MXPA98002806A - Process to conduct eterificacy reactions - Google Patents

Abstract

An improved process for conducting an etherification reaction of alcohols with olefins has been discovered. The process employs a cation exchange resin catalyst, strong acid, macroporous prepared at a temperature of 120 ° C or higher with a reduced amount of divinylbenzene crosslinker. The etherification catalysts produced in the invention showed equivalent or higher catalytic activity than conventional catalysts and are less expensive to produce than conventional catalysts due to the reduced amounts of crosslinking.

Description

PROCESS TO CONDUCT ETHERIFICATION REACTIONS The present invention concerns an improved process for conducting etherification reactions in which a cation exchange resin, of strong macroporous acid, which is prepared under high temperature conditions with a reduced amount of divinylbenzene crosslinker, is employed. Tertiary alkyl ethers, such as methyl f-butyl ether (MTBE) and ethyl butyl ether (ETBE), are extremely useful as octane boosters and fuel oxygenators in gasoline. These ethers are conveniently prepared by the acid catalyzed electrophilic addition of primary alcohols to so-butene. Commercially, certain cation exchange resins, of strong acid, prepared by sulfonating macroporous monovinyl aromatic monomer / divinylbenzene copolymers, provide ideal catalytic and physical properties for such etherification reactions; see, for example, W. Neier in "Ion Exchangers," Konrad Dorfner, Ed., Walter de Gruyter, Berlin-New York, 1991, p. 1002-1009. Cation exchange resins, of strong acid, specifically developed and sold for catalytic applications in manufacture of i-alkyl ethers, for example, resins AmerlystMR A-15 and A-35 from Rohm & Haas, the Dowex ™ M-31 resin from Dow and the resin CT-175 from Purolite are all derived from macroporous styrene / divinylbenzene copolymers having at least 20 weight percent of divinylbenzene crosslinker. Resins made from lower levels of crosslinker generally exhibit lower catalytic activity. U.S. Patent 5,244,926 describes the advantages of performing suspension polymerizations to produce monovinyl aromatic monomer / divinylbenzene copolymers under adiabatically achieved high temperature conditions, i.e., under conditions in which a high temperature, 120 ° C or higher, of the The contents of the reactor are reached by not removing the heat in the reactor that is generated by the polymerization reaction. These advantages include better reactor utilization, shorter reaction times and increased product yield. The patent teaches only that these resulting ion exchange copolymers and resins are useful for separating chemical species from solutions and for preparing polymeric adsorbents. However, when the suspension polymerizations using the recipes developed for commercial resins / copolymers are run at high temperatures, i.e., 120 ° C or higher reached adiabatically or otherwise, and the resins are subsequently sulfonated to prepare exchange resins of cations, of strong acid, to be used as etherification catalysts, the catalytic activity of the resulting resins is adversely affected, that is, the conversion rate of alcohol and olefin to ether is reduced. Another disadvantage associated with conventional processes is the high cost of the divinylbenzene crosslinker used therein. In this way, it would be very advantageous if a new process were available, which could take all the advantages of the benefits associated with a high temperature polymerization process without reducing the catalytic activity of the subsequently sulphonated monovinyl aromatic monomer copolymer products. divinylbenzene. Furthermore, it would be very commercially attractive if the new process for making the copolymer required less than a very expensive material, such as the divinylbenzene crosslinker. The present invention concerns an improved process for conducting etherification reactions in which a strong, macroporous acid cation exchange resin catalyst, which is prepared under high temperature conditions with a reduced amount of divinylbenzene reactant, is employee. In the processes of the prior art, for example, FR-A-1, 314, 120, mixtures of monomers from 80 to 99 percent by weight of monovinyl aromatic monomer and from 1 to 20 percent by weight of polyvinyl crosslinker are polymerized in the presence or absence of solvents at temperatures below 100 ° C to preparing copolymers, which are subsequently sulfonated to produce strong acid cation exchange resins useful as catalysts for industrial etherification reactions. When the amounts of divinylbenzene used as a crosslinker at a high temperature, i.e., the temperature of the contents of the reactor is 120 ° C or higher, the polymerization of the suspension of one or more monovinyl aromatic monomers is from 10 to 18 percent. by weight of monomer mixture, the resulting copolymers, after which they are subsequently sulphonated to produce cation exchange resins, of strong acid, are especially useful as catalysts for etherification reactions. Catalysts prepared with amounts of crosslinker within this range under the lower temperature conditions of the prior art are generally less effective. Catalysts prepared with amounts of crosslinker outside this range at higher temperatures are also generally less effective. In addition to achieving the benefits associated with the high temperature process in preparing the resins, ie, shorter reaction times and increased reactor capacity, the amounts and cost of the most expensive component, ie, the divinylbenzene crosslinker, are reduced. More surprisingly, the catalytic activity of said etherification catalysts prepared using 10 to 18 weight percent crosslinker, equals or exceeds that of catalysts made using conventional levels, at least 20 weight percent, of crosslinker which are currently used commercially in the etherification reactions. The copolymers of the present invention used to prepare the cation exchange resins, of strong acid, are typically in a macroporous bead array. The term "macroporous" is a term well known in the art which describes the porosity of the copolymer bead and means that the copolymer has both mesopores and macropores. Mesoporos have pore sizes of 2 nanometers (nm) at 50 nm, while macropores have pore sizes greater than 50 nm at 10, 000 nm.

Cation exchange resins, of strong acid, are those cation exchange resins having acid functional groups, such as sulphonic acid groups, substituted on the matrix of copolymer beads. The strong acid cation exchange resins can then act as an acid catalyst in, for example, etherification reactions such as the production of primary C? -C4 alkyl f-butyl ethers from the reaction of an alcohol of C? -C4 with / 'so-butene, for example, methyl "f-butyl ether produced from methanol e /' so-butene and ethyl f-butyl ether produced from ethanol and / or-butene. The macroporous copolymers used in this invention are typically prepared using suspension polymerization. The suspension polymerization comprises suspending drops of a monomer or mixture of monomers and an organic diluent (a solvent which usually dissolves the monomer or mixture of monomers but not the copolymer) in a medium in which none is soluble. This is usually achieved by adding the monomer or mixture of monomers and the organic diluent to a suspending medium, such as water, which contains a dispersing or suspending agent. When the medium is stirred, the organic phase (monomer or organic diluent) is dispersed in droplets. The polymerization is then achieved by heating the suspension in the presence of a free radical initiator. The suspension polymerization of the present invention is carried out under high temperature conditions. The high temperature conditions mean that the temperature of the reactor contents (usually a mixture of monomer, organic diluent, suspending medium, dispersing or suspending agent, initiator, and any desired additive) reaches at least 120 ° C, preferably by at least 130 ° C during the suspension polymerization. Although any way to reach these temperatures is useful, including the addition of heat via external heating in stages or continuous to the contents of the reactor throughout the polymerization, it is often the most convenient that the substantially adiabatic conditions are employed. Substantially adiabatic conditions are conditions under which a substantial amount of the exothermic heat, usually 40 percent or greater of the exothermic heat, preferably 60 percent or greater of the exothermic heat, more preferably 80 percent or greater of the exothermic heat developed during the suspension polymerization , it is retained within the suspension and results in an increase in the temperature of the reactor contents, which is sufficient to sustain the polymerization reaction without further addition of heat. Typically, the exothermic heat retention developed during the polymerization results in an increase in temperature of the reactor contents to at least 120 ° C, preferably at least 130 ° C after the polymerization has started. The monovinyl aromatic monomer used in the present invention may be a mixture of one or more monomers as described, for example, in U.S. Patent No. 5,244,926. Preferably, the monovinyl aromatic monomer or monomers include styrene or ethyl vinylbenzene or mixtures thereof. As is known in the art, other monomers, such as acrylates and acrylonitriles, may be present in the monomer mixture in order to control and effect the properties of the resultant copolymer beads, for example, pearl porosity or pearl strength. . The divinylbenzene crosslinker is used in a concentration from 10 to 18, preferably from 12 to 18, more preferably from 14 to 16, percent by weight of the monomer mixture of monovinyl aromatic monomers and aromatic divinyl crosslinking monomers. It has been found that this amount maximizes the catalytic activity of the cationic resins derived from the copolymer produced during the polymerization of high temperature suspension. The maximized catalytic activity of the etherification catalyst results in a maximized conversion rate in the production of ethers from alcohols and olefins. The increased rate can increase the amount of methyl f-butyl ether produced from the reaction of methanol e / so-butene or the amount of ethyl f-butyl ether produced from the reaction of ethanol and / or-butene, when the cationic resin catalysts are produced from copolymers produced at high temperatures and having a concentration from 10 to 18, preferably from 12 to 18, more preferably from 14 to 16, percent by weight of divinylbenzene as the crosslinker. This concentration of divinylbenzene as crosslinker not only results in increased catalytic activity, but also significantly reduces the cost of copolymer production since divinylbenzene is typically the most expensive raw material.

The organic diluents / solvents useful in the present invention are those solvents which are suitable for forming pores and / or displacing insoluble polymer chains during polymerization. The characteristics and use of such diluents / solvents in the formation of macroporous resins are described in U.S. Patent No. 4,224,415. These diluents / solvents can be any of those, or mixtures thereof, which are described in, for example, U.S. Patent No. 4,224,415 or U.S. Patent No. 5,231,115. Typically, C6-C12 saturated aliphatic hydrocarbons , such as heptane e / so-octane, and the C 4 -C 0 alkanols, such as f-amyl alcohol, sec-butanol and 2-ethylhexanol, are particularly effective. A sufficient concentration of the organic diluent is required to effect the phase separation or polymer chain shift. Normally, the organic diluent comprises from 25 to 50 percent by weight of the total weight of the monomer mixture and diluent. The free radical initiator or combination of such initiators can be any compound or compounds capable of generating free radicals in the polymerization of vinyl aromatic monomers. Suitable initiators are mentioned in, for example, U.S. Patent Nos. 4, 192,921; 4,246,386; and 4,283,499. Azo compounds such as azobisisobutyronitrile and peroxygen compounds such as benzoyl peroxide, f-butylperoctato, and f-butylperbenzoate can usually be employed with most vinyl aromatic monomers. The amount of initiator or combination of initiators used will vary with the type of initiator and type of monomer ratio being polymerized as those skilled in the art will appreciate. Generally, 0.02 to 1 percent by weight of the initiator based on the total weight of the monomer mixture is adequate. The suspending medium used in the process of the present invention is usually water containing a suspending agent such as gelatin, polyvinyl alcohol or a cellulosic such as hydroxyethylcellulose, methyl cellulose or carboxymethyl methyl cellulose. Generally, the suspending medium is employed in an amount of at least 35 percent by volume of the total volume of the organic phase (mixture of monomers and porogenic solvent) and suspending media. However, the amount of suspending medium employed must not be below the point where the suspension failure occurs. That is, the continuous phase of the suspending medium / monomer mixture should be the suspending medium, typically water, and the suspended monomer mixture should remain dispersed in the medium. Usually, the lower limit for the amount of suspending medium is 35 percent by volume of the total volume of the organic phase (mixture of monomers and porogenic solvent) and suspending medium. Polymerization usually begins when the temperature of the suspending medium is elevated to at least 40 ° C, preferably to at least 70 ° C, and no more than 120 ° C when initial heat is applied from an external source. If the polymerization of suspension by stages, that is, not substantially adiabatic, is employed, more heat is added or excess heat is removed externally in stages or continuously until the temperature of the reactor contents reaches at least 120 ° C, and preferably at least 130 ° C and remains at that temperature until at least 70 percent by weight, preferably at least 80 percent by weight, most preferably up to at least 90 percent by weight of the polymerizable monomer based on the total weight of the monomer has polymerized. Most preferably, substantially adiabatic conditions are employed for the reasons mentioned above. In this case, the temperature of the suspending medium is elevated to at least 40 ° C, preferably to at least 70 ° C and not more than 120 ° C when applying heat from an external source. The heat is added or the elevated temperature is maintained until at least the time when the exothermic heat developed from the polymerization of the copolymer monomers is sufficient to maintain the polymerization without further addition of heat to the suspending medium. Using substantially adiabatic conditions, the temperature of the contents of the reactor will advantageously increase to at least 120 ° C, and preferably to at least 130 ° C, for a sufficient time to polymerize at least 80 weight percent, preferably at least 90 , more preferably at least 99 percent by weight, or more of the polymerizable monomers. The copolymers can be functionalized for cation exchange resin catalysts, strong acid by any method capable of adding sulfonic acid groups on the matrix of copolymer beads, for example, as shown in US Patent Nos. 3,266,007; 2,500, 149; 2,631, 127; 2,664,801; and 2,764,564. Typically, functionalization using sulfuric acid and chlorinated solvent as a swelling solvent is effective. However, if a higher degree of sulfonation is desired, ie, more than one sulfonate group per aromatic nucleus, then a variety of over-sulfonation agents can be employed as will be apparent to one skilled in the art. For example, oleum, that is, smoked sulfuric acid, can be employed as discussed in U.S. Patent No. 4,839,331. Once functionalized, the cation exchange resins, of strong acid, are useful for catalyzing etherification reactions and particularly useful in the production of methyl f-butyl ether from methanol and / or sobutene or in the production of ethyl. f-butyl ether from ethanol and / so-butene. The invention is further illustrated by the following examples.

Example 1 A strong acid 12/32 macroporous cation exchange resin catalyst (12 percent divinylbenzene by weight of the total monomers / 32 percent by weight of the diluent of the total organic phase) was prepared in the following manner. Batch polymerizations were conducted in a 2 liter stainless steel reactor (I) equipped with agitation. The monomer phase comprised 338 grams (g) of styrene, 52 g of active divinylbenzene in solution (55 percent of divinylbenzene, 44 percent of ethyl vinylbenzene, and 1 percent of diethylbenzene), 2.31 g of 50 percent of fer-butyl peroctoate and 0.77 g of fer-butyl perbenzoate. In this way, the total monomers weighed 433 g and were mixed with 203 g of commercial isooctane. The aqueous phase comprised 504 g of water, 130 g of 1 percent of carboxymethyl methyl cellulose (suspending agent) and 2.4 g of 60 percent of sodium dichromate (latex polymerization inhibitor). Both phases were loaded into the reactor, which was then sealed and the pressure was tested. The reactor was purged with nitrogen and stirring, revolutions per minute (rpm) was established. The reactor temperature was boosted at 80 ° C to start charging the monomer and heated as fast as possible, ie, in about half an hour, to the final adiabatic temperature (170 ° C) to simulate the heating ramp itself what would happen if the reaction were run on a large scale. The reactor was held at that temperature for one hour and then cooled. The copolymer was coated from the reactor, washed, dismounted with steam, filtered, dried and sieved. The copolymer in the bead form was functionalized by sulfonating with an excess of 99 percent sulfuric acid in the absence of a swelling solvent. The sulfonated beads were hydrated with increasing diluted sulfuric acid and then countercurrently deionized water to form a macroporous strong acid cation exchange resin catalyst.

Example 2 A 14/32 strong acid macroporous cation exchange resin catalyst (14 percent divinylbenzene by weight of the total monomers / 32 percent by weight diluent of the total organic phase) was prepared in the same manner as the catalyst. Example 1, except that 61 g of active divinylbenzene in solution (55 percent of divinylbenzene, 44 percent of ethyl vinylbenzene, and 1 percent of diethylbenzene) and 322 g of styrene were used.

Example 3 A strong 16/30 macroporous cation exchange resin catalyst (16 percent divinylbenzene by weight of the total monomers / 30 percent by weight diluent of the total organic phase) was prepared in the same manner as the catalyst. Example 1, except that 69 g of active divinylbenzene in solution (55 percent of divinylbenzene, 44 percent of ethyl vinylbenzene and 1 percent of diethylbenzene) and 308 g of styrene were used and the final adiabatic temperature was 165 ° C.

Example 4 A strong 18/32 macroporous cation exchange resin catalyst (18 percent divinylbenzene by weight of the total monomers / 32 percent by weight diluent of the total organic phase) was prepared in the same manner as the catalyst. Example 1, except that 78 g of active divinylbenzene in solution (55 percent of divinylbenzene, 44 percent of ethyl vinylbenzene, and 1 percent of diethyl benzene) and 291 g of styrene were used.

The macroporous strong acid cation exchange resin catalysts prepared in Examples 1, 2, 3 and 4 were milled, sieved and tested for catalytic activity in the production of methyl fer-butyl ether by the following method. The tested resin catalysts of Examples 1-4 exhibited equivalent yields, within experimental error, or higher compared to macroporous strong acid cation exchange resin catalysts produced at high temperatures having conventional amounts of divinylbenzene crosslinker, that is, 20 weight percent of divinylbenzene of the total monomers. The results are summarized in Table I. The laboratory system used to test the cation resin catalysts consisted of a stainless steel reaction mixture feed tank, a Beckamn 1 10B high pressure liquid chromatography (HPLC) pump, a stainless steel reactor of 1. 6 centimeters by 20.3 centimeters contained in a heated aluminum block, and a pressure control valve, all connected with 0.16 centimeter stainless steel tubing and needle valves. The reactor was capped at both ends and adapted with a thermocouple receptacle and a 10 cubic centimeter (cc) bed of glass beads contained between two glass wool plugs. A bed of 12 cc of catalyst could be charged into the reactor at the top of the glass bead layer. The reactor was contained in an aluminum block of 5 1 centimeters in diameter by 20.3 centimeters in length adapted with a thermocouple and two electric heaters of 100 watts connected to a temperature controller. A premixed reaction mixture containing 1 1 percent methanol, 17 percent sobutene, and 72 percent butane was pumped into the reactor from a one liter stainless steel feed tank using a Beckman 1 10B HPLC pump. . The 1 liter feed tank could be periodically filled from a larger cylinder (35 liters) of the reaction mixture. The pressure in the reactor was controlled by a pneumatically controlled control valve by a pressure transducer and a pressure controller. The system was piped through two pneumatically activated rotary valves to allow analysis of both the feed mix and the product mix. To avoid danger of explosion, the system was fixed in a dedicated housing containing no other electrical equipment and the HPLC pump was continuously purged with nitrogen. Analysis of the reaction mixture or product mixture was conducted by gas chromatography using a Hewlett Packard 5890 gas chromatograph adapted with a CHROMPAKMR 10m PORAPLOTMR U column, a flame ionization detector, and a sample injection system and automated sampling, which allowed an analysis of the feed mix or product mix every 20 minutes. The detector response factors for each of the components to be analyzed (MeOH, isobutene, butane and MTBE) were obtained using a mixture containing heavy amounts of each component. In a typical catalyst evaluation, the water was removed from a 20 cc portion of cationic resin by chromatographic washing with approximately 20 milliliters (ml) of dry methanol in a column. A packed vibrator, 12 cc portion of the wet methanol resin was charged into the reactor and a glass wool plug was placed on top of the resin bed to avoid resin loss during a run. In some runs, the resin was broken in a mixer and sieved to give a mesh resin of minus 60 to plus 70 (210 to 250 microns), which was then washed with dry methanol and loaded into the reactor. After the reactor was placed in the heated aluminum block and reattached to the system, the thermocouples were placed in a hole in the aluminum block and in the thermocouple cavity of the reactor. The H PLC pump was turned on at a flow rate of 0.6 to 1.2 milliliters per minute (ml / min) and the system was pumped to a pressure of 2.38 MPa. The heaters were then turned on and the aluminum block was heated to a desired temperature (usually between 45 ° and 55 ° C). The maximum temperature in the catalyst layer was monitored by correctly placing the thermocouple in the thermocouple cavity of the reactor at each chosen flow rate. Depending on the flow rate of the reaction mixture, the reaction exotherm usually gave a temperature higher than 3o at 7 ° C in the catalyst bed than in the heated block. The catalyst evaluations were conducted at two different flow rates, 3 bed volumes per hour (BV / h) at 50 ° C maximum temperature in the catalyst bed and 6BV / h at 60 ° C maximum temperature in the bed of catalyst. After reaching the desired temperature at a given flow rate, the reactor was allowed to run until the equilibrium conditions were established and the concentration of MTBE in the product mixture remained relatively constant during at least three consecutive sample analyzes. The yield of MTBE was calculated from the average concentration in the last three samples divided by the concentration calculated at 100 percent MTBE yield based on isobutene in the feed mix. The MTBE yield results for ground and sieved particles of 210-250 microns in size for Examples 1, 2, 3 and 4 are summarized in Table 1 below.

Table 1

Claims (9)

1. CLAIMS 1 . In a method for conducting an etherification reaction employing as the catalyst a cation exchange resin, of strong acid, wherein said resin is prepared by a process in which a monomer mixture comprising one or more monovinyl aromatic monomers and a divinylbenzene crosslinker in an amount of from 1 to 20 percent by weight are polymerized in the presence of an organic diluent, producing a macroporous copolymer, which is subsequently sulphonated to produce the cation exchange resin, of strong acid, the improvement to prepare the copolymer being characterized by limiting the concentration of divinylbenzene crosslinker in a range from 10 to 18 weight percent of the monomer mixture and heating the monomer mixture to a temperature above 120 ° C.
2. 2. The method of claim 1, wherein the concentration of divinylbenzene crosslinker is from 12 to 18 percent by weight of the monomer mixture.
3. 3. The method of claim 1, wherein the concentration of divinylbenzene crosslinker is from 14 to 16 percent by weight of the monomer mixture.
4. 4. The method of claim 1, wherein the monomer mixture comprises styrene or ethyl vinylbenzene or mixtures thereof.
5. The method of claim 1, wherein the etherification reaction comprises reacting a primary alkanol from Ci to C4 with / so-butene.
6. 6. The method of claim 3, wherein the primary alkanol of d to C4 is methanol. The method of claim 3, wherein the primary alkanol from Ci to C4 is ethanol. The method of claim 1, wherein the temperature of the contents of the reactor has been obtained under conditions where the heat is added via an external medium. The method of claim 1, wherein the temperature of the reactor contents has been obtained under substantially adiabatic conditions.