PRODUCTION OF ETHERS FROM LINEAR OLEFINS

Abstract: A catalytic process is provided for the manufacture of ethers by reacting a linear monoolefin with a primary or secondary alcohol having up to 4 carbon atoms. The process selectiviely forms methyl isopropyl ether from a propylene feed and methanol by contact with a zeolite such as Zeolite Beta or ZSM-5, or by contact with a macroreticular sulfonated ion-exchange resin.

Description: This invention is concerned with the manufacture of ethers from linear monoolefins. In particular it is concerned with the manufacture of ethers by the catalytic reaction of linear monoolefins with primary alcohols. It is further concerned with the manufacture of methyl isopropyl ether. U.S. 4,262,145 to Selwitz et al. discloses the catalytic reaction of a branched olefin such as isobutylene, 2-methylpentene-2, 2-methylbutene-2 and 2,3-dimethyloctene-2 with a lower alkanol such as methanol to form a mixed ether such as methyl tert-butyl ether. The catalyst disclosed is silicotungstic acid. EPA 0 055 045 discloses a prcess for the production of an ether which comprises contacting and olefin and an alcohol with a catalyst comprising a zeolite having an XO₂/Y₂O₃ ratio equal to or greater than 10, wherein X is silicon and/or germanium and Y is one or more of aluminium, iron, chromium, vanadium, molybdenum, arsenic, manganese, gallium or boron, the zeolite being predominately in the hydrogen form. There is a need for an efficient catalytic process to manufacture ethers from linear monoolefins, thereby augmenting the supply of high-octane blending stock for gasoline. The lower molecular weight ethers, such as methyl isopropyl ether, are in the gasoline boiling range and are known to have a high blending octane number. In addition, by-product propylene is usually available in a fuels refinery. The petrochemicals industry also produces linear olefin streams in the C₃ to C₁₅ molecular weight range, and the conversion of such streams or fractions thereof to ethers can provide products useful as solvents as blending stocks for fuels. This invention provides a process for producing ethers from a hydrocarbon feed and a primary alcohol, which process comprises: passing (1) a hydrocarbon feed comprising one or more linear monoolefins having from 3 to 5 carbon atoms and (2) methanol or ethanol to a reaction zone that contains an insoluble crystalline zeolite which is zeolite Beta, contacting the hydrocarbon feed and alcohol with the catalytic solid under conditions effective to form the ethers, the conditions comprising a pressure of 101 to 30400 kPa, a temperature of 50 to 300°C and a WHSV of 0.05 to 50 hr⁻¹. In a particularly preferred embodiment, methanol and propylene are reacted to selectively from methyl and isopropyl ether (MIPE). Figure 1. Batch conversion, Amberlyst 15 catalyst (comparative). Figure 2. Batch conversion, ZSM-5 catalyst (comparative). Figure 3. Continuous Reactor, Zeolite Beta catalyst. The process of this invention is based on the discovery that linear monoolefins, under the proper reaction conditions, react in the presence of an insoluble crystalline zeolite which is zeolite Beta with methanol or ethanol to selectively produce the mixed ethers. Linear monoolefins and mixtures thereof useful in the process of this invention include those having from 3 to 5 carbon atoms, and these have the structure R₁ - CH = CH - R₂ wherein: R₁ or R₂ represents a hydrogen atom or an n-alkyl group and the total number of carbon atoms in R₁ and R₂ is from 1 to 3. Particularly preferred is propylene. Although the hydrocarbon feed to the process may be substantially pure linear olefin (i.e. greater than 90 wt% of olefin), it is a feature of the invention that the reaction proceeds well in the presence of paraffin. For example, the by-product liquid propane gas (LPG) recovered from catalytic cracking in a typical petroleum refinery and containing 20-80 wt% propylene mixed with propane can be used as feed. Branched olefins such as isobutylene may be present up to about 10 mol% of the total olefin content of the feed. Under the process conditions of this invention, branched olefins are very rapidly converted to higher boiling oxygenates or oligomers which if desired, may readily be separated from the feed or the ether products. Small amounts of dienes, such as up to about 2 mol% of the olefin content of the hydrocarbon feed, also may be present. The process of this invention my be conducted batchwise, as will be illustrated by Examples 1 and 2 (comparative). However, it is generally advantageous, and therefore preferred, to conduct the process as a continuous operation. Since the reaction is exothermic, temperature control is facilitated by a continuous cascade operation with two or more reactors in sequence and with interstage cooling. Operable reaction conditions are given in Table I. The weight hourly space velocity (WHSV) referred to in Table I and elsewhere herein, unless explicitly stated to be otherwise, is based on reactants, i.e. the total weight of linear olefin plus alcohol divided by the total weight of binder - free insoluble acid catalyst per hour. The corresponding contact times, of course, apply to batch conversions. REACTION CONDITIONS Mol Ratio Alcohol/Olefin Temp.,°C Total Pressure kPa (Atm) WHSV Hr⁻¹ Broad 0.1 - 10 50 - 300 101 - 30400 (1.0 - 300) 0.05 - 50 Preferred 0.3 - 3 80 - 250 506 - 20300 (5 - 200) 0.2 - 20 Most Preferred 0.5 - 2 100 - 210 1010 - 10130 (10 - 100) 0.5 - 10 The principal ether product or products produced depends on the linear olefin and the alcohol charged. In the case of methanol and propylene, for example, the principal reaction product is methyl isopropyl ether. With butene-1 or the cis- or trans-butene-2, methyl sec-butyl either is formed. In brief, the ethers formed are those predicted by the Markovnikov rule for addition to the double bond of the linear olefin. In the case of the higher molecular weight linear monoolefins, or mixtures of olefins, the principal reaction product is a mixture of such ethers. The principal by-products formed in the conversion are the ether and water resulting from the autocondensation of the alcohol charged. Other by-products include alcohol resulting from the hydration of the linear monoolefin, and the ether formed by the self-condensation of the latter alcohol. Also formed in a small amount of hydrocarbon believed to be the oligomer of the olefin charged. This hydrocarbon by-product appears to account for substantially less than 5 wt% of the total olefin converted under moderate temperatures, such as at a temperature not higher than about 160°C. A particularly preferred embodiment of this invention utilizes a hydrocarbon feed consisting of about 20 to 100 wt% propylene and 0-80 wt% propane, and reacts this feed with methanol. The product formed is separated into a fraction comprising methyl isopropyl ether useful as a gasoline blending component. Unreacted propylene, methanol, and by-product dimethyl ether together with up to one mol of water per mol of ether, either individually or in any combination, can be combined with fresh feed and recycled to the process. In another embodiment of this invention, it is contemplated to feed dimethyl ether and about a stoichiometric amount of water to form the requisite methanol in situ. Zeolite Beta is utilised in the present invention because of its high activity and its high selectivity for producing methyl isopropyl ether with reduced formation of dimethyl ether. Crystalline Zeolite Beta and its conventional preparation are taught by U.S. Patent 3,308,369. It has an X-ray diffraction pattern which distinguishes it from other known crystalline silicates. EXAMPLES This invention will now be illustrated by examples. In the tables which follow, and sometimes elsewhere, products and by-products will be abbreviated as follows: dimethyl ether (DME); isopropyl alcohol (IPA); methyl isopropyl ether (MIPE); and diisopropyl ether (DIPE). EXAMPLE 1 (COMPARATIVE) This example illustrates a batch operation wherein methanol and propylene are converted to methyl isopropyl ether. A 50 gram sample of Amberlyst 15 in the hydrogen form was charged to a 300 ml stirred autoclave, purged in helium, and brought to about 120°C in flowing helium at atmospheric pressure. The autoclave was isolated and 3.0 mols of methanol were added followed by the addition of 1.5 mols of propylene. Periodically temperature and pressure were recorded and the liquid contents of the autoclave were sampled by withdrawing 1 to 2 gram quantities through an internal filtered dip-tube. Samples were analyzed by GC-TCD using a temperature programmed Porapak-QS column (60°C to 240°C at 10⁰C/min.). All major components were identified by GC-MS (50 m DB 1 column). MIPE (methyl isopropyl ether) was also verified by H-NMR. Data work-up assumed that water, methanol, isopropanol, MIPE and DIPE ratios in the liquid sample represented those in the autoclave. Neglecting hydrocarbons, the product distributions and conversions were calculated from the charge composition, product stoichiometry, and the above ratios. Product distributions for various contact times are given in Table II and in Figure 1 of the drawing. Example 2 (COMPARATIVE) Example 1 was repeated but 50 grams of extrudate consisting of 65% ZSM-5 having a silica to alumina ratio of 70:1 and 35% alumina binder was substituted for the Amberlyst 15. The ZSM-5 was in the hydrogen form. The results are summarized in Table III and Figure 2 of the drawing. Examples 3-7 Examples 3-7 illustrate the present invention with a continuous flow, flooded reactor, for the conversion of propylene and methanol to MIPE with different catalysts. In all of these examples the propylene and methanol were fed in equimolar ratio to an up-flow fixed bed reactor (20mm I.D.) that was charged with 18 to 30 grams of catalyst diluted with sand to bring bed volume to 70cc (except 43cc for Amberlyst). ISCO (continuous positive displacement) pumps fed methanol and propylene at 8270 kPa (1200 psi) in a molar ratio of 1:1. The reaction conditions were about 160°C (150⁰C for Amberlyst), 6900 kPa.g (1000 psig), and WHSV's of from 3 to 0.1 hr⁻¹. System pressure was maintained by a back pressure regulator. Liquid product condensed at system pressure and 20°C was collected at atmospheric conditions. Gas flows were measured with a wet test meter. Analysis of products was by gas chromatograph (thermal conductivity detector) using a 6 foot Porapak-QS column temperature programmed from 70°C to 240°C. Example 3 In this example the catalyst used was 65 wt% Zeolite Beta in 35 wt% alumina binder. The zeolite had a silica to alumina ratio of 37:1. The zeolite was in the hydrogen form. The results are shown in Table IV. Example 4 (COMPARATIVE) In this example 30 grams of extrudate consisting of 65 wt% ZSM-5 having a silica to alumina mol ratio of 70:1 and 35 wt% of alumina binder was used. The zeolite was in the hydrogen form. The results are summarized in Table V. Example 5 (COMPARATIVE) In this example 31 grams of extrudate consisting of 65 wt% ZSM-12 having a silica to alumina mol ratio of 73:1 and 35 wt% alumina binder was charged to the reactor. The zeolite was in the hydrogen form. The results are summarized in Table VI. Example 6 (COMPARATIVE) In this example 20 grams of Amberlyst 15 macroreticular ion-exchange resin, purchased from the Rohm & Haas Company, Philadelphia, Pa. was charged to the reactor. The resin was in the acid form. The results are summarized in Table VII. Example 7 (COMPARATIVE) In this example 20 grams of Ultra Stable Zeolite Y, purchased from the Davison Chemical Division, W. R. Grace & Co., Baltimore, Maryland, was charged to the reactor in the hydrogen form. The results are summarized in Table VIII. As will be evident from the foregoing examples, the principal reaction products from propylene and methanol are methyl isopropyl ether and dimethyl ether. This is clearly brought out in Example 3 with the Zeolite Beta catalyst, and with the graphical representation of the date in Figure 3 of the drawing.

Claims: A process for producing ethers from a hydrocarbon feed and a primary alcohol, which process comprises: passing (1) a hydrocarbon feed comprising one or more linear monoolefins having from 3 to 5 carbon atoms and (2) methanol or ethanol to a reaction zone that contains an insoluble crystalline zeolite which is zeolite Beta, contacting the hydrocarbon feed and alcohol with the catalytic solid under conditions effective to form the ether, the conditions comprising a pressure of 101 to 30400 kPa, a temperature of 50 to 300°C and a WHSV of 0.05 to 50 hr⁻¹. A process according to claim 1 wherein the hydrocarbon feed comprises 20 to 100 wt % of propylene and 0.1 to 10 mols of methanol is used per mole of propylene contained in the hydrocarbon feed. A process according to claim 2 wherein the hydrocarbon feed comprises 90 to 100 wt.% of propylene and 0.5 to 2 mols of methanol is used per mole of propylene contained in the hydrocarbon feed. A process according to any preceding claim wherein the insoluble crystalline zeolite having the crystal structure of zeolite Beta is in the hydrogen form. A process according to and preceding claim wherein the conditions comprise a temperature from 100°C; a total pressure from 1010 to 10130 kPa; and a WHSV form 0.5 to 10.

Inventors: BELL, WELDON KAY, HAAG, WERNER OTTO
Applicants: MOBIL OIL CORPORATION
Application year: 1986
Main classification: C07C41
IPC codes: B01J29, C07B61, C07C41, C07C43