CS199659B2 - Continuous process for preparing alkylate - Google Patents

Abstract

(4888 A) IMPROVED CATALYTIC ALXYLATION PROCESS In the process for the catalytic alkylation of isobutane with an olefin to produce alkylate, the liquid reactor effluent stream comprising a hydrocarbon mixture of alkylate, isobutene and inert alkanes is used to provide cooling to the various condensers in the alkylation process.

Description

Catalytic alkylation of isobutane is well known since it is used in the production of a high octane branched hydrocarbon (alkylate) mixture by alkylating isobutane with an olefin in the presence of an acid catalyst. The alkylate obtained is of importance for use as fuel for aircraft and other internal combustion engines. Specifically, the olefin is reacted with isobutane in the reactor in the presence of an acid catalyst to produce an exothermic reaction. The acid is then separated from the mixture leaving the reactor. The de-acidized product leaving the reactor is then passed through a series of distillation columns to separate the inert alkanes, unreacted isobutane, recycle stream, and recover the alkylate. Some fractions of product leaving the reactor are additionally free of acid residues and undesired reaction products.

Hydrocarbon Processing (September 1974, p. 206) describes a variation of this process in which the reactor is cooled by evaporating a portion of the product leaving the reactor.

The prior art alkylation process has several disadvantages: A large amount of refrigerant, usually air or water, has to be used to condense the overhead column streams. While cooling the reactor, only part of the product from the reactor evaporates. The steam obtained is used as an isobutane recycle. The remaining alkylate-containing liquid and a large amount of isobutane must then be treated to remove impurities such as residual acid and then separated by distillation into isobutane and the alkylate. The larger the stream, the larger the isobutane separation column, and the greater the amount of heat to separate.

The present invention reduces or eliminates these disadvantages while substantially reducing the amount of energy that is required in the process.

SUMMARY OF THE INVENTION The present invention provides a continuous process for the production of an alkylate by reacting an olefin with a molar excess of isobutane in an alkylation zone in the presence of an acid to a liquid stream to be withdrawn from the alkylation zone. The vapors are condensed by cooling, characterized in that the vapors are cooled by indirect heat exchange with a liquid stream leaving the alkylation zone.

According to the invention, the procedure is as follows:

a) the olefin is contacted with a molar excess of isobutane and inert alkanes in the liquid phase in the presence of an acid catalyst in the reactor, wherein substantially all of the olefin reacts to form a liquid stream containing the acid catalyst and a hydrocarbon mixture containing alkylate, isobutane and inert alkanes;

(b) separating the acid catalyst from the hydrocarbon mixture, then

c) separating the hydrocarbon mixture from step b) into a liquid bottom stream comprising isobutane and an alkylate and a vapor overhead stream comprising isobutane and inert alkanes in a liquid-vapor separator;

d) compressing and condensing the steam obtained as the overhead stream in step (c) in the downstream compression condenser to form a condensed overhead steam stream, then

e) in one or more distillation columns equipped with one or more column capacitors, the liquid bottom stream of step c] or the condensed overhead vapor stream of step d) separates the isobutane from the inert alkanes and the alkylate, evaporating part of the hydrocarbon mixture from step b) to cool one or more condensates selected from the group consisting of column capacitors or downstream compression condensers.

Using the process of the invention, the amount of isobutane to be treated and isolated in the distillation column is greatly reduced, there is no need to use cooling water in the overhead condenser attached to the distillation column, and the various distillation columns can operate at substantially lower pressures, thereby intensifying division process.

It is an essential feature of the invention to use a reactor effluent stream to cool capacitors in an alkylation process. Such use of this stream will result in a substantial reduction in operating costs and, in the case of new units, also in investment costs.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a simplified block diagram of the invention; Fig. 2 shows a process of alkylation according to the invention in more detail; Fig. 3, similar to Fig. 2, shows an alternative of the invention n-butane gas is removed from the reactor and the isobutane separation column; FIG. 4 describes in detail the steam system which may be used as the steam system illustrated in the block diagram of FIG. 2 and FIG. 5 shows yet another variant of the process of the invention; wherein the process of the invention is carried out in conjunction with an alkylation reactor producing both a liquid and a gaseous product.

The olefin and isobutane feedstocks (FIG. 1) enter the reactor containing the acid catalyst. The reactor effluent stream comprises an acid catalyst, an alkylate, isoutane, and inert alkanes. This stream is fed to an acid separator where the acid catalyst is separated from the hydrocarbon mixture and returned to the reactor. The resulting hydrocarbon mixture is then fed to one or more condensers where it provides the necessary cooling. The core of the invention is the use of this hydrocarbon mixture for cooling capacitors. The current coming from the capacitors is then fed to the separator vapor liquid, where isobutane is recovered partially in the form of vapor. By treatment not shown in the figure, the steam is compressed, condensed and returned to the reactor.

The liquid phase from the separator then proceeds to the isobutane separation column, where isobutane (which is then recycled) is obtained as the overhead product and alkylate as the bottom product.

The olefin and isobutane are combined (FIG. 2) in line 101 and fed to the reactor 103 where they are mixed with the acid catalyst and reacted to form an alkylate. The product is discharged from the reactor via line 105 to the acid separator

107. Here, the acid is separated from the hydrocarbon mixture and returned to the reactor via a line

108. The hydrocarbon mixture containing the alkylate, isobutane and inert alkanes exits the separator via line 109.

The hydrocarbon mixture goes to condensers where it mediates cooling via line 111, 112. With respect to line 111, the figure shows an alternative of the invention applied to the isobutane separation column. The hydrocarbon mixture is passed through a conduit 111 to a condenser 115 where at least a portion of the hydrocarbon mixture is evaporated, thereby providing condenser cooling. The hydrocarbon mixture, after heat removal in the condenser, is passed through line 116 to the liquid-steam separator 117. In the same way, cooling of other condensers, such as other column capacitors and compression condensers for the product effluent is ensured by removing the hydrocarbon mixture through line 112, at least a portion of this hydrocarbon mixture is evaporated in the condenser and the condenser mixture is passed through line 114 to the liquid-vapor separator 117. In the same way, the hydrocarbon mixture is used to cool the reactor (line 110 and then discharged via line 113 to the liquid-vapor separator).

The separator 117 separates the liquid from the steam. The vapor contains mainly isobutane and inert alkanes and the liquid contains isobutane and alkylate. The steam is passed through line 118 where it is compressed and condensed to a steam system 119. In the steam system 119, one or more columns are used to separate inert alkanes, such as propanes, from isobutane. The isobutane stream is then discharged via line 120 to a second separator 121 for separating liquid and steam. The isobutane liquid stream is returned to the reactor through line 122 and the steam is returned to the steam system through line 118.

The liquid from the first separator 117, containing isobutane and an alkylate, then passes through line 123 to section 125 where the acid and acidic compounds are removed from the hydrocarbon mixture. After this treatment, the liquid is passed through line 129 to the isobutane removal column 131. The column is heated via line 133. Isobutane is distilled off, leaving the top of the column as steam through line 135. This vapor is condensed in the overhead condenser 115 and the condensed isobutane is then separated into reflux for the column and recycled stream to the reactor. The alkylate is obtained as a liquid stream from the bottom of the column and is discharged through line 139.

Giant. 3 is similar to FIG. 2 and shows another alternative according to the invention. The hydrocarbon mixture containing the alkylate, isobutane and inert alkanes leaves the separator 107 for separating the acid through line 109. The hydrocarbon mixture then goes to the condensers through lines 111, 112 where it provides cooling. Regarding line 111, a downstream valve 141 is placed upstream of the column condenser 115. This valve maintains the hydrocarbon mixture in line 111 in a liquid state. The valve also allows the pressure of the hydrocarbon mixture flowing into the condenser 115 and entering the line 116. The pressure is reduced sufficiently to allow the hydrocarbon mixture to evaporate in the condenser 115. A similar pressure-reducing valve 140 is located in line 110 through which it provides cooling of the reactor 103. Other pressure reducing valves (not shown) may also be located in the conduit 112 leading to other condensers.

Giant. 3 also shows the isobutane separation column 131 from which the gaseous sidestream 142. is withdrawn. This line 142 discharges the n-butane vapor in the form of a column and then condenses in the column condenser 143. Cooling of the condenser 143 is usually effected by refrigeration via line 144 However, this cooling can also be effected by means of the hydrocarbon mixture contained in line 112 if a suitable pressure reducing valve is included in the system. The side stream of n-butane can also be withdrawn with alternatives to the invention other than the particular one shown specifically in Figure 3.

Giant. 4 illustrates a steam system that can be used as a steam system 119 in the apparatus shown in FIG. 2. The hydrocarbon mixture, when used as a refrigerant, is discharged via line 113 to a liquid-steam separator 117 where steam is separated from the liquid. . The vapors are passed through line 118 to the compressor 145. In the compressor, the vapors are compressed and exit via line 146 to the condenser 147 for the stream leaving the compressor. Condenser 147 is cooled through line 148 and compressed vapor is condensed therein. Cooling water may be used as the cooling medium, but according to another alternative of the invention, hydrocarbon mixtures from line 112 may also be used when a suitable pressure reducing valve is included in the system. The compressed condensed steam is discharged from the condenser via line 149. A portion of this compressed condensed steam stream is discharged via line 150 to distillation column 152. The remainder is discharged via line 151 to a second liquid / steam separator 121, also shown in Figure 2.

The distillation column 152 is typically a propane separation column. Heat is supplied to the column via line 153. Propane is distilled off and discharges the top of the column in the form of vapors through line 154. This vapor is condensed in the overhead condenser 155. According to the invention, a hydrocarbon mixture from line 112 is used to cool this condenser. The hydrocarbon mixture, after cooling, is discharged via a line 114 to a liquid-vapor separator 117 as shown in FIG. 2.

The condensed propane from condenser 155 is then divided into reflux for the column (line 156) and also discharged to line 157. The product from the bottom of the column containing predominantly isobutane is discharged via line 138 to the steam-liquid separator 121.

Yet another variant of the present invention is shown in FIG. 5. According to this variant, the alkylation reaction is conducted by removing both gaseous and liquid streams from the alkylation reactor.

Such procedures are well known, see, for example, U.S. Patent No. 3,187,066 (Nathan).

As shown in FIG. 5, the feed is fed to reactor 172 from line 174 where alkylation is performed. The gaseous reaction product formed is discharged from the reactor 172 through line 176 and then fed to a conventional steam system 178 where isobutane is recovered. The liquid reaction product leaves the reactor 172 through line 180 and is sent to a condenser 182 where it is partially evaporated. The partially vaporized liquid effluent from the reactor is then passed through line 184 to a separator 186 where the liquid is separated from the steam. The separated steam passes through line 188 to the steam system 178 where it is treated together with the gaseous product generated in the reactor 172. The liquid stream exiting the liquid separator 186 and the vapor passes through line 190 to the isobutane separation column 192. where it divides. From the isobutane separation column 192 the produced alkylate is separated via line 194 as a product from the bottom of the column, while the isobutane-rich vapors are discharged from the column 192 via; The isobutane-rich vapor in line 196 is then passed through a condenser 182 where indirect heat exchange occurs with the liquid stream exiting the reactor 172.

Due to the cooling that is achieved at the expense of evaporation of the liquid stream from the reactor 172 in the condenser 182, the isobutane-rich vapors in the condenser 182 condense to the isobutane-rich liquid stream.

Part of this isobutane-rich liquid stream is discharged to reflux through line 198, while the remainder is recycled to reactor 172 via line 200. The condensed isobutane recovered from steam system 178 is also recycled to reactor 172 through line 202.

As will be appreciated by those skilled in the art, the steam system 178 normally includes a compressor to facilitate the condensation of the steam introduced therein. According to the invention, the compressor may, if desired, be a multi-stage compressor and, moreover, the steam introduced into the compressor from the liquid-steam separator 188 or a similar liquid-steam separator 121 in Fig. 2 need not be fed to the first, but second or subsequent stage.

The present invention has various advantages. On the one hand, since the feed rate for the isobutane separation column is reduced, the volume of the stream to be treated is reduced. This treatment typically involves washing with caustic soda and then water. In the process according to the invention, the caustic treatment apparatus can be reduced, thereby saving the investment costs of the apparatus. A second advantage is the size of the isobutane separation column. Since larger amounts of isobutane are evaporated in the stream leaving the reactor, smaller amounts of isobutane need to be separated in a distillation column. This achieves both a reduction in the column size and a reduction in the heat required to provide this operation. Yet another advantage is the use of the reactor effluent as a cooling medium for overhead condensers located on the isobutane separation column and other distillation columns such as the propane separation column and the butane separation column. The use of the reactor effluent allows the columns to be operated at lower temperatures and pressures than would be achieved by using water or air. In addition, the elimination of water as a coolant means that the size of downstream devices, such as a cooling tower, can be reduced or can be omitted at all. Reducing the operating temperature and column pressure serves to increase the relative volatility of the key. This means that less energy is required in the form of heat to perform the desired separation. This achieves unique savings since it is not necessary to use water to condense the overhead product and reduce the amount of heat required to operate the manifold.

In a preferred embodiment of the process of the invention, the stream leaving the reactor after separation of the acid is fed to overhead condensers on distillation columns. This arrangement is preferred because a lower temperature can be achieved by using a stream leaving the reactor than by using cooling water. At lower column temperatures and pressures, the separation process is intensified. When more than one of the capacitors is cooled by the current leaving the reactor, these capacitors may be connected in parallel or in series. Preferably, they are connected in parallel to minimize investment costs.

Typically, at least two distillation columns are present, a column for separating isobutane from an alkylate and a column for separating lighter propane from isobutane. In some cases, a third column is also present to separate the butane from the alkylate.

According to an alternative embodiment of the invention, the reactor effluent is used at other locations in the process where cooling is required. The cooling of these additional devices may be carried out simultaneously with or instead of cooling the distillation column overhead condensers. These other devices are condensers and condensers located elsewhere than on the distillation columns, for example by cooling the liquid streams from the bottom of the columns or by condensing the side vapor streams. For example, in a process, butane can be separated as a vapor from a particular point in the isobutane separation column. The reactor effluent can be used to condense this steam to a liquid butane product.

Another variant consists in using a stream coming from the reactor to cool the pressurized steam leaving the first liquid-steam separator. These compressed vapors, containing isobutane and some inert alkanes, must be sent before being sent to further distillation columns or returned as recycled. isobutane, condense.

The reactor effluent can be used in a condenser for the effluent from the steam compressor, thereby eliminating further use of cooling water.

The process of the invention can be used in any catalytic alkylation using an acid catalyst. Acid catalysts which can be used are known in the art. Non-limiting examples include sulfuric acid and hydrofluoric acid. According to the invention, sulfuric acid is preferably used as the catalyst.

The reaction conditions and parameters are not affected by the invention. The reactor normally operates at an overpressure of 6.9 kPa to 1360 · kPa and at a temperature of -10 to 50 ^° C. Typically, the hydrocarbon having from 2 to 5 carbon atoms is used as the olefin feed for the alkylation process, and this parameter is not affected by the invention. Normally the composition of the olefinic feed depends on the specific application, but propylene, butylenes or amylenes may be used · The olefinic feed may also contain various inert alkanes such as propane and butane. The olefin is mixed with isobutane either before being introduced into the reactor or in the reactor. Normally, the higher the isobutane to olefin ratio in the feed, the higher the alkylate yield. This ratio is usually 5: 1, but may be 11: 1 or higher. The present invention takes advantage of this ratio in that isobutane for recycling is obtained in a more efficient and less expensive manner than in the prior art. Using the present invention in existing units, this ratio can be increased, thereby improving the octane number of the product without limiting the isobutane separation column size.

As already mentioned, the hydrocarbon mixture used in the cooling may be passed through a condenser or a pressure reducing valve before being introduced into the condensers. The pressure is reduced sufficiently to allow evaporation and the tens to achieve greater cooling of the condenser. The pressure may be reduced to a pressure of 6.9 kPt up to about 345 kPa. Preferably, the pressure is reduced to a value in the range of about 20 to about 50 psi.

Example 1 and Comparative Example A

The alkylation process described in Hydrocarbon Processing 9, 1974, p. 206. is simulated using a computer. Sulfuric acid is used as the acid catalyst. The reagent feed in both examples is shown in Table I. The feed consists of a mixture of isobutane, butylene and inert alkanes.

TABLE I

By comparison, the amount of product and its octane number of 98.5 were kept constant in both examples. The amount of isobutane in the reaction zone is maintained at 80% of the total batch plus recycle. Due to the larger amounts of inert alkanes recycled in the stream used for cooling according to the invention, the proportion of isobutane / olefin in the reactor increases. The other operating conditions in the reactor are the same in both examples.

Comparative Example A describes the prior art process. The reactor effluent is used to cool the reactor after acid separation. After the current fulfills its cooling function, the liquid-steam separator is fed. The liquid from this separator forms a stream that is treated and fed as a feed to the isobutane separation column. Water is used as the cooling medium in the overhead condenser of this column.

In Example 1, illustrating the present invention, the reactor effluent stream is used not only to cool the reactor but is also fed in parallel to the isobutane separation column overhead. After the stream has performed its cooling function, a liquid-vapor separator is fed to the first separator. Table II shows the results of these two experiments. Quantities are given in m ³ / hour.

Handling of reagents for alkylation

process isobutane 25.34 m ³ / hour butylene 20.46 m ³ / hour Inert alkanes 9.14 m ³ / hour TABLE II

Comparison of the prior art alkylation with the alkylation of the invention

Comparative Example A Example 1 according to the invention

1. isobutane in the batch 25.34 25.34 2. ratio of isobutane to olefin in reactor 15.9 18.2 3. isobutane in steam leaving the separator 17.21 34.82 4. isobutane separation column isobutane in the batch 17.87 10.39 isobutane in the overhead product 17.61 10.13 capacitor power · 54.4 40.8 digester output · 63.0 47.2 column diameter (m) 3.45 2.99

Note: * MM BTU / hr

As can be seen from Table II, much more isobutane contained in the reactor effluent stream is vaporized in the process of the invention, which provides more efficient recovery. The process of the invention reduces the amount of isobutane feed for the isobutane separation column by more than 40%, thereby reducing both the size of the column and other distillation apparatus.

Example 2

If the same batch composition is used and working under the conditions specified in

Claims (13)

SUBJECT CLAIMS 1. A continuous process for the production of an alkylate by reacting an olefin with a molar excess of isobutane in an alkylation zone in the presence of an acid to a liquid stream which is discharged from the alkylation zone. The vapor is condensed by cooling, characterized in that the vapor is cooled by indirect heat exchange with the liquid stream leaving the alkylation zone. 2. A process according to claim 1, wherein the liquid stream leaving the alkylation zone is partially vaporized during the heat exchange with the vapors. 3. The process of claim 2 wherein the pressure of the liquid stream from the alkylation zone fed to the indirect heat exchange with vapors is sufficiently reduced prior to indirect heat exchange such that at least partial evaporation of the liquid stream from the alkylation zone occurs during cooling. 4. The process of claim 3 wherein the liquid stream from the alkylation zone used for indirect heat exchange with vapors is conducted directly from the alkylation zone via a pressure reducing valve to indirect heat exchange. 5. A process according to claim 3, characterized in that the liquid stream from the alkylation zone is subjected to distillation after its partial evaporation. 6. The process of claim 3 wherein the liquid stream obtained by treating the liquid stream from the alkylation zone is distilled in an isobutane separation column to recover isobutane-rich vapors and an alkylate-rich liquid bottom product, wherein the vapor-rich vapors are recovered. isobutane is cooled and condensed by indirect heat exchange with a liquid stream leaving the alkylation zone. 7. The process of claim 6, wherein treating the liquid stream from the alkylation zone comprises partially vaporizing the stream to form a liquid stream. The example illustrates the effect of cooling the isobutane overhead condenser to separate the isobutane only with the reactor effluent stream. The cooling water is completely eliminated and the cooling effect of the reactor effluent stream allows the isobutane separation pressure to be reduced from 1035 kPa to 117.3 kPa. The pressure reduction improves the distribution and makes it possible to reduce the amount of heat for this operation to 35.7 MM BTU / h, which is 40 θ / heat less than that required in the prior art method of Comparative Example A. The liquid stream of the present invention is formed from a liquid stream from an alkylation zone and a steam stream, the resulting liquid stream being fed to an isobutane separation column. 8. A process according to claim 7, wherein the partial evaporation of the liquid stream from the alkylation is achieved by conducting the stream to indirect heat exchange with the reaction mixture in the alkylation zone. 9. The method of claim 7, wherein the liquid stream from the alkylation zone is divided into first and second portions, the first portion of said stream being indirectly exchanged with the reaction mixture in the alkylation zone, the second portion being directed indirectly. heat with the vapors to achieve their cooling, whereby the first part of the liquid alkylation stream used is mixed with the second part and the combined stream is sent to a liquid-steam separator where the liquid stream obtained from the liquid stream from the alkylation and steam stream. 10. The method of claim 8, wherein the steam stream is condensed by cooling, wherein cooling is effected by indirect heat exchange with a liquid product leaving the alkylation zone. 11. A method according to claim 10, characterized in that a portion is condensed. the vapor stream leads to a propane separation column where propane-rich vapors are separated by distillation and condensed by means of a liquid stream leaving the alkylation zone. 12. The process of claim 3, wherein treating the stream leaving the alkylation zone to obtain the alkylate comprises recovering the propane in the vapor form by distillation, wherein the propane vapor is condensed by cooling and the propane vapor is cooled by indirect heat exchange with the liquid stream leaving from the alkylation zone. 13. A process according to claim 3, wherein the treatment of the liquid stream leaving the alkylation zone is carried out by evaporating at least partially the liquid stream and steam stream, the steam stream being separated from the liquid stream by indirect heat-liquid exchange. current and condensed by cooling, whereby the current leaving the alkylation zone, the condensation of the steam 4 sheets of drawings