BACKGROUND OF THE INVENTION During the last two decades the federal government, in response to increasing concerns raised about secondary exposure to certain compounds previously used to enhance the octane rating of motor fuels, has severely limited the amounts of lead, and more recently, certain aromatic hydrocarbons that refiners may include in such fuels. As a result of these regulations, refiners have turned to oxygenated components to maintain the octane rating of fuels produced for motor vehicles. The compounds most extensively used are ethers, particularly methyl tert- butyl ether (MTBE) and methyl tert-amyl ether (TAME).

The most commonly used process for producing such ethers involves contacting methanol with isobutylene and/or isoamylenes in the presence of a sulfonic acid polystyrene resin catalyst; that is, polystyrene resin in which a sulfonic acid group (HSO3) has been substituted for one, on average, of the hydrogens on the benzene ring. This catalyst deactivates during extended exposure to hydrocarbons and methanol by a) dissociation of some of the sulfonic acid groups from the benzene rings and b) displacement of the hydrogen ions in the sulfonic acid groups by cations such as sodium. Although the former type of deactivation (i. e., loss of HS03 groups) is permanent, the latter type can be reversed by treatment with inorganic acid.

In most ether applications the amount of permanent catalyst deactivation during a period of operation is small relative to the amount of reversible deactivation. That is, the number of resin sites containing sulfonic acid groups from which the hydrogen ion has been displaced by a cation is far greater than the number of such sites from which the HS03 group has been lost.

If the cations on all or most of the former sites could be replaced with hydrogen ions, the catalyst would be returned to an activity level close enough to that of fresh catalyst to justify its re-use.

Nonetheless, although the potential for regeneration has been known for some time, common practice in ether production has been to replace the used catalyst when it has been deactivated through normal use to a point where continued operation becomes uneconomical. The used

catalyst has usually been discarded because, prior to the present invention, the percentage of cations that can be replaced, through treatment with acid, with hydrogen ions has not been high enough to return the catalyst to an activity level where its re-use would be cost-effective. In addition to creating disposal problems, this practice of disposing of used catalyst increases the expense of ether production due to the need regularly to purchase new catalyst to replace that which has been discarded.

The same sulfonic acid resin catalysts presently used in ether production are also extensively used for water treatment wherein contaminants in water are removed by ion exchange. In contrast with catalyst used in ether production, when used in water treatment service these same catalysts are routinely regenerated in situ by treatment with inorganic acid.

Sulfonic acid resin catalysts have been studied for decades, and some of that study has been directed to regeneration of resin catalysts previously used in ether production. U. S. Patent <BR> <BR> N° 2,813,908 (Young) teaches the use of such resin to catalyze ether production from C2-C4 olefins. At the time of Young's work (i. e., the mid-1950's), the resin was commercially available in the form of sodium salts. Young teaches that such salt can be readily converted to the acid type by washing with an aqueous solution of sulfuric or hydrochloric acid"in a manner well known by itself'and that this washing replaces the sodium ions with hydrogen ions. Young also teaches washing the acidified resin with distilled water to remove free sulfate ions from the "regenerated"acidic resin. However,'908 teaches nothing about the activity of regenerated catalyst previously used in ether production; reusing such catalyst was not a concern at that time.

Other researchers have taught the use of sulfonic acid resin catalysts for the production <BR> <BR> of ethers and tertiary alcohols. For example, U. S. Patent Nu 4,423,251 (Pujado et al.) teaches a process for producing tertiary butyl alcohol and/or MTBE using such catalyst, but is silent on <BR> <BR> regeneration of the catalyst. U. S. Patent Ng 4,540,831 (Briggs) teaches a process for ether production, but is also silent on catalyst regeneration.

Still other researchers have taught regeneration of sulfonic acid resin catalyst by treatment with strong inorganic acid, but none of these have taught regeneration of such catalyst previously used in the production of ether. Examples of such patents include U. S. Patent Nul'4,423,251 <BR> <BR> (Harper et al.) which teaches regeneration of sulfonic acid resin catalyst with strong inorganic acid when such catalyst has been previously used in a process for separating cobalt and <BR> <BR> manganese from trimellitic acid process residue; U. S. Patent N ! 2 5,124,290 (Erpenbach et al.)

which teaches regeneration of such catalyst used in a process for removing metallic corrosion products from carbonylation reactions; U. S. Patents NQ 5,094,995,5,233,102 and 5,315,033 (Butt et al.) which teaches regeneration of such catalyst previously used in a process to oligomerize or hydrate olefins and hydrolize esters; and finally, U. S. Patent N-5,672,782 (Hattori et al.) which teaches regeneration of such catalyst previously used in a process to produce tertiary alcohol.

It is clear that, despite the extensive work done in related fields, no researcher has addressed the unique problems presented by regeneration of sulfonic acid resin catalyst used in the production of ethers. A cost-effective process is clearly needed.

SUMMARY OF THE INVENTION This invention provides a method for regeneration of sulfonic acid polystyrene resin catalyst that has been deactivated through use in a process for making ethers such as MTBE, TAME, higher ethers and mixtures of same. The key element of this invention is the removal of substantially all of the ether remaining on such catalyst prior to treating with inorganic acid and rinsing with demineralized water, the latter two steps being previously known to those skilled in the art. Removal of residual ether prior to treatment with acid reduces the amount of acid needed to effect replacement of cations with hydrogen ions and, more importantly, increases the percentage of cations so replaced to a level which makes re-use of the catalyst economically attractive. Although regeneration of sulfonic acid polystyrene resin catalyst used in ether production by this invention is not effective in reversing whatever permanent deactivation that has occurred, at least 98 %, and sometimes as much as 100 %, of the sites that have been temporarily deactivated by cation substitution is reversed by the present process.

DETAILED DESCRIPTION OF THE INVENTION The process of the present invention for regenerating sulfonic acid polystyrene catalyst previously used in producing ethers comprises removing substantially all ether remaining on such catalyst, treating with inorganic acid to replace metal ions on the S03 groups with hydrogen ions and then washing with demineralized water. The process may be carried out on the used catalyst either after removing the catalyst from the process vessel in which it resides during the etherification process or without removing the catalyst from the vessel (i. e., in situ).

The reason that residual ether remaining on the used catalyst to be regenerated interferes with replacement of cations with hydrogen ions is not well understood. While it is known that the acid proton will react with ether as well as with cations on the catalytic sites, a simple increase in the amount of acid employed, to compensate for the amount of ether remaining on the catalyst, will not bring about equivalent regenerated catalyst.

Removing Residual Ether from Used Catalyst The removal of substantially all (i. e., to below about 5000 vppb) of the ether remaining on catalyst that is to be regenerated is a key step in the method of the present invention. Any of several methods may be used including washing the used catalyst with water, purging the used catalyst with hot nitrogen, applying a vacuum to the catalyst and purging the used catalyst with steam (steaming). Steaming the used catalyst is the preferred method because the ether residue can be reduced to under 5000 vppb in the shortest amount of time, usually in under 20 hours.

When steaming the used catalyst, it is important to maintain the steam temperature between about 120°C. and about 150°C. because exposure of the catalyst to temperatures above about 150°C. will lead to its thermal deactivation and reduce its potential for regeneration. The amount of steam used should be set so that the time required for removal of substantially all of the residual ether is between about 16 and 20 hours.

Treating Catalyst with Acid After removal of residual ether from the used catalyst, the catalyst should be treated with an inorganic acid. Any inorganic acid capable of effecting replacement of cations on the catalyst's 803'groups with hydrogens ions may be used, with aqueous solutions of hydrochloric acid or formic acid being preferred, and aqueous solutions containing between about 5 % and about 6 % hydrochloric acid being particularly preferred. If the preferred 5-6% HCl solution is used, the amount of solution used should be between about 160 kg/m3 (10 lbs./cu. ft.) and about 190 kg/m3 (12 lbs./cu. ft.) of used catalyst, applied to the used catalyst over a period of about 2 hours. If another inorganic acid or solution strength is used, the amount of such should be consistent with application of an equivalent amount of H+ ions to the used catalyst over the 2 hour period. The aqueous acid solution should be above about 25 °C. when applied to the used catalyst.

Washing with Water Following treatment with inorganic acid, the used catalyst is washed with water to remove substantially all of the acid remaining thereon. Water used in this step should be free of cations, and demineralized water is preferred. Water should be applied to the used catalyst at a rate sufficient to apply a minimum of about 3,000 kg of water/m3 (27 gal./cu. ft.) of regenerated catalyst over a period of at least 20 minutes.

Effectiveness of the Method A number of tests of the effectiveness of the regeneration method of the present invention were conducted on actual batches of catalyst previously used commercially in ether production.

The results of regeneration, using this method, of two loads of catalyst previously used for production of MTBE are presented in Table 1 and Table 2. These results are representative of those achieved with a number of other tests of the present method on loads of catalyst previously used by others for ether production.

Each load of used catalyst was divided into batches sized to be contained in the vessels available for regeneration. In both tables below, analyses of a sample of the regenerated catalyst from each batch are presented. In the tables,"DWC"means Dry Weight Capacity which is a measure of the number resin sites having a sulfonic acid group per unit of catalyst;"WVC" means Wet Volume Capacity which is a direct measure of the number of catalytic protons available in the catalyst;"WRC"means Water Retention Capacity, a measure of the amount of water physically associated with the catalyst beads, and an indirect measure of the number of resin sites having an S03 group per unit of catalyst; and H+ Conversion is a measure of the efficiency of regeneration, that is, the percentage of SO3-sites available for replacement of cations with H+ ions that were so replaced, calculated by comparing the DWC of the regenerated catalyst against the DWC of another sample of the same catalyst that had been determined to be free of cations.

It is obvious from the tables that when the catalyst has previously been used in the production of ether, regeneration by the present method restores almost all of the catalytic activity previously lost through replacement of H+ ions with cations. This was the result with all tests on loads of catalyst that had been used for ether production.

TABLE 1 Catalyst Used by Arco Products for MTBE Production Batch Number DWC, meq/gm WVC, meq/gm WRC, % H+ Convers., % 1 4.82 1.73 52.7 100 2 4.89 1.76 53.3 100 3 4.7 1.72 53.4 100 4 4.7 1.7 52.9 100 5 4.62 1.7 53 97.5 6 4.7 1.7 52.9 97 7 4.7 1.7 52.6 97 Average 4.73 1.72 53 98.8 New Catalyst 4.7 1.7 53 TABLE 2 Catalyst used by Phillips Petroleum for MTBE Production Batch Number DWC, meq/gm WVC, meq/gm WRC, % H+ Convers., % 1 4.5 1.61 50.6 99.4 2 4.52 1.64 51.7 98.8 3 4.5 1.61 50.9 98.2 4 4.52 1.62 51.4 98.5 5 4.65 1.66 50.8 99.5 Average 4.54 1.63 51.1 98.8 New Catalyst 4.7 1.7 50-54

The following examples describe laboratory tests that were conducted to compare the process of the present invention with a process in which residual ether was not removed prior to treatment with acid. The catalyst used in all examples was Rohm & Haas A-35 that had been used by Phillips Petroleum in its Sweeny, Texas MTBE process unit until catalyst activity had declined to a level where it was economically necessary to either replace or regenerate it.

Laboratory analysis determined that the catalyst had a wet volume capacity, WVC, of about 1.87 meq/gm and a water retention capacity, WRC, of about 51 %, indicating that the catalyst had not suffered so much permanent deactivation through loss of S03 groups that it was no longer suitable for regeneration.

In all four of these tests the amount of acid per volume of catalyst was almost four times the amount of acid that would be required in a commercial application. This was done to demonstrate that it is not possible to compensate for failure to remove ether from the catalyst by using more acid. That is, the use of an amount of acid far in excess of that which would be required to react with all of the cations on the used catalyst plus all of the remaining ether does not result in equivalent regenerated catalyst dry weight capacity. This demonstrates that residual ether interferes in some way with effective regeneration other than simply by consumption of acid.

EXAMPLE 1 (Comparative) In this example, a sample (designated"A"in Table 3 below) of catalyst previously used in the Phillips Sweeny unit was treated with an aqueous solution containing 5 % hydrochloric acid in the amount of 718 kilograms of solution per m3 (44.87 lbs./cu. ft.) of catalyst and then rinsed with sufficient demineralized water to remove un-reacted acid. The condition of the regenerated catalyst sample is shown in Table 3.

EXAMPLE 2 In this example, three samples (designated"B","C", and"D"in Table 3 below) of catalyst previously used in the Phillips Sweeny unit (the same catalyst as used in Example 1) were treated to remove residual ether remaining prior to being treated with acid and rinsed with water as in Example 1. Sample B was washed with 10 volumes of demineralized water per

volume of sample, then treated with 703 kilograms of 5 % acid solution per m3 (43.92 lbs./cu. ft.) of catalyst and then rinsed with demineralized water; sample C was subjected to a vacuum distillation at 93°C for 12 hours, treated with 718 kilograms of 5 % acid solution per m3 (44.87 lbs./cu. ft.) of catalyst and then rinsed with demineralized water; and sample D was washed with sufficient water to insure that no measurable ether remained on the catalyst (over 20 volumes of water per volume of sample), treated with 718 kilograms of 5 % acid solution per m3 (44.88 lbs./ cu. ft.) of catalyst and then rinsed with demineralized water. The condition of the regenerated catalyst samples is shown in Table 3. TABLE 3 Sample Residual MTBE, ppb* DWC, meq/gm H+ Convers., % A 10,000,000 4.78 96.7 B 3400 4.86 98.4 C 4.4 4.89 99.0 D Undetectable 4.94** 100 * Ether remaining on sample prior to treatment with acid.

** Determined to be the DWC for sample after replacement of all cations with hydrogen ions.

The difference between the regeneration efficiencies (represented by H-i+ Conversion % in Table 3) may not appear to be significant. However, this difference would result in improved profitability for a 13.25 m3/hour (2000 barrel per day) MTBE plant of about $190,000 per year, and is sufficient to induce regeneration of the used catalyst rather than replacement with new.