REMOVAL OF IMPURITIES FROM HYDROCARBONS AND ALCOHOLS

Abstract: As method is described for the removal of cationic and ammoniacal impurities from alcohols and aliphatic hydrocar­ bons by contact with an acid cation exchange resin which is not capable of promoting acid-catalyzed reactions in the mat­ erial being treated.

Description: REMOVAL OF IMPURITIES FROM HYDROCARBONS AND ALCOHOLS FIELD OF THE INVENTION This invention relates generally to a method for the removal of impurities from hydrocarbons and alcohols, and more particularly to a method for the removal of cat ionic and ammoniacal impurities using specific acid cation exchange resins. BACKGROUND OF THE INVENTION An extremely large number of chemical reactions utilize alcohols and hydrocarbons as starting materials. In many of these reactions the purity of the starting materials is critical to the production of acceptable products. The presence of cationic impurities or basic impurities, such as ammonia, has been particularly troublesome. Traditionally, the removal of cationic and basic impurities from hydrocarbons has been accomplished by acid and water washing or by treatment with strong acid ion exchange resins. Purification of alcohols has also been carried out with strong acid ion exchange resins. However, these treatments have drawbacks, particularly in those instances where the hydrocarbon or alcohol is susceptible to acid-catalyzed reactions. Many relatively pure hydrocarbons will react when exposed to strong acid, for example olefins will react to form dimers, trimers and higher polymers. Alcohols will dehydrate to water, and olefins or ethers. Such sensitivity to acid-catalyzed reactions is especially important in instances such as the etherification or alcoholification of olefins, where the starting materials may be combined prior to their reaction in the presence of a catalyst. A method for treatment of the starting materials to remove catalyst-poisoning impurities, which does not itself cause detrimental reactions in the starting materials, would bed highly desirable. SUMMARY OF THE INVENTION It has been discovered that cationic and ammoniacal impurities can be efficiently removed from alcohol and C4-C6 liquid hydrocarbon feed streams, either singly or combined, by contact with acid cation exchange resins in the hydrogen form. The cation exchange resins are selected on the basis of their inability to promote acid-catalyzed reactions in the alcohol and hydrocarbon feed. DETAILED DESCRIPTION OF THE INVENTION Although the invention will be described with specific reference to the removal of cationic and ammoniacal impurities from olefins and alcohols used in the production of ethers, it should be understood that this invention pertains to the removal of such impurities from other liquid hydrocarbons and hydrocarbon mixtures. In the production of ethers it is necessary to remove such impurities because they are catalyst poisons. However, the removal of impurities for any reason, while avoiding acid-catalyzed reaction of the materials being treated, is within the scope of the invention. The reaction of isobutylene and methanol to form methyl tertiary-butyl ether (MTBE), a gasoline additive, is particularly well-suited to describe the invention. Other olefins such as isopentane and isohexane can also be used with alcohol reactants to form a variety of ethers. Water can be substituted for the alcohol reactant and will form an alcohol product upon reaction with the olefin. Tertiary-butyl alcohol, also a gasoline additive, is a common application of the addition of water to an olefin. A typical process for the preparation of MTBE uses an isobutylene (isobutene) containing hydrocarbon and methanol as the starting materials. Pure isobutylene may of course be used, but hydrocarbon mixtures con,taining 10 to 50 percent isobutylene are also useful. Such mixtures may contain, in addition to isobutylene, n-butane, isobutane, butene-l and butene-2. For example, the C4 fractions which are obtained by thermal cracking, steam cracking and catalytic cracking can be conveniently used. Commercially available methanol is satisfactory for use in the process. The reactants are introduced in separate or combined streams into a suitable reactor, typically of the fixed bed shell and tube type, or a fluidized bed. Methanol is typically fed in stoichiometric excess. In passing through the catalyst bed of strongly acid cation exchange resin, the isobutylene and methanol are heated by the strongly exothermic reaction. The C4 hydrocarbons other than isobutylene pass through the catalyst bed unreacted. The product MTBE and unreacted methanol and C4 hydrocarbons are separated downstream of the reactor by distillation. Examples of strong acid ion exchange resins used as the catalyst bed for MTBE synthesis include LewatitX SPC 118, Amberlys 15, Do MSC-1, DuoliteX C-26H and Duolite ES-276. Clearly, if cationic impurities are present in the feed stream to the catalyst, they will bind to the acid sites of the catalyst and render them inactive. Further, ammonia in the feed will form the ammonium ion in the acidic environment and behave similarly. While strong acid ion exchange resins in the hydrogen form may be used to purify methanol prior to its introduction into the reactor, such resins cannot be used to clean the C4 stream as isobutylene is extremely susceptible to dimerization and polymerization under these conditions. The isobutylene polymer thus formed is not available as a reactant, and further acts as a catalyst poison by presumably accumulating in the pores of the catalyst in the reactor. Strong acid ion exchange resins not in the hydrogen form (e.g. sodium form) gre not suitable for C4 stream purification since the sodium ions eluted would also poison the reactor catalyst. While acid and water washes are an acceptable method of cleaning the C4 feed stream to an MTBE reactor, this procedure cannot be used for purifying the methanol feed stream due to its miscibility with water. Further, it is not feasible to combine the two feed streams and purify them simultaneously using a strong acid ion exchange resin. Under these conditions the formation of MTBE will be catalyzed by the ion exchange resin. Using existing technology two cleaning techniques are required to remove impurities from the feed to an MTBE reactor, one for the isobutylene-containing C4 stream and one for the methanol stream. Typical impurities found in the C4 stream include basic compounds such as ammonia and amines. Commercial methanol also generally contains traces of ammoniacal compounds as well as cationic impurities, usually metal cations such as Cu, Fe, Ni and Cr. It has unexpectedly been found that such reactants can be combined and the impurities efficiently and economically removed by contacting the reactants with a weak acid cation exchange resin which does not promote acid-catalyzed reactions in the combined feed. Such resins can be generally characterized by their ability to be converted or regenerated to the hydrogen form by contact with a nearly stoichiometric quantity of acid. This characteristic contrasts with that of the strong acid cation exchange resins, which require a large excess (usually 4 to 5 times) of strong acid in high concentration to achieve complete conversion of the resin to hydrogen form. Acid cation exchange resins having the required properties usually have phosphonic, sulfonic or carboxylic functional groups, and can be in gel form (sulfonic functional groups) or in macroporous form. The invention is more fully described in the following specific examples. EXAMPLE 1 A mixture of C4 aliphatic hydrocarbon containing 45 percent isobutylene, 35 percent isobutane and 20 percent l-butene was obtained and 2.6 pounds were weighed into a one gallon, stirred, isothermal autoclave. The C4 mixture was spiked with 40 ppm ammonia. A measured volume of liquid C4 was removed and expanded to a gas in a sealed vial with a known quantity of 0.01N sulfuric acid, then shaken. The ammonia content of the C4 thus reacted with the acid to form ammonium sulfate, and the resulting solution was analyzed by ion exchange chromatography to determine the initial ammonium ion concentration. About 10 g of dried gel sulfonic acid cation exchange resin in the hydrogen form (Duolite C-225 x 10) was injected into the autoclave containing the spiked liquid C4 mixture, under a nitrogen blanket. After one hour of stirring at 500C a sample was removed, acidified and analyzed as described above. The analysis indicated that the ammonia had been completely removed from the C4 mixture. The experiment was repeated using a macroporous phosphonic acid cation exchange resin in the hydrogen form (Duolite ES-467) and a macroporous carboxylic acid cation exchange resin in the hydrogen form (Duolite C-464). Both resins completely removed ammonia from the C4 mixture. EXAMPLE 2 The three cation exchange resins described in Example 1 were evaluated for their ability to remove copper ions from methanol. Methanol was spiked with 300 ppm Cu+2 derived from cupric sulfate. The methanol was then passed through a 26 ml vertical column filled with the cation exchange resins at a rate of 30 bed volumes per hour at room temperature. Cupric ion concentration in the effluent was monitored by a visible spectrophotometer. All of the resins effectively removed copper from the methanol, with initial breakthrough from the column as follows: phosphonic acid resin - 10 bed volumes; carboxylic acid resin - 3 bed volumes; sulfonic acid resin - 150 bed volumes. EXAMPLE 3 The resins described in Example 1 were evaluated for their catalytic effect on the formation of isobutylene dimers. About 2.6 pounds of the C4 mixture of Example 1 was weighed into the one gallon autoclave reactor. The reactor temperature was raised to 700C and at time zero the dry equivalent of 120 ml of wet resin was injected into the reactor. Samples were taken periodically and analyzed by gas chromatography for isobutylene dimer. In order to compare the catalytic effect of the resins, the data of percent conversion versus time was fitted to a rate law and the remitting rate constants were compared. A first order rate law of the following form was assumed: r = kCIB = kCo(1-X) where r is the rate of consumption of isobutylene in g moles/l of resin per hour. CIB is the concentration of isobutylene, CO is the initial isobutylene concentration, X is the fraction of isobutylene reacted and k is the rate constant with units of hour The rate constants for isobutylene dimer formation at 700C are shown in Table I. TABLE I Rate Resin (hydrogen form) Constant Sulfonic acid cation exchange (Duolite C-225 x 10) 0.01 Phosphonic acid cation exchange (Duolite ES-467) 0.00 Carboxylic acid cation exchange (Duolite C-464) 0.00 None of the resin had a significant catalytic effect on the formation of isobutylene dimer. The trace amounts of dimer produced by the sulfonic acid resin were not significant due to the extremely small quantity formed. EXAMPLE 4 Typical feed streams of olefin and methanol for the preparation of MTBE were combined and treated by the process of the invention to demonstrate that the treatment does not catalyze the MTBE reaction. A one gallon autoclave reactor was charged with 460 ml of methanol and 2.6 pounds of the C4 mixture described in Example 1. At time zero the dry equivalent of 120 ml of wet resin expanded in water was injected into the reactor with nitrogen. Samples were taken periodically and analyzed by gas chromatography for isobutylene content. The percent isobutylene conversion was plotted against time, and the data was fitted to a rate law of the following form: r kforwardClB - reverse MTBE = kC0(1-X-KX) where K is an equilibrium constant equal to 0.0526 at 700C. Table II lists the rate constant for the MTBE reaction in the presence of cation exchange resins useful in the invention, and also in the presence of a strong acid macroporous cation exchange resin known to be a good catalyst for MTBE formation. TABLE II Rate Resin (hydrogen form) Constant Sulfonic acid cation exchange (Duolite C-225) 0.2 Phosphonic acid cation exchange (Duolite ES-467) 0.0 Carboxylic acid cation exchange (Duolite C-464) 0.0 Sulfonated strong acid cation exchange (Duolite ES-276) 3.1 The quantity of MTBE produced by contact with resins useful in the process of the invention is not significant. Impurities can be removed using these resins on a combined feed stream without generating sufficient MTBE to require additional heat removal equipment for the exothermic reaction.

Claims: CLAIMS: 1. A method for the removal of cationic and ammoniacal impurities from a feed stream comprising alcohols and C4-C6 liquid hydrocarbons by contacting the feed stream with an acid cation exchange resin in the hydrogen form, characterized in that the resin employed is not capable of significantly promoting acid-catalyzed reactions of the feed stream. 2. A method according to claim 1, wherein the feed stream contains olefins. 3. A method according to claim l or 2, wherein the feed stream contains methanol. 4. A method according to claim 3, wherein the feed stream is methanol and isobutylene. 5. A method according to claim 4 wherein the acid-catalyzed reaction is the formation of methyl tertiary-butyl ether. 6. A method according to any of claims 1 to 3, wherein the acid-catalyzed reaction is the formation of C4-C6 hydrocarbon dimers. 7. A method according to any preceding claim, wherein the cationic impurities are metal ions. 8. A method according to any preceding claim, wherein the resin-can be converted to the hydrogen form by contact with about a stoichiometric quantity of acid. 9. A method according to any preceding claim, wherein the resin contains functional groups selected from sulphonic acid, phosphonic acid and carboxylic acid groups and mixtures thereof. 10. A method for the productior ov methyl tertiarybutyl ether by the reaction of isobutylene and methanol in the presence of an ion exchange catalyst, characterized in that isobutylene and methanol feed streams are combined and the combined stream is contacted, prior to undergoing the reaction, with an acid cation exchange resin in the hydrogen form which is not capable of significantly promoting acid-catalyzed reactions in the feed stream

Inventors: GILLIGAN III, THOMAS J., ROTHSCHILD, WALTER G.
Applicants: ROHM AND HAAS FRANCE, S.A.
Application year: 1984
Main classification: C07C29
IPC codes: C07C29, C07C27, C07C7, C07C11, C07C41, C07C31, C07C67, C07C1