Production of Phenol

This invention relates to the production of phenol and more particularly to a process for the production of phenol and acetone from cumene hydroperoxide.

Our copending U.S. patent application Ser. No. 492,104, filed May 6, 1983 (concurrently with this application) describes a process for the production of phenol and acetone using a different catalyst (intermediate pore size zeolites).

Phenol is an important organic chemical with a wide variety of industrial uses. It is used, for example, in the production of phenolic resins, this one use constituting over half the total usage, bisphenol-A, caprolactam and many other materials. A number of processes are currently in use for the production of phenol but the single process providing the largest proportion of the total production capacity is the cumene process which now accounts for over three quarters of the total U.S. production. The basic reaction involved in this process is the cleavage of cumene hydroperoxide into phenol and acetone:

The reaction takes place under acid conditions with the yield of both phenol and acetone generally being 40 percent or more.

On the industrial scale, the cumene hydroperoxide is usually treated with dilute sulphuric acid (5 to 25 percent concentration) at a temperature of about 50.degree. to 70.degree. C. After the cleavage is complete, the reaction mixture is separated and the oil layer distilled to obtain the phenol and acetone together with cumene, alpha-methylstyrene, acetophenone and tars. The cumene may be recycled for conversion to the hydroperoxide and subsequent cleavage. The phenol produced in this way is suitable for use in resins although further purification is required for a pharmaceutical grade product.

Although the process described above is capable of producing both phenol and acetone in good yields, it would be desirable to find a process which would reduce the need for the product separation and purification steps which are consequent upon a homogeneous process of that kind.

The heterogenous cleavage of cumene hydroperoxide (CHP) over various acidic solids has already been reported. For example, the use of amorphous aluminosilicates for this purpose is described in J. Macromol Sci-Chem. A5(5), 995-1005, August 1971 and U.S. Pat. No. 3,305,590 describes the use of silica-alumina composites in this reaction. The use of silica-alumina gels is also described in Stud. Univ. Babes-Bolyai Ch. 16(1), 61-67(1971). Other materials whose utility as catalysts for this reaction include various zeolites such as sillimanite, as described in Zh. Prikl. Khim 54, No. 8, 1793-9 (1981) and zeolites X and Y in certain cationic forms, as reported in Z. Chem. 15 Jg. (1975) 152-153 (Heft 4). The decomposition of other peroxides over zeolites X and Y is reported in Collection Czechoslov. Chem. Commun Vol. 40, 865-874 (1975).

It has now been found that cumene hydroperoxide may be converted to phenol and acetone in good yields and with high rates of conversion and selectivity to the desired products by the use of a solid heterogenous catalyst comprising zeolite beta. The yields, conversions and selectivities are generally superior to those produced by the use of the large pore zeolites X and Y, especially with extended continuous operation. It is believed that this superior performance may be attributable to the greater resistance of this zeolite to coke precursors which otherwise would tend to deativate the catalyst and render it less selective.

The cumene hydroperoxide starting material may be obtained in the conventional way, by oxidation of cumene in an alkaline medium, in which the hydroperoxide product is stable. Cumene, normally obtained by the alkylation of benzene with propylene, is usually emulsified in an aqueous alkaline solution such as sodium carbonate, at a pH of 8.5 to 10.5 with an emulsifying agent such as sodium stearate. Oxidation with air or oxygen at mildly elevated temperatures of about 70.degree. to 130.degree. C. follows, with a final conversion of about 30 percent being common. The unreacted cumene may be separated by distillation and recycled to give the cumene hydroperoxide or it may be carried through the subsequent cleavage reaction and then recycled.

The catalyst which is used in the present process is a solid, heterogeneous catalyst which comprises a crystalline zeolite having acidic functionality.

Many crystalline aluminosilicate zeolites are known. Some occur (at least so far) only in nature, for instance paulingite and merlinoite; some occur only as a result of synthesis, for instance zeolites A and ZSM-5; and some occur in both natural and synthetic forms, for instance mordenite, a synthetic counterpart of which is known as Zeolon, and faujasite, synthetic counterparts of which are known as zeolites X and Y. Counterparts are of course demonstrated as such by correspondence of their X-ray diffraction data, the indicia by means of which the individuality of a zeolite is established. Such data are a manifestation of the particular geometry of the three-dimensional lattice, formed of SiO.sub.4 and AlO.sub.4 tetrahedra crosslinked by the sharing of oxygen atoms and including sufficient cationic complement to balance the resulting negative charge on the AlO.sub.4 tetrahedra, of which a zeolite consists.

The zeolite catalyst used in the present process enable the CHP to be cleaved to acetone and phenol at high conversions and with good selectivity, even at high space velocities. The zeolite catalysts which are used according to the present invention comprise zeolite beta.

Zeolite beta is a known zeolite and is described in U.S. Pat. Nos. 3,308,069 and Re 28,341, to which reference is made for a description of the zeolite, its preparation and properties. As described in those patents, zeolite beta may be directly synthesized in forms having silica:alumina ratios up to 100:1, generally in the range of from 30:1 to 100:1. Regardless, however, of the silica:alumina ratio, the presence of the characteristic structure (as manifested by the X-ray diffraction pattern) is the determinant of zeolite identity.

The silica:alumina ratios referred to in this specification are the structural or framework ratios, that is, the ratio for the SiO.sub.4 to the AlO.sub.4 tetrahedra which together constitute the structure of which the zeolite is composed. This ratio may vary from the silica:alumina ratio determined by various physical and chemical methods. For example, a gross chemical analysis may include aluminum which is present in the form of cations associated with the acidic sites on the zeolite, thereby giving a low silica:alumina ratio. Similarly, if the ratio is determined by thermogravimetric analysis (TGA) of ammonia desorption, a low ammonia titration may be obtained if cationic aluminum prevents exchange of the ammonium ions onto the acidic sites. These disparities are particularly troublesome when certain treatments such as dealuminization methods which result in the presence of ionic aluminum free of the zeolite structure are employed.

Because the present process is acid-catalyzed, the extent of acidic activity possessed by the catalyst will govern both the yield and the speed of the reaction. The acidity of the zeolite catalyst may be conveniently controlled in a number of different ways, for example, by base exchange, by steaming or by control of the silica:alumina ratio of the zeolite. Base exchange with alkali metals particularly sodium will tend to reduce the acidity of zeolites in the hydrogen form because the acidic protons become replaced with sodium ions. Conversely, alkali metal forms of the zeolite may be converted to the more acidic hydrogen form by ammonium base exchange followed by calcination. Either kind of exchange may, of course, be complete or partial in order to achieve the desired variation in acid acitivity. Steaming is generally effective to reduce activity by removal of the aluminum active sites, although certain zeolites respond more to this treatment than others. Control of silica/alumina ratio affects acidic activity by controlling the proportion of AlO.sub.4 tetrahedra in the zeolite which are available for protonation; high silica zeolites therefore tend to have lower acidic activity than those with lower silica:alumina ratios. For the purposes of the present process, it is preferred to use a catalyst with an acidity, measured by alpha value, from 5 to 1000, preferably 10 to 500. The significance of the alpha value and a method for its determination are described in U.S. Pat. No. 4,016,218, to which reference is made.

The zeolite may be catalytically inactive when prepared in the presence of organic cations, possibly because the intracrystallin free space is occupied by organic cations from the forming solution. The zeolite may be activated by heating in an inert atmosphere at 540.degree. C. for one hour, for example, followed by base exchange with ammonium salts followed by calcination at 540.degree. C. in air. The presence of organic cations in the forming solution may not be absolutely essential to the formation of the zeolite; however, the presence of these cations does appear to favor their formation. More generally, it is desirable to activate this type catalyst by base exchange with ammonium salts followed by calcination in air at about 540.degree. C. for from about 15 minutes to 24 hours.

It may be desirable to incorporate the zeolite in another material resistant to the temperatures and other conditions employed in the process. Such matrix materials include synthetic or naturally occurring substances as well as inorganic maerials such as clay, silica and/or metal oxides. The latter may be either naturally occurring or in the form of gelatinous precipitates or gels including mixtures of silica and metal oxides. Naturally occurring clays which can be composited with the modified zeolite include those of the montmorillonite and kaolin families. Such clays can be used in the raw state as originally mined or initially subjected to calcination, acid treatment or chemical modification.

The zeolite may also be composited with a porous matrix material, such as silica-alumina, silica-magnesia, silica-zornia, silica-thoria, silica-berylia, silica-titania as well as ternary compositions, such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia and silica-magnesia-zirconia. The matrix may be in the form of a cogel. The relative proportions of zeolite and inorganic oxide gel matrix may typically vary with the zeolite content ranging from 1 to 99, and more usually from 5 to 80 percent by weight of the composite.

The cleavage reaction may conveniently be carried out in the liquid phase at elevated temperatures, usually at a temperature from 50.degree. C., preferably 80.degree. to 120.degree. C. The reaction proceeds readily at temperatures within this range, without undue production of undesired by-products such as alpha-methylstyrene and acetophenone. However, if greater amounts of these materials can be tolerated, higher temperatures, for example, up to 200.degree. C. may be used although care should be taken to prevent temperature excursions caused by the exothermic nature of the reaction. Temperatures of approximately 100.degree. C. are preferred in order to obtain adequate reaction speed and to avoid by-product formation.

The cumene hydroperoxide is preferably dissolved in a solvent such as benzene, toluene, acetone, cumene, or another hydrocarbon which is inert to the reaction. Alternatively, and somewhat less desirably, the cumene hydroperoxide may be suspended in an inert solvent such as an aliphatic hydrocarbon or a halocarbon. The use of a solvent is particularly preferred because intimate contact with the catalyst will be assured and, in addition, evaporation of the solvent will assist in dissipating the heat of the reaction (about 60 KCal/mole). The temperature of the reaction may therefore be controlled at least to some degree by controlling the circulation rate of the reaction solution. A volatile suspension medium offers similar advantages except that close contact with the catalyst is not so readily assured.

The reaction, being a liquid phase reaction, is preferably conducted in a fixed bed or a slurry reactor. If a fixed bed is used, the exotherm can be controlled by the circulation rate over the bed, with rates of 1 to 100, preferably 10 to 50 WHSV having been found suitable. It may be preferable further to operate with a diluted catalyst, e.g. a catalyst in a non-acidic, inert matrix or supported on an inert support. Alternatively, a slurry reactor may be used, with a solution of the cumene hydroperoxide flowing vertically upwards through the catalyst bed at a sufficient velocity to maintain the bed in an ebullient state. This form of operation will be favored because the efficient thermal transfer within the bed promotes uniformity of conditions within the bed. Control of the exotherm may also be effected by permitting the solvent to evaporate from the bed, after which it may be recycled.

Extremely high conversions of the cumene hydroperoxide may be obtained by the present process, accompanied by good selectivity to the desired phenol and acetone products. In this respect, the present process is superior to that of the known processes which make significant amounts of methylstyrene, acetophenone, 2-phenyl-propan-2-ol and 4-cumyl phenol as by-products. In addition, the use of a solid, heterogeneous catalyst facilitates product recovery as there is no acid to separate from the reaction products or to dispose of afterwards.

The invention is illustrated in the following Examples. All percentages, parts and proportions are by weight.

A vertically disposed downflow reactor containing 3 ml. of the catalyst being tested was connected for the CHP feed to be supplied at the top with product removal at the bottom. Temperature control was arranged by external heating jacket with an internal temperature monitor in the bed. Product analysis was by gas chromatograph.

The feed composition is shown in Table 1 below.

The catalysts used were as follows:

Example 1: Zeolite beta (silica:alumina ratio 30:1)

Example 2: Zeolite ZK-5 (alpha value 15)

Example 3: Quartz chips ("Vycor"-trademark)

The ZK-5 zeolite (small pore zeolite used for purposes of comparison.

The results are shown in Tables 2 to 4 below in terms of the product distribution, selectivity to phenol and acetone and CHP conversion after varying times on stream. The temperatures at these times are also indicated. The superiority of the zeolite beta catalyst is apparent from the figures for conversion and selectivity.

A sample of zeolite Y in the hydrogen form (0.5 cc) was mixed with 5 cc quartz chip ("Vycor") and used for the cleavage of CHP in a heat exchanger reactor at a temperature of 100.degree. C. as different space velocities varying from 16 to 84 LHSV.

The compositions of the feed and of the products obtained at the different space velocities are shown in Table 5 below.

A sample of zeolite beta in the hydrogen form (0.5 cc) mixed with 5 cc 20/30 mesh quartz chip ("Vycor") was used for the cleavage of CHP in a heat exchanger reactor in the same CHP feed. The compositions of the feed and of the reaction products at different space velocities are shown in Table 6 below.

Compared to HY (Example 4), zeolite beta shows greater conversion and selectivity.

A sample of zeolite beta in the hydrogen form (0.5 cc) mixed with 5.5 cc 20/30 mesh quartz chip ("Vycor") was used for the cleavage of CHP in a vertical downflow reactor at a temperature of about 100.degree. C. and at different space velocities ranging from 38 to 138 LHSV.

The compositions of the feed and of the products obtained at the different space velocities are shown in Table 7 below.

These Examples illustrate the effect of using a dilute CHP feed (26.3% CHP) at different reaction temperatures. Both Examples used 0.5 cc zeolite beta mixed with 5.5 cc 20/30 mesh quartz chip ("Vycor") in a vertical downflow reactor.

The compositions of the feed and of the products obtained at the different temperatures are shown in Tables 8 and 9 below.