t~ ~~ O ^ ~ O q-l ~ O J~ H
-H H O ~ P~m ~ ~ s c> o 0 ~ ~ o P~ ; o ~ ~ ~ ..

' 1062~Z9 As can be seen from the data above, the process of the present inventlon provides an efficient method for the removal of fluoro compounds from spent alkylation cata-lyst. With reference to Examples I-III, it can be seen that the distillation step effects substantial removal of the fluoro compounds from the spent catalyst. As can be seen from Examples IV-X, the secondary treatment stage, i.e. the adsorption stage, provides a spent acid catalyst free from substantial amounts of fluoro compounds. By comparing Example IV and V wlth Example VI, it can be observed that for approximately the same total amount of alumina contain-ing material added to the spent catalyst, multiple additions of the adsorbent, (Examples IV and V) is superior to a 1' single addition of the adsorbent (Example VI), even though - the actual alumina content of the adsorbent in Examples IV
and V is considerably less than that of the adsorbent em-. ~ . .`~ ployed in Example VI.
With reference to Example XI, it is to be ob-served that the process herein provides an e~ficient method ` 20 of regenerating fluorosulfonic acid from the spent catalyst.
`~ Note that overall fluoride balances of 75 and 85% were observed for the two runs.
It can be seen that by employing the process of the present invention, potential damage to the refractory lining in the furnace of the sludge conversion unit, and any loss of the V205 oxidation catalyst by fluoride vaporization of the vanadium can be virtually eliminated.
The present invention has been described with reference to several specific embodiments thereof, and accordingly, it will be apparent that many modifications, ,, ' .

, - .

substitutions, and omissions will be readlly suggested to a person of ordinary skill in the art without departing from the spirit of the present lnvention. Therefore, it is to be understood that the scope of the invention ls to be determlned solely by the clalms appended hereto.

~2 .

:' :
., . . . .

Claims (5)

The embodiments of the invention in which an ex-clusive property or privilege is claimed are defined as follows:

1. A process for the removal of fluoro compounds from spent sulfuric-acid - fluorosulfonic acid alkylation catalyst, wherein said fluoro compounds comprise about 15,000 -30,000 ppmw, calculated as HF, of said spent catalyst; which process comprises:
a) reacting, in a hydrolysis zone, said spent catalyst, at subatmospheric pressure, at a temperature in the range of from about 50 to about 120°C in the presence of at least about 3 weight percent water for a period in the range of about 1-8 hours, for production of a first vapor phase comprising mainly hydrogen fluoride and a first liquid phase comprising sulfuric acid, and containing about 800 ppmw or less fluoro compounds;
b) contacting, in an absorption zone, said first liquid phase with a fluidizable silica-alumina cracking catalyst in an amount equivalent to about 0.3-5 weight percent of said first liquid phase for a period of time in the range of about 1-8 hours, at a temperature in the range of 50-120°C for production of a second liquid phase comprising said sulfuric acid and a first solid phase comprising cracking catalyst containing fluoro compounds; and c) separating, in a solid-liquid separation zone, said second liquid phase from said first solid phase for production of an effluent acid containing the greater part of said sulfuric acid present in said spent catalyst and containing about 10 ppmw or less fluoro compounds.

2. The process of Claim 1 wherein the reaction of hydrolysis step (a) is conducted at a pressure of about 1 psia or less, at a temperature in the range of about 80-110°C, and in the presence of from about 8-15 weight percent water, for a period of from about 4 to about 8 hours, for reducing residual fluoride content of said first liquid phase to about 100 ppmw or less, calculated as hydrogen fluoride.

3. The process of Claim 2 wherein the first liquid phase and a first portion of said fluidizable silica-alumina cracking catalyst are charged to the absorption zone at the beginning of absorption step (b), and wherein a second portion of said cracking catalyst is added to the absorption zone after a period of about 2 hours, for increased reduction of fluoride compounds in the effluent acid.

4. A process for the regeneration of spent sulfuric acid-fluorosulfonic acid alkylation catalyst containing about 15,000-30,000 ppmw, calculated as HF, fluoro compounds, which process comprises:
a) reacting, said spent catalyst, in a hydrolysis zone, at subatmospheric pressure, at a temperature in the range from about 80 to about 110°C in the presence of about 3-15 weight percent water for a period in the range of about 4-8 hours, for production of a first vapor phase comprising mainly hydrogen fluoride and a first liquid phase comprising sulfuric acid and containing about 800 ppmw or less residual fluoro compounds;
b) flowing said first vapor phase overhead from said hydrolysis zone into a fluorosulfonic acid generation zone;

c) treating said first vapor phase with sulfur trioxide to form regenerated fluorosulfonic acid in said hydrogen fluoride present in said first vapor phase;
d) flowing said first liquid phase from said hydrolysis zone into an absorption zone;
e) contacting in said absorption zone, said first liquid phase with a fluidizable silicia-alumina cracking catalyst in an amount equivalent to about 0.3-5.0 weight percent of said first liquid phase for period of time in the range of about 1-8 hours, at a temperature in the range of about 50-120°C sufficient to react a major portion of said residual fluoro compounds of said cracking catalyst;
f) separating in a solid-liquid separation zone, said first liquid phase from said cracking catalyst for production of an effluent acid free of cracking catalyst, comprising sulfuric acid and containing about 10 ppmw or less fluoro compounds;
g) combusting said effluent acid to convert said sulfuric acid to sulfur dioxide;
h) converting at least a portion of sulfur dioxide to sulfur trioxide;
i) absorbing a portion of said sulfur trioxide from step (h) into a sulfuric acid solution for production of regenerated sulfuric acid;
j) flowing a portion of said sulfur trioxide from step (h) to said fluorosulfonic acid regeneration zone of step (c) and k) combining said regenerated fluorosulfonic acid with said regenerated sulfuric acid in a weight ratio of from about 0.11/1 to about 0.32/1 respectively to produce fresh alkylation catalyst.

5. The process of Claim 4 wherein said reaction in said hydrolysis zone is conducted at a pressure of about 1 psia or more in the presence of from about 8 to about 15 weight percent water.