WO1997032838A1

WO1997032838A1 - Production of a high purity butene-1 product from butadiene-rich c4 stream

Info

Publication number: WO1997032838A1
Application number: PCT/US1997/003621
Authority: WO
Inventors: Gary Ray Patton; Mark Lee Gravley; Mark Dennis Scharre; Robert Ovington Dunn; Harold Ray Hunt
Original assignee: Phillips Petroleum Company
Priority date: 1996-03-08
Filing date: 1997-03-05
Publication date: 1997-09-12
Also published as: AU1989797A; ID16149A

Abstract

A process for the production of a high purity butene-1 product stream (34), having a low concentration of diolefin, and ether (28) for a mixed hydrocarbon stream (14) having a high concentration of diolefin is disclosed. The process includes the steps of diolefin hydrogenation, etherification, product separation and linear olefin isomerization.

Description

PRODUCTION OF A HIGH PURITY BUTENE-1 PRODUCT FROM BUTADIENE-RICH C4 STREAM The present invention relates to a method of producing a high purity butene-1 product from a mixed hydrocarbon stream having a high concentration of butadiene.

It can be desirable to recover butene-1 from a mixed hydrocarbon stream containing hydrocarbons having four or more carbon atoms. It is particularly desirable to produce a high purity butene-1 product stream, but one difficulty that is sometimes associated with the production of such butene-1 product, is its recovery from a mixed hydrocarbon stream containing a high concentration of butadiene. It is thus an object of this invention to provide a process for producing a high purity butene-1 product from a mixed hydrocarbon feedstock that has a high concentration of butadiene.

Another object of this invention is to also provide for the production of ether compounds using as reactants olefins from the mixed hydrocarbon feedstock having a high concentration of butadiene.

Accordingly, the inventive process provides for the production of an ether product and a high purity butene-1 product from a mixed hydrocarbon feedstrearn containing hydrocarbons having four or more carbon atoms per molecule. The process includes passing a mixed C4 stream, having a high concentration of butadiene and containing hydrocarbons having at least four carbon atoms per molecule, to a butadiene saturation system for hydrogenation of at least a portion of the butadiene contained in the mixed C4 stream to monoolefin to provide a product stream. The product stream is passed to a hydroisomerization system whereby at least a portion of the diolefin contained in said product stream is hydrogenated to monoolefins and a hydroisomerate stream is produced. The hydroisomerate stream is passed to an etherification system for reacting isoolefin with a primary alcohol to form ether to thereby produce an ether product, containing ether, and a raffinate stream, containing linear butenes. The raffinate stream is charged to a fractionation system for separating the raffinate stream into a high purity butene-1 stream, containing butene-1, and a fractionation system stream, containing paraffins and butene-2. The fractionation system stream is passed to a paraffin separation system for separating the fractionation system stream into a butene-2 stream, containing butene-2, and a paraffin stream, containing at least one paraffin compound. The butene-2 stream is passed to an isomerization system to isomerize at least a portion of the butene-2 in the butene-2 stream to isobutene and to produce an isomerate stream containing isobutene. In the accompanying drawing:

FIG. 1 provides a schematic representation of one embodiment of the inventive process.

The inventive process provides for the processing of a mixed hydrocarbon stream, preferably including hydrocarbons having four carbon atoms per molecule (also referred to herein as a "mixed C4 stream"), to produce a high purity butene-1 product and an ether product. The inventive process is particularly advantageous in allowing for the processing of a mixed C4 stream having a high concentration of diolefin, including butadiene, to make such high purity butene-1 product and the ether product.

The feedstock charged to the inventive process is generally a mixed hydrocarbon stream containing paraffins, olefins and diolefins. Included among the olefin compounds of the mixed hydrocarbon stream are linear olefins and isoolefinβ. It is particularly desirable for the mixed hydrocarbon stream to contain hydrocarbons having four carbon atoms per molecule, thus, the mixed hydrocarbon stream preferably comprises butene compounds such as isobutene and the linear buteneβ of butene-1 and butene-2. The mixed hydrocarbon stream may also contain paraffin hydrocarbons among which is butane. Therefore, the mixed hydrocarbon stream is preferably a mixed C4 stream comprising paraffins, butene-1, butene-2, and isobutene. The inventive process is particularly useful in the processing of a mixed C4 stream having a high butadiene concentration. Generally, the butadiene concentration of the mixed C4 stream will range from about 5 weight percent to about 50 weight percent. More typically, however, the butadiene concentration in the mixed C4 stream will range from about 7.5 weight percent to about 40 weight percent. But, most specifically, the butadiene concentration in the mixed C4 stream shall range from 10 weight percent to 30 weight percent.

The mixed C4 stream is passed or charged to a butadiene saturation system for the hydrogenation of at least a portion of the butadiene contained in the mixed C4 stream. The product stream from the butadiene saturation system has a concentration of butadiene that is significantly reduced below such concentration in the mixed C4 stream generally being less than 3 weight percent of the product stream. Preferably, the concentration of butadiene in the product stream is less than 1 weight percent, most preferably, the concentration is less than 0.5 weight percent.

The catalyst utilized in the butadiene saturation system of this invention can be any suitable catalyst that provides for a selective hydrogenation of a substantial portion of the butadiene contained in the mixed C4 stream. Such catalyst may include a palladium metal supported on a carrier such as alumina. But, because of the high concentration of butadiene in the mixed C4 stream, a catalyst composition found to be especially effective for selectively hydrogenating butadienes is that described in U.S. Patent No. 5,475,173 containing palladium, silver and alkali metal fluoride on a support material. U.S. Patent No. 5,475,173 is incorporated herein by reference.

The selective hydrogenation reaction of the butadiene saturation system is generally carried out by contacting the mixed C4 stream and molecular hydrogen with the catalyst (generally contained in a fixed bed) . Generally, about 1-10 moles of hydrogen are employed for each mole of diolefin. The temperature necessary for the selective hydrogenation of the butadiene depends largely upon the activity of the catalyst and the desired extent of diolefin hydrogenation. Generally, temperatures in the range of about 95°C. to about 39 °C. are used. A suitable reaction pressure generally is in the range of about 20 to 2,000 pounds per square inch gauge (psig) . The liquid hourly space velocity (LHSV) of the hydrocarbon feed can vary over a wide range. Typically, the space velocity of the feed will be in the range of about 3 to about 100 liters of hydrocarbon feed per liter of catalyst per hour, more preferably about 20 to about 80 hr"¹. The hydrogenation process conditions should be such as to avoid significant hydrogenation of monoolefinε (formed by hydrogenation of diolefins and/or being initially present in the feed) to paraffins. The product stream from the butadiene saturation system is charged or passed to a hydroisomerization system, whereby diolefins are selectively hydrogenated to form olefins and at least a portion of the butene-1 in the product stream may be isomerized to butene-2, to produce a hydroisomerate stream having a concentration of diolefin less than the concentration of diolefin in the product stream from the butadiene saturation system but which is less than about 200 parts per million weight (ppmw) , preferably less than about 100 ppmw, and most preferably, less than 20 ppmw. The catalysts utilized in the hydroisomerization system of this invention comprise the noble metals of Group VIII of the Periodic Table of Elements. The catalysts intended to be included in the group of nobel metals of Group VIII specifically are ruthenium, rhodium, palladium, osmium, iridiu , and platinum.

Any of the usual catalyst supports can be employed, such as alumina (preferred) , silica alumina, glass beads, and carbon. Catalysts in the form of pellets, spheres, and extrudates are satisfactory.

A preferred hydroisomerization catalyst is palladium on a carrier, the carrier preferably being alumina. The catalyst should contain from about 0.005 to about 2.0 percent palladium on alumina, preferably about 0.1 to about 1.0 weight percent palladium on alumina. Most preferably, the catalyst should contain from about 0.3 to about 0.8 weight percent palladium on alumina. A suitable catalyst weighs about 40 to about 60 pounds per cubic foot, has a surface area of about 30 to about 150 square meters per gram, a pore volume of about 0.35 to about 0.50 ml per gram, and a pore diameter of about 200 to about 50θA.

As an example, a suitable commercial hydroisomerization catalyst satisfactory for use in this invention is manufactured by Mallinckrodt

Specialty Chemicals Company, designated as Calsicat catalyst number E-144 SDU. The commercial catalyst contains about 0.55 weight percent palladium on alumina.

The hydroisomerization process is conducted at a reaction temperature of about 100° to about 300°F. preferably 130°-200°F.

The hydroisomerization process of this invention can be most effectively practiced at relatively low pressure conditions while maintaining the hydrocarbon most preferably in the liquid phase, although vapor phase operation can be used. Pressures employed for the liquid phase process are from about 100 to about 600 psig, preferably from about 150 to about 300 psig. Liquid hourly space velocities, LHSV, are maintained from about 2 to about 50, preferably from about 3 to about 10.

Hydrogen is utilized in the hydroisomerization process by preferably being mixed with the hydrocarbon feed stream prior to contacting the stream with the hydroisomerization catalyst. The hydrogen is necessary to effect double bond isomerization of the 1-olefin with the hydroisomerization catalysts and to provide for hydrogenation of diolefins to olefins. The hydrogen is added in amounts from 0.1 to 20.0 mole percent, preferably in amounts of about 1.0 to about 10.0 mole percent.

The hydroisomerate stream from the hydroisomerization system, generally comprising isobutene, butene-1, butene-2 and at least one paraffin compound, is charged or passed to an etherification system whereby the iβoolefins present in the hydroisomerate stream are converted to ethers by reaction with primary or secondary alcohols in the presence of an acid ion exchange resin catalyst. The alcohols which may be utilized in the etherification reaction include the primary and secondary aliphatic alcohols having from 1 to 12 carbon 838

- 7 - atoms, such as methanol, ethanol, propanol, isopropanol, the primary and secondary butanols, pentanols, hexanols, ethylene glycol, propylene glycol, butylene glycol, the polyglycols, and glycerol, etc., or mixtures of two or more thereof. The preferred alcohol of the etherification reaction is methanol because when reacted with isobutene, it yields methyl tertiary butyl ether (MTBE) which has utility, among other uses, as an octane improver for gasoline. It is generally preferred for the isoolefin and the alcohol to be passed through the etherification reaction zone of the etherification system in the presence of diluents which do not have an adverse effect upon the etherification reaction. Examples of suitable diluents include alkanes and straight chain olefins. The feed to the etherification reactor, excluding alcohol, is generally diluted so as to include about 2 to about 80 weight percent isoolefin, preferably about 10 to about 50 weight percent. The acid ion-exchange catalysts useful in the etherification reaction zone of the etherification system are relatively high molecular weight carbonaceous material containing at least one SO3H functional group. These catalysts are exemplified by the sulfonated coals (^wZeo-Karb H", "Nalcite X" and

"Nalcite AX") produced by the treatment of bituminous coals with sulfuric acid and commercially marketed as zeolitic water softeners or base exchangers. These materials are usually available in a neutralized form and in this case must be activated to the hydrogen form by treatment with a strong mineral acid such as hydrochloric acid and water washed to remove sodium and chloride ions prior to use. The sulfonated resin type catalyst are preferred for use in the present invention. The catalysts include the reaction products of phenolformaldehyde resins with sulfuric acid ("Amberlite IR-1", "Amberlite IR-100" and "Nalcite 32838 PC17US97/03621

- 8 -

MX") . Also useful are the sulfonated resinous polymers of coumarone-indene with cyclopentadiene, sulfonated polymers of coumarone-indene with cyclopentadiene, and furfural and sulfonated polymers of cyclopentadiene and furfural. The most preferred cationic exchange resins are strongly acidic exchange resins consisting essentially of sulfonated polystyrene resin, for instance, divinylbenzene cross-linked polystyrene matrix having from 0.5 to 20 percent and preferably from 4 to 16 percent of copolymerized divinylbenzene therein co which are attached ionizable or functional nuclear sulfonic acid groups. These resins are manufactured and sold commercially under various trade names such as "Dowex 50", "Nalcite HCR" and "Amberlyst 15". As commercially obtained they have solvent contents of about 50 percent and can be used as is or the solvent can be removed first.

The resin particle size of the acid ion-exchange catalysts is not particularly critical and therefore is chosen in accordance with the manipulative advantages associated with any particular size. Generally, mesh sizes of 10 to 50 U.S. Sieve Series are preferred. The reaction may be carried out in either a stirred slurry reactor or in a fixed bed continuous flow reactor. The catalyst concentration in a stirred slurry reactor should be sufficient to provide the desired catalytic effect. Generally catalyst concentration should be 0.5 to 50 percent (dry basis) by weight of the reactor contents with from 1 to 25 percent being the preferred range.

Acid ion exchange resins, such as Rohm & Haas Amberlyst 15 and Dow Chemical Dowex M-31, are currently the most preferred catalysts for the etherification. The temperature for the etherification reaction zones and the space velocity for the feed to the etherification reactor zone can be selected as desired depending upon the degree of conversion desired 2838

and the temperature at which oligomerization becomes a problem. Generally, the temperature of the reaction zone will be in the range of about 86°F. to about 248°F., preferably about 95°F. to about 176°F. Pressures are generally selected to ensure that the charges and the products remain in the liquid phase during the reaction. Typical pressures are in the range of about 30 to about 300 psig. Generally, the liquid hourly space velocity (LHSV) of feed in the reactors will be in the range of about 2 to about 50 hr^_1.

The molar ratio of alcohol to isoolefin in etherification system feed will generally be in the range of about 0.5/1 to about 4/1, preferably about 0.8/1 to 1.2/1, most preferably about 1/1.

The etherification reaction zone effluent is passed to a separation system within the etherification system for separating the etherification reaction zone effluent into an ether product stream, containing ether, and a raffinate stream, containing hydrocarbons that did not react within the etherification reaction zone and, preferably, linear butenes. Any suitable separation system known to those skilled in the art can be used to separate the etherification reaction zone effluent to provide the ether product stream and the raffinate stream. Generally, the etherification reaction zone effluent can pass to a conventional fractionator for separating ether from the remaining portion of the etherification reaction zone effluent to give an ether product stream. The remaining portion of the etherification reaction zone effluent is then passed to a solvent extraction system to separate the alcohol and hydrocarbons. The alcohol can be recycled as a feed to the etherification reaction zone, and the separated, unreacted hydrocarbons are passed from the etherification system as the raffinate stream.

The raffinate stream principally contains paraffins and the linear butenes, butene-1 and butene-2. The raffinate stream is passed to a fractionation system for separating butene-1 from paraffins and other linear butenes such as butene-2. Standard fractionation methods are well known in the art. The arrangement of fractionation equipment is such as to provide a high purity butene-1 product stream generally containing at least about 95 weight percent butene-1. Preferably, the high purity butene-1 product stream contains at least about 98 weight percent butene-1, most preferably, it contains at least 99.5 weight percent butene-1. Because of the prior butadiene saturation and hydroisomerization steps, the diolefin concentration in the high purity butene-1 product is minimal, preferably being less than about 5 ppm and, most preferably, less than 1 ppm.

A fractionation system stream, which contains those compounds of the raffinate stream not recovered with the high purity butene-1 stream, passes to a paraffin separation system for separating the fractionation system stream into a butene-2 stream, containing butene-2, and a paraffin stream, containing at least one paraffin compound. While any suitable means can be used to separate the fractionation system stream into the butene-2 and paraffin streams, one preferred means is the use of extractive distillation.

Extractive distillation is utilized to separate paraffins and olefins, particularly, butanes from butenes. Extractive distillation is a known separation method and is described in detail in literature such as Perry's Chemical Engineers' flandboofc Sixth Edition, published by McGraw-Hill Company 1984, page 13-53 through 13-57 and U.S. Patent No. 3,687,202, both of which are incorporated herein by reference.

Any conventional extraction solvent can be utilized in the extractive distillation system which permits the separation of the paraffins and olefins of the feed mixture. Examples of suitable extraction solvents include acetonitrile, dimethylformamide, furfural, acetone, dimethylacet mide, n-methylpyrridone, dimethylsulfoxide, sulfolane, and n-for ylmorpholine. These solvents can be used alone or with a cosolvent such as water. The preferred extraction solvents include acetonitrile, n- methylpyrridone and sulfolane.

The raffinate stream, comprising paraffins and butenes, is fed to an extractive distillation tower where it is contacted with a solvent. The solvent alters the relative volatilities of the paraffins and butenes thereby permitting the separation of such compounds into a first overhead stream, or paraffin stream, comprising at least one paraffin compound and a bottoms stream. The bottoms stream from the extractive distillation tower is passed to a stripping tower, which provides a second overhead stream, or butene-2 stream, comprising at least one olefin.

The butene-2 stream is passed to an olefin isomerization system for skeletally isomerizing the linear olefins to tertiary olefins along with an added water and steam diluent, present in an amount of at least about 0.1 mole of water or steam per mole of olefin, to an isomerization reaction zone of the isomerization system containing an acidic alumina catalyst. The isomerization reaction is an equilibrium type reaction in which butene-2 is isomerized to isobutene.

The acidic alumina catalysts utilized in the reaction zone of the isomerization system are those known in the art. Preferably, the alumina should have a surface area of at least 50 m²/g. In the practice of the present invention, the alumina is used without the incorporation of substantial amounts of inert solids and does not contain substantial amounts of impurities. Good results are obtained with aluminas having a purity of at least about 99.50 weight percent. The alumina can be in any desired form suitable for contact with the olefin including, for example, granules, spheres, microspheres, pellets, tablets fluid powder, etc. Preferably alumina catalysts include catalytic beta-alumina and gamma-alumina. The isomerization catalyst can be employed in any manner conventional within the art, such as in a fixed bed, a fluidized bed and the like.

The isomerization reaction can be carried out either batch-wise or continuously, using a fixed catalyst bed, stirred batch reactor, a fluidized catalyst chamber, or other suitable contacting techniques. The isomerization process conditions should be suitable to carry out the conversion of the linear olefins involved. In general, the isomerization reaction can be carried out at a temperature from 600°F. to 1200°F., preferably from about 850°F. to about 1000°F. Any convenient pressure can be used, with the lowest practical pressure preferred in order to minimize side reactions such as polymerization. Pressures ranging from atmospheric to 200 psig are particularly suitable. The LHSV is generally in the range of about 0.1 to 30 hr^"1, preferably about 0.2-20.

The isomerization system serves to convert linear olefins that are not reactive in the etherification system to tertiary olefins. The conversion of the linear olefins to tertiary olefins allows for the recycling, directly or indirectly, of the isomerate stream to the etherification system to be used as a reactive feedstock.

Now referring to FIG. 1, there is provided a schematic representation of process system 10 of this invention. A mixed C4 stream, preferably containing butene-1, butene-2 and isobutene, and further having a substantial concentration of butadiene, is charged to butadiene saturation system 12 by way of line 1 . Butadiene saturation system 12 provides for the selective hydrogenation of at least a portion of the butadiene contained in the mixed C4 stream to monoolefin and to provide a product stream having a butadiene concentration less than that of the mixed C4 stream. The product stream from butadiene saturation system 12 passes by way of line 16 to hydroisomerization system 18. Hydrogen is provided to butadiene saturation system 12 and hydroisomerization system 18 through line 20.

Hydroisomerization system 18 provides for the hydrogenation of the diolefins contained in the product stream from butadiene saturation system 12 to olefins to provide a feedstock that can suitably be charged to etherification system 22. A hydroisomerate stream, which as a result of the hydroisomerization reaction contains a substantially reduced concentration of diolefin, is passed by way of line 24 to etherification system 22 wherein the isobutene reacts with a primary alcohol, provided through line 26, to form ether. Etherification system 22 provides an ether product, containing ether, which passes downstream from etherification system 22 by way of line 28. A raffinate stream, containing linear butenes, passes from etherification system 22 by way of line 30 and is charged as a feed to fractionation system 32.

Fractionation system 32 provides for the separation of butene-1 from paraffins and other linear butenes and thereby providing a high purity butene-1 stream, containing butene-1, and a fractionation system stream, containing paraffins and butene-2. Due to the selective hydrogenation of diolefins by butadiene saturation system 12 and hydroisomerization system 18, the high purity butene-1 stream will have a minimal concentration of diolefin. The high purity butene-1 stream passes from fractionation system 32 by way of line 34. The fractionation system stream passes from fractionation system 32 through line 36 and is charged to paraffin separation system 38. Paraffin separation system 38 provides for the separation of paraffins and linear olefins, particularly butene-2, to provide a paraffin stream, containing at least one paraffin compound, and a butene-2 stream, containing butene-2. The paraffin stream passes from paraffin separation system 38 through line 40. The butene-2 stream passes from paraffin separation system 38 and is charged to isomerization system 42 via line 44.

Isomerization system 42 provides for the isomerization of butene-2 in the butene-2 stream to isobutene thereby providing an isomerate stream containing isobutene. The conversion of linear butenes to isobutene provides a feedstock for etherification system 22. The isomerate stream may be recycled as a feed to either hydroisomerization system 18 or etherification system 22 by way of line 44.

Calculated Example To illustrate the inventive process shown in FIG. 1, this calculated example is provided. The material balance of the calculated example is provided in Table 1. The stream numbers shown in Table 1 correspond to those represented in FIG. 1. As the material balance of Table 1 shows, a high purity butene-1 product stream, having a minimal concentration of diolefin, and an ether product are produced from a mixed C4 feedstream having a high concentration of butadiene and further containing linear butenes and isobutenes. -15-

Reasonable variations and modifications are possible within the scope of the foregoing disclosure, drawing and appended claims.

Claims

C A I M S 1. A process comprising the steps of: passing a mixed C4 stream, having a high concentration of butadiene and containing hydrocarbons having at least four carbon atoms, to a butadiene saturation system for hydrogenation of at least a portion of the butadiene contained in said mixed C4 stream to monoolefin to provide a product stream; passing said product stream to a hydroisomerization system whereby at least a portion of the diolefin contained in said product stream is hydrogenated to monoolefins and a hydroisomerate stream is produced; passing said hydroisomerate stream to an etherification system for reacting isoolefin with a primary alcohol to form ether to thereby produce an ether product stream containing ether and a raffinate stream containing linear butenes; charging said raffinate stream to a fractionation system for separating said raffinate stream into a high purity butene-1 stream containing butene-1 and a fractionation system stream containing paraffins and butene-2; passing said fractionation system stream to a paraffin separation system for separating said fractionation system stream into a butene-2 stream containing butene-2 and a paraffin stream containing at least one paraffin compound; and passing said butene-2 stream to an isomerization system to isomerize at least a portion of the butene-2 in said butene-2 stream to isobutene and to produce an isomerate stream containing isobutene.

2. A process as recited in claim 1, further comprising the step of: passing at least a portion of said isomerate stream to said hydroisomerization system.

3. A process as recited in claim 2, wherein said high concentration of butadiene is in the range of from about 5 weight percent to about 50 weight percent.

4. A process as recited in claim 3, wherein the diolefin contained in said product stream is less than about 3 weight percent.

5. A process as recited in claim 4, wherein said high purity butene-1 stream has a concentration of butene-1 of at least about 95 weight percent butene-1.

6. A process as recited in claim 5, wherein the concentration of diolefin in said hydroisomerate stream is less than 10 ppm.