BE508435A - - Google Patents

Description

       

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  BENZENE ALKYLATION PROCESS.



   The present invention relates to a process for treating a mono-nuclear aromatic hydrocarbon with an olefin in order to obtain a high yield of mono-alkylated, mono-nuclear aromatic hydrocarbon.



  More specifically, the invention relates to the production of mono-isopropyl benzene in the presence of a particular catalyst and under operating conditions giving high yields of mono-isopropyl benzene.



   Mono-isopropyl benzene is particularly important as a constituent of motor fuels having boiling points close to those of gasoline and having a high anti-explosive value. It is also in great demand as an intermediate in the synthesis of high molecular weight aromatic hydrocarbons, such as cymene and other polyalkylated benzene hydrocarbons containing at least one isopropyl group per molecule.



   The catalytic alkylation of aromatic hydrocarbons has generally been known for some time. However, the present invention differs from the art known in the art by the employment of special operating conditions which have been found necessary in the presence of a solid phosphoric acid catalyst in order to obtain high yields of mono-. isopropyl benzene with a relatively low production of higher propyl benzene.



   According to a specific embodiment, the present invention comprises a process for the production of mono-isopropyl benzene by contacting benzene and propylene with a solid phosphoric acid catalyst at a temperature of between about 150 and about. 450 C at a pressure of at least 6.8 atmospheres.



   Benzene which is alkylated with propylene according to the process of the present invention can be obtained from several sources, including

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 the distillation of coal the dehydrogenation of naphthenic hydrocarbon fractions containing cyclohexane, as well as the dehydrogenation and cyclization of aliphatic hydrocarbons containing 6 carbon atoms per straight chain molecule such as normal hexane and chain hexenes straight chain such as normal hexane and straight chain hexenes.



   The propylene employed as the alkylating agent in the present case can be obtained from the gases produced in the cracking of petroleum hydrocarbons, by the dehydration of propyl or isopropyl alcohols, and by any other means resulting in the formation of either propylene practically. - cally pure, or of a hydrocarbon fraction containing appreciable quantities of this olefinic hydrocarbon. These propylene-containing fractions generally also contain certain amounts of propane when derived from gases produced by the cracking or dehydrogenation of hydrocarbons.



   An essential substance used in the preparation of the preferred solid alkylation catalysts is phosphoric acid which may constitute 80% or more of the catalyst substance, and in most cases represents more than 30% by weight of that. -this. Of the various phosphorus acids, orthophosphoric or pyrophosphoric acids are generally preferred because of their alkylating capacity, their inexpensiveness, and the ease with which they can be obtained, although the invention is not limited to their use but can use catalyst mixtures formed from any of the other acids of phosphorus which are catalytically active particularly those in which phosphorus has a valence of 5, since these are generally more active than those in which phosphorus has a value of 3.

   This does not mean, however, that the phosphorus acids which may be employed will have identical effects on the alkylation reaction, as each acid will exert its characteristic activity. The alkylation activity of a given catalyst also depends on the ratio of acid to siliceous adsorbent employed to produce the calcined mixture of catalytic substances.



   Solid phosphoric acid catalysts which are particularly useful in the present alkylation process can be obtained by mixing a phosphorus acid such as orthophosphoric acid, or pyrophosphoric or tetra-phosphoric with a carrier. a finely divided solid, usually siliceous, (such as diatomaceous earth) some prepared forms of cilica, raw or acid-treated clays, etc.) to form a rather moist paste; calcining at temperatures generally below about 500 ° C to produce a solid cake; by crushing and sifting to produce grains of usable dimensions.

   If the calcination is carried out at temperatures above about 300 ° C, it is sometimes desirable to re-hydrate the catalyst grains at a temperature between about 200 ° C and about 300 ° C, preferably at about 260 ° C. to produce an acidic composition corresponding to a strong alkylating activity. The mode of preparation of the catalyst can be varied by forming particles of the original paste, by extrusion, or by nodulization methods, after which the particles formed are calcined, and, if necessary, rehydrated.



   In the reactions which take place during calcination, it is evident that a certain amount of acid is attached to the carrier and it is probable that a certain amount of metaphosphoric acid, which is not active under these conditions , was formed. The re-hydration phase obviously produces an acid composition closely corresponding to pyro acid, the formula of which is: H402O7. Unless re-hydration is performed, a temperature of about 300 ° C should generally not be exceeded during calcination. This description of a solid phosphoric acid catalyst and its preparation is not complete, as they have been described in US Patents Nos. 1,993,513; 2,120,702; 2,157,208; and others.

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   Because of the possibility of varying both the active constituents of phosphoric acid and the relatively inert adsorbents which will form the solid catalyst masses of phosphoric acid, there are a number of alternative catalysts, each of which has its value. clean catalyst which will not be exactly equivalent to those of other masses of different compositions. The various solid phosphoric acid catalysts which can be prepared as described herein are hygroscopic and therefore are generally crushed, graded or formed, and stored for use with the avoidance of unnecessary contact with humid air.



   By carrying out the reaction between benzene and propylene by the process according to the present invention, the reacting hydrocarbons are contacted with the solid phosphoric acid catalyst at a temperature preferably between about 150 and about 325 ° C. but the alkylation will continue to proceed slowly even at a temperature of about 100 C. Temperatures higher than those just mentioned but not generally exceeding about 450 C are used sometimes, but when When temperatures are too high, there is generally a relatively rapid loss of catalyst activity, probably due in part to the loss of water as well as the build-up of carbonaceous and hydrocarbonaceous deposits.

   It is preferable that the reaction mixture is maintained at a pressure generally between about 6.8 and about 68 atm or more. While lower pressures, for example around atmospheric pressure, can be used to some extent, it is not desirable to employ these low pressures as more polyisopropyl benzenes are then formed and the presence of polyisopropyl benzenes is formed. catalyst life will be shorter than when the pressure is sufficient to maintain part of the benzene and / or propylated benzenes in the liquid state. Pressures above about 68 atmospheres are generally not necessary.



  In order that the catalyst can retain its alkylating activity for a relatively long period of time, it is preferable that the operating pressure is sufficient to maintain in the liquid state an appreciable proportion of the benzene or at least of the isopropyl benzene resulting from the reaction. between propylene and benzene.



   The intimate contact of benzene and propylene with the catalyst can be effected by directing these materials continuously through a reactor containing a fixed layer of solid phosphoric acid catalyst in the form of grains or in the form of a solid. otherwise, and in this way mono-isopropyl benzene and relatively small amounts of more strongly propylated benzenes are formed.



   The hydrocarbon mixture subjected to alkylation preferably contains from about 2 to about 20 and more, molecular proportions of benzene to 1 molecular proportion of propylene, so that the formation of the mono-isopropyl benzene The main reaction of the process is. Under these conditions there is only relatively little formation of more highly alkylated benzenes and the formation of polymers is also little or practically absent. The product of such an alkylation reaction is fractionated into mono-isopropyl benzene, more strongly propylated benzenes, and unconverted benzene, the latter being returned to the alkylation circuit.



   Benzene and a hydrocarbon fraction containing appreciable amounts of propylene such as a propane-propylene fraction can be mixed and passed through a reactor containing a solid phosphoric acid catalyst, or the benzene can be introduced into the reactor. such a reactor, while the fraction containing propylene or else a mixture of benzene and propylene is introduced at various points located between the inlet and the outlet of the alkylation reactor such that the reaction mixture which comes into contact with the catalyst will contain a high molecular ratio of benzene to propylene throughout the reaction and thus promote the formation of mono-isopropyl benzene rather than polyisopropyl benzene.

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   The continuous alkylation treatment other than that described above can also be carried out in the presence of a powdered catalyst in other types of apparatus constructed to contact the hydrocarbons with carbon. solid catalyst in finely divided state.



   While the method of passing benzene and propylene, either together or against the current, through a suitable reactor with a fixed layer of solid catalyst particles is generally the usual method, the reaction between these hydrocarbons can also be carried out in an operation of the non-continuous type in which some of the components are preferably in the liquid phase and in which the catalyst, generally in a finely divided state, is kept in dispersion or in suspension by any method. agitation.



   Calcined mixtures of a phosphorus acid and a silica adsorbent are the preferred catalysts employed for the production of mono-isopropyl-benzene because they allow continuous reaction of benzene with propylene in the presence of a fixed layer of catalyst thereby rendering possible to eliminate practically any over-alkylation in polyisopropyl-benzene and to simplify some mechanical problems, as well as to avoid the corrosion difficulties encountered when this reaction is carried out in the presence of a liquid phosphoric acid .

   In addition, the solid phosphoric acid catalysts described herein have these advantages over aluminum chloride used for the same purpose, that said catalysts hardly form stable addition compounds or complexes with aromatic hydrocarbons. and / or olefinic as is characteristic of catalysts containing aluminum chloride. Also, the product obtained in the presence of solid phosphoric acid catalyst is generally ready immediately for distillation and does not have to be washed or otherwise treated to remove the catalyst as is the case when the catalyst. alkylation is aluminum chloride.



   While the alkylation reaction according to the present process is not fully understood, it results in the combination of benzene with propylene to produce isopropyl-benzene, which in turn may undergo further reaction. with one or more molecular proportions of propylene to produce the di- and poly-isopropyl-benzenes.



   Within certain limits, it is possible to produce mainly mono-isopropyl-benzene by appropriate adjustment of the activity of the catalyst, the ratio of benzene to propylene and operating conditions such as temperature, pressure, feed rate of reacting hydrocarbons, etc. In general, when the operating temperature is relatively high, the rate of the feed is greater than that employed with the lower reaction temperatures.

   Also, the higher pressures are generally preferred when the higher catalyst temperatures are used because a higher superatmospheric pressure helps to keep some of the benzene or propylated benzenes in a liquid state, the latter being formed. by the alkylation reaction. We believe that such a liquid substance present in the alkylation reactor washes the catalyst, thus practically preventing the accumulation thereon of carbonaceous and hydro-carbonaceous deposits, these deposits generally causing a build-up. appreciable decrease in catalyst activity, necessitating periodic reactivation of the catalyst by heating it in an oxygen-containing gas and then in a vapor atmosphere.

   A high molar ratio of benzene to propylene throughout the reaction results in the formation of relatively high yields of mono-isopropylene-benzene and relatively small amounts of poly-isopropyl-benzene. More polyisopropyl-benzene and less mono-isopropyl-benzene are formed when the ratio of benzene to propylene is relatively low. If more than 1 molecular proportion of propylene is introduced per molecular proportion of benzene, relatively large amounts of polyisopropyl benzenes are formed at the expense of monoisopropyl benzene, and some of the propylene may undergo polymerization.

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   In general, the products of the reaction between propylene and a molar excess of benzene are separated from unreacted benzene, by suitable means such as distillation, and the unreacted part of the benzene originally introduced is returned to the process and mixed with additional amounts of fresh benzene and propylene or the propane-propylene fraction. The total alkylation product thus liberated from the excess benzene originally introduced with the feed is separated into isopropyl-benzene and more strongly alkylated benzenes by distillation at ordinary pressure or at reduced pressure or by any other suitable means.

   Sometimes a poly-isopropyl-benzene fraction is returned to the process and mixed with benzene and propylene to be contacted with the catalyst.



   An advantage of this procedure is to wash the catalyst and remove therefrom hydrocarbon deposits which tend to reduce its catalytic activity. Another advantage could be to increase the ratio of mono-isopropyl-benzene formed relative to the poly-propyl-benzenes. If the propylene reacts incompletely with the benzene, as can happen when the loading rates of benzene and propylene are too high, the unreacted propylene can be separated by absorption in benzene or by any other suitable means and re-introduced into the process cycle.



   When the alkylation is carried out at a temperature above about 200 to 250 ° C., it is sometimes advantageous to add to the alkylation mixture a small amount of an aqueous fluid in order to compensate for the deterioration of the acid. catalyst due to dehydration. In general, an amount of not more than about 5%, and preferably between about 0.1 and about 2% by weight of an aqueous fluid such as water or steam is employed in order to maintain inactivity. Alternatively, small amounts of propyl or isopropyl alcohols can be introduced with the benzene and propylene to provide the amount of water necessary to prevent undesirable dehydration of the catalyst.

   This use of a propyl alcohol is generally possible at temperatures above about 250 ° C. because, under the operating conditions, the propyl or isipcopyl alcohol undergoes a certain dehydration in propylene and in water, the propylene being usable in the reaction of 'alkylation while water helps prolong the active life of the catalyst
The following examples show the kind of results obtained in specific embodiments of the process according to the present invention, but it is understood that the examples should not be interpreted in a sense limiting the scope of the invention. .



  EXAMPLE I.



   A mixture of 3.8 molecular proportions of benzene and 1 molecular proportion of propylene was passed through a steel reactor containing a solid phosphoric acid catalyst formed beforehand by calcining a mixture of pyrosphosphoric acid and diatomaceous earth. In this phase of the treatment, the temperature of the catalyst was 280 ° C., the pressure was 6.8 atmospheres, and 1 volume of benzene was introduced per hour per 1 volume of reactor space as the filling material. Of the propylene introduced, 50% reacted by passage and an alkylation product was formed containing 76 mole percent mono-isopropyl benzene and 24 mole percent of a mixture of poly-isopropyl benzene.

   Unconverted propylene recovered from the alkylation product was suitable for re-entry into the alkylation cycle.



  EXAMPLE II.



   A mixture of equal molecular proportions of benzene and propylene was passed through a steel reactor containing a solid phosphoric acid catalyst and maintained at 277 ° C. under a pressure of 8.2 atmospheres. The reaction mixture was introduced at a rate such that 0.7 volume of benzene passed per hour into one volume of the reactor space filled with the catalyst layer. During this treatment, 27%

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 by weight of the propylene reacted per pass to give an alkylation product consisting of 58% by weight of mono-isopropyl benzene and 42% by weight of a mixture of polyisopropyl benzene.

   Unconverted propylene recovered from the reaction mixture was suitable for re-introduction into the process cycle.



    EXAMPLE III.



   A mixture of 8 proportions of benzene and 1 molecular proportion of propylene was continuously passed through a steel reactor containing a solid phosphoric acid catalyst maintained at the temperatures and pressures shown in the Table which follows.



  In each of the three operations for which the data is given in this table, the mixture of benzene and propylene was introduced at an hourly liquid space rate of 3.0, that is, 3, 0 volumes of liquid were charged per hour per volume of reactor space containing the catalyst layer. In each of the operations substantially all of the propylene reacted forming mono-isopropyl benzene and polyisopropyl benzenes with virtually no polymer formation. The pressures employed in the operations indicated in the table were sufficient to maintain in the liquid state an appreciable proportion of the benzene and the propylated benzene.
BOARD.



     (Alkylation of benzene with propylene)
 EMI6.1
 
<tb> Operation <SEP> N
<tb>
<tb>
<tb>
<tb> 1 <SEP> 2 <SEP> 3
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Catalyst <SEP> temperature <SEP>, <SEP> C <SEP> 205 <SEP> 232 <SEP> 275
<tb>
<tb>
<tb>
<tb> Pressure <SEP> in <SEP> atmospheres <SEP> 272, <SEP> 37.4 <SEP> 61.2
<tb>
<tb>
<tb>
<tb> Duration <SEP> of <SEP> the <SEP> operation <SEP> in <SEP> hours <SEP> 60 <SEP> 72 <SEP> 300
<tb>
<tb>
<tb>
<tb>
<tb> The <SEP> produced <SEP> of <SEP> the <SEP> reaction <SEP> contained, in
<tb>
<tb>
<tb> for <SEP> hundred <SEP> in <SEP> weight <SEP> of
<tb>
<tb>
<tb>
<tb> Benzene <SEP> mono-isopropyl <SEP> 15.7 <SEP> 15.9 <SEP> 15.0
<tb>
<tb>
<tb>
<tb> Benzene <SEP> polyisopropyl <SEP> 0.6 <SEP> 0.6 <SEP> 0,

  77
<tb>
<tb>
<tb>
<tb> Ratio <SEP> between <SEP> the <SEP> benzenes <SEP> mono-isopro-
<tb>
<tb>
<tb> pylic <SEP> and <SEP> poly-isopropyl <SEP> formed <SEP> 26.0 <SEP> 26.5 <SEP> 19.5
<tb>
<tb>
<tb>
<tb> Yield <SEP> in <SEP> mono-isopropyl benzene <SEP>,
<tb>
<tb>
<tb> in <SEP> for <SEP> hundred <SEP> in <SEP> weight <SEP> of alkylated <SEP> benzene <SEP>
<tb>
<tb>
<tb> total <SEP> 96.4 <SEP> 96.4 <SEP> 95.2
<tb>
<tb>
<tb>
<tb> Rate <SEP> of <SEP> production <SEP> of <SEP> benzenes <SEP> isôpropy-
<tb>
<tb>
<tb> liques, <SEP> in <SEP> kgs. <SEP> by <SEP> hour <SEP> by <SEP> kg. <SEP> of <SEP> cata-
<tb>
<tb> lyser <SEP>: <SEP>
<tb>
<tb>
<tb>
<tb>
<tb> Mono <SEP> 0.430 <SEP> 0.446 <SEP> 0.428
<tb>
<tb>
<tb>
<tb> Poly <SEP>:

   <SEP> 0.016 <SEP> 0.017 <SEP> 0.022
<tb>
 
The catalysts employed in the above operations were still active and could have been used for longer periods of time.



  These operations, in which the ratio of benzene to propylene in the feed was 8: 1 and the pressure was sufficient to give a catalyst wash, yielded alkylation products containing 95% by weight or more of monoisopropyl benzene. and not more than 5% more highly alloyed benzenes.



   The above examples show that in order that at least 75% by weight of the product of the alkylation of benzene consists of mono-benzene

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   isopropyl, it is necessary that more than 3 molecular proportions of benzene are present throughout the reaction per molecular proportion of propylene introduced with the charge.

   With benzene to propylene ratios of about 5: 1 and higher, the alkylation product contains 90% or more of mono-isopropyl benzene. An operating pressure of at least 6.8 atmospheres is also required not only to ensure long catalyst life, but also because higher yields of mono-isopropyl benzene compared to polyisopropyl benzenes are obtained. when the operating pressure is sufficient to give a wash of the catalyst.

   It is preferred to employ catalyst temperatures of from about 150 to about 325 ° C for the alkylation of benzene in order to obtain high yields of mono-isopropyl benzene.



   The novelty and utility of the process according to the present invention is evident from the foregoing specification and the examples given therein, but no part of the specification should be construed in a sense limiting the scope of the invention.


    

Claims (1)

CLAIMS AND SUMMARY. 1. Process for the production of mono-isopropyl benzene, in which benzene and propylene are subjected in molar proportions greater than 3: 1 in contact with a solid catalyst consisting of phosphoric acid under alkylating conditions between about 150 and about 325 ° C and at a pressure of at least 6.8 atmospheres, so that the formation of mono-isopropyl benzene is the main reaction of the process. 2. Process for the alkylation of benzene with propylene in the presence of a solid catalyst consisting of phosphoric acid, in which benzene and propylene are contacted in molar proportions greater than 3: 1. with the catalyst under temperature conditions of from about 150 to about 450 ° C and under a pressure of at least 6.8 atmospheres, so that formation of monoisopropyl benzene is the main reaction. 3. Process for the alkylation of benzene with propylene in the presence of a solid catalyst * consisting of phosphoric acid, in which benzene and propylene are contacted in molar proportions greater than 5: 1 with the catalyst under temperature conditions of from about 150 ° to about 450 ° C and under a pressure of at least 6.8 atmospheres, such that the alkylated benzenes formed comprise at least 90% mono benzene. -isopropyl. 4. In a process for the alkylation of benzene with propylene in the presence of a solid catalyst of phosphoric acid under conditions such that the alkylation of benzene is the main reaction of the process, the improvement which comprises contacting benzene and propylene in a molar ratio greater than 3: 1 with the catalyst at a temperature of between about 150 and about 325 ° C. under a sufficiently high pressure greater than 6.8 atmospheres to maintain the temperature. at least some of the hydrocarbons present are liquid. 5. A process for the alkylation of benzene, substantially as described.