USOO6489527B1

(12) United States Patent (10) Patent No.: US 6,489,527 B1

(54) PROCESS FOR IMPROVING PURITY OF 4,100,215. A 7/1978 Chen .......................... 585/467
PARA-XYLENE PRODUCT 4,584,422 A 4/1986 Barile et al. ................ 585/481
5,055,630 A 10/1991 Puppel ....................... 585/814
(76) Inventors: John Di-Yi Ou, 14643 Redwood Bend 5,177.295 A * 1/1993 Oroskar et al. ............. 585/805
Trail, Houston, TX (US) 77062; Harold FOREIGN PATENT DOCUMENTS
William Helmke, 3807 Fawn Creek,
Kingwood, TX (US) 77339; Dana GB 1108178 * 4/1968
Lynn Pilliod, 2104 Brook Haven Dr., OTHER PUBLICATIONS
League City, TX (US) 77573
D. Nightingale, et al., “Orientation Effects in the Alkylation
(*) Notice: Subject to any disclaimer, the term of this of m-Xylene by Various Procedures and Reagents,” Journal
patent is extended or adjusted under 35 of the American Chemical Society, vol. 64, pp. 1662–1665,
U.S.C. 154(b) by 1314 days. Jul 1942.
D. Nightingale, et al., “The Alkylation of o- and p-Xylene,”
(21) Appl. No.: 08/575,443 Journal of the American Chemical Society, vol. 66, pp.
154–155, Jan., 1942
(22) Filed: Dec. 20, 1995 B. B. Corson, et al., “Separation of Positional Isomeric
Dialkylbenzenes,” Industrial and Engineering Chemistry,
Related U.S. Application Data vol. 48, No. 7, pp. 1180–1182, Jul. 1956.
(63) Continuation of application No. 08/106,326, filed on Aug. Chemical Abstract 116(6):43394n (1992).
13, 1993, now abandoned, which is a continuation-in-part of * cited b
application No. 07/888,577, filed on May 26, 1992, now cited by examiner
abandoned. Primary Examiner Walter D. Griffin
(51) Int. Cl." .............................. C07C 2/66; CO7C 7/00 (57) ABSTRACT
(52) U.S. Cl. ........................................ 585/467; 585/805
(58) Field of Search .................................. 585/467, 805 A process for producing 99.5+ wt.% para-xylene by Selec
tive alkylation has been discovered. A mixure of isomers of
(56) References Cited para-xylene having at least about 90.0 wt.% purity may be
reacted with an alkylating agent having at least one tertiary
U.S. PATENT DOCUMENTS butyl moiety in the presence of an acidic catalyst under
2,585,525 A 2/1952 Yates ......................... 585/805 conditions where the catalyst is in good molecular contact
2,648,713 A 8/1953 Schneider .. ... 260/674 with the non-para-Xylene isomers. The catalyst may be a
2.801271 A 7/1957 Schlatter .... ... 260/674 high Surface area acidic heterogeneous catalyst Such as a
2.816,940 A * 12/1957 Schlatter ....... ... 585/805 proton-exchanged Zeolite. Upon distillation, para-Xylene is
s: A
2- - - 2
8. E. in et al. .
II . . . . . . . . .
--- :
----
recovered in 99.5 wt.% purity or higher. The selective
3,770.841. A * 11/1973 Meyers, Jr. ... ... 585/805 alkylation gives little or no alkylation of the para-xylene, the
3,793,385 A * 2/1974 Bond et al. .... ... 585/805 most predominant Species, and very little or no isomeriza
3,813,452. A * 5/1974 Bieser ....... ... Ssssos tion to the other, non-desirable isomers.
4,002,697 A * 1/1977 Chen ...... ... 585/454
4,021,499 A 5/1977 Bieser ........................ 585/805 35 Claims, No Drawings
 US 6,489,527 B1
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PROCESS FOR IMPROVING PURITY OF liquid hydrogen fluoride at a temperature in the range X10 to
PARA-XYLENE PRODUCT 100° C. The quantity of isobutylene employed is sufficient to
alkylate a Substantial proportion of the meta-xylene con
This is a continuation, of application Ser. No. 08/106, tained in the Xylene fraction. The alkylation reaction product
326, filed Aug. 13, 1993, now abandoned, which is a is fractionally distilled to Separate a para-Xylene rich fraction
continuation in part of application Ser. No. 07/888,577, filed and a fraction comprising tertiary-butyl-meta-xylene. The
May 26, 1992, now abandoned. latter fraction and a Straight run petroleum distillate are
contacted with a silica-alumina catalyst in a catalytic crack
FIELD OF THE INVENTION ing Zone at a temperature in the range 800 to 1000 F. The
latter fraction is cracked forming predominantly meta
The invention relates to methods for producing para Xylene and isobutylene. The effluent from the cracking Zone
Xylene, and more particularly, the invention relates, in one is fractionally distilled to Separate a fraction rich in
aspect, to processes for purifying para-Xylene in exception isobutylene, and the isobutylene rich fraction is then
ally high purity from its isomers. returned together with additional Xylenes to the alkylation
BACKGROUND OF THE INVENTION 15 Step. Again, this process is a bulk Separation process; the
only example (Example 1) to the alkylation Separation Step
There exist Several technologies for recovering para yielded a para-xylene purity of 48%.
Xylene from its mixture with its isomers which are ortho Purified meta-xylene is obtained by alkylating a mixture
Xylene, meta-Xylene and ethylbenzene. Adsorption-based containing m- and p-Xylene with a Small but effective
methods and crystallization-based processes are commonly amount of isopropylating agent in the presence of a Small but
used in industry. These two processes can produce 99.6 to Sufficient amount of aluminum chloride catalyst, according
99.8 wt.% purity para-xylene very efficiently. Achieving to U.S. Pat. No. 3,539,650. The alkylation mixture is main
purities on the order of 99.9+ wt.%, however, is very tained at a temperature within the range of about 70° C. to
difficult and costly. Other techniques for Xylene Separation about 100° C. for about thirty minutes to one hour after
Such as hydrogen-fluoride extraction, Sulfonation and alky 25 which the catalyst is destroyed, an isopropyl meta-xylene
lation have not been able to demonstrate an efficiency fraction recovered, and the recovered fraction deisopropy
comparable to that of the adsorption and crystallization lated to produce meta-xylene above 95% purity. It is appar
proceSSeS. ent that meta-xylene concentrations much above 98% may
The chemistry for xylenes alkylation has been studied for not be readily attainable, however, given the best Examples
Several decades. D. Nightingale, et al. in "Orientation in Table IV of this patent, which focuses only on the
Effects in the Alkylation of m-Xylene by Various Procedures meta-xylene product, rather than the para-Xylene material.
and Reagents,” Journal of the American Chemical Society, U.S. Pat. No. 5,055,630 describes a process for obtaining
Vol. 64, pp. 1662–1665, 1942; and D. Nightingale, et al. in a para-xylene final product more than 98% pure from a
“The Alkylation of o- and p-Xylene,” Journal of the Ameri crystalline starting material with a purity of about 98%,
can Chemical Society, Vol. 66, pp. 154-155, 1944, indicate 35 which includes the Steps of intermixing the Starting material
that ortho-Xylene, meta-xylene and ethylbenzene can be with precooled water and feeding back the recovered para
alkylated with molecules containing tertiary butyl moiety Xylene in a mixer at a temperature of 0 to 13 C. to form a
(e.g. isobutylene, tertiary butyl chloride, tertiary butyl para-Xylene-crystal-water mixture containing para-Xylene
benzene, di-tertiary butyl hydroxyl toluene, etc.). para crystals and water. The mixture is continuously transferred
Xylene, however, was found to be quite difficult for tertiary 40 as Soon as it contains 30% by weight para-Xylene crystals
butylation. It is theorized that a steric effect has hindered the into a purifying centrifuge via a dewatering filter to form a
insertion of the bulky tertiary butyl group to the more fluid phase and a para-Xylene crystal Slurry. The fluid phase
restricted aromatic ring of the para-Xylene molecule. Partial is separated further from the para-Xylene crystals in a first
Separation of para-Xylene from meta-xylene and ortho Stage of a purifying centrifuge, mixing the para-Xylene
Xylene based on the Selective alkylation concept has been 45 crystal slurry in a Second Stage with a partial flow of final
demonstrated; see, e.g., U.S. Pat. Nos. 2,648,713, 2,801,271 product, heating at about 13 C. and Subsequently liberating
and B. B. Corson, et al., Industrial and Engineering from the fluid phase Still adhering, whereby the para-Xylene
Chemistry, Vol. 48, No. 7, pp. 1180, 1956. crystals are drawn off into the heated vessel. Next, the
U.S. Pat. No. 2,648,713 provides a process for the sepa para-Xylene crystals melted in the heated vessel are drawn
ration of ortho-xylene from an admixture thereof with 50 off as the final product with the desired purity. A partial flow
meta-xylenes by the Successive Steps of alkylation, distilla of final product is also drawn off which is fed back to the
tion and dealkylation. para-Xylene may also be present in Second Stage of the purifying centrifuge, being heated pre
the Xylene mixture and remains unalkylated with the meta viously to a temperature from 60 to 80 C. and feeding the
Xylene. The alkylating agent is preferably an olefin or fluid phase Separated from the para-Xylene crystals to the
cycloolefin having a tertiary carbon atom, Such as isobuty 55 Second Stage of the centrifuge for recovery of additional
lene, diisobutylene, trimethylethylene 2,4-methylpentene-2, para-Xylene which becomes part of the final product Stream.
3-methylbute ne-2, 4-methylcyclohexene -1 and It would be advantageous if a method could be devised for
1-methylcyclohexene-1. This process, as the ones previ obtaining high purity para-Xylene which was less complex
ously discussed, is limited to bulk Separation; in the best and costly than that described in U.S. Pat. No. 5,055,630.
Example recorded therein (Example 2) the percent conver 60 The Separation of close-boiling meta-xylene and para
sion of ethyl benzene and ortho-xylene was 89 and 54, Xylene Via Selective alkylation and Subsequent dealkylation
respectively. or transalkylation was recently Studied according to Chemi
U.S. Pat. No. 2,801,271 describes an integrated process cal Abstract 116(6):43394n (1992). The alkylation was
for Separating Xylene isomers and producing high octane carried out with isobutylene or diisobutylene with concen
gasoline which involves contacting isobutylene with a 65 trated HSO catalyst at -10 to +20 and Filtrol-24 acid clay
Xylene fraction having Substantial quantities of para-Xylene at 80-130, respectively. meta-Xylene reacted very selec
and meta-xylene. The contact is done in the presence of tively (Filtrol-24 gave selectively 5-tert-butyl-meta-xylene),
 US 6,489,527 B1
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and the alkylated products could be dealkylated at higher purity, it is accomplished only with a significant capacity
temperatures in the presence of Filtrol-24 catalyst, to give debit. For example, in one conventional process, the
relatively pure meta-xylene and isobutylene which could be increase from producing 99.8 to 99.9 wt.% para-xylene
recycled. para-Xylene purity is not mentioned in the results in a 15% reduction in capacity. That is, there is a
Abstract. production capacity/purity trade off which cannot be over
There remains a need for a process which provides a high come. Prior commercial processes are Separation processes
yield to para-Xylene in very high purity which is relatively only, whereas the Subject proceSS uses reactive purification
Simple and cost-effective. The linking of two conventional and reaction processes. In the present invention, one does
para-Xylene purification processes together is generally leSS not have to Sacrifice capacity to increase purity.
efficient. Additionally, the reaction to make para-Xylene is DETAILED DESCRIPTION OF THE
reversible under many of the conditions to Selectively alky INVENTION
late the Xylene mixture, often in the attempt to make very It has been discovered that it is not economical nor
high purity para-Xylene, an isomerization Side reaction efficient to produce 99.9+ wt.% para-xylene via any single
occurs to make more of the less desirable meta-xylene Separation process, whether adsorption, crystallization,
and/or ortho-Xylene. At relatively high purities, e.g. 98 wt. 15 hydrogen-fluoride extraction, Sulfonation or other processes.
%, attempts to increase purity of the already pure product It has been Surprisingly found that the best proceSS arrange
result in degradation of the product rather than improvement ment to maximize purity and productivity appears to be
through these Side reactions. Also, para-Xylene does alkylate attaching an alkylation process at the back end of an
to some extent and there is a great tendency when 98 wt.% adsorption or crystallization process. Such a hybrid System
of the product is para-Xylene that the alkylation will more can easily achieve the desired 99.5+ wt.% purity without
readily occur with the para-Xylene, rather than with the Small any significant productivity loSS. Of course, the final para
proportion of impurities which are more difficult for the Xylene purity must be greater than that of the mixture of
catalyst to come into contact with. Attempts often result in Xylene isomers before purification.
removing alkylated para-Xylene and/or isomerizing para In the first treatment of the hybrid system, a conventional
Xylene with the overall result of a relatively increased 25 para-xylene recovery technology such as the PAREXOR)
proportions of impurity and a product with a lowered purity adsorption process or a crystallization process will be used
to para-Xylene. to produce a product stream with 99.0 to 99.8 wt. %
Many of the prior processes do not discuss the problems para-xylene. PAREX is a registered trademark of UOP Inc.
of side reactions and reversible reactions. Most of them only Other processes that produce a mixture of isomers of para
are concerned only with bulk Separations and are Satisfied Xylene include, but are not necessarily limited to, hydrogen
with conversions of about 50%. As discussed, only U.S. Pat. fluoride extraction, Sulfonation, fractionation, membrane
No. 5,055,630 attempts to achieve high purity para-xylene, separation and selective toluene disproportionation (STDP).
and it is only accomplished via a complicated crystallization Essentially, the method of this invention can be used to
proceSS involving a multi-stage centrifuge. It is anticipated purify a mixture of isomers of para-Xylene produced by any
that in the near future there will be a great need for ultra-pure 35 process known in the art except or exclusive, of a Selective
para-xylene, on the order of 99.9+ wt.% purity. alkylation process. Such mixtures of isomers para-Xylene
may contain more than about 90 wt.% para-Xylene, alter
SUMMARY OF THE INVENTION natively from 90 to 99.9 wt.% para-xylene, in one embodi
Accordingly, it is an object of the present invention to ment from 95 to 99.9 wt.% para-xylene and in a narrower
provide a process for recovering para-Xylene in at least 99.5 40 range from 98 to 99.9 wt.% para-xylene. These commercial
wt.% purity, and to 99.9+ wt.% purity, if desirable. processes are very efficient in Such purity ranges. AS
explained, what is more difficult is how to upgrade the
It is another object of the present invention to provide a product purity to 99.5+ wt.% efficiently. Unexpectedly, it
proceSS for giving para-Xylene in very high purity by Selec was discovered that further para-Xylene purification is better
tive alkylation in a Straight-forward, Simple manner. 45 done via Xylene-Selective alkylation; the Second treatment of
Another object of the present invention is to provide a the hybrid System of this invention. An acidic catalyst is
proceSS for yielding para-Xylene in Very high purity by used to Selectively alkylate just the ethylbenzene, meta
selective alkylation with extremely high selectivity and little Xylene and ortho-Xylene while leaving para-Xylene alone
or no reverse reactions and Side reactions. unalkylated. Since the alkylated para-Xylene isomers boil at
In carrying out these and other objects of the invention, 50 Substantially higher temperatures compared to unalkylated
there is provided, in one form, a reactive purification para-Xylene, a simple post-alkylation fractionation or a post
employing Selective alkylation for producing at least 99.5 alkylation carbon adsorption provides efficient removal of
wt.% para-Xylene from a mixture of isomers of para-Xylene the heavies and produce 99.5+ wt.% para-xylene. Moreover,
having more than about 90 wt. % para-xylene and the the inventive process does not have appreciable side
mixture being produced by a process exclusive of a Selective 55 reactions, reverse reactions, or alkylation of para-Xylene
alkylation process. The purification process involves (a) which decreases yield or conversion to high purity para
alkylating Substantially all of the isomers of para-Xylene in Xylene.
the mixture of Xylene isomers with an alkylating agent, The purification via alkylation process of this invention
while alkylating Substantially none of the para-Xylene; and can be accomplished with either an acidic heterogeneous
(b) separating the para-xylene in at least 99.5 wt.% purity 60 catalyst, Such as proton-exchanged Zeolites or an acidic
and at least greater than the concentration of para-Xylene in homogeneous catalyst Such as aluminum chloride at a tem
the mixture of Xylene isomers, from the alkylated Xylene perature ranging from about 1 to 300° C. preferably between
isomers to give the final product Stream. about 1 to about 100 C., most preferably between about 10
The present invention is distinct from U.S. Pat. No. to about 50° C. and a pressure from Sub-atmospheric to 1000
5,055,630, described earlier, in that the former purifies via 65 psig, in one embodiment. In one embodiment, the LHSV
alkylation whereas the latter uses crystallization. Although it ranges from about 0.1 to about 100, and preferably ranges
is possible in some prior processes to achieve 99.9 wt.% from about 0.1 to about 10.
 US 6,489,527 B1
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The Selective alkylation may, in one embodiment, be done prevents destruction of the major product while Selectively
in the presence of an acidic catalyst. Preferably, Steps are removing only the contaminants. This is unusual as all
taken So that there is good molecular contact between the previous Selective alkylation processes are not this Selective,
catalyst and the Xylene isomers which are not para-Xylene. but rather only Selectively alkylates the non-para-Xylene
Without being bound by any one theory, it is hypothesized isomers to a much lower eXtent than in this process. The
that the Success of the present invention is due at least in part System of this invention avoids (1) isomerization of the
to excellent molecular contact between the catalyst and the desired para-Xylene and (2) alkylation of the para-xylene
non-para-Xylene isomers. This contact may involve a par (even in the presence of high concentrations thereof), and (3)
ticular high Surface area catalyst, extensive mixing or both. polymerization of the alkylating agent, e.g. dimerization of
Extensive mixing includes, but is not limited to mixing by the isobutylene. Only by avoiding these other reactions are
preSSure drop, mixing orifices, Static mixers, distribution the extraordinarily high Selectivities achieved using the
heads and high Speed mixing mechanisms. By “high Surface inventive process which Sets it apart from conventional
area' is meant a catalyst having a Surface area in excess of processes which can only achieve a lower Selectivity ratio.
about 100 m/g and in one embodiment in excess of about Another advantage of the present invention is that the
200 m/g, and preferably one with a Surface area in excess 15 t-butyl-meta-xylene and -ortho-Xylene adducts which may
of about 300 m/g. A most preferred high surface area have a lower value will not have a significant effect on the
catalyst has a surface area in excess of about 450 m/g. process economics due to the low levels produced. Thus,
Additionally, the catalyst should be one which does not although Some Small amount of lower value byproducts are
polymerize the alkylating agent. For example, the catalysts produced, the proceSS remains economically attractive. The
should not be one which substantially dimerizes isobutylene, purification method of this invention may be expanded So
if this is the alkylation agent. that the purified para-Xylene may be further purified using an
In one embodiment, the catalyst is a high Surface area additional Selective alkylation Step to achieve ultrapure
heterogeneous catalyst, and more preferably may be a high para-Xylene.
Surface area catalyst including, but not necessarily limited That is, after the production of para-Xylene by more than
to, proton-exchanged Zeolites, bentonite clay, acid-treated 25
clay, acidic alumina, Solid acids, proton-exchanged resins, of 90 wt.% purity by any of the conventional methods, the
and the like. The most preferable catalysts are proton purification process of this invention could be applied to the
eXchanged Zeolites. In another embodiment of the invention, mixture of Xylene isomers two or more times in Series to
homogeneous acidic catalysts Suitable for this invention achieve Small increments of yet higher purity.
include, but are not limited to, aluminum chloride, alkyl The invention will be illustrated more completely by the
aluminum chlorides, hydrofluoric acid, Sulfuric acid and the following Examples, which are not intended to limit the
like. invention, but are simply instructive thereto.
The Selective alkylation step of the present invention may EXAMPLE 1.
be conducted at a temperature in the range of from about 10
to about 300° C., preferably from about 10 to about 150° C. 35 The para-xylene product from Exxon Chemical PAREX(R)
and most preferably from about 10 to 50° C. Reaction Adsorption Units (PAU) was used to evaluate the invention.
temperatures greater than about 300° C. are not desired as The PAU para-xylene contained 99.70 wt.% para-xylene,
the tendency for isomerization increases with increasing 0.15 wt.% meta-xylene, 0.10 wt.% ethylbenzene and 0.05
temperature (the para-xylene isomerizes to ortho-xylene, wt.% ortho-xylene. The alkylation catalyst in this test was
meta-xylene and/or ethylbenzene), as does the undesired 40 a proton-exchanged Y Zeolite in the form of extrudate
alkylation of para-Xylene. The alkylation reaction may be (LZY-82, obtained from UOP Inc.). The catalyst was cal
conducted in the liquid phase or the vapor phase and thus cined at 300° C. under nitrogen prior to testing. The alky
may be conducted from Sub-atmospheric to about 1000 psig, lation reactor was a 0.5" I.D. and 3.0" long stainless steel
preferably from Sub-atmospheric to about 500 psig, and tubing packed with 2.91 g calcined catalyst. A feed Solution
most preferably from Subatmospheric to about 300 psig. 45 containing 99.70 wt.% PAU-para-xylene and 0.30 wt.%
Further, the best alkylating agents were found to contain at isobutylene was pumped through the reactor at 1 liquid
least one tertiary butyl moiety. In one embodiment, the hourly space velocity (LHSV), ambient temperature and 200
alkylating agent is Selected from the group consisting of pSig. Gas chromatograph analysis revealed that the alkyla
isobutylene, tertiary butyl chloride, tertiary butylbenzene, tion product contained 0.08 wt.% C compounds, 0.01 wt.
di-tertiary butyl hydroxyl toluene, isobutylene oligomers 50 % ethylbenzene, 0.05 wt.% meta-xylene, 99.36 wt.%
and the like. The amount of alkylating agent is dependent on para-xylene and 0.50 wt.% butylated xylenes and other
other parameters, for example, it is necessary to have heavy compounds. Ortho-Xylene was completely butylated.
enough alkylating agent to react with all of the impurities. After distillation to remove the C-materials and the heavies,
Thus, the amount of alkylating agent should be an effective a para-Xylene product containing 0.01 wt.% ethylbenzene,
amount to So alkylate the impurities desired to be removed. 55 0.05 wt.% meta-xylene and 99.94 wt.% para-xylene can be
A large excess of alkylating agent Should be avoided. obtained.
Under the conditions of this invention, the loSS of para EXAMPLE 2
Xylene to alkylation is only in the range of Several tenths of
one percent. That is, the Selectivity of alkylation of non This Example was conducted similarly to Example 1. The
para-Xylene isomers to para-Xylene is a Surprising 300:1 to 60 catalyst was an extrudate of 80 wt.% proton-exchanged
3000:1 ratio. Even a relatively high ratio of 30:1 would be ultra stable Y zeolite (VALFOR CP304-37, obtained from
unacceptable inasmuch as too much of the para-Xylene The PQ Corp.) and 20 wt.% bentonite clay (obtained from
would be lost, as has been established in the prior art. In Aldrich Co.). The catalyst was ground to 18/30 mesh and
prior processes, the Selectivity was always less than 100:1; calcined at 300° C. prior to loading in the 0.5"x3.0" reactor.
the Selectivities achievable with this proceSS are Surprisingly 65 A feed solution composed of 99.50 wt.% PAU-para-xylene
higher. The selectivity achieved with this invention is unex and 0.50 wt. % di-tertiary butyl hydroxyl toluene was
pected and extraordinary. The process of this invention pumped through the reactor at 0.5 LHSV, ambient tempera
 US 6,489,527 B1
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ture and 200 psig. The alkylation product contained 0.01 wt. ortho-Xylene. Thus, it is demonstrated that the process of this
% C compounds, 0.01 wt.% ethylbenzene, 0.09 wt.% invention may be Successfully performed using a homoge
meta-xylene, 99.00 wt.% para-xylene, 0.89 wt.% alkylated neous catalyst.
Xylenes and heavies. There was no Ortho-Xylene detected. EXAMPLE 5
After distillation, a para-Xylene product containing 0.01 wt.
% ethylbenzene, 0.09 wt.% meta-xylene and 99.90 wt.% This Example demonstrates the use of a mordenite Zeolite
para-Xylene was obtained, as analyzed by gas chromato catalyst for purifying para-Xylene. A mixture of 0.5% isobu
graph. tylene and 99.5% PAU para-xylene product (99.70% para
xylene, 0.15% meta-xylene, 0.10% ethylbenzene, 0.05%
COMPARATIVE EXAMPLE 3 ortho-xylene) was prepared. 3.02 Grams of the mixture was
brought into contact with 1.09 g. of a mordenite extrudate
This Example demonstrates the fact that a simple exten obtained from UOP Inc. in a sealed bottle at ambient
Sion of a previously known Xylenes-alkylation technique is temperature and pressure for 2 hours. According to GC
not suitable for the present purpose of producing 99.9+ wt. analysis, the Xylenes product contained 99.76% para-Xylene,
% purity para-Xylene. The Example includes the following 0.15% meta-xylene, 0.07% ethylbenzene, 0.03% ortho
two experiments. 15 Xylene. It is thus demonstrated that another catalyst may be
(A) Experiment A demonstrates the feasibility of using a used in the process of this invention.
conventional alkylation technique for the bulk Separation of Many modifications may be made in the process of the
Xylene mixtures. A mixture of 50.00% para-xylene and present invention without departing from their Spirit and
50.00% ortho-xylene was prepared. 3.09 Grams of the Scope, which are defined only in the appended claims. For
example, one skilled in the art may find that a certain
mixture was then thoroughly mixed with 3.02 g of tertiary combination of alkylating agent and catalyst may give
butyl chloride in a sealed vial. After the mixing, about 0.10 particularly advantageous results. Or one of ordinary skill in
g. of aluminum chloride catalyst was added to the Solution. the art may determine that certain embodiments of the
The System was allowed to react at ambient conditions for present inventive process if used in Series may give a
30 minutes. A Sample of the hydrocarbon phase was taken 25 para-Xylene product of extraordinary purity.
and analyzed using gas chromatography. It was found that We claim:
the xylenes fraction of the reaction product contained 97.50 1. A reactive purification process for producing at least
wt.% para-xylene and 2.50 wt.% ortho-xylene indicating a 99.5 wt.% para-xylene from a mixture of isomers of xylene
good Separation from the original 50.00% para-Xylene and which contains more than about 90 wt.% para-xylene and
50.00% ortho-xylene. which has been produced by a process eXclusive of a
(B) Experiment B demonstrates the failure of using a Selective alkylation process consisting essentially of the
conventional alkylation technique for producing para-Xylene Steps of
in very high purity. 39.91 Grams of a high purity para-xylene (a) alkylating Substantially all of the isomers of xylene
stream (99.70% para-xylene, 0.18% meta-xylene, 0.07% other than para-Xylene in the mixture of Xylene
ethylbenzene and 0.05% ortho-xylene) was mixed with 0.11 35 isomers, wherein the mixture of Xylene isomers con
g. tertiary butyl chloride. 5.00 Grams of the mixture was tains between about 90 and 99.8 wt.% para-xylene,
then brought into contact with 0.46 g. of aluminum chloride with an alkylating agent, while alkylating Substantially
catalyst. The mixture was then allowed to react at ambient none of the para-Xylene, and
conditions for 30 minutes. A Sample of hydrocarbon phase (b) separating the para-xylene in at least 99.5 wt.% purity
was analyzed using gas chromatography. The Xylenes frac 40 and at least greater than the concentration of para
tion of the reaction product contained 99.53% para-xylene, Xylene in the mixture of Xylene isomers, from the
0.32% meta-xylene, 0.09% ortho-xylene and 0.06% ethyl alkylated Xylene isomers to give the final product
benzene. It is apparent that the alkylation was accompanied Stream.
by a Small amount of Side reactions Such as para-Xylene 2. The process of claim 1 where in Step (a) the alkylating
isomerization; note the increase in meta-xylene and ortho 45 is conducted in the presence of an acidic catalyst.
Xylene fractions. As a result, the product had more isomers 3. The process of claim 2 where the catalyst is a high
and para-Xylene purity decreased. Such low levels of Side Surface area heterogeneous catalyst having at least 100 m/g.
reactions would not even be detected in bulk Separations. 4. The process of claim 2 where the catalyst is a homo
But they would be detrimental for purifying high purity geneous catalyst.
products and, as shown, overall para-Xylene purity would 50 5. The process of claim 3 where in step (a) the alkylating
decrease. is conducted in the presence of an acidic heterogeneous
EXAMPLE 4 catalyst Selected from the group consisting of proton
eXchanged Zeolites, bentonite clay, acid-treated clay, acidic
This Example illustrates the use of a homogeneous cata alumina, proton-exchanged resins and mixtures thereof.
lyst for purifying para-xylene. 20.00 Grams of a PAU 55 6. The process of claim 1 where in step (a) the alkylating
para-xylene product (99.69% para-xylene, 0.18% meta is conducted at a temperature in the range of about 1 to about
xylene, 0.07% ethylbenzene, 0.06% ortho-xylene) was thor 300° C.
oughly mixed with 10.16 g.98% sulfuric acid in a container 7. The process of claim 1 where in Step (a) the alkylating
at ambient temperature and pressure. A mixture of isobuty agent contains at least one tertiary butyl moiety.
lene and PAU para-xylene (0.30% isobutylene and 99.70% 60 8. The process of claim 7 where the alkylating agent is
PAU para-xylene product stream) was placed in a buret and Selected from the group consisting of isobutylene, tertiary
added drop-wise to the XyleneS/Sulfuric acid mixture over a butyl chloride, tertiary butyl benzene, di-tertiary butyl
45 minute period. A high Speed magnetic Stirrer was used to hydroxyl toluene, isobutylene oligomers and mixtures
provide Sufficient mixing. The hydrocarbon phase was thereof.
sampled and analyzed by GC at the end of the reaction. It 65 9. The purification process of claim 1 where the mixture
was found that the xylenes product contained 99.75% para of xylene isomers has between 95 and 99.9 wt.% para
Xylene, 0.16% meta-xylene, 0.06% ethylbenzene and 0.03% Xylene.
 US 6,489,527 B1
9 10
10. The purification process of claim 1 where the mixture 24. The purification process of claim 12 where the mix
of xylene isomers has between 98 and 99.9 wt.% para ture of xylene isomers has between 98 and 99.9 wt.%
Xylene. para-Xylene.
11. The purification process of claim 1 where alkylating 25. The purification process of claim 12 where alkylating
Step (a) and separating Step (b) are each repeated in Sequence Step (a) and separating Step (b) are each repeated in Sequence
at least once. at least once.
12. A reactive purification process for producing at least 26. A purification process for producing at least 99.5 wt.
99.5 wt.% para-xylene from a mixture of isomers of xylene % para-Xylene from a mixture of isomers of Xylene having
which contains more than about 90 wt.% para-xylene and between 90 and 99.8 wt.% para-xylene and which has been
which has been produced by a proceSS eXclusive of a produced by a proceSS eXclusive of a Selective alkylation
Selective alkylation process consisting essentially of the process consisting essentially of the Steps of:
Steps of:
(a) alkylating Substantially all of the isomers of xylene (a) alkylating Substantially all of the isomers of xylene
other than para-Xylene in the mixture of Xylene other than para-Xylene in the mixture of Xylene
isomers, wherein the mixture of Xylene isomers con 15 isomers, wherein the mixture of Xylene isomers con
tains between about 90 and 99.8 wt.% para-xylene, tains between about 90 and 99.8 wt.% para-xylene,
with an alkylating agent having at least one tertiary with an alkylating agent having at least one tertiary
butyl moiety in the presence of an acidic catalyst and butyl moiety at a temperature in the range of about 1 to
with molecular contact between the catalyst and the about 300° C. in the presence of an acidic, heteroge
Xylene isomers, while alkylating Substantially none of neous catalyst with a high Surface area of at least 200
the para-Xylene, and m/g and with molecular contact between the catalyst
(b) separating the para-xylene in at least 99.5 wt.% purity and the Xylene isomers, while alkylating Substantially
and at least greater than the concentration of para none of the para-Xylene, and
Xylene in the mixture of Xylene isomers, from the 25
(b) separating the para-xylene in at least 99.5 wt.% purity
alkylated Xylene isomers to give the final product and at least greater than the concentration of para
Stream. Xylene in the mixture of Xylene isomers, from the
13. The process of claim 12 where the catalyst is a high alkylated Xylene isomers to give the final product
Surface area heterogeneous catalyst having at least 100 m/g. Stream.
14. The process of claim 12 where the catalyst is a 27. The process of claim 26 where in step (a) the alky
homogeneous catalyst. lating is conducted in the presence of an acidic heteroge
15. The process of claim 12 where in step (a) the alky neous catalyst Selected from the group consisting of proton
lating is conducted in the presence of an acidic heteroge eXchanged Zeolites, bentonite clay, acid-treated clay, acidic
neous catalyst Selected from the group consisting of proton alumina, proton-exchanged resins and mixtures thereof.
eXchanged Zeolites, bentonite clay, acid-treated clay, acidic 35
28. The process of claim 26 where in step (a) the alky
alumina, proton-exchanged resins and mixtures thereof. lating is conducted at a temperature in the range of about 1
16. The process of claim 12 where in step (a) the alky to about 100° C.
lating is conducted at a temperature in the range of about 1 29. The process of claim 27 where the alkylating agent is
to about 300° C. Selected from the group consisting of isobutylene, tertiary
17. The process of claim 12 where the alkylating agent is 40
butyl chloride, tertiary butyl benzene, di-tertiary butyl
Selected from the group consisting of isobutylene, tertiary hydroxyl toluene, isobutylene oligomers and mixture
butyl chloride, tertiary butyl benzene, di-tertiary butyl thereof.
hydroxyl toluene, isobutylene oligomers and mixtures 30. The process of claim 26 in which the para-xylene
thereof. produced at least 99.9 wt.% purity.
18. The process of claim 12 where the alkylating agent is 45
31. The process of claim 26 in which the alkylating is
isobutylene and the catalyst is one which does not Substan conducted from sub-atmospheric to about 1000 psig.
tially dimerize the isobutylene. 32. The process of claim 26 in which the alkylating is
19. The process of claim 12 in which the para-xylene conducted at a liquid hourly space velocity (LHSV) between
produced at least 99.9 wt.% purity. about 0.1 and about 100.
20. The process of claim 12 in which the alkylating is 50
33. The purification process of claim 26 where the mix
conducted from Sub-atmospheric to about 1000 psig. ture of xylene isomers has between 95 and 99.9 wt.%
21. The process of claim 12 in which the alkylating is para-Xylene.
conducted at a liquid hourly space velocity (LHSV) between 34. The purification process of claim 26 where the mix
about 0.1 and about 100. ture of xylene isomers has between 98 and 99.9 wt.%
22. The purification process of claims 12 where the 55
para-Xylene.
mixture of xylene isomers contains between about 90 and 35. The purification process of claim 26 where alkylating
about 99.9 wt.% par-xylene. Step (a) and separating Step (b) are each repeated in Sequence
23. The purification process of claim 12 where the mix at least once.
ture of xylene isomers has between 95 and 99.9 wt.%
para-Xylene.