GB2101597A - Process for producing isopropanol - Google Patents

Abstract

Isopropanol is produced by the hydration of propylene by a process which includes the steps of reacting a propylene-containing feedstock with water in the presence of a cation exchange catalyst in the acid form under mixed phase direct hydration conditions including a temperature of from 275-375 DEG F (135-191 DEG C, a pressure of from 1000 to 2000 psi, a water to propylene molar ratio of from 5 to 15 and a propylene liquid hourly space velocity of from 0.15-1.5 and thereafter recovering from the crude product an aqueous isopropanol solution, which can be used in the production of a high octane gasoline composition by continuously blending the isopropanol from the aqueous solution of isopropanol directly into a stream of gasoline blending hydrocarbon by mixing the aqueous solution and the gasoline, rapidly separating the resulting mixture into two phases, for example, by passing it through water coalescer means, and recovering the organic phase which consists essentially of the gasoline and isopropanol.

Description

SPECIFICATION Process for producing isopropanol This invention relates to a process for the production of isopropanol by the hydration of propylene. The isopropanol product can be used for the production of an oxygenated fuel composition comprising gasoline and isopropanol. It is, therefore, possible by using isopropanol produced in accordance with the present invention to obtain a high octane fuel composition without the necessity for alkylation.

The process of the present invention is also more economical than prior processes, since it employs a dilute feed. In accordance with the present invention, it is possible to achieve reasonably high conversions without resorting to a costly pre-reactor C3=C3 splitter to concentrate propylene in the feed.

As is well known, alkylation can produce a premium grade gasoline component from olefins by reaction with isoparaffins such as isobutane or isopentane, such alkylation can be conducted thermally at high temperatures and very high pressures, but is preferably done at low temperatures in the presence of catalysts. Such catalytic alkylation proceeds quite readily and, as long as a sufficient excess of the C4 or C5 isoparaffin is present, results in substantially complete conversion of the olefinic feed constituents into valuable C7 to C9 branched chain paraffins of high antiknock value and relatively low volatility.

Refineries have, however, experienced a shortage of isoparaffins, particularly isobutane and, therefore, have an excess of olefins. So a way to place these olefins into the motor gasoline pool is needed.

At the same time, gasoline octane requirements have increased and use of the traditional leadcontaining gasoline additives has been largely discontinued. It has, therefore, become necessary to find alternative means to produce high octane fuel compositions without the necessity for alkylation.

Oxygenated compounds such as ethanol, isopropanol and methyl-t-butyl ether are high octane components that are now finding their way into the motor gasoline pool. In making alcohols by the hydration of olefins, the raw product from the reactor generally contains a substantial quantity of water in addition to the alcohol. Dehydrating the aqueous alcoholic solution has heretofore required energy intensive procedures, such as extractive distillation or azeotropic distillation.

According to the present invention there is provided a process for the production of isopropanol by the hydration of propylene, which comprises the steps of reacting a propylene-containing feedstock with water under mixed phase hydration conditions in the presence of a cation exchange catalyst in the acid form, said hydration conditions including a temperature of from 27 5--37 5 0 F, a pressure of from 1000 to 2000 psi, a water to propylene molar ratio of from 5 to 1 5 and a propylene liquid hourly space velocity of from 0.1 5-1.5, and thereafter recovering from the resulting crude product an aqueous isopropanol solution.

The present invention also provides a continuous process for blending isopropanol from an aqueous solution of isopropanol into a stream of gasoline blending hydrocarbons. The process comprises mixing an aqueous solution of isopropanol having an isopropanol content of at least 50% by weight obtained by the aforementioned process with a gasoline blending hydrocarbon stream, allowing the mixture to separate into two phases, the first being an organic phase which consists essentially of the gasoline blending hydrocarbon and the isopropanol and the second being an aqueous phase which consists essentially of water, and then recovering the organic phase. In an embodiment of the continuous process of the invention, the mixing is accomplished by use of in-line mixers and the phase separation is accomplished rapidly, for example, by using water coalescer means.

The process of the present invention enables one to use excess C3 olefins and incorporate them as high octane components into the motor gasoline pool without alkylation.

The hydration method of the present invention employs a feedstock comprising C3 hydrocarbons generally having a propylene content of from 60% to 85%. Preferred is a feedstock consisting substantially entirely of C3 hydrocarbons having a propylene content of from 60 to 85%, such as that which could be obtained by distilling off a C3 cut from a fluid catalytic cracker. Surprisingly, it is possible by using the combination of reaction conditions of the present invention to obtain a high conversion per pass even employing such dilute feedstocks.

The feedstock containing propylene is reacted with water in the presence of a cation exchange catalyst. The catalyst is preferably a sulfonated macroreticular copolymer of styrene and divinylbenzene in the acid form. Catalysts modified by chlorination to withstand higher temperatures, such as Amberlyst (RTM) XN 1011 and Amberlite (RTM) XE 372, manufactured by Rohm and Haas, are particularly preferred. Other catalysts suitable for the direct hydration of propylene and methods for their preparation are described in U.S. Patent No. 2,813,908.

In direct hydration, the propylene-containing feedstock is mixed with water in a ratio of water to propylene generally of from 5 to 1 5, preferably from 8 to 12 and most preferably about 8. The mixture is then fed to a reactor, preferably in a downflow, trickie bed configuration, to contact the catalyst.

Hydration conditions include a pressure of from about 1 000 to 2000, preferably 1,400 to 1,500 psig, and a temperature of from 275 to 3750 F, preferably from 290 to 3550F. The conditions are selected so that the propylene is in a super-critical gas phase and the water is primarily in the liquid phase. Finally, the propylene liquid hourly space velocity is from 0.1 5 to 1.5 per hour, preferably from 0.4 to 0.5 per hour.

In the direct hydration stage, the percent propylene conversion should be maintained at a substantially constant predetermined level, generally from 50% to 90%, preferably about 67%. To do so, the temperature in the reactor should be raised incrementally to compensate for the loss of catalyst activity during the course of the reaction.

The crude product which emerges from the bottom of the reactor contains water, isopropanol, diisopropyl ether (a by-product), propylene and propane as well as any C4 hydrocarbons present in the feed or traces of alcohols or ethers derived from reactions of C4 hydrocarbons in the reactor. This crude product may be passed through one or more conventional gas-liquid separators to separate the gases, i.e., propane, unreacted propylene and trace C4 and lower hydrocarbons from the liquids, i.e., isopropanol, water and diisopropyl ether.

The separated gases, generally contain at least 40% unreacted C3 olefins. Such olefins, of course, may be fed to a conventional alkylation plant where they are allowed to react with isoparaffins in the presence of a suitable catalyst such as HF or sulfuric acid. The resultant alkylation product, presumably a mixture of high-branched C7 paraffins is a high octane product suitable for direct addition to the motor gasoline pool, As discussed, the desirability of alkylation is limited by the shortage and high expense of the requisite isobutane.

The propylene obtained from the overhead of the liquid-gas separator may be catalytically oligomerized to make olefinic gasoline, a high octane gasoline pool component. Such oligomerization obviates the need to alkylate excess olefins, significantly reducing the process cost.

The crude liquid product from hydration which contains water, isopropanol, diisopropyl ether and perhaps traces of C4 olefin-derived ethers and/or alcohols, is generally caustic neutralized. This product is then passed through a first distillation column which is generally operated at near atmospheric pressure at a temperature so that the product taken overhead is primarily diisopropyl ether (actually the low-boiling azeotrope which also contains 4% isopropanol and 5% water, b.p. 620C). The bottoms from this first distillation column, containing primarily isopropanol and water, are passed through a second distillation column. The overhead from the first column, primarily diisopropyl ether, may be blended into gasoline directly, since diisopropyl ether has a high octane number.

The second distillation column containing the isopropanol and water, is operated generally at or near atmospheric pressure and at a temperature such that the isopropanol-water azeotrope (b.p. 800 C) having the composition of 87.8 weight percent isopropanol and 12.2 weight percent water is taken overhead. The column bottoms which consist primarily of a very dilute aqueous salt solution may be either (a) desalted by treatment with an ion exchange resin and the pure water recycled with make-up water to the hydration reactor or (b) discarded.

Isopropanol is typically separated from the isopropanol-water azeotrope so it can be blended with a gasoline blending hydrocarbon stream resulting in an oxygenated fuel-containing blending stock which can be used directly in the motor gasoline pool. The isopropanol in such an aqueous isopropanol solution having an isopropanol content of preferably at least 50 weight percent can be directly blended into a gasoline blending hydrocarbon, thus eliminating the need for azeotropic distillation. This process also eliminates any requirement for extractors such as mechanically agitated columns, rotary-agitated columns, reciprocating plate columns and centrifugal extractors, the operation of which consume much energy, decreasing the efficiency of a process in which isopropanol can be incorporated into the motor gasoline pool from an aqueous solution.

In a process according to one embodiment of the invention, an aqueous isopropanol solution is mixed with gasoline blending hydrocarbons. The gasoline blending hydrocarbon may be any hydrocarbon that can be added to the motor gasoline pool including straight run, alkylate, FCC gasoline, reformate or their mixtures such as Chevron Unleaded Regular gasoline (ULR). The gasoline blending hydrocarbons may also comprise diesel and/or jet fuel. The gasoline blending hydrocarbons extract the isopropanol out of the aqueous solution, and after the phases separate, an organic phase which comprises an oxygenated fuel composition is produced. In the process of the invention, isopropanol is continuously, simultaneously extracted from an aqueous solution and blended with a component of the motor gasoline pool.

In a batch process, gasoline blending hydrocarbons are mixed with an isopropanol-water azeotrope and the mixture is allowed to separate into two phases, for example, in a large settling tank.

The organic phase consists essentially of the gasoline blending hydrocarbons and the isopropanol. The aqueous phase consists essentially of water.

Separation of the mixture into two phases can take a long time but in accordance with the process of the present invention, the phase separation is achieved rapidly without any detrimental effect on the composition of the organic phase. The present invention, therefore, also provides a continuous process for producing an oxygenated fuel composition from an aqueous solution of isopropanol.

In accordance with this process, an aqueous solution of isopropanol, preferably the azeotrope, is mixed with a stream of gasoline blending hydrocarbons by using a conventional in-line mixer such as those manufactured by Komax Systems, Inc. A milky emulsion forms on mixing. Surprisingly, this emulsion separates rapidly into two phases by passing it through a water filter coalescer such as a Racor Model 2000 SM Filter Separator, preferably after modification to avoid deterioration of polymeric components. Other such separators are available from Facet Enterprises, Inc. Although separation is rapid, extraction is essentially complete. The composition of the resulting phases is unaffected despite the short phase separation time.

The water in the emulsion may be coalesced by employing any conventional water coalescer means including coalescers, separating membranes and certain electrical devices.

Coalescers are generally mats, beds or layers of porous or fibrous solids whose properties are especially suited for the purpose at hand. Their action appears to be twofold: (1) protective, highviscosity films surrounding the dispersed-phase droplets are ruptured and wiped away by the coalescer; (2) the droplets preferentially wet the solid, attach themselves thereto, and grow in size by coalescing with others similarly caught. The enlarged drops are then carried away by the flowing stream of continuous phase. The coalescer is, therefore, generally a solid of large surface to volume ratio, with uniformly small passages to ensure action on all the dispersion, of low pressure drop for flow, and for best results it should be preferentially wet by the dispersed phase.

A coalescer should also be mechanically strong enough to resist the pressure drop prevailing, and chemically inert toward the liquids. Beds of granular solids such as sand and diatomaceous earth, and bats of excelsior, steel wool, copper turnings, glass wool, Fiberglas, and the like have been used.

Materials such as mineral wool may be coated with substances such as silicones and resids to provide the preferential wetting characteristics.

Water coalescers and method for resolving water and oil emulsions are disclosed in U.S. Patent Nos. 2,288,532; 2,522,378 and 2,746,607.

Subjecting electrically conducting emulsions or dispersions to high-voltage electric fields may cause rupture of the protective film about a droplet and thus induce coalescence. This has been used particularly for the desalting of petroleum emulsified with brine, and for similar applications, see, e.g., U.S. Patent No. 2,527,690.

By using this continuous scheme, it is possible to obtain substantial capital savings. After appropriate scale-up, the estimated capital investment for extractive blending in a plant producing two thousand barrels per-day of isopropanol (about twenty thousand barrels per day of a 10% isopropanol-gasoline blend) would be only about forty thousand dollars for the requisite pumps and large scale water coalescer instead of the high costs associated with energy-intensive- distillation purifications.

In this continuous process, the aqueous isopropanol solution should preferably contain at least 50 weight percent isopropanol. The isopropanol-water azeotrope is particularly preferred. For each volume of azeotrope, at least 2 volumes, preferably about 10 volumes of hydrocarbon extractant should be used. For more concentrated aqueous solutions, less hydrocarbon is required for extractive blending.

Examples The following Examples demonstrate the process of the present invention and its advantages.

The Examples are merely illustrative and are not intended to be construed as a limitation.

Example I A catalyst charge of Rohm and Has Amberlite XE 372 having a volume of 10 cc when swollen in water was loaded into the mid-section of a 3/8" O.D. teflon internally coated 31 6 stainless steel reactor tube. Two beds of 20 to 32 mesh alundum particles which were each 5" long were placed in the reactor, one above and one below the catalyst bed to provide for mixing of the reagents and for supporting the catalyst change, respectively. Water and a liquefied C3 cut from a fluid catalytic cracker were fed concurrently into the top of the reactor tube at the rates of 1 2 cc and 6 cc liquid per hour, respectively, which corresponds to a molar ratio of water to propylene of 12:1.The C3 cut had the following composition in weight percent: propylene 76.9 propane 1 6.8 isobutane 4.06 isobutene 0.93 i-butene 0.56 trans-2-butene 0.30 n-butane- 0.19 cis-2-butene 0.15 ethane 0.08 The reactor was maintained at a temperature of 2930F and a pressure of 1,440 psig. A propylene conversion of 69% was achieved. Propylene selectivities were about 90% to isopropanol and about 10% to diisopropyl either.

Example It The procedure of Example I was conducted except that the molar ratio of water to propylene and the temperatures were varied as indicated in the following Table I.

Table I TOF H2O:C3= Conversion (%) Selectivity (%) 295 12:1 70 90 295 8:1 67 86 295 3:1 65 82 350 12:1 72 68 350 8:1 70 66 350 3:1 59 48 Table I shows that both conversion of propylene and selectivity to isopropanol suffer drastically at low water to propylene molar ratios. The present invention, therefore, permits one to operate a continuous process at essentially constant conversion with the accompanying temperature increase and yet maintain good selectively to the desired product.

Example Ill In the runs set forth in Table II, the separations were accomplished by gravity in a separatory funnel, except for those marked with an asterisk for which a Racor Model 2000 SM Filter Separator was used.

Table II Aqueous Phase Organic Phase Wt % -Wt% Extractant/ % Extraction Volume Extractant/ Alcohol/ Alcohol % Water Run Mixture Weight (g) (cc) Alcohol/Water Water Extractant Removed A LSR/IPA-H2O(A) NA/NA/NA 1000/100 90.2/9.4/0.40 0/28.5/71.5 96. 68.

B ULR/IPA-H2O(A) 744.9/79.59 1000/100 91.2/8.3/0.41 0/25/75 97. 65.

C ULR/IPA-H2O(A) 374.8/80.66 500/100 83.5/15.3/1.2 0/31.3/68.7 97. 48.

D ULR/IPA-H2O(A) 187.9/80.85 250/100 70.4/26.3/3.3 0/42/58 99. 11.

*E ULR/IPA-H2O(A) NA/NA 250/100 70.4/26.3/3.3 NA/NA/NA NA NA F ULR/EtOH-H2O 372/40.3 500/50 92.6/7.0/0.44 6.3/73.4/20.4 77.3 56.5 (90-10) *G ULR/EtOH-H2O NA/NA 500/50 92.8/6.8/6.4 NA/NA/NA NA NA (90-10) *H ULR/IPA-H2O(A) NA/NA 1000/100 NA/NA/.31 NA/NA/NA NA NA I ULR/IPA-H2O 368.5/41.85 500/50 92.2/7.5/0.35 0/22.3/77.7 94.8 86.9 (75-25) J ULR/IPA-H2O 554.5/42.06 750/50 94.8/5.01/0.22 0/20.8/79.2 92.8 82.8 (75-25) NA=Not Analyzed RunsA-E, and H-J of Table II include the results of conducting a process in accordance with the present invention and demonstrate the effects of the composition of the hydrocarbon extractant, the ratio of extractant to alcohol solution, and coalescer treatment.Runs A-D, I and J were gravity separations in which the parenthetically indicated amounts in weight percent of the extraction mixture components were mixed in a separatory funnel and the phases were allowed to separate. Runs E and H were filter coalescer treatments in accordance with the invention in which the extraction mixture components were mixed and passed through a Racor Model 2000 SM Filter Separator.

In Run A, a light straight run gasoline (LSR) was used as the extractant in a 10 to 1 volume ratio with the isopropanol-water azeotrope (lPA-H20(A)). The top layer after extraction consisted of 91.6% LSR, 8.1% IPA and 0.30% H20 by volume. Over 96% of the isopropanol in the azeotrope was extracted in the gasoline. About 68% of the water originally present is the azeotrope separated into a lower layer.

In a commercial operation, the very small layer ( < 1/100 of the total gasoline volume) could be recycled to the azeotrope-producing distillation unit resulting in no net loss of isopropanol. The hydrocarbon layer (upper IPA-gasoline layer) had octane values about 4.3 F-l and 2.9 F-2 units higher than the base gasoline used in the blending process. So gasoline upgrading is easily and economically accomplished by the process of the present invention.

Comparison of Runs A and B indicates that the nature of the hydrocarbon mixture does not significantly affect the composition or the relative quantities of the layers obtained.

Comparison of Runs B and H and D with E demonstrates that rapid filter coalescer phase separation procedure and slow gravity phase separation procedure produce layers having the same relative composition and amount.

Runs B, C and D all using Chevron Unleaded Regular (ULR) demonstrate the effect of varying the hydrocarbon to azeotrope ratio. Initially, it is noted that for all ratios, no detectable amount of hydrocarbon is lost to the aqueous layer. In addition, more than 97% of the isopropanol was extracted into the hydrocarbon. As noted above, the isopropanol remaining in the aqueous phase could be recycled to the azeotrope-producing distillation unit to eliminate loss of isopropanol.

As the hydrocarbon to azeotrope ratio decreases, the amount of water in the resulting blend increases. At a ratio of 2.5 to 1 (Run D), the gasoline-isopropanol blend contains 3.3 weight percent water, an unacceptably high level. In such cases the relative amount of water can be reduced by simply adding more hydrocarbon blending components to the extracted mixture. This will also decrease the relative amount of isopropanol in the blend, which may be undesirable.

Runs F and G demonstrate the unexpectedly beneficial results obtainable with the present process. For comparison in Run F, unleaded regular gasoline was used to extract ethanol out of a 90 10 wt % ethanol-water mixture, which approximates the composition of the isopropanol-water azeotrope. At a hydrocarbon to aqueous solution ratio of 10:1, only 77.3% of the ethanol was extracted from the solution. Moreover, the aqueous phase contained 6.3% gasoline, whereas no gasoline was lost to this phase where isopropanol was used.

Claims (15)

Claims

1. A process for producing isopropanol comprising the steps of reacting a feedstock comprising propylene with water under mixed phase hydration conditions in the presence of a cation exchange catalyst in the acid form, said hydration conditions including a temperature of from 275-3750F, a pressure of from 1000 to 2000 psi, a water to propylene molar ratio of from 5 to 1 5 and a propylene liquid hourly space velocity of from 0.15-1.5, and thereafter recovering from the resulting crude product an aqueous isopropanol solution.

2. A process according to Claim 1, wherein the feedstock comprises C3 hydrocarbons having a propylene content of from 60 to 85%.

3. A process according to Claim 2, wherein the feedstock consists essentially of C3 hydrocarbons having a propylene content of from 60 to 85%.

4. A process according to Claim 1, 2 or 3, wherein the temperature is from 290--3500F, the pressure is from 14001500 psi, the liquid hourly space velocity is from 0.4 to 0.5 and the water to propylene molar ratio is from 8 to 12.

5. A process according to Claim 1, 2, 3 or 4, wherein the water to propylene molar ratio is about 8.

6. A process according to Claim 1, 2, 3, 4 or 5, wherein the conversion of propylene is maintained at a substantially constant level between 50 and 90%.

7. A process according to Claim 6, wherein the conversion is maintained at about 67%.

8. A process according to any preceding claim, wherein the catalyst is a sulfonated macro reticular copolymer of styrene and divinylbenzene in the acid form.

9. A process according to Claim 8, wherein said catalyst is in a chlorinated form.

10. A process according to any preceding claim, wherein the aqueous isopropanol solution has an isopropanol content of at least 50 weight percent.

11. A continuous process for producing an oxygenated gasoline composition, which comprises the steps of: (a) producing a first stream comprising an aqueous isopropanol solution having an isopropanol content of at least 50% by weight by means of the process claimed in Claim 10; (b) mixing said first stream with a second stream comprising a gasoline blending hydrocarbon; (c) coalescing water out of the resulting mixture; and (d) recovering the resulting organic phase which consists essentially of isopropanol and the gasoline blending hydrocarbon stream.

12. A process according to Claim 11, wherein the aqueous isopropanol solution is an isopropanol-water azeotrope.

13. A process according to Claim 11 or 12, wherein the gasoline blending hydrocarbon stream is comprised of a mixture of hydrocarbons boiling in the gasoline range.

14. A process according to Claim 11, 1 2 or 13, wherein the gasoline blending hydrocarbon stream and the isopropanol solution are mixed at a volume ratio of at least 2:1.

15. A process according to Claim 14, wh'erein the volume ratio is at least 10:1.

1 6. A process according to any one of Claims 11 to 15, wherein step (c) is conducted by passing the mixture through water coalescer means.

1 7. A process according to Claim 16, wherein the water coalescer means is a filter separator.