It is known to those skilled in the art that ethers, including both symmetrical and unsymmetrical ethers, may be prepared by reacting an alcohol with another alcohol to form the desired product. The reaction mixture, containing catalyst and/or condensing agent may be separated and further treated to permit attainment of the desired product. Such further treatment commonly includes one or more distillation operations.
Hydrogenation catalysts are known and are generally selected from Group VIII of the Periodic Table. Suitable metals include, but are not limited to, platinum, palladium, tin, nickel and copper alone, or in combination.
In U.S. Pat. No. 3,955,939 to Sommer et al. (1976), there is disclosed the production of a water-free mixture of isopropyl alcohol, diisopropyl alcohol, diisopropyl ether and by-products by the catalytic hydration of propylene in the gaseous phase at temperatures of 140.degree.-170.degree. C., wherein the water-free mixture formed according to the process can be used directly as an additive to gasoline fuel.
Conversion of acetone to MIBK is addressed in U.S. Pat. No. 3,953,517. The catalyst is a noble metal. In U.S. Pat. No. 5,059,724 a method is disclosed for the selective production of methyl isobutyl ketone.
In U.S. Pat. No. 5,017,729 there is disclosed a multistage process for producing phenol, wherein acetone is hydrogenated in the fourth step.
Phosphate catalysts are known in the art. Among such materials are aluminum phosphates, both stoichiometric A1PO.sub.4 and non-stoichiometric Al(PO.sub.4).sub.x where x is less than 1. For instance, U.S. Pat. No. 3,904,550 describes the preparation of such materials and their use as desulfurization catalysts. U.S. Pat. No. 3,801,704 teaches that aluminum phosphates can be used for catalytic dehydration. U.S. Pat. No. 4,524,225 demonstrates that such phosphates also function as hydrogenation catalysts. Other cited uses of aluminum phosphates include cracking (U.S. Pat. No. 4,382,878), ether rearrangement (U.S. Pat. No. 4,538,008), and polyolefin synthesis (U.S. Pat. Nos. 4,364,839; 4,547,479; 4,424,139; 4,397,765; 4,596,862; 4,504,638; and 4,364,864). In all of these cases stoichiometric or non-stoichiometric aluminum phosphates are taught and methods for making them described.
U.S. 5,189,182 discloses a method of preparation of 5-methyl butyrolactone over a zeolite and/or one of several phosphate catalysts, including silica aluminum phosphate (SAPO).
The use of catalysts of the formula M(PO.sub.4).sub.y X' wherein M is a transition metal, X' is an anionic species and y is from about 0.1 to about 0.9 is disclosed in U.S. Pat. No. 4,910,329 as useful in the preparation of hydroxyalkyl esters of acrylic and methacrylic acid.
In U.S. Pat. No. 5,001,102, there is also disclosed the use of iron phosphate catalysts in the production of unsaturated hydroxyalkyl esters.
In U.S. Pat. No 5,144,061 it is disclosed that, in addition to certain zeolites, aluminum phosphates can be used as catalysts for preparing alkene carboxylic acid esters.
Silicoaluminophosphates are also known in the art. Early attempts to prepare them occurred during research efforts to isomorphously replace a portion of the SiO.sub.2 tetrahedra of zeolitic aluminosilicates with PO.sub.2 tetrahedra during the synthesis process. Barrer et al. (J. Chem. Soc. 1965, pp. 6616-6628).
No evidence of isomorphous substitution of phosphorus for silicon was found, although in U.S. Pat. 3,443,892 there is disclosed the preparation of a faujasite-type zeolite containing P205.RTM.Substantial success in preparing zeolite analogues containing phosphorus was reported by Flanigen and Grose, Molecular Sieve Zeolites-I, ACS, Washington, D.C. (1971), using synthesis technique utilizing gel crystallization involving controlled copolymerization and coprecipitation of all the framework component oxides.
In U.S. Pat. No. 4,440,871 there is disclosed a novel class of silicon-substituted aluminophosphates which are both crystalline and microporous and exhibit properties which are characteristic of both the aluminosilicate zeolites and aluminophosphates which have a three-dimensional microporous crystal framework structure of PO.sub.2.sup.+, AlO.sub.2.sup.- and SiO.sub.2 tetrahedral units.
In U.S. Pat. No. 4,528,414 there is disclosed a process for the oligomerization of linear and/or branched chain C.sub.2 to C.sub.12 olefins with non-zeolitic molecular sieves of the description just mentioned above in U.S. Pat. No. 4,440,871.
Non-zeolitic molecular sieves, identified by the acronyms SAPO, TAPO, MeAPO and FAPO are described and explained in U.S. Pat. No. 4,440,871 (SAPOs), incorporated herein by reference and in U.S. Pat. Nos. 4,500,651 (TAPOs), 4,567,029 (MeAPOs) and 4,554,143 (FAPOs).
In European Patent 323138 and U.S. Pat. No. 4,906,787, there is disclosed a catalytic process for converting light olefins to ethers suitable as high octane blending stocks carried out by contacting the olefin, especially propene, with water and alcohol recovered from a downstream distillation operation in an olefin conversion unit in the presence of an acidic zeolite catalyst. In this work diisopropyl ether (DIPE) was prepared from C.sub.3 H.sub.6 and aqueous iso-PrOH in the presence of silica-bound zeolite Beta catalyst at 166.degree..
In another European Patent, EP 323268, light olefins are converted to alcohols and/or ethers in the presence of .beta.-zeolite.
In U.S. Pat. No. 5,144,086, to Harandi et al., there is disclosed an integrated multistage process for the production of diisopropyl ether and substantially pure propene wherein in the second stage isopropanol containing about 0%-20% water is contacted with an acidic large pore zeolite etherification catalyst which comprises a .beta.-zeolite having a Si:Al ratio of about 30:1 to 50:1.
In U.S. Pat. No. 5,208,387, also to Harandi et al., there is disclosed a process for the acid catalyzed production of DIPE from propene and water feed stream that eliminates the propene recycle stream to the olefin hydration reactor and achieves high propene conversion. This process is carried out in two stages wherein the first stage comprises a zeolite catalyzed hydration and etherification of propene employing a minimum of water feed and the second stage converts unconverted propene from the first stage reactor by hydration and etherification to DIPE.
In an article titled "Race to License New MTBE and TAME Routes Heats Up", Rotman, D., Chemical Week, Jan. 6, 1993, p. 48, there is a review of new technology at several different companies which centers around skeletal isomerization, particularly of C.sub.4 and C.sub.5 olefins. The interest in this technology is fueled by the promise of dramatically increased and relatively inexpensive isobutylene and isoamylene that could boost MTBE and TAME production, often constrained by the amounts of available isobutylene in refinery or steam cracker streams. DIPE production from propylene is also discussed.
Mobil Corp. has disclosed new etherification technology that can produce fuel oxygenates based only on olefinic refinery streams and water. This process has the potential to allow refiners to produce oxygenates without having to rely on an external supply of alcohols. The technology is developed around diisopropyl ether (DIPE) based on propylene. The DIPE has similar physical and blending activities to MTBE and TAME and is a perfectly acceptable fuel oxygen source. Wood, A., Chemical Week, Apr. 15, 1992, p. 7.
None of the available references would suggest the combination of a bifunctional catalyst comprising one or more metals from Group IB, VIB or VIII on one of several classes of phosphate catalysts for the one-step conversion of low value crude acetone in a by-product stream into useful oxygenate products. The portion of said by-product stream which typically comprises acetone is about 20% to 80%. It would greatly enhance the economics of any process to produce MTBE or other oxygenates if acetone from a by-product stream could be converted in one step to useful oxygenate products which could be fractionated to isolate diisopropyl ether (DIPE) and isopropyl tertiary butyl ether (IPTBE).