US3903196A - Isomerization - Google Patents

Abstract

The deactivation rate for a supported HF-antimony pentafluoride catalyst, used in a process for isomerizing C5, C6, or C7 normal paraffin at low temperature, is sharply reduced by including sufficient isobutane in the feed so that the feed isobutane content is more than 25 weight per cent.

Description

United States Patent Related US. Application Data Kem 14 1 Se t. 2, 1975 ISOMERIZATION 2,392,284 1/1946 Gage 260/683.68 2,425,268 8/1947 Sensel 260/683.68 [75] Invemo lamb Kemp El Cemto, 3,201,494 8/1965 Oelderik et al.. 260/683.68 [73] Assignee: Chevron Research Company, Sa 3,394,202 7/1968 Oeldenk 260/683.68

Francisco, Calif. 22 Filed; D 7 1973 Primary Examiner-Delbert E. Gantz Assistant ExaminerG. J. Crasanakis [21] APP! N05 422,621 Attorney, Agent, or Firm-G. F. Magdeburger; R. H.

Davies I Continuation-impart of Ser. No. 268,296, July 3,

1972, abandoned. 57] ABSTRACT [52] US. Cl 260/683.68; 260/683.5l The deaQtivation rate for a supported HF-antimony [51] Int. Cl. C07c 5/28 m fl rid tal t, used in a process for isomeriz- [58] Field of Search..... 260/683.68, 683.65, 683.48, ing C C or C normal paraffin at low temperature, -5 is sharply reduced by including sufficient isobutane in the feed so that the feed isobutane content is more [56] References Cited than 25 weight per cent.

UNITED STATES PATENTS 6 C 2 Dr F 2,331,429 /1943 Sensel et al 260/683.68 aw'ng gums (I U IL u .2 0.0001 Z 9 '2 Z u M 0 1 1 1 1 Q o 40 so so '70 ISOBUTANE IN HEXANE OR n-HEXANE/n-BUTANE FEED PATENTEUSEP '21915 SHEET 10E 2 l l l I J 7 2O 4O 6O 80 100 "70 ISOBUTANE IN HEXANE OR n-HExANE/n-BLJTANE FEED FIG.1

PATENTEDSEP 2197s O O O O O O O O O O O O O O O O O 60 so 7, ISOBUTANE IN n-HEXANE FEED FIG.2

ISOMERIZATION CROSS REFERENCE TO RELATED' APPLICATIONS This application is a continuation-in-part of US. pa tent application Ser. No. 268,296, filed July 3, I972 now abandoned.

BACKGROUN D OF THE INVENTION TABLE I Hydrocarbon Research octane Motor octane Clear 3 cc TEL Clear 3 cc TEL n-Pentanc 62 89 62 84 iPcntane 92 I09 90 I05 n-Hcxane 25 65 16 65 2-Methylpentane 73 93 74 9 I 3-Methylpentane 75 93 74 91 2,2-Dimethylbutane 92 I06 93 I 13 (neohexane) 2.3-Dimcthylbutane I03 I I9 94 I 12 (diisopropyl) lsomerization processes can be divided into high, low, and ultra low temperature processes. Rough temperature ranges are: 500800F. for high temperature isomerization; l50-400F. for low temperature isomerization; and 50F. to I50F. for ultra low temperature isomerization. In the past, commercial operation for low temperature isomerization typically has utilized a catalyst containing AlCl In typical high temperature isomerization, a pentanehexane feed, combined with a normal pentane recycle stream, is fractionated to take i-pentane overhead. The fractionator bottoms are mixed with hydrogen, preheated, and charged to a reactor. Reactor effluent is cooled and flashed to separate recycle hydrogen from the product, which is stabilized and then depentanized, the pentanes being recycled to the deisopentanizer. i-Pentane overheads from the deisopentanizer and the i-hexane bottoms from the depentanizer constitute the product.

Typical reaction conditions are:

For typical low temperature isomerization the catalyst used is AlCl plus hydrogen chloride. Low temperature isomerization feed stock, dried and preheated to reaction temperature, is combined with a recycle stream (if recycling is practiced), mixed with hydrogen chloride, and passed through a reactor and an aluminum chloride recovery section. Reactor effluent is cooled and flashed to discharge any light gases through a small absorber that recovers hydrogen chloride carried off in the gases. Liquid from the flash drum is stripped to recover hydrogen chloride, and is causticwashed to remove the last traces of acid. The stripping column is usually operated at a pressure high enough that the stripped hydrogen chloride can be returned directly to the reactor. If recycling of unconverted nor mal paraffin is practiced, the recycle stream is then fractionated from the product.

Typical reaction conditions are:

HCL conc., wt /r 5 Conversion 60 Ultra low temperature isomerization so far has not been commercially employed. However, there is considerable incentive to develop a commercially attractive low temperature isomerization process because the lower the temperature the more favorable is the equilibrium for isoparaffln relative to normal paraffins. Ultra low temperatures are especially attractive for substantial production of the very high octane dimethyl butanes.

US. Pat. No. 2,956,095 describes an ultra low temperature isomerization process employing a fluosulfonic acid catalyst instead of a Friedel-Crafts type catalyst such as AICI According to the US. Pat. No. 2,956,095, process reaction conditions include a temperature between 32 and F, pressure between 0 and 50 psig, and added hydrogen of 0200cubic feet per barrel of feed. The process of the US. Pat. No. 2,956,095 also employs a compound capable of form ing a stable carbonium ion as part of the catalyst system. Preferably tertiary butyl alcohol is used as the favored compound to form a stable carbonium ion; the tertiary butyl alcohol is said in the patent to be a carbonium ion activator.

Since the reaction mechanism for isomerization is thought to involve carbonium ions it is of course desirable to have a species that will form carbonium ions to start isomerization reaction chains. lsomerization reaction mechanisms are discussed in chapter 28 by Pines and Hoffman in FriedeLCrafts and Related Reactions, Vol. 2, Edited by G. A. Olah, Interscience Publishers 1964); see especially p. 1223.

US. Pat. No. 2,956,095 is not directed to the use of any species such as isobutane for improving the catalyst life of a strong acid catalyst used in ultra low temperature isomerization.

US. Pat. No. 3,20l .494 and US. Pat. No. 3,394,202 are also directed to ultra low temperature isomerization and are especially pertinent to the present inven tion.

US. Pat. No. 3,201,494 is directed to liquid phase isomerization of hydrocarbons using a hexafluoro-antimonic acid catalyst in hydrofluoric acid, which catalyst 3 is obtained, according to example 1 of the patent, by dissolving antimony pentafluoride in hydrofluoric acid.

U.S. Pat. No. 3,394,202 is also directed to isomerization also using an antimony fluoride-hydrochloric acid catalyst but in the U.S. Pat. No. 3,394,202 the catalyst is supported on a base such as fluorided alumina. According to U.S. Pat. No. 3,394,202,

fparaffin isomerization [with the supported antimony fluoride catalyst] is effected at about 1 to 60C., preferably to 50C. In C -C isomerization, the reaction rate may be increased appreciably by the addition of 525% w., isobutane, which does not participate in the reaction. Examples of other conversions which may be carried out with the present catalysts are described in copending application Ser. No. 284,806 [now U.S. Pat. No. 3,20 l ,494], as discussed.

Gradual deactivation of the catalyst, which may occur because of presence of impurities in the feed or because of small amounts of polymerization products, may be suppressed by effecting the reaction in the presence of 13% in. hydrogen, based on the hydrocarbon feed. This hydrogen may be fed to the reactor as a gas, or may be partially or completely dissolved in the hydrocarbon feed.

Example 7 of U.S. Pat. No. 3,201,494 shows the acceleration of n-pentane isomerization by adding isobutane. As can be seen from Table III of the patent, no acceleration was obtained for isobutane contents above 9.2 wt. in the feed. The highest isobutane content of any of the feeds isomerized in U.S. Pat. No. 3,201,494 was 22.8 wt. isobutane for the feed in example VIII.

The feedstocks of the examples in U.S. Pat. No. 3,394,202 were n-pentane plus methylcyclopentane containing no isobutanes.

U.S. Pat. No. 3,394,202 discloses, as can be seen from the portion quoted above, without any exemplary data, that 5-25 wt. isobutane may be used to increase the C,-,C isomerization reaction rate. There is no enabling disclosure in either U.S. Pat. No. 3,394,202 or U.S. Pat. No. 3,201,494 that isobutane of any concentration is helpful to improve the stability of the antimony-pentafiuoride catalyst system, nor is there any disclosure of improved stability of the catalyst system for isobutane contents above 25 wt.

SUMMARY According to the present invention, in a process for isomerizing a C C or C normal paraffin feed, which comprises contacting the feed with a catalyst comprising hydrofluoric acid-antimony pentafluoride supported on a porous solid support, and wherein the contacting is carried out at a low temperature between 1 0 and 400F., the improvement is made which comprises reducing the deactivation rate of the catalyst by including sufficient isobutane in the feed so that the feed isobutane content is more than 25 wt The paraffin feed which can be isomerized according to the process of the present invention includes at least one C C or C normal paraffin and may contain other isomerizable paraffins such as cycloparaffins (sometimes referred to as naphthenes). The feedstocks to the process of the present invention will contain at least one normal paraffin, i.e., a C,-, through C normal paraffin and may contain cycloparaffins as well as mixtures of C -C normal paraffins. In the case of both normal paraffins and cycloparaffins, preferably only C,-, to C paraffins are included in the feed. The most preferred 4 feedstocks to the process of the present invention are a C, and/or C normal paraffin feed.

The catalyst used in the process of the present invention is HF-antimony pentafluoride. This catalyst is used in solid phase as HF-antimony pentafluoride on a porous solid support, most preferably fluorided alumina.

The temperature used in the process of the present invention is below 400F., preferably below 150F., and more preferably below 120F.

The present invention is based largely on my discovery that isobutane dramatically reduces the deactivation rate of the strong acid catalyst, especially the hydrofluoric acid-antimony pentafuoride catalyst, used in the subject isomerization process. In my initial work on this system, using an l-IF-SbF catalyst, I found a deactivation rate for the catalyst of about 0.02 (with the deactivation rate defined as the decrease of the logarithm of the fractional concentration of product isomer per hour). In an effort to reduce this deactivation rate, which is a high deactivation rate, I tried saturating the feed to the isomerization catalyst system with hydrogen. Using the hydrogen, 1 obtained a seven-fold reduction in catalyst deactivation rate. However, even this reduced deactivation rate was still a considerable rate so that the process had little commercial attraction. Subsequently, I tried using added hydrogen fluoride in addition to the saturation hydrogen, but instead of improving the deactivation rate, the deactivation rate for the isomerization of a normal pentane feedstock actually became higher, that is, worse. In still further exper iments I found that methylcyclopentane, which of course contains a tertiary carbon atom, increased the deactivation rate when it was present in a normal pentane feedstock to the subject isomerization process.

After the above, I tried a normal pentane feedstock which contained isobutane in an amount of about 25 wt. and I surprisingly found a substantially lower deactivation rate than when feeding normal pentane without the isobutane in the normal pentane. I also noticed that lowering the feed benzene content considerably lowered the deactivation rate. However, taking out benzene is not sufficient to achieve a very low deactivation rate. I

I then made a more dramatic unexpected finding in view of the prior art, which was that if the isobutane content in the feedstock was above at least about 25 wt. e.g., 40 wt. isobutane, then the catalyst deactivation rate was almost nil for a purified paraffinic feed to the subject isomerization process. Furthermore, even for a feed that was not highly purified, e.g., a feed which contained benzene, isobutane at substantial levels such as above about 25 wt. would dramatically reduce the deactivation rate of the antimony-pentafluoride catalyst system used in the present invention.

In the process of the present invention preferred amounts of isobutane in the paraffinic feedstock are 40 weight per cent and above, and 50 wt. and above is particularly preferred. Particularly preferred temperature for the isomerization reaction in the present invention has been found to be in the range of about 30 to 80F., more preferably 4070F., as I have found that temperature above about F, and especially above F can contribute to increased deactivation rate for the isomerization catalyst used in the present invention.

In the preferred isomerization process of the present invention, 1 have found that normal butane is isomerized to only avery slight extent (approximately nil) at the preferred isomerization temperatures which are larly above about 25 wt. 70, is especially effective in reducing the deactivation rate was further confirmed by experiments in which substantially all conditions were held constant, except that the ratio of isobutane to normal butane in the hexane feedstock was varied. Thus,

when the isobutane content was decreased the normal IO butane content was increased so that the total butane content of the feedstock remained constant. I found in these experiments that isobutane was especially effective in reducing the deactivation rate of the catalyst 6 solid supports are coated with a thin layer of inert fluoride.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings are graphs showing the sharp decrease in deactivation rate of the isomerization catlyst used in the presentinvention when the isobutane content of the feed is increased to levels above about 25 wt.

DETAILED DESCRIPTION OF THE DRAWINGS The ordinate of FIG. 1 shows the deactivation rate as the change in the log of the fractional concentration of the isomer products per unit time (per hour). The graph is based on isomerization of a normal pentane compared to the effectiveness of normal butane. feedstock and the isomer products include 2-2- The hydrofluoric acid-antimony pentafluori'de catadimethyl butane, 2-3-dimethyl butane, Z-methyl penlyst used in the present invention is supported on a potane, and 3-methyl pentane. The abscissa in the drawrous solid inert support. By porous solid support is ing is the weight per cent isobutane in the normal hexmeant an inert support material having a porous strucane feedstock to the isomerization reaction zone. ture and a surface area typically in the range of 1 to The HF-antimony pentafluoride catalyst used to genabout 300 m lgram or even higher. Preferably, the surcrate the data upon which FIG. 1 had a fluorided aluface area will be in the range of about 1 to 100 mina porous solid support. The catalyst was prepared m lgram. The porous solid support of the invention typby treating fluorided alumina with HF--SbF The ically has pore diameters ranging from 10 to I000 A. HF-SbF, was prepared by adding anhydrous HP to The porous solid support of the subject invention is liquid antimony pentafluoride. preferably selected from the inorganic oxide group consisting of alumina, zirconia, silica, silica-alumina, The unmysisonhe camlystwas; magnesia, chromia, boria, and mixtures and combina- T rented alumina base trons thereof. Other porous solid supports may also be source Camp, ammim, used such as natural and synthetic crystalline WLr/l of i y l .l. t rt h 6 rt X Y m rde Wtf/r Fluorine 62.0 a ummasi lea e 260'] es, sue as o 1 o n surface arm 2/g 10 ite, erionite, etc., as well as other natural materials such Liza/rid Acgd added 3 t.7r 0 catalyst 9... as bauxite, kres elguhr, kaolin, bentomte, dlatomaceous WW! SbFs 718 earth and the like. ww. HF 26.2

Particularly preferred porous solid supports are made from alumino or are alumina containing, e.g., fluorided alumina. l have found that fluoriding the alumina to a Table 2 summarizes the data upon which FIG. 1 is substantial extent so as to obtain 60 wt. fluorine or based. As can be seen from the table, the very low demore in the fluorided support results in an improved activation rate for 60% isobutane in the normal hexane support for the HF-antimony pentafluoride compared 40 feed was checked after the isobutane content of the to an alumina support which has only been mildy fluofeed had been lowered to 29.3% and was also checked rided such as one which has been fluorided only on the after the isobutane had been lowered to 1 l.4%. Thus most exterior surfaces of the alumina. the data point in FIG. 1 at 60% isobutane in the feed Other porous solid supports such as polytetrafluorohas been checked severalfold to confirm the surprisethylene, carbon, e.g., charcoal, polytrichlorofluoroingly low deactivation rate at 60% isobutane in the ethylene, and the like may also be used. Charcoal used feed. as the porous solid support may have a surface area as FIG. 1 shows that the deactivation rate for the catahigh as I200 m /gram. Basically, the support should be lyst used in the normal hexane isomerization run was substantially inert to HF--SbF,-, and insoluble in the 180 times worse, i.e., 180 times higher, for a normal mixture under isomerization reaction conditions. While hexane feed containing 1 1.4% isobutane compared to a the porous solid support may initially be reactive to normal hexane feed containing isobutane.

TABLE 2 Hours on Fouling Conv. Level, stream at Rate. Alog wt. 71 in feed wt. 71 n hexane Hours on which F.R. conv. per nC nC, lC, Temp. LHSV converted stream measured hour 39.8 60.2 F 1.4 0-790 623-790 .0001 1 39.6 31 29.3 80F 1.4 75 790-834 794 .0007i 40 60 80F 1.4 73 834-960 834960 .00011 39 49 1 1.4 80F 1.4 52 960-978 960-978 .02 40.8 59.2 80F 1.4 42 978-1005 978l( 40 60 80F 0.7 66 1005-1 1005-1 125 .00010 *1 reactivation period HF--SbF the supports may be rendered inert by expo sure to non-aqueous solutions of antimony pentafluoride and HF. Upon removal of the liquid, the porous In another isomerization run the effect of using 2- methyl pentane was studied. Z-methyl pentane, of course, contains a tertiary carbon atom just as isobutane contains a tertiary carbon atom. However, I found that when isomerizing normal hexane using about 60.

-wt. 2-methy1 pentane in the feed. there was a rapid decline in activity of the catalyst, that is,a rapid deactivation rate. The reaction conditions were substantially the same as in the case of feeding 60% isobutane-40% normal hexane as per Table 2 above, but in the case of the normal hexane feed containing 60% 2-methy1 .pentane the deactivation rate was at least 100 times greater than the deactivation rate when using the same amount of isobutane. v

The ordinate of FIG. 2 shows the deactivation rate as the change in the log of the fractional concentration of the isomer products per unit time (per hour). The graph is based upon the isome rization of a normal hexane feedstock and the isomer products include 22- dimethyl butane, 2-3dimethyl butane, 2-methyl pentane, and 3-methyl pentanc. The abscissa inthe drawing is the weight per cent isobutane in the normal hexane feedstock to the isomerization reaction zone.

, 8 Reaction conditions are summarized in the table. The table also shows at the bottom how the conversion of the normal hexane to isohexane products descreased as the run time progressed. As can be seen from the data at the bottom of the table and from the graph of this data, the deactivation rate of the catalyst dropped dramatically with increased isobutane content in the feed, especially for isobutane contents above about 25 wt.

What is claimed is:' i 1. In a process for isomerizing a paraffin feed comprising a C,-,, C or C normal paraffin by contacting the feed with a catalyst comprising hydrofluoric acidantimony pentafluoride supported on a porous solid support substantially inert to said hydrofluoric acidantimony pentafluoride and wherein the contacting is carried out at a low temperature between -10" and 120F., the improvement which comprises reducing the deactivation rate of the catalyst byj' ineluding' sufficient isobutane in the feed so that the feed isobutane content Table 3 below summarizes the data upon which FIG. is more than wt.

2 is based. 2. A process in accordance with claim 1 wherein the TABLE 3 o lSOMERlZATlON OF n-HEXANE WITH HF-SbF ON FLUORlDED ALUMINA EFFECT OF ISOBUTANE RUN No: 125140 125-141 125-142 Reaction Conditions:

Temperature, F 50 50 LHSV 0.42 0.58 0.83 Pressure. psig 300 300 300 Feed saturated with H No No No Run duration. hours 0-160 43.5-207 0308 Feed Analysis, wt. 7! Feed Feed Feed Cl C a iC 23.4 40.6 61.15 nC. c

nC 22 DMB 23 DMB 3 MP nC 76.2 59.1 38.65

MCP CHX 0 4 0.3 0 2 C BZ Start End Start End Start End 1 of of of of of of Activity Level: Run Run Run Run Run Run 7: isoC in C parafi'ms 87 49 67 64 44 43.9 & DMB in C paraffins 51 19 29.6 27 17.5 17.5

A log C Small. Deactivation rate. 0.0017 0.00013 not measurable m -C, Component contained 150 PPM Benzene isobutane content in the feed is more than 40 wt. %1.

3. A process in accordance with claim 1 wherein the porous solid support is fluorided alumina-containing at "least 60 wt. fluorine. 4. A process in accordance with claim 1 wherein th contacting is carried out at a temperature between about 30F. and F.

5. A process in accordance with claim 4 wherein said paraffin feed comprises a -C or C normal paraffin.

6. A process in accordance with claim 1 wherein said paraffin feed comprises a C,-, or C normal paraffin.

Claims (6)

1. IN A PROCESS FOR ISOMERIZING A PARAFFIN FEED COMPRISING A C5, C6, OR C7 NORMAL PARAFFIN BY CONTACTING THE FEED WITH A CATALYST COMPRISING HYDROFLUORIC ACID-ANTIMONY PENTAFLUORIDE SUPPORTED ON A POROUS SOLID SUPPORT SUBSTATIALLY INERT TO SAID HYDROFLUORIC ACID-ANTIMONY PENTAFLUORIDE AND WHEREIN THE CONTACTING IS CARRIED OUT AT A LOW TEMPERATURE BETWEEN -10* AND 120*F., THE IMPROVEMENT WHICH COMPRISES REDUCING THE DEACTIVATION RATE OF THE CATALYST BY INCLUDING SUFFICIENT ISOBUTANE IN THE FEED SO THAT THE FEED ISOBUTANE CONTENT IS MORE THAN 25 WT. %.

2. A process in accordance with claim 1 wherein the isobutane content in the feed is more than 40 wt. %.

3. A process in accordance with claim 1 wherein the porous solid support is fluorided alumina containing at least 60 wt. % fluorine.

4. A process in accordance with claim 1 wherein the contacting is carried out at a temperature between about 30*F. and 80*F.

5. A process in accordance with claim 4 wherein said paraffin feed comprises a C5 or C6 normal paraffin.

6. A process in accordance with claim 1 wherein said paraffin feed comprises a C5 or C6 normal paraffin.

Images