IL29923A - Process for alkylating aromatic hydrocarbons - Google Patents

Description

PROCESS FOR ALKYLATING AROMATIC HYDROCARBONS The present invention relates to the alkylation of an aromatic hydrocarbon with an olefinic hydrocarbon. More particularly, the present invention relates to an improved process for alkylation of benzene with propylene to produce cumene.

The present invention finds broad application in the production of alkylated aromatic hydrocarbons for use in subsequent chemical synthesis. The present invention particularly finds application in the production of isopropylbenzene, or cumene, which is utilized in the synthesis of phenol, acetone, alpha-methylstyrene, and acetophenone . These cumene-derived chemicals are intermediates in the synthesis of resins for plastics and nylon.

In the commercial manufacturing of cumene it is known to charge liquid benzene and liquid propylene into a reactor containing a solid phosphoric acid catalyst. It is further known to charge the benzene and propylene downflow through the reaction zone. Since it is desired to minimize the dialkylation of benzene it is common to use a molar excess of benzene, and normally the ratio of benzene to propylene is about 8s 1. At some conditions of temperature and pressure, a substantial portion of the liquid propylene will flash to the vapor state but the benzene will remain liquid. The liquid benzene tends to channel down through the catalyst beds, this channeling stemming from two causes. First, the influence of gravity is more pronounced upon the liquid than the vapor and tends to draw circulation of liquid benzene downward While there is greater freedom for the vapor to back-flow upwardly in eddy currents within the reactor. Secondly, the liquid benzene will follow the wetted surfaces of the catalyst, and there is a pronounced resistance for the liquid to spread out horizontally to otherwise dry catalyst surfaces. Since the liquid benzene is channeling down through the reactor, propylene vapor tends to accumulate in pockets at the top of the reactor vessel or to channel without contacting liquid benzene, even though there is a molar excess of benzene present in the reactor. Therefore, some propylene does not react with liquid benzene and thereby oligomerizes on the catalyst to produce propylene-dimer, propylene-timer, or even heavier olefinic materials, all of which are undesirable.

Although the resulting product cumene will contain only small amounts of these olefinic contaminants (hexenes, nonenes, and dodecenes) , these olefinic by-products must be removed from the product cumene. The reason for this is that in the subsequent utilization of cumene for the synthesis of phenols, trace olefins act as rate depressants in the oxidation reaction. Because these olefins interfere with the production of high quality phenol from cumene it is necessary to minimize the quantity of olefin in the cumene product.

The olefin contamination of the product cumene may be removed by several methods. One method is to remove the olefinic constituents by fractionation. A second and preferable method is to provide sufficient catalyst to alkylate the benzene in the reaction vessel with the contaminating olefins to produce heavy alkylbenzenes.

There are several disadvantages in attempting to remove olefins by fractionation of the cumene. First, it is difficult to remove nonene and heavier olefinic materials from the pure cumene and some cumene product must be lost with the olefin being removed. This cumene loss can be substantial in relation to the trace amount of olefin which must be removed. Another drawback to fractionation is that extensive recycling of fractions may be necessary in order to minimize cumene loss. Also, the required additional fractionation facilities are a burdensome capital expenditure.

Attempts are sometimes made to overcome the disadvantages of fractionation by merely providing enough catalyst in the alkylation reactor to enable the molar excess of benzene to be alkylated with the heavy olefins. This is accomplished by providing sufficient catalyst in the reactor so that the Liquid Hourly Space Velocity (LHSV) is less than 3.0 and is preferably 1.0 or less. The resulting heavy alkylbenzenes are then easily removed by fractionation from the cumene as a cumene bottoms fraction. However, this method of olefin removal also has its disadvantages in that the resulting heavy alkylbenzene product constitutes a yield loss, including not only the propylene which resulted in the heavy olefin but also a yield loss of the benzene itself.

Attempts to minimize the yield loss of both propylene and benzene in the reaction zone by utilizing novel catalysts have not been entirely successful. Attempts to minimize these yield losses by modification of the reaction system also have not been particularly successful.

In the process of the present invention, an inventive concept has been discovered whereby process improvements have been obtained in the synthesis of a monoalkylated aromatic hydrocarbon by modifying operations to react an aromatic and olefinic hydrocarbon in an upflow reaction zone in the presence of an inert vapor dispersant. For example, by operation in accordance with the practice of the present invention, product cumene of high purity is produced while minimizing loss of propylene and benzene to either olefinic or heavy alkylbenzene by-productSo The present invention may also be applied to obtain similar processing benefits in the synthesis of other alkylated aromatic hydrocarbons, as will be set forth hereinafter.

Accordingly, the present invention provides a process for producing a monoalkylated aromatic hydrocarbon wherein an aromatic hydrocarbon is reacted with an olefinic hydrocarbon in a reaction zone in the presence of a solid particle-form alkylation catalyst, characterized by introducing the entire amount of the aromatic and olefinic reactants and an unreactive vaporous dispersant into the lower portion of the reaction zone and passing said reactants and dispersant upwardly therein in mixed phase through at least one fixed bed of said catalyst, withdrawing from the upper portion of the reaction zone resulting reaction mixture comprising monoalkylated aromatic hydrocarbon, excess unreacted aromatic hydrocarbon and vaporous dispersant, and recovering therefrom said monoalkylated aromatic hydrocarbon.

The preferred aromatic hydrocarbons which may be alkylated in accordance with this invention are monocyclic aromatic hydrocarbons. These aromatic hydrocarbons include benzene, toluene, ortho-xylene, meta-xylene, para-xylene, ethyl-benzene, ortho-ethyltoluene, meta-ethyltoluene, para-ethyltoluene, normal propylbenzene, isopropylbenzene and n-butylbenzene. aromatic h drocarbons are also suitable as reactants and include aromatic hydrocarbons such as hexylbenzene, nonylbenzene and dodecylbenzene. Other suitable alkylatable aromatic hydrocarbons include those with two or more aryl groups such as diphenyl, diphenylmethane, triphenyl, triphenylmethane, fluorene, stilbene, and so forth. Examples of alkylatable aromatic hydrocarbons within the scope of this invention utilizable as reactants and containing condensed aromatic rings include naphthalene, alkyl-naphtha-lenes, anthracene, phenanthrene and naphthacene.

Of the alkylatable aromatic hydrocarbons of use within the process of this invention the monocyclic aromatic hydrocarbons are preferred and benzene is particularly preferred.

As indicated above, the aromatic hydrocarbons which may be utilized as aromatic reactant include compounds already having one, or even two, alkyl groups attached to the aromatic ring. Accordingly, it is understood that the expression "producing a monoalkylated aromatic hydrocarbon", as used in the present specification and claims, refers to the introduction of a single alkyl group as a substituent on the aromatic ring, whether it be the sole alkyl substituent on the final alkylaromatic product, or whether it be additional to one or more alkyl groups initially present in the aromatic hydrocarbon used as aromatic hydrocarbon reactant.

The preferred olefin hydrocarbons are the mono-olefins. The mono-olefins may be either normally gaseous or normally liquid at ambient temperature and include ethylene, propylene, 1-butenes, 2-butenes, isobutylene, and higher molecular weight normally liquid olefins such as various pentenes, hexenes, and heptenes. Cyclo-olefins such as cyclopentene, methyl-cyclopentene, cyclohexene and methyl-cyclohexene, may also be utilized.

As previously noted, the particularly preferred embodiment of this invention comprises the process wherein the aromatic hydrocarbon is benzene, the olefin hydrocarbon is propylene, and the desired mono-alkylated aromatic compound is high purity cumene. The following examples and the summary of Table I are derived from experimental operating data and are presented to afford a better understanding of the effectiveness of the present invention.

EXAMPLE I A cumene unit containing 44,600 kg. of solid phosphoric acid catalyst in the reactor was operated with a downflow charge of reactants in the standard prior art manner. The reactants consisted of 86.7 CMSD (cubic meters per steam-day) of fresh benzene, 655 CMSD of benzene recycled from the fractionation section of the unit in order to maintain the desired 8s 1 molar excess of benzene in the reaction zone, and 87.1 CMSD of liquified propylene-propane fresh feed. The propylene-propane fresh feed was 94.9 mole percent propylene and comprised 82.3 CMSD of propylene and 4.8 CMSD of propane. The total combined feed entered the reactor at 194°C. and 34 atms., gauge pressure, at the rate of 828.7CMSD. The effluent left the reactor at 228°C. and was sent to a depropan-izer fractionation column wherein 4.8 CMSD of propane product was produced overhead and sent to the fuel gas line. The resulting depropanizer bottoms was sent to a benzene fractionation column wherein 655 CMSD of benzene was removed overhead and returned to the reactor as the recycle benzene stream.

T c um oms was sent to a cumene fractionation V head and sent to product storage while 8.1 CMSD of cumene bottoms product (heavy alkylbenzenes) was removed to byproduct storage. The cumene product had a Bromine Index of 390 and a cumene purity in excess of 99.8 mole percent.

(Bromine Index is typically determined by ASTM Method D-1492-60 and is one method of analysis which is utilized in determining olefinic contamination of the cumene.) EXAMPLE II The cumene unit was charged downflow in the standard prior art manner at the rate of 870.5 CMSD of combined feed. The benzene charge was 703 CMSD comprising 84 CMSD of fresh benzene feed and 619 CMSD of benzene recycle. The propylene-propane feed was 50.1 mole percent propylene and comprised 80.9 CMSD of propylene and 86.6 CMSD of propane. The combined feed entered the reactor at 196°C. and 34 atms. gauge pressure and the effluent left the reactor at 229°C. The effluent was fractionated to provide 86.6 CMSD of propane product, 619 CMSD of benzene which was recycled to the reactor, 126 CMSD of cumene product . and 8.3 CMSD of cumene column bottoms (heavy alkylbenzene by-product) . The cumene product had a purity in excess of 99.8 mole percent and a Bromine Index of 84.

EXAMPLE III The cumene unit was charged downflow in the standard prior art manner at the rate of 955.5 CMSD of combined feed. The benzene charge was comprised of 85 CMSD of fresh benzene and 627 CMSD of recycle benzene. The liquid propylene-propane feed contained 35.2 mole percent of propylene and comprised 128.1 CMSD of propylene-propane fresh feed and 115.2 CMSD of propane which was recycled from the depropanizer column in order to reduce the concentration of propylene. The propylene-propane fresh feed comprised 81.2 CMSD of propylene and 46.9 CMSD of propane. The combined feed entered the reactor at 196°C. and 34 atms. gauge pressure. The effluent left the reactor at 229°C. and was depropanized to provide 162.1 CMSD of propane overhead, of which 46.9 CMSD was removed as product and 115.2 CMSD was recycled to the reactor. The depropanizer bottoms was further fractionated to provide 627 CMSD of benzene which was recycled to the reactor, 127.3 CMSD of cumene which was sent to product storage, and 8.4 CMSD of cumene bottoms (heavy alkylbenzene) which was sent to by-product storage. The cumene product had a purity in excess of 99.8 mole percent and had a Bromine Index of 62.

EXAMPLE IV The cumene unit was modified to provide for entry of the charge at the bottom of the reactor and withdrawal of effluent from the top of the reactor. The reactor contained the same catalyst loading of 44,600 kg. of solid phosphoric acid catalyst, but was now charged in an upflpw manner. The combined feed consisted of 84.2 CMSD of fresh benzene, 645 CMSD of benzene recycled from the fractionation section of the unit in order to maintain the desired molar excess of benzene in the reaction zone, and 84.8 CMSD of liquified propylene-propane fresh feed. The propylene-propane fresh feed was 94.8 mole percent propylene and comprised 80 CMSD of propylene and 4.8 CMSD of propane. The total combined feed entered the reactor at 193°C. and 34 atms. gauge, at the xate of 813 CMSD. The effluent left the reactor at 227°C. and was sent to the depropanizer fractionation column wherein 4.8 CMSD of propane product was produced. The resulting depropanizer bottoms was sent to the benzene fractionation column wherein 645 CMSD of benzene was removed overhead and returned to the reactor as the recycle benzene stream.

The benzene column bottoms was sent to the cumene fractionation column wherein 126.7 CMSD of cumene product was produced overhead and sent to product storage while 7.9 CMSD of cumene bottoms product (heavy alkylbenzenes) was removed to byproduct storage. The cumene product had a Bromine Index of 350 and a cumene purity in excess of 99.8 mole percent.

EXAMPLE V The cumene unit was charged upflow at the rate of 870.5 CMSD of combined feed. The benzene charge was 706.6 CMSD comprising 83 CMSD of fresh benzene feed and 623.6 CMSD of benzene recycle. The propylene-propane feed was 50.2 mole percent propylene and comprised 79.2 CMSD of propylene and 84.7 CMSD of propane. The combined feed entered the reactor at 196°C. and 34 atms. gauge, and the effluent left the reactor at 229°C. The effluent was fractionated to provide 84.7 CMSD of propane product, 623.6 CMSD of benzene which was recycled to the reactor, 125.6 CMSD of cumene product and 6.4 CMSD of cumene column bottoms (heavy alfcylbenzene by-product). The cumene product had a purity in excess of 99.8 mole percent and a Bromine Index of 58.

W EXAMPLE VI The cumene unit was charged upflow at the rate of 947.7 CMSD of combined feed. The benzene charge was comprised of 83.3 CMSD of fresh benzene and 621.1 CMSD of recycle benzene. The liquid propylene-propane feed contained 34.8 mole percent of propylene and comprised 126.9 CMSD of propylene-propane fresh feed and 116.4 CMSD of propane which was recycled from the depropanizer column in order to reduce the concentration of propylene. The propylene-propane fresh feed comprised 80.5 CMSD of propylene and 46.4 CMSD of propane. The combined feed entered the reactor at 196°C. and 34 atms. gauge. The effluent left the reactor at 230°C. and was depropanized to provide 163 CMSD of propane overhead, of which 46.4 CMSD was removed as product and 116.4 CMSD was recycled to the reactor. The depropanizer bottoms was further fractionated to provide 621.1 CMSD of benzene which was recycled to the reactor, 127.6 CMSD of cumene which was sent to product storage, and 5.1 CMSD of cumene bottoms (heavy alkylbenzenes) which was sent to byproduct storage. The cumene product had a purity in excess of 99.8 mole percent and had a Bromine Index of 40.

EXAMPLE VII The operation defined in Example VI above was continued, but the through-put of the unit was increased until the fractionation section had reached the limit of its capacity. At this point of stable operation at maximum through-put, the cumene unit was being charged upflow at the rate of 1,226.7 CMSD of combined feed. The benzene charge was comprised of 109.6 CMSD of fresh benzene and 804.7 CMSD of recycle benzene. The liquid propylene-propane feed contained .1 mole percent of propylene and comprised 164.6 CMSD of propane propylene-propane fresh feed and 147.9 CMSD of~p_=Gpy-iei¾& which was recycled from the depropanizer column. The propylene-propane fresh feed comprised 104.4 CMSD of propylene and 60.1 CMSD of propane. The combined feed entered the reactor at 197°C. and 34 atms. gauge. The effluent left the reactor at 230°C. and was depropanized to provide 208 CMSD of propane overhead, of which 60.1 CMSD was removed as product and 147.9 CMSD was recycled to the reactor. The depropanizer bottoms was fractionated to provide 804.7 CMSD of benzene recycle, 168.5 CMSD of cumene which was sent to product storage, and 6.7 CMSD of cumene bottoms (heavy alkylbenzene) which was sent to byproduct storage. The cumene product had a purity in excess of .99.8 mole percent and had a Bromine Index of 60.

The data of the examples are condensed and summarized in Table I wherein flow rates are converted to moles per hour and other significant calculations are reported. It will be . noted that the operation during the test periods summarized in the examples was relatively constant. The reactor was held at a pressure of 34 atomosphers and at a reactor inlet temperature of about 196°C. , . while the benzene to propylene mole ratio was held constant at about 8 to 1. The liquid hourly space velocity on the combined feed was in the range of from 0.67 to 0.77 during the first six examples and the space velocity of propylene across the catalyst bed was in the range of from 0.060 to 0.067 during the first six test periods Descriptive Summary of Example Standard Downflow CMSD q. -Mol/hr Combined Feed 828.7 8 Propylene-Propane Feed 87.1 44.8 1 Propylene 82.3 42.5 Propane 4.8 2.3 Mole % Propylene 94.9 Propane Recycle — . — Total Propylene-Propane to Reactor 87.1 44.8 1 Propylene 82.3 42.5 Propane 4.8 2.3 Mole % Propylene 94.9 Propylene to Propane Mole Ratio 18.5:1.0 Total Benzene 741.6 349.3 7 Fresh Benzene 86.6 40.8 Recycle Benzene 655 308.5 6 Benzene to Propylene Mole Ratio 8.23:1.0 Product Flow Rates Propane Product 4.8 2.3 81 TABLE I (Continued) IV Descriptive Summary of Example New Upflow New U Kg-Mol CMSD per hr CMSD Combined Feed 813 870.5 Propylene-Propane Feed 84.8 43.6 163.9 Propylene 80.0 -41.3 79.2 Propane 4.8 2.3 84.7 Mole % Propylene 94.8 50. Propane Recycle Total Propylene-Propane to Reactor 84.8 43.6 163.9 Propylene 80.0 41.3 79.2 Propane 4.8 2.3 84.7 Mole % Propylene 94.8 50. Propylene to Propane Mole Ratio' 18.2:1.0 1.01: Total Benzene 729.2 343.9 706.6 Fresh Benzene 84.2 39.7 83.0 Recycle Benzene 645 304.2 623.6 Benzene to Propylene Mole Ratio 8.33:1.0 8.14: Product Flow Rates Propane Product 4.8 2.3 84.7 Cumene Bottoms Product 7.9 1.76 6.4 Cumene Product 126.7 38.0 125.6 (Bromine Index of Cumene Product) (350) (5 Moles Moles Moles Moles Reactor Inlet Temperature, °C. 193 Reactor Outlet Temperature, °C. 227 LHSV on Total Combined Feed 0.661 0. LHSV on Liquid Propylene 0.0659 0.

Examples I through III were downflow operation in the standard prior art manner. It must be noted that the use of decreasing concentration of propylene in the propylene-propane feed had no beneficial influence on the production of heavy alkylbenzene as exemplified by the rate of cumene bottoms production. A decrease in the Bromine Index of the cumene product shows that the olefin content of the cumene was reduced by decreasing the concentration of propylene in the propane-propylene mixture. But this reduction was not due to any decrease in the oligomerization of propylene to form the olefinic contaminants. This reduction was caused by increased alkylation of benzene with the olefin contaminants as is indicated by the corresponding increase in the amount of heavy alkylbenzene produced. Thus at a propylene purity of 94.9 mole percent the cumene bottoms by-product was 8.1 CMSD while at a propylene purity of 35.2 mole percent the cumene bottoms was 8.4 CMSD. This amounted to an increase of from 0.0427 moles of bottoms per mole of propylene feed to 0.0454 moles of bottoms per mole of propylene feed, while the consumption of propylene in moles per mole of cumene increased slightly, from 1.089 to 1.099.

Examples IV, V, and VI were upflow in the manner of the present invention. It will be seen from the data that as the concentration of propylene in the propylene-propane feed mixture was decreased, not only was there the anticipated decrease in the Bromine Index of the cumene product, but there was also a pronounced decrease in the amount of alkyl-benzene by-product produced (cumene bottoms product) . Thus at 94.8% propylene purity the production of bottoms by-product was 0.0429 moles per mole of propylene, but at 34.8% propylene purity the bottoms rate was only 0.0273 moles per mole of propylene. This is contrary to what was experienced in the standard downflow operating examples as noted above, and indicates that there was an actual decrease in the rate of oligomerization of propylene to form olefinic contaminants.

This is substantiated by the raw material consumption figures which are presented in the table. The data indicate that when synthesizing cumene in the upflow manner of the present invention there was a substantial reduction in the consumption of both propylene and benzene' per mole of cumene product as the concentration of propylene in the propylene-propane feed was decreased. When synthesizing cumene in the known downflow manner there was no decrease in raw material consumption regardless of the propylene concentration in the propylene-propane feed.

A comparison of Examples III, VI, and VII indicates that the operation in the upflow manner of the process of the. invention not only resulted in a beneficial decrease of heavy alkylar om atic by-product production but that it also increased the capacity of the existing cumene unit without incurring capital expenditures. It will be seen that operation during Examples III and VI were conducted at a liquid hourly space velocity (on the combined feed) of about 0.77, whereas Example VII was conducted at a liquid hourly space velocity (on combined feed) of about 1.0. The increased through-put in Example VII resulted in an increased capacity for the unit of about 32% per day with no detrimental effect. Although the increased through-put of Example VII increased the amount of alkylbenzene by-product production (cumene bottoms product) on a cubic meter per day basis above that of Example VI, it remained below Example III and did not, in fact, cause an increase in the amount of by-product production on a mole per mole means of comparison. The actual raw material consumption of benzene and propylene per mole of product cumene remained below the prior art downflow valves with no increase due to increased through-put .

A comparison of the downflow data with the upflow data indicates a further benefit in that the cumene product from upflow process was of a consistently higher purity as indicated by reduced Bromine Index at a given propylene concentration in the propylene-propane feed. Thus, a comparison of Examples I and IV indicates that the Bromine Index was reduced from 390 to 350 when the propylene-propane was about 95% propylene, while Examples III and VI show that the' Bromine Index was reduced from 62 to 40 at a propylene concentration of about 35%.

It must be noted that flow of the reaction mixture through the reactor vessel when operated using the known down-flow operation is more characteristic of vapor flow, while the flow through the reactor vessel under upflow operation is more characteristic of liquid flow. Thus the downflow reactor vessel contains an atmosphere of predominantly propane vapor with liquid benzene channeling down through the catalyst bed. The upflow reactor vessel is primarily full of benzene with streams of propane and propylene bubbling up through the liquid- full catalyst bed. In light of the operational data, it is believed that the advantage of the upflow process is not only due to the substantially liquid-full reactor of the inventive upflow process, but that there is also a definite need for a substantial concentration of propane in the propylene-propane feed. The data indicate that at about 95% propylene concentration there is no reduction in cumene bottoms production or in raw material consumption (Examples I and IV) upon changing operation from downflow to upflow. However, upon reduction to about 50% propylene there is a significant reduction in cumene bottoms production and raw material consumption in operating upflow as compared to downflow (Examples II and V) . This benefit is even more pronounced at the 35% propylene concentration (Examples III, IV, and VII).

It is believed that the propane vapor acts as a dispersant in the catalyst bed and provides for increased contacting of vapor and liquid, The propane acts to disperse the propylene more effectively through the catalyst bed so that there is increased opportunity for the propylene to contact liquid and alkylate the benzene. There is thus a reduced tendency for the propylene to oligomerize to heavier olefins and thereby produce heavy alkylbenzene by-product (cumene bottoms). The net effect thus is to reduce raw material consumption per mole of cumene product. In addition, whatever heavier olefins are produced by oligomerization of propylene are more effectively dispersed through the liquid in the catalyst bed so that there is increased opportunity for the heavy olefinic by-product to- alkylate with benzene. The net effect is thus to reduce the Bromine Index of the final cumene product. Because the propylene is more effectively dispersed the through/benzene liquid, there is also a reduction in the tendency of the propylene to polyalkylate the benzene. Since there is less di-isopropyl benzene produced, this effect also contributes to the reduction in the amount of cumene bottoms by-product and to the reduction in raw material consumption. -■ '19 'τ 29923/2 Since the 'propane diluent in the propylene-propane feed is required as a dispersant, it may be seen that any vaporous dispersant which is chemically inert under the reaction conditions, would be equally effective. Methane, ethane, and nitrogen are some of the inert vapor s that could also be utilized as unreactive vaporous dispersant within the scope of the inventive process.

Although the process of this invention has been disclosed in reference to the synthesis of cumene it has equal application, iii other processing. ' For example, the synthesis of ^-cymene may be undertaken by alkylation of toluene with The system is similar in that propylene tends to oligomerize to produce contaminating olefins. The product p-cymene may then be oxidized to produce paracresol and the ; olefinic contamination will interfere with the cresol production in a manner similar to that disclosed for phenol. Therefore, · it may be seen that the process of the invention will be equally effective in eliminating or minimizing this problem. The following example points out the significant ■- ' reduction in olefinic content of the alkylation product, as indicated by the bromine index, with the hew upflow operation as compared to the. standard' downflow operation in cymene production.

. It is to be noted that the operating conditions as set forth in the examples are specific to the operations disclosed and are in no way to be construed as limiting upon the process. As previously noted, in the alkylation of aromatic hydrocarbons with olefin it is known to provide a molar excess of the aromatic compound. This molar excess is maintained by holding the aromatic to olefin molal ratio in the range of from about 2:1 to about 30:1, with a preferred range of about 4:1 to about 16:1. This molar excess is required in order to minimize polyalkylation of the aromatic hydrocarbon. When utilizing a solid phosphoric acid catalyst in the reaction zone it is a particularly preferred embodiment that the ratio of aromatic to olefin should be about 8:1 when synthesizing cumene.

In the synthesis of cumene, the temperature of the reaction zone may be from 300°F. to about 600°F. and when utilizing a solid phosphoric acid catalyst will normally range from 177° to 232°C. The pressure of the alkylation reaction may be from 20.4 to 68 atmospheres or even higher, provided that the vapor dispersant is not condensed to a liquid due to the pressure. The liquid hourly space velocity of the combined feed in the reaction zone may range from about 0.5 to 5.0, but will normally be in the range of 0.5 to 1.5. In addition, it is to be noted that the temperature rise across the catalyst beds in the example was maintained at about 33°C. However, the operating conditions of inlet temperature, space velocity, concentration of inert vapor dispersant, and the like, may be adjusted to maintain any temperature rise as desired in order to hold the catalyst temperature at a point sufficient to maintain the olefin content of the cumene product at the desired value while minimizing raw material consumption. The specific reactor operating conditions which are required for alkylation of any aromatic hydrocarbon or other alkylatable aromatic compound when utilizing a solid phosphoric acid catalyst or any other catalyst are readily ascertainable by those skilled in the art.

From the data presented it will be seen that the effectiveness of the present invention is not only dependent upon passing the reactants upflow through the catalyst bed, but that the presence of a substantial concentration of unreactive vapor dispersant is also critical and that this effectiveness is enhanced as the concentration of dispersant is increased. At a 95% concentration of propylene in the propylene-propane feed stream there was no significant benefit to be found in operating the reactor in upflow manner. While the Bromine Index was reduced from 390 in the standard downflow operation to 350 under the upflow operation, this was accompanied by a slight increase in the cumene bottoms by-product loss. At a 50% propylene concentration, however, the cumene product purity increased (Bromine Index decreased) while the cumene bottoms by-product loss was significantly reduced. At a 35% propylene concentration these benefits were more greatly enhanced. It is believed that the effectiveness of substantial propane disperant becomes pronounced enough to be of commercial significance when the concentration of propylene in the propylene-propane feed is about 67%, and that the inventive upflow process should be applied to cumene synthesis under conditions sufficient to alkylate benzene with propylene with a propylene-to-propane ratio not greater than about 2;1. While the benefits of the inventive process could be further enhanced by decreasing the propylene concentration below about 35% it is not believed commercially advisable to do so. Such operation would require the fractionation and recycling of excessive quantities of propane, with the result that the increased operating expenses and increased capital expenditure for larger capacity equipment could not be justified by the resulting purity of product cumene or by the resulting reduction in cumene bottoms byproduct loss.

A particularly preferred embodiment of the present invention comprises a process for the production of cumene which comprises passing benzene and propylene in a molar ratio of about 8:1 into the bottom of a reaction zone containing a solid phosphoric acid catalyst under alkylating conditions in the presence of an unreactive vapor dispersant comprising propane, said dispersant being present in a molar ratio of propylene to dispersant of about Is 2; withdrawing from the top of the reaction zone unreacted benzene, unreactive vapor dispersant, and cumene; and recovering high purity cumene from the effluent.

Claims (4)

1. A process for producing a monoalkylated aromatic hydrocarbon wherein an aromatic hydrocarbon is reacted with an olefinic hydrocarbon in a reaction zone in the presence of a solid particle-form alkylation catalyst, characterized by introducing the entire amount of the aromatic and olefinic reactants and an unreactive vaporous dispersant into the lower portion of the reaction zone and passing said reactants and dispersant upwardly therein in mixed phase through at least one fixed bed of said catalyst, withdrawing from the upper portion of the reaction zone resulting reaction mixture comprising monoalkylated aromatic hydrocarbon, excess unreacted aromatic hydrocarbon and vaporous dispersant, and recovering therefrom said monoalkylated aromatic hydrocarbon..

2. Process of Claim 1, further characterized in that the aromatic hydrocarbon comprises benzene, the olefinic hydrocarbon comprises propylene, and the unreactive vaporous dispersant comprises propane.

3. Process of Claim 2, further characterized in that the alkylation catalyst is a solid calcined composite of phosphoric acid and a siliceous adsorbent.

4. Process of Claim 3, further characterized in that the molar ratio of benzene to propylene is in the range Of from about 4s 1 to about 16 si and the molar ratio of propylene to propane is not greater than about 2 i. 5„ Process of Claim 4, further characterized in that the molar ratio of propylene to propane is about l 2 and the molar ratio of benzene to propylene is about 8:1. -24-