WO2000012651A1

WO2000012651A1 - Use of catalytic distillation to remove impurities from solvents by hydrogenation

Info

Publication number: WO2000012651A1
Application number: PCT/US1999/018662
Authority: WO
Inventors: Steven E. Silverberg; Nicola Torre; Ram N. Bhatia
Original assignee: Exxon Chemical Patents Inc.
Priority date: 1998-08-28
Filing date: 1999-08-16
Publication date: 2000-03-09
Also published as: AU5567399A; AR020261A1

Abstract

A process is disclosed for hydrogenating impurities in a solvent feed, wherein the solvent feed and hydrogen are fed to a catalytic distillation tower, the impurities in the solvent feed are hydrogenated in the catalytic distillation tower to form a hydrogenation product, the hydrogenation product is fed to a distillation tower, and the hydrogenation product is distilled in the distillation tower to produce a product solvent. The light components and treatgas are distilled from the hydrogenation product in the catalytic distillation tower, before the hydrogenation product is fed to the distillation tower. The catalytic distillation tower includes a catalytic zone, and the solvent feed is fed to the catalytic distillation tower above the catalytic zone. Furthermore, hydrogen is fed to the catalytic distillation tower below the catalytic zone. Preferably, the catalytic zone is retrofitted with catalytic distillation packing within a standard distillation tower. In addition, the process includes the step of removing heavy by-products as bottoms from the distillation tower.

Description

USE OF CATALYTIC DISTILLATION TO REMOVE IMPURITIES FROM SOLVENTS BY HYDROGENATION

The present invention relates generally to the production of aliphatic solvents having reduced amounts of impurities. In particular, it relates to the production of solvents from which impurities are removed by hydrogenation, wherein a single catalytic distillation tower replaces the fixed-bed reactor and light component distillation tower that are used in known processes for production of solvents having reduced impurity levels. For the purposes of this application, an impurity is a material selected from the group consisting of olefms, diolefins, aromatics, oxygenates and combinations thereof.

BACKGROUND OF THE INVENTION Aliphatic solvents can be purified of various olefinic or aromatic impurities by hydrogenation. For example, an isoparaffinic solvent feed containing olefinic components can be saturated by hydrogenating the olefinic compounds according to the following reaction:

C„H_2n + H, → C_nH_2n+2 According to known methods, the isoparaffm solvent feed containing olefinic components is saturated by hydrogenating the olefinic compound in a fixed-bed reactor. Following hydrogenation, the reactor effluent is sent to a first tower, where the treatgas and light components are removed, preferably to conform with IBP specifications. Bottoms from the first tower are fed to a second tower, where olefm-free isoparaffm solvent is recovered as liquid distillate. Thus, three separate vessels are required for this hydrogenation purification process.

Similarly, aliphatic solvent feeds, e.g., naphtha, kerosene or other refinery streams from which solvents are derived that contain aromatic compounds such as benzene, can be dearomatized and thus purified by hydrogenating the aromatic compounds. According to known methods, the hydrogenation step takes place in a fixed-bed reactor according to the following reaction: C₆H₆ + 3 H₂ → C₆H₁₂ As discussed above in relation to the removal of olefinic components, the resulting reactor effluent is sent to a first tower where treatgas and light components are removed to meet IBP specification. Bottoms from the first tower are fed to a second tower where product solvent is recovered as liquid distillate. Thus, three separate reaction vessels are also required for this process.

Both of these processes require a fixed-bed reactor and at least two distillation towers, as shown in Figure 1. Figure 1 depicts a standard hydrogenation process employed in the art. This prior art process for the removal of impurities from solvent employs a multi-component system generally referred to by reference numeral 10. System 10 includes fixed-bed reactor 12, first tower 14 and second tower 16. First tower 14, second tower 16, and fixed-bed reactor 12 are linked in series by conduits 18 and 20, respectively.

First tower 14 also has a conduit 22 leading into it. The light components are separated from the solvent feed from conduit 22 by distillation and taken overhead from first tower 14 via conduit 27. The first distillation product is fed by conduit 18 into second tower 16. In second tower 16, the second distillation product is removed by known distillation methods from the effluent, and is taken overhead via conduit 20 to fixed bed reactor 12. The heavy byproducts are taken as bottoms from second tower 16 via conduit 17. Conduit 26 brings hydrogen, preferably in the form of H₂ gas, into conduit 20 where it intermingles with the effluent of towers 14, 16 for delivery to fixed-bed reactor 12. The impurities in the solvent feed are then hydrogenated in fixed-bed reactor 12. The hydrogenation product effluent of fixed-bed reactor 12 is then fed by conduit 25 under elevated pressure into flash unit 29, where H₂ gas is removed overhead via conduit 31. The effluent from flash unit 29 is conveyed via conduit 33 to third distillation tower 35. The product solvent is removed from tower 35 as bottoms via conduit 37. Accordingly, at least four separate reaction vessels are required to remove the impurities from the solvent. As such, substantial operating costs are incurred to maintain the four distinct reaction vessels. In addition, initial capital costs are high.

Accordingly, a need exists for an improved, simplified, more efficient process for the hydrogenation purification of solvent feeds.

It has been suggested in the past to apply catalytic distillation to a wide variety of processes such as butene isomerization (see US-A-2403672 to M.P. Matuzak); the hydrolysis of low molecular weight olefin oxides to produce mono- alkylene glycols (see US-A-2839588 to A.S. Parker); and the production of methyl tertiary butyl ether (MTBE) (see US-A-3634535 to W. Haunschild). These early disclosures did not lead to commercialization. Catalytic distillation is only now emerging as a commercially viable hydrocarbon conversion and petrochemical processing tool.

Advantages attributed to the catalytic distillation concept, wherein reaction products are continuously separated from the reactants and removed from the reaction zone by fractional distillation performed concurrently with the reaction, include a decrease in the capital cost of the plant needed to perform the process, the ability to achieve a higher degree of conversion, and the ability to perform processes which formerly were performed only in a batch type operation on a continuous basis. These advantages result from performing the reaction in a separation zone capable of removing the reaction products from the reactants and catalyst. Hence, it is only necessary to provide one primary vessel and the reaction is not limited by chemical equilibrium. The present inventors have developed a unique two-step process which is capable of producing a high yield of hydrogenated solvent with high selectivity without the use of a fixed-bed reactor.

Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the annexed drawings.

SUMMARY OF THE INVENTION A process is disclosed for hydrogenating impurities in a solvent feed, wherein the solvent feed and hydrogen are fed to a catalytic distillation tower, the impurities in the solvent feed are hydrogenated in the catalytic distillation tower to form a hydrogenation product, the hydrogenation product is fed to a distillation tower, and the hydrogenation product is distilled in the distillation tower to produce a product solvent. The light components and treatgas are distilled from the hydrogenation product in the catalytic distillation tower, before the hydrogenation product is fed to the distillation tower.

In the preferred embodiment, the catalytic distillation tower includes a catalytic zone, and the solvent feed is fed to the catalytic distillation tower above the catalytic zone. Furthermore, hydrogen is fed to the catalytic distillation tower below the catalytic zone. The catalytic zone is preferably retrofitted with catalytic distillation packing within a standard distillation tower. In addition, the process includes the step of removing heavy by-products as bottoms from the distillation tower.

The processes of the present invention are streamlined and cost-efficient, providing both capital and operating cost savings. Moreover, high selectivity can be achieved with the two-component hydrogenation system of this invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 (discussed above) is a schematic representation of the prior art process wherein a solvent stream is hydrogenated in a fixed-bed reactor, light components and treatgas are separated in a first tower, and the product solvent is then distilled out of the effluent in a second tower;

Figure 2 is a schematic representation of the process according to a preferred embodiment of the present invention wherein the solvent feed is hydrogenated, and treatgas and light components are removed overhead, in a catalytic distillation column or tower, and the effluent is then distilled out in a second tower;

Figure 3 is a schematic representation of a second preferred embodiment of the process of the present invention;

Figure 4 is a schematic representation of a third preferred embodiment of the process of the present invention; and Figure 5 is a schematic representation of a fourth preferred embodiment of the process of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment according to the present invention is depicted in Figure 2. Instead of the four-component system of the prior art, the present invention requires only a two-component system, generally referred to in Figure 2 by reference numeral 34. System 34 includes catalytic distillation tower 35 and distillation tower 36. Catalytic distillation tower 35 includes catalytic zone 37, preferably situated in a middle portion of catalytic distillation tower 35. Catalytic zone 37 preferably includes a known hydrogenation catalyst, such as massive nickel, nickel-molybdenum, cobalt molybdenum, platinum, palladium, copper chromite and combinations thereof. Catalytic zone 37 can be retrofitted within a conventional distillation column by means of catalytic packing. Catalytic distillation tower 35 may preferably contain: a lower fractionation zone having multiple vapor-liquid contacting trays, a central catalytic zone 37 having one or more catalyst beds in packing structure, and an upper fractionation zone having one or more fractionation or equilibrium trays. Preferably, lower fractionation zone includes between about one to about 50 vapor-liquid contacting trays, and upper fractionation zone includes between about one to about 50 fractionation trays.

In a tower, such as catalytic distillation tower 35, equilibrium exists between gas and liquid throughout the length of the column. In addition, the column is preferably operated at a pressure at or below about 50 psig. Because the reaction product is continuously being separated from the reactants by fractional distillation in catalytic distillation tower 35, the process can run on a continuous basis instead of a batch-type basis. Thus, the reaction is not curtailed by reaching chemical equilibrium.

The solvent feed is fed into catalytic distillation tower 35 through conduit

38, preferably from storage tank 39, and enters catalytic distillation tower 35 at a location above catalytic zone 37. Hydrogen, preferably in the form of H₂ gas, is fed into catalytic distillation tower 35 via conduit 40. It is preferred that the hydrogen gas be fed into catalytic distillation tower 35 at a location below catalytic zone 37. Various impurities in the solvent feed, as illustrated further below, are hydrogenated in catalytic distillation tower 35. Treatgas (preferably including H₂ gas) and light components are selectively distilled away from catalytic zone 37 as hydrogenation takes place, thus eliminating the need for a separate distillation column to remove those components. This light component and treatgas vapor phase is taken overhead via conduit 42. The resulting effluent of catalytic distillation tower 35 is taken as bottoms and fed via conduit 44 to distillation tower 36. In distillation tower 36, the desired product solvent is recovered as liquid distillate via conduit 46. Heavy by-products of the reactions are taken as bottoms from distillation tower 36 via conduit 48. It is preferred that the solvent feed consists essentially of a commodity chemical which provides the specific function of solvating a substance and then ultimately evaporating.

Two preferred examples of the foregoing process are the dearomatization of aliphatic solvents, and the removal of olefins from isoparaffinic solvents. First, dearomatized aliphatic solvents can be produced by this process. Aromatic components in an aliphatic solvent feed are hydrogenated using catalytic distillation according to the present invention. Preferred solvent feeds for use in the present invention include hexane-rich naphtha or Varsol. The aliphatic solvent feed and hydrogen are fed to catalytic distillation tower 35, where the aromatic compounds are hydrogenated in the catalytic reaction zone 37 according to the following equation:

C₆H₆ + 3 H₂ → C₆H₁₂ Preferably, the catalytic distillation tower 35 can be a distillation column (as used in the prior art process) that has been retrofitted internally with catalytic distillation packing to become a catalytic distillation tower. In order to meet IBP specifications, the light components and treatgas are removed as overhead, and the dearomatized solvent is recovered as the bottoms product. The hydrogenation reaction and light component separation take place simultaneously in catalytic distillation tower 35. Accordingly, this eliminates the need for an external fixed- bed reactor, and permits the reaction to run continuously.

Similarly, olefins in isoparaffinic solvents can be hydrogenated using this catalytic distillation process. The isoparaffinic solvent feed and hydrogen are fed to catalytic distillation tower 35, where the olefinic components are hydrogenated in the catalytic reaction zone 37, which preferably contains catalytic distillation packing, according to the following general equation:

C„H_2n + H₂ → C_nH_2n+2 The treatgas and light components are removed as overhead and the substantially olefm-free solvent is simultaneously recovered as the bottoms product and fed to distillation column 36, where the heavy by-products are separated from the product solvent by conventional distillation processes. This process eliminates the need for an external fixed-bed hydrogenation reactor, and permits the reaction to run continuously.

Generally, in the lower fractionation zone, lights are stripped from saturated materials and heavies; in the catalytic zone, the lights are hydrogenated, and saturated materials and heavies are separated from lights; and in the upper fractionation zone, saturated materials and heavies are separated out from lights. The solvent feed preferably includes aliphatic hydrocarbons, crude oil fractions, and isoparaffinic hydrocarbon alkylates. The crude oil fractions include naphtha, desulfurized crude oil fraction, kerosene or a combination thereof.

The following experimental data demonstrate the operating parameters of an embodiment of the present invention versus those of the prior art.

HEXANE

Conventional Catalytic

Hydrogenation Distillation

Pressure (psig) 200 and up 25/50

Temperature (°F) 200-450 (adiabatic) 200/230 (isothermal)

Catalyst Massive nickel Massive nickel hydrogenation catalyst hydrogenation catalyst

WHSV(weight hourly space velocity-lb/hour/ lb of catalyst) < 1.5 0.2 (distillate)

Treatgas Ratio

(hydrogen to feed ratio) > 1000 SCF/Bbl 900-1300 SCF/Bbl dist.

Reflux Ratio (R/D) - 2.8

Conversion > 99% 96%

The processes of the present invention provide the unexpected result of being able to hydrogenate at low pressures, i.e., full vacuum to about 50 psig, in a catalytic distillation reactor, versus normal hydrogenation processes which operate at pressures of 200 to 3,000 psig. In turn, lower capital costs are required to set up these low pressure systems. Furthermore, reduced energy costs are required to operate these low pressure systems. Typical operating temperatures will be consistent with standard distillation temperatures.

Figure 3 through 5 depict three alternative preferred embodiments of the process of the present invention. As shown in Figure 3, the process of Figure 2 can be modified such that catalytic distillation tower 35 is downstream from distillation tower 36. As shown in Figure 4, the process of Figure 2 can be modified by locating conduit 38, which brings the solvent feed from storage tank 39, below the height of catalytic zone 37. As shown in Figure 5, this modification can also be made to the process of Figure 3.

Thus, the more preferred embodiments of the invention include: A process for hydrogenating materials selected from the group consisting of olefins, diolefms, aromatics, oxygenates and a combination thereof in a solvent feed, or a method of removing impurites from a solvent feed, wherein said impurities comprise materials selected from the group comprising olefins, diolefms, aromatics, oxygenates and combinations thereof, said process comprising:

(a) feeding said solvent feed and hydrogen to a catalytic distillation tower; and

(b) hydrogenating said material in said solvent feed in said catalytic distillation tower to form a hydrogenation product; and a variation wherein said process further comprising:

(c) feeding said hydrogenation product to a distillation tower; and

(d) distilling said hydrogenation product in said distillation tower to produce a product solvent; or wherein said hydrogenation product includes light components and treatgas, and said light components and treatgas are distilled from said hydrogenation product before said hydrogenation product is fed to said distillation tower; or wherein said catalytic distillation tower includes a catalytic zone, and wherein said solvent feed is fed to said catalytic distillation tower above said catalytic zone; or wherein said catalytic distillation tower comprises a lower fractionation zone, an upper fractionation zone, and a catalytic zone disposed between said lower and upper fractionation zones; or wherein said catalytic distillation tower includes a catalytic zone, and wherein said hydrogen is fed to said catalytic distillation tower below said catalytic zone; or wherein said catalytic zone is retrofitted with catalytic distillation packing within a distillation tower; or further comprising the step of removing heavy by-products as bottoms from said distillation tower; or wherein said impurities are converted to saturates in an amount greater than about 95%; or wherein said catalytic distillation tower is operated at a pressure at or below about 50 psig; or wherein said catalytic distillation tower contains a catalyst selected from the group consisting of massive nickel, nickel-molybdenum, cobalt molybdenum, platinum, palladium, copper chromite and combinations thereof; or wherein said lower fractionation zone comprises between about one to about 50 vapor-liquid contacting trays; or wherein said upper fractionation zone comprises between about one to about 50 fractionation trays; ' or wherein in said lower fractionation zone, lights are stripped from saturated materials and heavies; in said catalytic zone, said lights are hydrogenated, and saturated materials and heavies are separated from lights; and in said upper fractionation zone, saturated materials and heavies are separated out from lights; or wherein said solvent feed includes aliphatic hydrocarbons, crude oil fractions, and isoparaffinic hydrocarbon alkylates; or wherein said crude oil fractions include a component selected from the group consisting of naphtha, desulfurized crude oil fraction, kerosene or a combination thereof; or a combination of the above variations, or variations described below.

In another preferred embodiment, the invention includes: a process of removing impurities from a solvent feed comprising feeding said solvent feed and hydrogen to a catalytic distillation tower and hydrogenating said impurities in said catalytic distillation tower to form a hydrogenation product; with even more preferred embodiments wherein said impurities are selected from the group consisting of olefins, diolefms, aromatics, oxygenates, and a combination thereof, or wherein said process consists essentially of the dearomatization of aliphatic solvents or the removal of olefins from isoparaffinic solvents, or wherein said said solvent feed is fed into said catalytic distillation tower above the catalytic zone, said hydrogen is feed into said catalytic distillation tower below the catalytic zone, or any combination thereof.

The invention having been thus described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

WE CLAIM::

1. A process for hydrogenating materials selected from the group consisting of olefins, diolefms, aromatics, oxygenates and a combination thereof, in a solvent feed, comprising: (a) feeding said solvent feed and hydrogen to a catalytic distillation tower; and

(b) hydrogenating said material in said solvent feed in said catalytic distillation tower to form a hydrogenation product.

2. The process according to Claim 1, wherein said catalytic distillation tower includes a catalytic zone, and wherein said solvent feed is fed to said catalytic distillation tower above said catalytic zone and said hydrogen is fed to said catalytic distillation tower below said catalytic zone.

3. The process according to Claim 1 , wherein said catalytic distillation tower includes a catalytic zone, and further wherein said catalytic zone is retrofitted with catalytic distillation packing.

4. The process according to Claim 1, wherein said catalytic distillation tower is operated at a pressure at or below about 50 psig.

5. The process according to Claim 1, wherein said catalytic distillation tower contains a catalyst selected from the group consisting of massive nickel, nickel-molybdenum, cobalt molybdenum, platinum, palladium, copper chromite and combinations thereof.

6. The process according to Claim 1, wherein said solvent feed is selected from aliphatic hydrocarbons, crude oil fractions, or isoparaffinic hydrocarbon alkylates.

- ╬╣:

7. The process according to Claim 6, wherein said solvent feed is selected from the group consisting of naphtha, desulfurized crude oil fraction, kerosene or a combination thereof.

8. A process of removing impurities from a solvent feed comprising feeding said solvent feed and hydrogen to a catalytic distillation tower and hydrogenating said impurities in said catalytic distillation tower to form a hydrogenation product, wheerein said impurities are selected from the group consisting of olefins, diolefms, aromatics, oxygenates, and a combination thereof.

9. The process according to Claim 8, said process consisting essentially of the dearomatization of aliphatic solvents or the removal of olefins from isoparaffinic solvents.

10. The process according to Claim 8, wherein said solvent feed is fed tinto said catalytic distillation tower above the catalytic zone and the hydrogen is fee into said catalytic distillation tower below the catalytic zone.