RO108958B1 - Para-diethylbenzene preparation process - Google Patents

Abstract

The present invention relates to a a process for the selective production of paradecylbenzene, by contacting with a catalyst modified zeolite, of a reaction mixture, composed of an alkylaryl precursor and hydrogen, under specific reaction conditions, in the presence or absence of ethylene. The process is particularly efficient and flexible, enabling it to be obtained pent-diethylbenzene in an integrated process to obtain ethylbenzene from the benzene resulting from the process selective disproportionation.

Description

The present invention relates to a process for the selective obtaining of ethylbenzene from ethylbenzene by catalytic reforming or synthesis.

Azra-diethylbenzene is known to be a very valuable product with multiple uses. The most widely used is as a desorbent for the separation / rare-xylene in the process involving the use of zeolite molecular sieves as a selective adsorbent. Paradietilbenzene is also used very successfully to obtain it. i v inilbenzene, which is a precursor for highly cross-linked ion exchange resins, or precursor for new types of plasticizers.

It is known that capar-diethylbenzene is a much more valuable product than the other isomers of diethylbenzene, namely metadiethylbenzene and orra-diethylbenzene. Commercially, these three isomers are usually obtained together, in proportions determined by thermodynamic equilibria. These three isomers have very close boiling points, the differences being about 5 ° C. This approximation of boiling points makes the separation / rare-diethylbenzene from the other isomers totally uneconomic if the classical fractionation procedure is applied. The separation of pnra-diethylbenzene by the technique of crystallization or adsorption on molecular sites is very difficult in terms of the technology used and expensive in terms of utilities and energy consumed.

For the purpose of obtaining a high purity paradietylbenzene, older processes are known, which refer to the preparation and reduction of pyrin-ethyl acetophenone, or the selective absorption of the para isomer from the mixture of diethylbenzene isomers, using X or Y-type zeolites containing barium and / or potassium.

More modern processes combine the process of selective sorption of the para isomer of diethylbenzene with a process of transalkylation of the products recovered from the adsorption - desorption zone, which results in a complex mixture which proceeds to the next fractionation step, where more is removed. fractions that are partially recirculated, partly separated and another part is transalkylated.

In order to simplify the process of obtaining p <3ra-diethylbenzene, great efforts have been made to use modified synthetic zeolites, with a strictly delimited physico-chemical structure, in selective conversion reactions of alkylaromatic hydrocarbons. The extension of the fundamental studies in the field of synthesis, characterization and modification of the synthetic zeolites has allowed significant progress in the reactions of the alkylaromatic hydrocarbons involving carbon ions.

These processes have the common disadvantage of the high complexity of the multiple units and operations, in the case of the variant of para-ethylacetophane reduction and of the selective sorption and, respectively, of the difficulties and the high consumption in the case of the technique of selective crystallization and adsorption.

Another disadvantage of the listed processes is the dependence on the source of diethylbenzene in the case of the selective sorption process and the acetophenone in the case of the reduction process.

In the case of the process of combining selective sorption with a transalkylation process followed by fractionation, in addition to the complication given by this sequence of processes, there is also the disadvantage of the corrosion and toxicity of the transalkylation catalyst.

The use of the new generation of modified synthetic zeolites partially eliminated these disadvantages, but it was not possible to simplify the flow of obtaining the catalyst and to achieve a high purity of the paradietilbenzene under economical conditions of the process.

The problem solved by the present invention is to obtain a zeolite with pore sizes close to those of ethylbenzene and with high acidity, of which, by a process of elimination of acid centers on the outer surface and dispersion in a special matrix , a catalyst is reached which selectively transforms ethylbenzene into pores only of zeolite.

The process according to the invention removes the mentioned disadvantages, in that the ethylbenzene is contacted, possibly, in the presence of an alkylating agent, with a modified zeolitic catalyst, which has been modeled the acidity of the outer surface, by impregnation with ammonium acid phosphate, so that the zeolite contains finally 3.97% phosphorus and 0.28% sodium, at a temperature between 375 and 475 ° C, preferably between 400 and 450 ° C, a pressure between 1 and 20 at, preferably 5 ... 10 at and a volume speed between 4 hours ' ¹ and 12 h' ¹ , preferably between 8 h ' ¹ and 10 h' ^! and a hydrogen / hydrocarbon molar ratio of 3/1 to 10/1.

According to the invention, ethylbenzene or selective disproportionation of ethylbenzene is carried out in the presence of a zeolite catalyst with physico-chemical properties directed from the zeolite synthesis phase and a controlled acidity obtained during the zeolite modification phase and, respectively, of obtaining the catalyst. Ethylation or disproportionation occurs by combining the aromatic compound with an alkylating agent, or passing only the aromatic compound over the catalyst, under specific conversion conditions, in the presence or absence of an inert diluent, such as hydrogen, nitrogen, carbon dioxide or methane. Selective conversion of the reactants takes place on a catalyst having a good adsorption capacity of benzene, minimum adsorption capacity for or / o-xylene, average crystallite dimensions of zeolite greater than 1 micron, a specific surface area of at least 300 m ² / g, a volume of pores (10 ... 300 Â) of at least 28 g / cm ³ , a ratio of silicon to aluminum of at least 11 and a sodium content of at least 0.3 percent.

The specific catalyst according to the present invention comprises a zeolite having a benzene sorption capacity of at least 10 g / 100 g zeolite, an absorption capacity of ortho-xylene of not more than 0.5 g / 100 g zeolite for 30 minutes at a temperature of 120 ° C and a partial pressure of 7 mm mercury column.

The matrix in which the zeolite, as well as the zeolite, were dispersed, were calcined separately before the formation of the catalyst at temperatures between 125 and 900 ° C for 1 to 36 h, preferably between 375 and 600 ° C, for a period of 1 to 16 h, and the final catalyst was treated with air + steam at temperatures between 350 and 600 ° C, for 1 ... 24 h.

In a preferred embodiment, the present invention achieves selective alkylation or disproportionation of ethylbenzene to predominantly or exclusively / wraethyl diethylene oxide, by a flexible process, at a temperature between 300 and 550 ° C, at a pressure between 0, 3 to 100 at, using a volume ethylbenzene volume ranging from 0.5 to 40 liters ethylbenzene / liter catalyst x hour.

When carrier gas is also used, the molar ratio carrier / reactant gas is generally between 1 and 25 mol / mol, and in the alkylation variant of ethylbenzene, the ratio between ethylbenzene and the ethylating agent is between 1 and 10 mol / mol.

The selective conversion of ethylbenzene is made only to hydrocarbons having a diameter close to the precursor, thus allowing the preferential diffusion of the para isomer, which has the same size as the initial reactant. The lack of acidity on the outer surface of the catalyst prevents successive isomerization reactions and allows the unique reaction product of paradietylbenzene to be obtained.

The process according to the invention has the following advantages:

- has great flexibility; in the absence of an alkylating agent one can only work with the alkylaromatic component in the variant of the disproportionate reaction;

- eliminates corrosion and toxicity.

Examples of carrying out the process according to the invention are given below.

Example 1. A. A solution, consisting of 245 g of sodium silicate (with 9.36% gr.Na2 and 29.5% gr.SiO ₂ ) and 305 g of water, is transferred into a stainless steel autoclave, lined with interior with Teflon.

In a separate vessel, another solution B is prepared by combining 416 g of water, 92 g NaCl, 60 g (C ₃ H ₇ ) ₄ NBr, 31 g C ₂ H ₅ OH and 18 g H ₂ SO ₄ concentrated ( 96% gr.), Mix well until the solution becomes clear and homogeneous. The solution thus obtained is poured over the solution A which is in the autoclave. It is stirred very well for 5 minutes, and the mixture thus obtained is heated under continuous stirring in the autoclave until the system pressure is 10.5 at. This pressure is maintained for 24 hours, after which the autoclave is cooled to room temperature, and the solid product is separated from the solution by filtration and then washed on the filter cloth several times with water, then dried at a temperature of 120 ° C in air stream, obtaining a white powder.

B. The product obtained as above was calcined overnight in air at 520 ° C, for the removal of the organic compounds, observing changes between the relative intensities of the X-ray diffractogram.

The specific surface measurements carried out by the BET method showed for the calcined powder a value of 357 m ² / g.

Benzene adsorption capacity determinations carried out under static conditions resulted in 12 g benzene / 100 g zeolite, and orzo-xylene adsorption capacity determinations resulted in 0.32 g wfo-xylene / lOO. g zeolite for 30 minutes at a temperature of 120 ° C and a partial pressure of 7 mm mercury column.

The calcined zeolite had an average crystallite size of between 1.7 and 2 microns, and the sodium content was 0.57% by weight.

C. The zeolite thus prepared was treated with a solution of ammonium nitrate prepared from 43 g of ammonium nitrate and 430 cm ^{3 of} water. Three volumes of solution for one volume of zeolite were used for ion exchange, under reflux conditions, using glass equipment, for 2 hours. After 2 hours the mixture was cooled, filtered and washed with demineralized water to neutral pH. . The wet zeolite cake thus obtained is dried in the oven for 2 hours, at a temperature of 120 ° C, after which the zeolite is calcined at 520 ° C, in an air stream, for 4 hours.

The ion exchange rate of the zeolite treated according to this procedure was 72%.

D. 100 grams of zeolite obtained according to the procedure described in point B was impregnated with a solution of ammonium acid phosphate, obtained by dissolving 75 g of ammonium acid phosphate in 190 ml demineralized water.

After impregnation, the zeolite is dried and then calcined at 520 ° C for 24 h.

The phosphorus content of the final product thus obtained was 4.12% by weight, and the sodium content was 0.5% by weight.

E. The modified zeolite according to the procedure described in point C was impregnated with ammonium acid phosphate according to the methodology described in point D, giving a zeolite which finally contained 3.97% phosphorus and 0.23% sodium .

F. The product obtained as in point D was mixed with a pseudoboehmite aluminum powder, consisting of 20 parts alumina calcined at 520 ° C and 80 parts alumina dried at 120 ° C, in a mixer, until the mixture was homogenized. The powder mixing ratio was 65% by weight zeolite and 35% by weight alumina. The new composition is gradually treated with 10 milliliters of concentrated nitric acid, dissolved in 210 ml of water, until the paste in the mixer becomes sufficiently plastic to be extruded.

The extrudates with a diameter of 1.5 mm are cut to a length of 2.7 ... 3.2 mm and calcined in air at 520 ° C for 8 hours, then cooled to room temperature and put into bags hermetically sealed plastic.

G. 100 cm ³ of the catalyst obtained according to the above procedure is diluted with 200 cubic centimeters of quartz or alpha alumina with the equivalent diameter of the catalyst, it is introduced in a stainless steel reactor resistant to pressure and temperature. The reactor is heated by means of an electric furnace, provided with three heating zones, which allows to obtain an isothermal zone for the zeolite catalyst. After charging the catalyst, it is activated in air at 520 ° C for 4 hours. It is cooled to 400 ° C and purged with pure nitrogen until all oxygen is removed, then pressurized with high purity hydrogen to the pressure of 10 at.

The catalyst thus activated was subjected to a catalytic activity test in the alkylation reaction of the alkylaromatic hydrocarbons. In the alkylation process, the aromatic component that can be alkylated contains at least one aromatic ring and at least one alkylable position. The most preferred aromatic hydrocarbons are benzene, ethylbenzene and toluene. The process also allows alkylation of a mixture of aromatic compounds, especially benzene and ethylbenzene or benzene and toluene.

As an alkylating agent, ethylene can be used, but also ethyl alcohol, ethyl bromide and chloride, and ethylmercaptan can be used successfully. In particular, any known alkylating agent may be used in the present process. The preferred alkylating agent for this invention is ethylene.

The alkylation temperature is between 275 and 500 ° C, preferably between 375 and 450 ° C. The alkylation pressure can be in the range of 1.5 at up to 30 at, preferably being in the range 5 at up to 25 at.

The molar ratio between the alkylaromatic hydrocarbon and the alkylating agent is between 1/1 and 20/1, preferably between 2/1 and 12/1.

If hydrogen is present in the process, the molar ratio of hydrogen to the alkylating agent is between 10/1 and 1/4. If another diluent gas is used, the abovementioned report shall be retained.

In the absence of an alkylating agent, one can only work with the alkylaromatic component in the variant of the disproportionate reaction. The latter variant is most preferable for obtaining para-diethylbenzene from ethylbenzene.

The process of obtaining paradietylbenzene in both alkylation and disproportionate variants involves volumetric speeds expressed as the ratio between the liquid hydrocarbon flow and the volume of large catalysts, between 1 and 20 h ' ¹ , preferably between 3 and 12 h ¹ , demonstrating high catalyst productivity.

The reaction conditions and the results obtained in the case of alkylation of ethylbenzene with ethylene are presented in the table below.

1.

Table 1

Reaction conditions Catalyst performance Tempe- rature, ° C Speed yourself. h ¹ Pressure, at Report Ethylbenzene Ethylene mol / mol Convert reactants Selectivity for para-diethyl-benzene Etilben- zen % mol Ethylene, % mol 1. 2. 3. 375 400 425 2 5 8 5 5 10 5 5 2 17.4 18.7 19.6 80.1 98.6 92.3 94.1 96.4 98.3

It is evident from the above results that this type of catalyst with a lower sodium content exhibits outstanding performances in the reaction of obtaining wu-diethylbenzene. The conversion of ethylene benzene is very close to the theoretical one (20 mol% due to the chosen molar ratio), and the selectivity to the para isomer. it is particularly high compared to that indicated by the thermodynamic balance (28.5% moles at 400 ° C). The isomer / meta / ortho ratio for test 3 was 98.3 / 1.69 0.01.

These performances demonstrate the uniqueness of the catalyst in the process of obtaining 7isra-diethylbenzene. This uniqueness translates into a well-determined porous structure of the zeolite, a high acidity present only inside the pores, an imposed sodium content and controlled diffusion of the reactants and reaction products due to their geometric shape, large crystallite dimensions of of the zeolite and the chosen thermal level.

Example 2. The catalytic activity test in the alkylation reaction of ethylbenzene with ethylene was resumed under the same conditions as in example 1, but taking as the catalyst the sample obtained according to example 1 point E.

The reaction conditions and the analytical results are summarized in the table

2.

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Table 2

Reaction conditions Catalyst performance Test no. Temper- shift, ° C Speed yourself. h ¹ Pressure, at Report Ethyl- benzene Ethylene mol / mol Convert reactants Selectivity to paradietil-benzene Ethyl benzene, % mol Ethylene, % mol 1. 2. 3. 375 400 425 2 4 8 5 5 10 5 5 2 12.9 14.3 14.1 76.2 84.6 82.7 94.1 98.4 98.9

The results obtained by me and this catalyst demonstrate a great selectivity of the catalyst with respect to the obtaining of para-diethylbenzene, with the mention that, due to the higher sodium content compared to the previous catalyst, the conversion of the reactants was lower. Taking into account technological considerations, it is required that at least the conversion of ethylene to be as close as 100%, from this point of view, the level of sodium in zeolite is very important.

Example 3. 50 cm ³ of catalyst obtained according to the example 1 point E were diluted with 100 cm ³ of inert alpha alumina with dimensions similar to that of the catalyst. After the catalyst was brought under reaction conditions in the same manner as in Example 1 pt.G the catalytic system was tested in the disproportionate reaction of ethylbenzene.

The reaction conditions and representative analytical results are shown in Table 3.

Table 3

Test.nr. Reaction conditions Catalyst performance Temper- shift, ° C Speed you. h ' ¹ Pressure, at Reaction time, hours conversion ethylbenzene, % mol Selectivity /? «Ra-diethyl benzene % 1. 4 18.1 96.3 2. 400 4 10 24 16.9 98.2 3. 48 14.1 98.8 4. 5 11.2 97.2 5. 375 4 10 4 11.7 98.2 6. 20 13.4 96.8 7. 4 26.3 94.6 8. 425 8 10 4 19.1 98.4 9. 12 14.8 99.0

From the data obtained for the disproportionation of ethylbenzene, it is also shown that in this case the selectivity to the para isomer is very high. The ratio of the para-metalbrto isomers being in the case of test 8 of 98,4 / 1,6 / 0 shows that in these reaction conditions the ortho undesirable isomer can be completely eliminated.

Another significant fact is that the paraselectivity tends to increase over time, as a result of the likely deposition of the coke on the surface and also as the volume velocity of the reactants increases.

Taking into account also the insignificant influence of the pressure on the performances of the catalyst, it results that the high volume speed for this process is of interest.

Example 4. The activity test from example 3 was resumed in this example, with the difference that hydrogen was introduced into the reaction system as a carrier gas, at a pressure of 10 at.

The results are summarized in Table 4.

Table 4

Test.nr. The reaction conditions Catalyst performance temperature for both ° C i, speed you. h ' ¹ Reaction time, hours Hydrogen / Ethylbenzene molar ratio conversion ethylbenzene, % mol Selectivity to / wra-diethylbenzene% 1. 4 18.3 97.1 2. 400 4 24 3 17.9 97.1 3. 4 48 18.0 97.3 4. 4 18.2 98.2 5. 425 8 48 5 18.1 98.4 6. 400 4 4 10 17.6 97.0 7. 48 17.5 97.1

The data obtained in this example show the positive effect of hydrogen in the alkylation process. This gas has an effect of increasing the stability of the catalyst over time and preventing the rapid deposition of the coke. Given that the selectivity to the para isomer and the conversion of ethylbenzene is practically maintained at the level of the freshly tested catalyst under hydrogen-free conditions, it turns out that the presence of hydrogen in a molar ratio between 3 and 10 is also an important feature of the process.

Example 5. Verification of the catalyst performance obtained according to example 1, point E, in the presence of hydrogen according to example 4, was done in an industrial plant with adiabatic reactor in which 5.7 t of catalyst were introduced, diluted with

3.5 t inert alumina, under reaction conditions defined by a temperature of 400 ° C, a pressure of 10 at, a volume velocity of 8 h ' ¹ and a ratio H _; / hydrocarbon = 5 mol / mol.

Under these conditions, the catalyst's performance was on average 520 days of operation as follows:

- ethylbenzene conversion 22.7% mol:

- selectivity for j> ara-diethylbenzene 98.9% mol.

As can be seen from this industrial test, the catalyst and the process conditions offer very good performance for the obtaining of / w-diethylbenzene, as well as a remarkable stability of the catalyst during the 520 days of operation.

Example 6. The reaction product obtained in Example 4 is passed over the catalyst obtained as in Example 1, point E, without separating the compounds from this product. Basically, through this process the product was passed through a complete recirculation over the same catalyst, under reaction conditions defined by: temperature: 400 ° C, pressure: 10 at and molar ratio hydrogen / ethylbenzene: 5/1.

The summary results are shown in table 5.

Table 5

Test.nr Speed volume flow Reactor passage number Catalyst performance conversion ethylbenzene, % mol Selectivity to para-diethylbenzene, % 1. 8 1 14.8 97.2 2. 8 2 22.9 97.3 4 2 26.6 96.8 3. 4 3 28.5 96.4

It is clear from the data obtained that the process performance can be increased by partial or total recirculation of the reaction product or by passing the reaction mixture through several reactors in series. The reactors may be from 1 to 5, and in a preferred example the reactors may be from 1 to 3.

Example 7. 300 grams of zeolite prepared according to the methodology presented in Example 1, point C, is pelleted with a press.

The pellets are then broken and placed so that particles with an equivalent diameter of 1.5 mm are retained. 100 cm ³ of these particles are charged to the reactor and tested in the alkylation reaction of benzene with ethylene. The procedure is similar as in Example 1, point G, the only difference is that of the aromatic component, which is benzene instead of ethylbenzene.

The reaction conditions and the results obtained are presented in table 6.

Table 6

Test.nr. Reaction conditions Catalyst performance Temperature, ° C Speed Pressure, Report Ethylbenzene,% mol Ethylene% mol selectivity, % mol you. h ' ¹ at. molar well- Zen / ethylene 1. 4 10 20.7 98.7 93.2 2. 400 4 15 22.3 99.1 96.6 3. 4 20 25.7 99.8 97.1 4. 8 23.8 99.3 98.3

The data obtained on the alkylation of benzene demonstrate very good performances of the zeolite obtained according to example 1 pt. C, in the reaction of obtaining ethylbenzene. Considering that from the conditions of molar ratio imposed the theoretical conversion is 25% mol, it can be seen that the values of the conversion are very close to the maximum values possible to obtain.

Example 8. The reaction product obtained in the alkylation reaction of Example 6 contains 20.7% ethylbenzene, 1.67% diethylbenzene, the remainder being mainly unreacted benzene. This product is subjected to a fractionation that allows to obtain a peak fraction (78.7% of the product), consisting mainly of benzene and another fraction which is at the base of the column, consisting mainly of ethylbenzene (92.6% purity). , unreacted benzene and diethylbenzene, in which paradietylbenzene represents 73.1%.

The recovered benzene is returned to the alkylation reactor, the reaction conditions and the results obtained are similar as in Example 6.

The concentrate of ethylbenzene and diethylbenzene from the base of the column is passed to the selective disproportionation under the reaction conditions similar to those of example 3, in order to selectively obtain paradietylbenzene.

Under the reaction conditions specific to the test 8 in Table 3, the conversion of ethylbenzene was 19.7% mol., And the selectivity to / tfa-diethylbenzene was 97.8%.

The obtained results demonstrate a high flexibility of the use of the basic zeolite within an integrated reaction complex, in which in the first reactor ethylbenzene is obtained from benzene and ethylene, and in the second reactor para-diethylene benzene is obtained from ethylbenzene by selective disproportionation. The benzene remaining unreacted in the alkylation process and the benzene resulting in the disproportionate process is returned to the alkylation reactor, and the fractionation section 10 can be used jointly, if a side cutter is provided in the fractionation column of the product resulting in the alkylation process. where will the ethylbenzene concentrate be taken. In this case, ara-diethylbenzene will be taken from the base 15 of this column.

From the examples given in this invention it follows that several variations can be made in the process of obtaining pnra-diethylbenzene, which allow us to obtain 20 para-diethylbenzene and ethylbenzene integrated or separately.

Claims (8)

claims 1. Process for the selective production of para-diethylbenzene, by disproportionating or alkylating ethylbenzene, characterized in that ethyl benzene is contacted, possibly, in the presence of an alkylating agent, with a modified zeolite catalyst, to which the acidity of the surface has been modeled. outer by impregnation with ammonium acid phosphate so that the zeolite finally contains 3.97% phosphorus and 0.28% sodium, at a temperature between 375 and 475 ° C, preferably between 400 and 450 ° C, at a pressure 3 5 between 1 and 20 at, preferably 5 ... 10 at, a volume velocity between 4 h ' ¹ and 12 h' ¹ , preferably between 8 h ¹ and 10 h ' ¹ and a hydrogen molar ratio / oil between 3/1 and 10/1. 40 Process according to Claim 1, characterized in that the zeolite catalyst comprises 35% pseudoboehmite alumina and 65% modified zeolite. Process according to claim 1, 45, characterized in that the modified zeolite has a specific surface area between 300 m ² / g and 400 m ² / g, preferably with a specific surface area between 300 m ² / g and 400 m ² / g, preferably 375 m ² / g, an adsorption capacity of benzene carried out under static conditions of 12 g benzene / 100 g zeolite and an adsorption capacity of orthoxylene of maximum 0.32 ortho-xylene / 100 g zeolite for 30 min, at a temperature of 120 ° C and a partial pressure of 7 mm Hg. 4. Process according to claim 1, characterized in that the zeolite has the average size of the crystals between 1.7 and 2 microns. 5. Process according to claim 1, characterized in that ethylbenzene is alkylated with ethylene at an ethylbenzene / ethylene molar ratio of 4/1 to 8/1. 6. Process according to claim 1, characterized in that the ethylbenzene used in the disproportionation or alkylation process is partially obtained by ethylene alkylation of the benzene resulting in the disproportionation phase, in a suitable reactor, under the same reaction conditions specific to the ethylbenzene disproportionation. at a molar / ethylene ratio of 4/1 to 8/1, in the presence of a modified zeolitic catalyst with the characteristics of claims 3 and 4, wherein the ion exchange rate of sodium is 72%. Process according to Claim 1, characterized in that it is carried out in one to 5 successive reactors or in a single reactor with 5 successive catalyst layers. 8. Process according to claim 1, characterized in that, in order to increase the overall efficiency of the process, the more efficient use of ethylbenzene and the reduction of energy consumption in the process of obtaining the / wrt-diethylbenzene, the fractionation sections of the a / v production plant. / ra-diethylbenzene and ethylbenzene, respectively, obtained from the benzene resulting from the disproportionate process, according to claim 6, can be combined into one, so as to ensure the recycling of benzene, ethylbenzene and the removal as a finished product of paradietylbenzene.