WO1999048845A1

WO1999048845A1 - Sulfuric acid alkylation reactor system with static mixers

Info

Publication number: WO1999048845A1
Application number: PCT/US1999/005712
Authority: WO
Inventors: Brian A. Cunningham; Saverio G. Greco
Original assignee: Mobil Oil Corporation
Priority date: 1998-03-20
Filing date: 1999-03-16
Publication date: 1999-09-30
Also published as: AU3451699A

Abstract

A sulfuric acid-catalyzed alkylation reactor system is provided for alkylating isoparaffins with olefins to produce hydrocarbon alkylates. The reactor vessel has a vertical cylindrical wall, a top, an inverted conical bottom portion, internal perforated baffles and multiple emulsion injection inlet pipes, disposed tangentially to and communicating with the interior of the reactor vessel. The emulsion injection inlet pipes have static mixers incorporated therein and tangential injection of the emulsion imparts a circular motion to the contents of the reactor vessel, resulting in partial phase separation of the reacted products. The reactor vessel communicates with a settling vessel through a transfer pipe having a vertical portion suspended within the central portion of the reactor vessel and a horizontal portion sealably extending through the cylindrical wall of the reactor vessel. The transfer pipe has a first end near the conical bottom portion of the reactor vessel and a second end at a top portion of the settling vessel. The reactor system enables a sulfuric-acid catalyzed reaction of olefins with isoparaffins utilizing static mixing of the reactants, and minimizing leakage of the reactants to the environment.

Description

1

SULFURIC ACID ALKYLATION REACTOR SYSTEM WITH STATIC MIXERS

In gasoline manufacture, it is known to alkylate short-chain isoparaffins with short- chain olefins, in the presence of an acid catalyst, to obtain longer-chain branched paraffins with an increased octane rating. However, handling of the acid catalyst causes environmental and safety concerns, due to the possibility of leaks in the reactor system.

The present invention reduces the possibility of leaks in the reactor system, by reducing the number of moving parts entering or exiting the reactor, which must be sealed against acid and hydrocarbon leakage.

Worldwide economic development has resulted in increasing demand for petroleum energy products, especially gasoline. However, health and safety concerns with respect to the aromatic content of gasolines may result in a decrease in octane rating of gasolines in the absence of other sources of high-octane blend stocks. Additionally, increasing phaseout of lead-based additives around the world exacerbates the problem of maintaining sufficient octane rating of gasolines for proper engine performance.

A class of petroleum-derived compounds known to have particularly high octane ratings are branched paraffins, having from 6 to 12 carbon atoms. Unfortunately, the amount of naturally occuring Cβ-ι₂ branched paraffins in crude petroleum is limited and is insufficient to meet the increasing demand for high octane blend stocks. Accordingly, the petroleum industry has developed methods for synthesizing branched paraffins from existing materials to supplement the naturally existing supply of such high-octane materials.

One important method of obtaining branched Cβ-i2 paraffins, termed "alkylates", is by acid catalyzed alkylation of short-chain isoparaffins with short-chain olefins, derived from various refinery processes. Presently, two commercially successful acid catalyzed alkylation systems are being utilized: A sulfiiric acid catalyzed system and a hydrofluoric acid (HF) catalyzed system.

Each system has its benefits and detriments. The sulfiiric acid catalyzed system is conducted at low-temperatures, from 2° to 7°C, while the HF catalyzed system is conducted at ambient to elevated temperatures from 20° to 40°C. Therefore, the sulfiiric acid catalyzed system is relatively more complex and energy intensive, requiring some source of refrigeration of the reactants and/or the reactor to work effectively.

Unfortunately, the high reactivity of HF also means that it is extremely corrosive, requiring the use of unusually inert (and expensive) materials of construction in the reactor system. In contrast, the relatively lower reactivity of sulfiiric acid, combined with its much lower vapor pressure, means that sulfiiric acid catalyzed systems are more easily and less expensively built and maintained. Still, sulfiiric acid is hardly innocuous, being itself highly reactive and corrosive, and the larger volume of sulfiiric acid catalyst necessary for use in sulfiiric acid catalyzed alkylation systems raises significant concerns with respect to liquid leakage.

Two major designs of sulfiiric acid reactor systems are currently in use, both of which were developed in the 1940's and have received few major improvements in the ensuing years. Both major systems, the horizontal contactor (Fig. 4), commonly known as the effluent refrigeration system, and the cascade reactor (Fig. 5), commonly known as the Cascade Auto Refrigeration system, employ stirrers or impellers 30 with externally mounted motors and rotating shafts running into the reactor vessel, which must be sealed against leakage to the ambient environment. The stirrers are used to create and maintain an emulsion within the system, assuring maximum reactive surface area and intimate contact between the reactants and the catalyst, so as to maximize the reaction efficiency. Notably, the horizontal contactors of Fig. 4, which are usually used in pairs due to their limited capacities (2500 BPSD), may potentially leak at the large diameter shaft seals. Likewise, in the Cascade Auto Refrigeration reactor of Fig. 5, which typically employs 5 to 7 stirrers, potential for leakage exists at each stirrer shaft seal.

Accordingly, isolation of the reactor contents from the ambient environment is difficult to maintain, especially at the seals around the¹ rotating shafts of the stirrer motors.

Therefore, it would be advantageous and desirable to reduce or eliminate the number of moving parts entering the alkylation reactor system which must be sealed against leakage, such as rotating motor shafts, while maintaining an emulsion within the reactor to maximize reaction efficiency. 3

A first object of the present invention is to provide a sulfiiric acid alkylation reactor system having few or no moving parts entering the reactor which must be sealed against leaks to the ambient environment.

A second object of the present invention is to provide a safer sulfiiric acid alkylation reactor system in which, in the event of a leak to ambient, the system can be easily and rapidly shut-down, so as to minimize the volume of the leak.

A third object of the present invention is to provide a sulfiiric acid alkylation reactor which is less expensive to build and maintain, relative to existing reactor systems, and also has a lower operating cost. A fourth object of the present invention is to provide a sulfiiric acid alkylation reactor system in which some degree of phase separation is achieved between the sulfiiric acid and hydrocarbon phases of the reaction products, so as to increase the efficiency of the phase separation step, and thereby the overall efficiency of the system.

The above objects are realized in that in one embodiment of the present invention, a sulfiiric acid-catalyzed alkylation reactor system is provided for alkylating isoparaffins with olefins, to produce hydrocarbon alkylates. The reactor vessel has a vertical cylindrical wall, a top, an inverted conical bottom portion and internal perforated baffles, and communicates with a settling vessel for separating the sulfiiric acid from the alkylate through a transfer pipe having a vertical portion suspended within the central portion of the reactor vessel and a horizontal portion sealably extending through the cylindrical wall of the reactor vessel. The transfer pipe has a first end near the conical bottom portion of the reactor vessel and a second end at a top portion of the settling vessel. Multiple emulsion injection inlet pipes are disposed tangentially to and communicate with the interior of the reactor vessel, for injecting emulsified reactants into the reactor vessel. In another embodiment, the present invention is directed to a process for alkylating at least one isoparaffin with at least one olefin, in the presence of sulfiiric acid catalyst, to produce a hydrocarbon alkylate. A first liquid stream comprising the isoparaffin(s) is combined with a second liquid stream comprising sulfiiric acid and the combined streams are passed through at least one static mixer to form an isoparaffin/ sulfiiric acid emulsion stream. A third liquid stream comprising the olefin(s) is combined with the isoparaffin/sulfuric acid emulsion stream and the further combined streams are passed through at least one static mixer 4 to form an olefin/isoparaffin/sulfuric acid emulsion stream. The olefin/isoparaffin/sulfuric acid emulsion stream is injected into a reactor vessel having a vertical cylindrical wall, in a direction tangential to the cylindrical wall and with sufficient force to impart a circular motion to the olefin/isoparaffin/sulfuric acid emulsion within the reactor vessel, wherein the olefin is reacted with the isoparaffin to form a hydrocarbon alkylate/isoparaffin/sulfuric acid mixture.

The above and other objects, features and advantages of the present invention will be better understood from the following detailed descriptions taken in conjunction with the accompanying drawings, all of which are given by way of illustration only, and are not intended to be limitative of the present invention. Fig. 1 is a cross-sectional diagram of the sulfiiric acid alkylation system of the present invention.

Fig. 2 is an enlargement of the cross-section of the reactor vessel of the present invention.

Fig. 3 is a horizontal section along line A-A of Fig. 2, which illustrates the internal arrangement of the elements in the reactor vessel of the present invention.

Fig. 4 is a cross-sectional diagram of the prior art horizontal contactor sulfiiric acid alkylation reactor system.

Fig. 5 is a cross-sectional diagram of the prior art cascade sulfiiric acid alkylation reactor system. The following detailed description of the invention is provided to aid those skilled in the art in practicing the present invention. Even so, the following detailed description of the invention should not be construed to unduly limit the present invention, as modifications and variations in the embodiments herein discussed may be made by those of ordinary skill in the art without departing from the spirit or scope of the present inventive discovery. The reactor system of the present invention is illustrated in Fig. 1, and incorporates a vertical, cylindrical reactor vessel 10 with an inverted conical bottom portion 10a, having disposed centrally therein a vertical portion of a U-shaped transfer pipe 25, with a first end disposed toward the inverted conical bottom portion 10a, for transfer of reacted materials and catalyst to a separator vessel 20. Ideally, the vertical portion of the transfer pipe is disposed coaxially with the axis of the cylindrical reactor vessel. The horizontal run of the transfer pipe extends through the vertical wall of the reactor vessel, and is sealed against leakage at its contact points with the vertical wall. The other vertical portion of the tranfer pipe 25 empties into the phase separation vessel 20, wherein the mixed emulsion of sulfiiric acid catalyst and hydrocarbon reaction products, including the desired alkylate, are left to settle and separate, based upon the differences in specific gravities between the two phases. The reactants for the system are derived from separate sources within a typical refinery, which are conventional and not depicted. The incoming isoparaffin, typically isobutane, passes from the isoparaffin source, not shown, through line 16, and combines with a sulfiiric acid-rich emulsion exiting the inverted conical bottom portion of the reactor. The combined isoparaffin/sulfiiric acid stream passes through emulsion pump 17, which partially emulsifies the stream by the action of the pump impeller, and is further combined with the relatively pure sulfiiric acid stream recycled from the bottom of the separator tank 20, and pumped through the acid pump 21, which effects further emulsification. The combined isoparaffin/sulfiiric acid stream then passes through the injection inlet pipe 11, which splits into multiple injection inlet ports near the reactor vessel 10. Each of the injection inlet pipes has disposed therein at least two static mixers 12 in series, more clearly illustrated in Figs. 2 and 3. The combined isoparaffin/sulfuric acid stream passes through at least one, but preferably multiple static mixers, so as to maximize the emulsification of the isoparaffin and sulfiiric acid. Downstream of the static mixers the olefin inlet line(s) 18 injects the olefin, typically butene, into the isoparaffin/sulfuric acid emulsion through a nozzle which disperses the olefin into small droplets. The thus-combined stream is passed through at least one more static mixer, to form an olefin/isoparaffin/sulfuric acid emulsion. The total number of static mixers in each injection inlet line may vary, but is preferably four: One or three before and one or three after the olefin inlet line connection.

As illustrated in Fig. 3, the injection inlet pipes are arranged tangentially around the cylindrical reactor vessel, and the emulsified reactant stream enters the reactor vessel with sufficient force and velocity to impart a circular motion to the emulsion within the reactor vessel. A suitable reactant stream velocity is 13 ft/sec. Within the reactor vessel are a number of perforated baffles 15, extending radially inward from the reactor vessel wall, or radially outward from the central transfer pipe, or preferably both radially inward from the reactor vessel wall and radially outward from the central transfer pipe. The perforated baffles act to further increase shear and mixing so as to maintain the reactants in the emulsified state within the reactor vessel, as the circulating emulsion contacts and passes through the baffle perforations.

In the process according to the present invention, at least one isoparaffin is alkylated with at least one olefin, in the presence of sulfiiric acid catalyst, to produce hydrocarbon alkylates. A first liquid stream comprising the isoparaffin(s) is combined with a second liquid stream comprising sulfiiric acid and the combined streams are passed through at least one static mixer to form an isoparaffin/sulfiiric acid emulsion stream. A third liquid stream comprising the olefin(s) is combined with the isoparaffin/sulfuric acid emulsion stream and the further combined streams are passed through at least one static mixer to form an olefin/isoparaffin/sulfuric acid emulsion stream, which is injected into a reactor vessel having a vertical cylindrical wall, in a direction tangential to the cylindrical wall and with sufficient force to impart a circular motion to the olefin/isoparaffin/sulfuric acid emulsion within the reactor vessel, wherein the olefin(s) is reacted with an excess of the isoparaffin(s) to form a hydrocarbon alkylate/isoparaffin/sulfuric acid mixture. It is believed that a majority, if not all, of the olefin is reacted within the last static mixer, although the inventors do not wish to be held to this theory.

Typically, the olefin feed is derived from one or more existing refinery processors, such as the fluidized catalytic cracker (FCC), a thermal cracking reactor or the coker. Any short chain olefin selected from C₂.₅ olefins, such as ethene, propene, 1-butene, 2-butene, pentenes or mixtures thereof are suitable as the olefin reactant feed stream, although the butenes are preferred.

The isoparaffin feed is derived from naturally occuring isoparaffins isolated in the refining of crude petroleum, such as isobutane, or is derived from various refinery processors, such as the FCC, coker, hydrocracker or the reformer. While isobutane is a preferred isoparaffin, the liquid fuel value of which is limited by its vapor pressure, other isoparaffins may be used, either alone or in combination with isobutane.

Therefore, the nature of the olefin and isoparaffin feeds is in theory limited only by the fact that the desired alkylate products should have boiling points within the gasoline fraction boiling range, from 40° to 200°C. Reaction parameters of the present invention are essentially the same as in the existing sulfiiric acid alkylation systems. Acid to hydrocarbon ratio is 1:1, while it is preferred that a large excess of isoparaffins relative to olefins be present, to maximize olefin conversion to alkylates. Typically, the isoparaffin: olefin ratio should be from 4:1 to 10:1, preferably 8:1 or greater. Reaction temperatures are subambient, ranging between 2° to 10°C, with cooling provided by evaporation of the isoparaffin from the surface of the reaction emulsion within the reactor vessel. Preferably, all cooling is provided by evaporation of the isoparaffin from the surface of the reaction emulsion. The evaporate is withdrawn from the top of the vessel, fed to a compressor, condensed and recycled into the system.

In contrast to the existing sulfiiric acid catalyzed alkylation processes, the olefin, the isoparaffin and the sulfiiric acid enter the reactor vessel of the present invention as an emulsion, rather than being mixed in the reactor vessel in the first instance. As the emulsion of the present invention circulates within the reactor vessel, it is maintained in the emulsion state by passing through the perforated baffles in the reactor to complete the alkylation reaction. That is, the static mixers and baffles, in combination with the emulsion and acid pumps, provide the mixing energy for forming the reactant emulsion, thus minimizing moving parts in the present system. In fact, moving parts are eliminated within the reactor vessel itself.

In further contrast to previously-known processes, the circular motion of the emulsion within the reactor vessel, in combination with the inverted conical bottom portion of the reactor vessel, acts to partially phase-separate the sulfiiric acid and hydrocarbon phases of the emulsion toward the bottom of the vessel due to the centrifugal force imparted to the emulsion and the greater specific gravity of the sulfiiric acid phase. That is, upon moving into the bottom of the reactor vessel, where the perforated baffles are absent, increased residence time is provided so that the heavier sulfiiric acid phase tends to concentrate toward the bottom portion of the vessel. This effect is enhanced by the inverted conical shape of the bottom of the reactor vessel, wherein the angular velocity and therefore the centrifugal force on the circulating acid-rich emulsion is increased.

Accordingly, the hydrocarbon/sulfuric acid mixture passing into the transfer tube or pipe 25 from the bottom of the reactor vessel is already enriched in the hydrocarbon phase, requiring less settling time in the settling tank 20 and/or a smaller settling tank. Phase separation is completed in the settling tank, with the less dense alkylate-containing hydrocarbon phase floating to the top and being collected through line 22. Any unreacted isoparaffin may be removed by flash-off or distillation, to recover the alkylate. As the process is a continuous one, level control within the system is optionally maintained by a level controller LC, the output of which is fed to control valve 23 (Fig. 1).

Therefore, the sulfiiric acid alkylation reactor of the present invention satisfies the stated objects of the present invention by eliminating moving parts which penetrate the reactor vessel, and the sealing surfaces therefor, by statically mixing the reactants and catalyst prior to their entry into the reactor vessel, and maintaining the emulsion within the vessel by static mixing through the perforated baffles. As such, the reactor system of the present invention is less expensive to build, run and maintain than previous reactor systems. And since the only moving parts which are likely to leak are the seals associated with the emulsion and acid pumps, leakage can be readily stopped by shutting down the pumps and isolating them by conventional automatic shut-off valving, thus minimizing leakage volume. In contrast, the two prior art systems will continue to leak until the entire system is depressurized.

Claims

CLAIMS:

1. A process for alkylating isoparaffins with olefins, in the presence of sulfiiric acid catalyst, to produce hydrocarbon alkylates, comprising: combining a first liquid stream comprising at least one isoparaffin with a second liquid stream comprising the sulfiiric acid and passing the combined streams through at least one static mixer to form an isoparaffin/sulfuric acid emulsion stream; combining a third liquid stream comprising at least one olefin with the isoparaffin/sulfiiric acid emulsion stream and passing the combined streams through at least one static mixer to form an olefin/isoparaffin/sulfuric acid emulsion stream; injecting the olefin/isoparaffin/sulfuric acid emulsion stream into a reactor vessel having a vertical cylindrical wall, in a direction tangential to the cylindrical wall and with sufficient force to impart a circular motion to the olefin/isoparaffin/sulfiiric acid emulsion within the reactor vessel; and reacting the olefin with the isoparaffin to form a hydrocarbon alkylate/isoparaffin/sulfuric acid mixture.

2. The process according to claim 1, wherein the circular motion effects partial phase separation of the hydrocarbon alkylate/isoparaffin/sulfuric acid mixture.

3. The process according to claim 1, further comprising transferring a portion of the hydrocarbon alkylate/isoparaffin/sulfuric acid mixture into a settling vessel, allowing the mixture to separate into hydrocarbon and sulfiiric acid phases, recirculating the sulfiiric acid phase into the second liquid stream and recovering the hydrocarbon phase.

4. The process according to claim 1, further comprising treating the hydrocarbon phase to separate the isoparaffin from the hydrocarbon alkylate, recirculating the isoparaffin into the first liquid stream and recovering the hydrocarbon alkylate.

5. The process according to claim 1 , wherein the isoparaffin comprises isobutane. 10

6. The process according to claim 1, wherein the olefin comprises butene.

7. The process according to claim 1, wherein the olefin comprises ethene.

8. The process according to claim 1, wherein the olefin comprises propene.

9. The process according to claim 1, wherein the olefin comprises pentene.