Integrated process for the production of diisopropyl ether and gasoline

Abstract: A process is disclosed for integrating etherification to produce diisopropyl ether (DIPE) with processes to convert oxygenates and hydrocarbons to gasoline boiling range hydrocarbons in a manner which eliminates the requirement to recycle unreacted C₃ hydrocarbons to the DIPE etherification zone. In the novel integrated process the unreacted C₃ hydrocarbons are separated as vapor and passed to a conversion zone in contact with acidic metallosilicate catalyst. Depending on the conversion conditions the unreacted C₃ hydrocarbons are converted to gasoline, distillate and/or aromatics, preferably in conjunction with additional feedstock containing lower oxygenates, olefins or paraffins. Also, isopropanol (IPA) and minor by-product dimers and trimers of propene from the DIPE reaction are separated and passed as a feedstream to the oxygenates and hydrocarbon conversion zone. In one embodiment, the water feedstream for the DIPE reactor is first passed to the DIPE effluent high pressure separator where it serves to extract a portion of the IPA in the effluent stream. The aqueous effluent from the high pressure separator is then introduced into the etherification zone for hydration of propene and etherification to form DIPE.

Description: This invention relates to the production of gasoline boiling range hydrocarbons and diisopropyl ether (DIPE). More particularly, the invention relates to the integration of C₃ hydrocarbon hydration and etherification with processes for the conversion of oxygenates, olefins and paraffins to higher molecular weight hydrocarbons. The process incorporates improvements in the product recovery section design for DIPE enhancing product separation and etherif ication reactor operating conditions. Lower molecular weight alcohols and ethers such as isopropanol (IPA) and diisopropyl ether (DIPE) boil in the gasoline boiling range and are known to have high blending octane numbers. In addition, by-product propylene from which IPA and DIPE can be made is usually available in a fuels refinery. An important aspect of research in the petroleum industry relates to processes to produce high octane gasolines blended with lower aliphatic alkyl ethers such as DIPE as octane boosters and supplementary fuels. The catalytic hydration of olefins, particularly C₃ and C₄ olefins, to provide alcohols and ethers is a well-established art and is of significant commercial importance. Representative olefin hydration processes are disclosed in US-A-2,262,913, 2,477,380, 2,797,247, 3,798,097, 2,805,260, 2,830,090, 2,861,045, 2,891,999, 3,006,970, 3,198,752, 3,810,848 and 3,989,762. The production of ether from secondary alcohols such as isopropanol and light olefins is known. As disclosed in US-A-4,182,914 DIPE is produced from IPA and propylene in a series of operations employing a strongly acidic cation exchange resin as catalyst. Recently, processes for the hydration of olefins to provide alcohols and ethers using zeolites as catalyst have been proposed. EP A 0 323 138 describes a process for producing ether which comprises contacting a light olefin with water and an alcohol in the presence of an acidic zeolite catalyst to provide a mixture of an alcohol and an ether; introducing the mixture into a distillation unit to provide an overhead fraction comprising the ether and minor amounts of the alcohol and water, and a bottoms fraction containing the aqueous alcohol; recycling a portion of the bottoms to the olefin conversion unit. This patent merely deals with etherification of olefins. There is no teaching concerning the integration of oxygenate and hydrocarbon conversion process with the DIPE process. In the conversion of a water feedstream and a C₃ hydrocarbon feedstream comprising propene and propane to DIPE and IPA, the conversion per pass is typically about 60%. Recycling of the unreacted C₃s unavoidably involves compression and recycling of unreacted propene to the etherification reactor. This, in turn, requires feeding and operating the reactor at higher pressures in order to maintain an effective propene partial pressure in the vessel, a situation inimical to improved process economics. Also, separating IPA from the reaction effluent and recycling IPA to the etherification reactor as typically carried out presents additional process problems. According to the present invention an integrated process for the production of diisopropyl ether and C₅+ gasoline range hydrocarbons, comprises contacting C₃ hydrocarbon feedstock rich in propene and water with acidic hydration and etherification catalyst in an etherification zone under etherification conditions to produce an effluent stream containing diisopropyl ether, isopropanol, unreacted water, unreacted C₃ hydrocarbons and higher olefinic hydrocarbons; separating said effluent stream to produce an aqueous stream containing a portion of said isopropanol and an organic stream containing said unreacted C₃ hydrocarbons and diisopropyl ether; separating said organic stream to recover diisopropyl ether and a stream containing said unreacted C₃ hydrocarbons; introducing said stream containing unreacted C₃ hydrocarbons to an oxygenates and hydrocarbons conversion zone in contact with acidic metallosilicate catalyst particles comprising shape-selective, medium pore, acid aluminosilicate zeolite under oxygenates and hydrocarbons conversion conditions to produce higher molecular weight C₅+ gasoline boiling range hydrocarbons. Further features of the invention are defined in the dependent claims. The process eliminates the incentive to recycle unreacted C₃ hydrocarbons to the DIPE etherification zone. In the integrated process the unreacted C₃ hydrocarbons can be separated as vapor and passed to a conversion zone in contact with acidic metallosilicate catalyst. Depending on the conversion conditions the unreacted C₃ hydrocarbons are converted to gasoline, distillate and/or aromatics, preferably in conjunction with additional feedstock containing lower oxygenates, olefins or paraffins. Also, IPA and by-product dimers and trimers of propene from the DIPE reaction are separated and passed as a feedstream to the oxygenates and hydrocarbon conversion zone. In one embodiment, the water feedstream for the DIPE reactor is first passed to the DIPE effluent high pressure separator where it serves to extract a portion of the IPA in the effluent stream. The aqueous effluent from the high pressure separator is then introduced into the etherification zone for hydration of propene and etherification to form DIPE. Reference is now made to the accompanying drawing which is a process flow schematic diagram illustrating an integrated process in accordance with the invention. Components of known processes are thus integrated in a manner providing a highly advantageous and surprising advancement in refinery technology leading to the production of DIPE as well as gasoline, distillate and/or aromatics. Known processes are combined in a unique configuration that provides enhancement of the performance of component processes, achieving surprising advantages for the integrated process. The processes integrated include C₃ olefins hydration to produce alcohols and ethers and olefins and/or oxygenates conversion over zeolite catalyst to produce gasoline ("MOG" - Mobil Olefins to Gasoline process), distillate ("MOGD" - Mobil olefins to Gasoline and Distillate process) or aromatics ("M-2 Forming" - Mobil Aromatization process). Various processes in the aforenoted field of oxygenates and/or olefins conversion technology are described in US-A-3,894,107, 3,928,483, 4,025,575, 4,252,479, 4,025,572, 4,328,384, 4,547,616, 4,450,311, 3,960,978, 4,021,502, 4,150,062, 4,211,640, 4,227,992, 4,456,779, 4,497,968, 4,433,185 and 3,845,150. The term "oxygenates or "oxygenate" as used herein denotes, individually or in combination, C₁-C₈ lower aliphatic, acyclic alcohols or alkanol and symmetrical or asymmetrical C₂-C₉ ethers. In the process to prepare DIPE a feedstock comprising propene or a refinery C₃ hydrocarbon stream comprising olefins and paraffins, i.e., propene and propane, is contacted at elevated pressure with an acidic catalyst and water as a reactant to hydrate propene to form isopropanol (IPA) and etherify IPA to DIPE. Minor amounts of addition products or propene are also formed in the acidic catalyst environment, particularly hexenes and nonenes. On a per pass basis, the conversion of propene generally is about 60%, or between 50% and 70%. The effluent from the hydration and etherification zone is conventionally passed to a high pressure separator wherein an aqueous stream is separated containing IPA and a stream that contains the unreacted C₃ hydrocarbons comprising propene and propane, if an olefin and paraffin feedstock has been used. In order to recover the unreacted C₃ hydrocarbons and recycle them to the etherification zone the temperature of the C₃ stream from the high pressure separator is raised and the stream is introduced to a flash evaporator under conditions sufficient to separate a major portion of unreacted C₃ hydrocarbons. This recycle stream, typically containing both propene and propane, is recompressed and fed to the pressurized DIPE reactor. Since the recycle stream is rich in propane the DIPE feedstock stream pressure is increased in order to maintain the partial pressure of propene in the reactor. However, in accordance with the invention it is not necessary to recycle any C₃ hydrocarbons. Conventionally, DIPE is recovered by distillation and/or extraction of the flash evaporator bottom stream. This recovery system also separates an IPA stream and light hydrocarbon stream such as a portion of unreacted C₃ hydrocarbons. The IPA stream is recycled to the etherification zone. The operating conditions of the olefin hydration and etherification process herein are not especially critical and include a temperature of from 60 to 450°C, preferably from 90 to 220°C and most preferably from 120 to 200°C, a pressure of from 100 to 3500 psi (690 to 24100 kPa), preferably from 500 to 2000 psi (3000 to 13900 kPa), a water to olefin mole ratio of from 0.1 to 30, preferably from 0.2 to 15 and most preferably from 0.3 to 3. The olefin hydration process can be carried out under dense phase, liquid phase, vapor phase or mixed vapor-liquid phase conditions in batch or continuous manner using a stirred tank reactor or fixed bed flow reactor, e.g., trickle-bed, liquid-up-flow, liquid-down-flow, counter-current, co-current, etc. A liquid hourly space velocity (LHSV) of from 0.1 to 20, preferably 0.1-2, when operating continuously is suitable. The catalyst employed in the olefin hydration and etherification operations is an acidic resin catalyst, such as sulfonated polystyrene, or a shape-selective acidic zeolite catalyst. In general, the useful catalysts embrace two categories of zeolite, namely the intermediate pore size variety as represented, for example, by ZSM-5, which possess a Constraint Index of greater than about 2 and the large pore variety as represented, for example, by zeolites Y, Beta and ZSM-12, which possess a Constraint Index no greater than about 2. Preferred catalysts include zeolite Beta, zeolite Y, ZSM-12, ZSM-5, and ZSM-35. Both varieties of zeolites will possess a framework silica-to-alumina ratio of greater than about 7. Constraint Index is defined in US-A-4,016,218. For purposes of this invention, the term "zeolite" includes the class of porotectosilicates, i.e., porous crystalline silicates, which contain silicon and oxygen atoms as the major components. Other components can be present in minor amounts, usually less than 14 mole %, and preferably less than 4 mole %. These components include aluminum, gallium, iron, boron, and the like, with aluminum being preferred. Zeolites which are substantially free of aluminum, i.e., having silica-to-alumina mole ratios up to and including infinity, are useful and can even be preferable in some cases. Constraint Index (CI) values for some zeolites which can be used in the process of this invention are described in the following table together with the temperature at which the test was made: ZEOLITE CONSTRAINT INDEX (At Test Temperature, º C) ZSM-4 0.5 (316) ZSM-5 6-8.3 (371-316) ZSM-11 5-8.7 (371-316) ZSM-12 2.3 (316) ZSM-20 0.5 (371) ZSM-35 4.5 (454) ZSM-48 3.5 (538) ZSM-50 2.1 (427) TMA Offretite 3.7 (316) TEA Mordenite 0.4 (316) Clinoptilolite 3.4 (510) Mordenite 0.5 (316) REY 0.4 (316) Amorphous Silica-Alumina 0.6 (538) Dealuminized Y 0.5 (510) Zeolite Beta 0.6-2.0 (316-399) The nature of the Constraint Index and the technique by which it is determined admit the possibility that a given zeolite can be tested under somewhat different conditions and thereby exhibit different Constraint Indices: Constraint Index may vary somewhat with severity of operation, presence or absence of binders, crystal size of the zeolite, the presence of occluded contaminants, and other factors. Therefore, it will be appreciated that it may be possible to so select test conditions, e.g., temperatures, as to establish more than one value for the Constraint Index of a particular zeolite. This explains the range of Constraint Indices for zeolite Beta. Useful zeolite catalysts of the intermediate pore size variety, possessing a Constraint Index of greater than about 2 up to about 12, include such materials as ZSM-5, ZSM-11, ZSM-23 ZSM-35 and ZSM-38, defined respectively by the x-ray diffraction data set forth in US-A-3,702,886, 3,709,979, 4,076,842, 4,016,245 and 4,046,859. The large pore zeolites which are useful as catalysts in the hydration and etherification step of the process of this invention, i.e. those zeolites having a Constraint Index of no greater than about 2, are well known to the art. Representative of these zeolites are zeolite Beta, zeolite Y, zeolite L, zeolite Y, ultrastable zeolite Y (USY), dealuminized Y (Deal Y), rare earth-exchanged zeolite Y (REY), rare earth-exchanged dealuminized Y (RE Deal Y), mordenite, ZSM-3, ZSM-4, ZSM-12, ZSM-20 and ZSM-50 and mixtures of any of the foregoing. Zeolite Beta, ZSM-3, ZSM-4, ZSM-12, ZSM-20 and ZSM-50 are defined by the x-ray data set forth in US-A-3,308,069, 3,415,736, 3,923,639, 3,832,449, 3,972,983 and 4,640,829 respectively. Low sodium ultrastable zeolite Y (USY) is described in US-A-3,293,192, 3,354,077, 3,375,065, 3,402,996, 3,449,070 and 3,595,611. Also included within the definition of the useful zeolites are crystalline porous silicoaluminophosphates such as those disclosed in US-A-4, 440,871, the catalytic behavior of which is similar to that of the aluminosilicate zeolites. The zeolite(s) selected for use herein will generally possess an alpha value of at least about 1 and preferably at least 10. For the olefins hydration reaction, the most preferred alpha value for fresh catalyst is at least 400. "Alpha value" is a measure of zeolite acidic functionality and is more fully described together with details of its measurement in J. Catalysis , 6 , pp. 278-287 (1966) and J. Catalysis , 61 , pp. 390-396 (1980). Zeolites of low acidity (alpha values of less than about 200) can be achieved by a variety of techniques including (a) synthesizing a zeolite with a high silica/alumina ratio, (b) steaming, (c) steaming followed by dealuminization and (d) substituting framework aluminum with other species. In practising the olefin hydration and etherification process step of the present invention, it can be advantageous to incorporate the zeolite(s), if used, into some other material, i.e., a matrix or binder, which is resistant to the temperature and other conditions employed in the process. Useful matrix materials include both synthetic and naturally-occurring substances, e.g., inorganic materials such as clay, silica and/or metal oxides, and are fully described in our EP-A-1695. In some cases, it may be advantageous to provide the zeolite hydration etherification catalyst(s) in the form of an extrudate bound with a low acidity refractory oxide binder employing the method described in US patent application Serial No. 44,639, according to which zeolite, water and a low acidity refractory oxide binder, e.g., silica, which contains at least an extrusion-facilitating amount of the binder in a colloidal state and which is substantially free of added alkali metal base and/or basic salt, is formed into an extrudable mass, the mass is extruded and the resulting extrudate is dried and calcined. The original cations associated with zeolite(s) utilized herein can be replaced by a wide variety of other cations according to techniques well known in the art, e.g., by ion-exchange. Typical replacing cations include hydrogen, ammonium, alkyl ammonium and metal cations, and their mixtures. Metal cations can also be introduced into the zeolite. In the case of metal cations, particular preference is given to metals of Groups IB to VIII of the periodic Table, including, by way of example, iron, nickel, cobalt, copper, zinc, palladium, calcium, chromium, tungsten, molybdenum, rare earth metals, etc. These metals can also be present in the form of their oxides. In accordance with the invention unreacted C₃ olefins, optionally together with recovered IPA from the hydration zone, are converted to gasoline, distillate or aromatics by the MOG, MOGD or M-2 Forming process in contact with metallosilicate zeolite-type catalyst such as ZSM-5. In the case of conversion to aromatics of the hydration zone effluent, paraffins in the effluent can also be converted to aromatics by the M-2 Forming process. Such processes have significance as safe, environmentally acceptable techniques for utilizing feedstocks that contain lower olefins, especially C₂-C₅ alkenes. The aformentioned US Patent Specifications disclose, inter alia, conversion of C₂-C₅ olefins, alone or in admixture with paraffinic components into higher hydrocarbons over crystalline zeolites having controlled acidity. A fluidized bed process for converting light olefinic streams to gasoline, sometimes referred to as the Mobil Olefin to Gasoline process (MOG), is described by Avidan et al., in US Patent Application 006,407, filed 23 January 1987. The conversion of paraffins and/or olefins to aromatics is described in US-A-3,760,024, 3,756,942 and 4,090,949. As described above for the C₃ olefin hydration and etherification reaction as conventionally practised, the hydrocarbon feed comprising propene is fed to the etherification zone along with a fresh water feedstream directly to the reactor. In one embodiment of the instant invention it has been discovered that the fresh water feedstream can be fed to the high pressure separator which receives the effluent from the DIPE reactor. In the high pressure separator the fresh water feedstream extracts IPA from the effluent and an aqueous stream is withdrawn from the separator and recycled to the DIPE reactor. In this embodiment the water reactant for the the etherification reaction is contained in the aqueous recycled stream which contains a significant portion of recycled IPA. In this way the need for downstream separation of IPA for recycle to the DIPE reactor is substantially reduced. Referring now to Figure 1, a C₃ hydrocarbon feed comprising propene and propane is fed 110 to a hydration and etherification reaction vessel 115 containing an acidic catalyst. In the etherification vessel the C₃ hydrocarbons react with water and IPA which has been recycled to the reactor through conduit 116 from a high pressure separator 120. The effluent 117 from the etherification zone contains DIPE, IPA, unreacted water, unreacted C₃ hydrocarbons and a minor amount of dimeric and trimeric addition products of propene. The effluent 117 from the reaction zone 115 is passed to the high pressure separator 120 in conjunction with a fresh water feedstream 118. In the high pressure separator the fresh water feed effectively extracts a portion of IPA from the effluent stream 117. The aqueous stream containing IPA is separated and pumped 119 through conduit 116 for recycle as previously noted. From the high pressure separator another stream containing DIPE, unextracted IPA, unreacted C₃ hydrocarbons is withdrawn 121 and optionally heated 122 to a temperature to effect the evaporation of a major portion of unreacted C₃ hydrocarbons in an optional high pressure flash evaporator 125. The C₃ hydrocarbon vapor 124 is withdrawn from the flash evaporator and a part of it may be recycled 126 to etherification zone 115 through a cooler compressor system 127. All or a part of the C₃ hydrocarbons are passed 128 to an oxygenates and hydrocarbon conversion zone 129. In accordance with the invention it is not necessary to have any recycle of the C₃ hydrocarbons. From the flash evaporator 125 a stream is withdrawn 130 containing a minor portion of unreacted C₃ hydrocarbons, a portion of IPA, and DIPE. This stream is separated in separator zone 131 to provide a DIPE product stream 132, a light hydrocarbon stream 133 comprising unreacted C₃ hydrocarbons and a stream 134 comprising IPA. The IPA stream 134 and stream 133 are passed to conversion zone 129 in conjunction with the flash evaporator vapor stream. A portion of stream 134 containing IPA can be recycled 135 to the DIPE reactor. In the oxygenates and hydrocarbon zone 129 the streams separated from the DIPE etherification zone effluent and identified as a portion of stream 128 and 134 and stream 132 are contacted with metallosilicate catalyst, preferably ZSM-5, where, depending upon the conditions selected, these oxygenates and hydrocarbons are converted to higher molecular weight hydrocarbons comprising gasoline, gasoline and distillate or aromatics. Preferably, the conversion reaction is carried out with a conventional oxygenates and/or hydrocarbon feedstream 136, as described for the MOG, MOGD or M-2 Forming processes cited hereinbefore. Continuing to refer to Figure 1, in another embodiment of the invention, stream 121 from the high pressure separator is passed to separator 131 with processing in the high pressure flash evaporator 125. DIPE is recovered from separator 131. Unreacted C₃ and unextracted IPA are introduced to conversion zone 129 for conversion to C₅+ gasoline boiling range hydrocarbons; optionally in conjunction with fresh oxygenate and/or hydrocarbon feed to the 129 conversion zone. From the foregoing description the advantages of the instant invention are clearly evident. The integration of the oxygenates and hydrocarbon conversion process with DIPE relieves the requirement to recycle unreacted C₃ hydrocarbons. This eliminates recompression costs associated with the recycle loop and also avoids the necessity of operating the DIPE reactor at higher pressures needed to maintain a satisfactory propene partial pressure. The unique process variation which extracts IPA in the high pressure separator also effectively relieves downstream IPA separation operations, to the benefit of overall process costs.

Claims: An integrated process for the production of diisopropyl ether and C₅+ gasoline range hydrocarbons, comprising contacting a propene-rich C₃ hydrocarbon feedstock and water with an acidic hydration and etherification catalyst in an etherification zone under etherification conditions to produce an effluent stream containing diisopropyl ether, isopropanol, unreacted water, unreacted C₃ hydrocarbons and higher olefinic hydrocarbons; separating said effluent stream to produce a first stream containing water and a portion of said isopropanol and a second stream containing said unreacted C₃ hydrocarbons and diisopropyl ether; recovering diisopropyl ether from said second stream; and passing at least a portion of said unreacted C₃ hydrocarbons to an oxygenates and hydrocarbons conversion zone in contact with a catalyst comprising a medium pore, acidic zeolite under oxygenates and hydrocarbons conversion conditions to produce higher molecular weight C₅+ hydrocarbons. A process according to claim 1 wherein said feedstock comprises propene and propane. A process according to claim 1 or claim 2 wherein said etherification conditions include a temperature of 60 to 450°C, a pressure of 6.9 to 241 bar and a water/olefin mole ratio of 0.1 to 30. A process according to any preceding claim wherein the etherification catalyst is an acidic resin or an intermediate- or large-pore zeolite. A process according to any preceding claim wherein the oxygenates and hydrocarbons conversion catalyst comprises zeolite ZSM-5. A process according to any preceding claim wherein there are fed to the oxygenates and hydrocarbon conversion zone, in addition to said unreacted C₃ hydrocarbons, fresh oxygenates and/or hydrocarbons comprising methanol, ethanol, propanol, lower aldehydes, lower ethers, C₂-C₆ olef ins and/or C₂-C₆ paraffins. A process according to any preceding claim wherein said C₅+ hydrocarbons comprise gasoline boiling range hydrocarbons, gasoline and distillate boiling range hydrocarbons, or aromatics. A process according to any preceding claim wherein the separating of said effluent stream to produce first and second streams is carried out in a high pressure separation zone in contact with fresh water. A process according to claim 8 wherein said first separated stream is recycled to the etherification zone. A process according to claim 8 or claim 9 wherein said second separated stream contains isopropanol. A process according to any of claims 8 to 10 wherein said second separated stream is heated and separated in a flash unit into a vapor stream containing unreacted C₃ hydrocarbons and a bottom stream containing diisopropylether, the balance of said isopropanol, the portion of unreacted C₃ hydrocarbons passed to said oxygenates and hydrocarbons conversion zone, and said higher olefinic hydrocarbons. A process according to claim 11 wherein a portion of said vapor stream is passed to said oxygenates and hydrocarbons conversion zone. A process according to claim 11 or 12 wherein said bottom stream is separated into streams comprising diisopropyl ether; unreacted C₃ hydrocarbons; and isopropanol and higher olefinic hydrocarbons. A process according to claim 13 wherein said separation is effected by extraction and distillation. A process according to claim 13 or claim 15 wherein said isopropanol is separately recovered. A process according to claim 15 wherein said isopropanol is recycled to said etherification zone. A process according to claim 13 or claim 15 wherein said unreacted C₃ hydrocarbons, isopropanol and higher olefinic hydrocarbons are passed to said oxygenate and hydrocarbons conversion zone.

Inventors: HARANDI MOHSEN, OWEN HARTLEY, HARANDI, MOHSEN, OWEN, HARTLEY
Applicants: MOBIL OIL CORP, MOBIL OIL CORPORATION
Application year: 1990
Main classification: C07C43
IPC codes: C10G1, C10L1, C07C41, C07C43, C07B61, C10G3, C07C1, C07C2