Method of producing high-boiling byproducts of isoprene production

Abstract

A method of processing high-boiling byproducts of isoprene production obtained at the first stage of isoprene production by the dioxane method into isoprene, isobutylene and formaldehyde which comprises the catalytic splitting of said products in the vapor phase in the presence of water with a weight ratio therebetween of 1:1/2, respectively, at 250-290.degree. C over aluminum oxide as catalyst. The resulting vapor mixture is catalytically split at 315.degree.-360.degree. C over calcium-phosphate catalyst with the formation of a reaction mixture containing isoprene, isobutylene and formaldehyde.

Description

The present invention relates to methods of processing high-boiling byproducts of isoprene production into isoprene, isobutylene and formaldehyde, and more specifically it concerns a method of processing high-boiling byproducts of isoprene production obtained at the first stage of isoprene production by the dioxane method.

Isoprene, isobutylene and formaldehyde are widely used in the manufacture of synthetic rubbers and other chemical products.

At the first stage of isoprene production by the dioxane method a reaction mixture is obtained which contains dimethyldioxane, as well as high-boiling byproducts distributed among the organic and aqueous layers of the reaction mixture.

A number of methods of processing such high-boiling byproducts of isoprene production are known. Thus, it is known to subject these products to hydrolysis in the presence of inorganic acids. Service problems, however, arise in developing the production method for such processes associated with the requirements of continuous operation of a plant and burning the resinous residues or wastes containing an inorganic acid.

It is also known to process high-boiling byproducts of isoprene production on the basis of their catalytic splitting in the vapour phase over solid catalysts at elevated temperature.

One of these methods involves the processing of high-boiling byproducts of isoprene production over a catalyst of the aluminosilicate type. By this method, high-boiling byproducts contained in the aqueous layer of the reaction mixture of dimethyldioxane synthesis (the first stage of isoprene production by the dioxane method) are fed for splitting without preliminary isolation from water, the organic layer of high-boiling byproducts being also fed for splitting. This method features a very low yield of isoprene which is only about 12% of theory.

It is also known to process high-boiling byproducts, their components or mixtures thereof with dimethyldioxane over calcium-phosphate catalyst. The process is conducted at about 350.degree. C with a ratio of high-boiling byproducts to water of 1:3. The main disadvantage of this method consists in a rapid coking of calcium-phosphate catalyst having a very developed surface and a large void volume. A long-term burning out of coke is required for recovery of the catalyst surface so that this method is rather inefficient. The yield of isoprene by this method is comparatively low.

It is an object of the invention to provide a method of processing high-boiling byproducts of isoprene production obtained at the first stage of isoprene production by the dioxane method which permits the achievement of an improved yield of isoprene.

With this and other objects in view, the invention consists in the provision of a method of processing high-boiling byproducts of isoprene production, wherein said high-boiling byproducts are catalytically split in the vapour phase in the presence of water with a ratio therebetween of 1:1+2, respectively, over a solid catalyst, and wherein, according to the invention, the catalytic of said high-boiling byproducts is conducted over aluminum oxide as catalyst at 250.degree.-290.degree. C to obtain a vapour mixture which is subsequently subjected to a catalytic splitting at 315.degree.-360.degree. C over calcium-phosphate catalyst with the formation of a reaction mixture containing isoprene, isobutylene and formaldehyde.

As mentioned above, high-boiling byproducts formed at the first stage of the process in preparing dimethyldioxane in isoprene production from formaldehyde and isobutylene comprise a complex mixture of various compounds exhibiting different chemical properties and reactivity. This includes three isomers of dioxane alcohols, pyran compounds, numerous ethers, as well as various formals of cyclic and linear structure and unidentified compounds especially including numerous heavy fractions boiling above the boiling point of dioxane alcohols.

Our studies show that at the present state of the art no satisfactory result can be obtained using any single catalyst in any single-stage process.

Thus, the catalytic splitting of high-boiling byproducts over aluminum oxide results in obtaining a negligible quantity of isoprene, isobutylene and a high yield of the total of unsaturated alcohols, formaldehyde, pyran compounds, etc. (see Tables 1 and 2).

TABLE 1______________________________________CONDITIONS OF PROCESSING HIGH-BOILINGBYPRODUCTS OVER ALUMINUM OXIDE CATALYSTTemperature Rate of feedingin the catalyst of high-boilingcolumn, .degree. C High-boiling products, mid- bot- byproducts/ g/h per g ofCatalyst top dle tom water ratio catalyst______________________________________Aluminumoxide 266 254 254 1:2 2.0______________________________________ TABLE 2__________________________________________________________________________YIELDS OF PRODUCTS IN SPLITTING HIGH-BOILING BYPRODUCTS OVERALUMINUM OXIDE CATALYST UNDER THE CONDITIONS SHOWN IN TABLE 1Starting high- Content Reaction mixture Yield % ofboiling bypro- of test Reaction products obtained conversionducts mixture, Organic Aqueous Gas, Total, Converted of high-boil-Components g layer,g layer,g g g g % g ing byproducts1 2 3 4 5 6 7 8 9 10 11__________________________________________________________________________ Carbon dioxide -- -- 2.37 2.37 2.37 1.02 Carbon oxide -- -- 0.27 0.27 0.27 0.12 Isobutylene 2.52 13.30 15.82 15.32 6.85 Isoprene 10.22 5.20 15.42 15.42 6.65 Methanol -- 14.35 -- 14.35 14.35 6.19 Trimethylcarbinol 1.79 8.39 -- 10.18 10.18 4.39Unsaturated Unsaturated alco-alcohols 6.48 hols C.sub.5 28.61 22.30 -- 50.91 44.43 19.15C.sub.5 Methylenetetra- hydropyran 4.42 1.36 5.78 5.78 2.5 Methyldihydropyran 12.45 4.68 -- 17.13 17.13 7.38 p-Xylene 0.17 -- -- 0.17 0.17 0.07 Dimethyldioxane 5.58 10.50 -- 16.08 16.08 6.93Methylvinyldioxane 1.53 Methylvinyl- -- -- -- -- 1.53 100.0 -- -- dioxaneMethylbutandiol 4.86 Methylbutan- 3.95 2.72 6.67 -- -- 1.81 0.78ethers 1.08 diol ethers -- 1.51 1.51 -- -- 0.43 0.19Pyran alcohol 7.26 Pyran alcohol 0.79 8.01 8.80 -- -- 1.54 0.67Methylbutandiol 35.22 Methylbutandiol 0.37 4.69 5.06 30.16 85.5 -- --Dioxane alcohol Dioxane alcoholethers 13.35 ethers 4.57 1.44 6.01 7.34 54.2 -- --Dioxane alcohol Dioxane alco-formals 10.26 hol formals 0.34 1.13 1.47 8.79 86.0 -- --Dioxane alcohols 122.07 Dioxane alcohols 5.48 14.19 19.67 102.4 79.4 -- --Total of unidenti- Total of unidenti-fied products 8.91 fied products 15.25 4.54 19.79 -- -- 10.88 4.70Heavy products Unidentifiedboiling above di- heavy products 3.82 -- 3.82 81.59 95.5 -- --oxane alcohols 85.41Total of high-boil-ing byproducts inthe test 296.43 -- -- Formaldehyde 7.05 53.29 60.34 -- -- 60.34 6.03Water 603.57 Water 7.42 602.9 610.32 6.75 2.92 Losses and coke -- -- -- 8.06 8.06 3.48Total 900.0 Total 114.8 756.0 21.14 900.0 231.81 77.3 231.81 100.0__________________________________________________________________________

The basic part of the mixture obtained after the splitting may not be directly used (without separation) for the production of isoprene. In separating such mixture, e.g. by a rectification reformation of some starting compounds present in the high-boiling byproducts may take place, mainly due to water and formaldehyde addition at double bonds (Prince reaction).

The employment of calcium-phosphate catalyst for direct splitting high-boiling byproducts also cannot give desired results (see Tables 3 and 4).

TABLE 3______________________________________CONDITIONS OF PROCESSING HIGH-BOILINGBYPRODUCTS OVER CALCIUM-PHOSPHATE CATALYST______________________________________ Feeding rate of high-boil- High-boiling ing byproducts, Temperature, byproducts/ g/h per 1 gCatalyst .degree. C water ratio of catalyst______________________________________Calcium-phos-phate catalyst 320-325 1:2 1.0______________________________________ TABLE 4__________________________________________________________________________YIELDS OF PRODUCTS IN SPLITTING HIGH-BOILING BYPRODUCTS OVERCALCIUM-PHOSPHATE CATALYST UNDER THE CONDITIONS SHOWN IN TABLE 3Starting high- Content Reaction mixture Yield % ofboiling bypro- of test Reaction products obtained conversionducts mixture, Organic Aqueous Gas, Total, Converted of high-boil-Components g layer,g layer,g g g g % g ing byproducts1 2 3 4 5 6 7 8 9 10 11__________________________________________________________________________ Carbon dioxide -- -- 0.91 0.91 -- -- 0.91 0.02 Carbon oxide -- -- 0.23 0.23 -- -- 0.23 0.16 Isobutylene 3.43 -- 1.50 4.93 4.93 3.34 Isoprene 23.18 -- 1.83 25.01 -- -- 25.01 16.90 Methanol 6.06 0.88 6.94 -- -- 6.94 4.70 Trimethylcarbinol 0.35 1.37 1.72 -- -- 1.72 1.17Unsaturated Unsaturatedalcohols 3.67 alcohols C.sub.5 2.20 0.71 2.91 0.76 20.7 -- --C.sub.5 Methylenetetra- hydropyran 1.27 -- 1.27 -- -- 1.27 0.86 Methylidihydropyran 6.43 0.35 6.78 -- -- 6.78 4.58 p-Xylene 0.48 -- 0.48 -- -- 0.48 0.32 Dimethyldioxane 2.23 1.63 3.86 -- -- 3.86 2.51 Methylvinyldioxane 0.72 -- 0.72 0.72 0.49Methylbutandiol 2.68 Methylbutandiol -- 1.19 1.19 1.49 55.5 -- --ethers ethers -- 0.57 0.57 -- -- 0.57 0.39Pyran alcohol 4.41 Pyran alcohol 0.51 1.46 1.97 2.47 55.3 -- --Methylbutandiol 21.96 Methylbutandiol 0.40 1.06 1.46 20.50 93.5 -- --Dioxane alcohol 7.52 Dioxane alcohol 2.19 1.01 3.20 4.32 57.5 -- --ethers ethersDioxane alcohol 5.37 Dioxane alcohol 0.45 0.97 1.42 3.95 73.5 -- --formals formalsDioxane alcohols 67.70 Dioxane alcohols 0.45 11.29 11.74 55.96 82.5 -- --Total of unidenti-fied compounds 6.17 Total of unidenti- fied compounds 15.91 0.13 16.04 -- -- 9.87 5.56Heavy components Heavy unidentifiedboiling above components 0.51 -- 0.51 57.80 99.0 -- --dioxane alcohols 58.34Total of high-boil-ing byproducts 177.82 --Water 362.18 Water 1.80 390.05 391.85 -- -- 29.67 20.25 Formaldehyde 2.33 28.36 30.69 -- -- 30.69 20.75 Coke and losses 23.60 23.60 16.00Total 540.0 Total 70.9 441.0 4.47 540.0 147.25 83.1 147.25 100.0__________________________________________________________________________

While the isoprene yield is higher here than in the case of using aluminum oxide, the yields of other valuable products, such as isobutylene and formaldehyde, are rather insufficient. But an important result is that with the direct processing of high-boiling byproducts over calcium-phosphate catalyst having a fine-porous structure the coke formation is materially increased. The yield of coke and losses attains 16%. This fact itselt does not permit the use of this catalyst for decomposition of high-boiling byproducts.

However, it has been found that the successive operation with the two catalysts effected the elimination of the difficulties encountered where they are used separately. As a result of splitting of high-boiling byproducts over aluminum oxide, a vapour mixture with a low content of isoprene is obtained. This permits the carrying out of a rather deep conversion process without any risk of occurrence of secondary reactions. The splitting of the resulting vapour mixture which thus contains a negligible quantity of high-molecular compounds over calcium-phosphate catalyst permits the elimination of a rapid coking of the catalyst and results in the formation of a reaction mixture containing isoprene, isobutylene and formaldehyde so that the rectification of this mixture is not associated with losses of valuable products in the course of chemical reactions.

Thus, by conducting a successive splitting of high-boiling byproducts over aluminum oxide and calcium-phosphate catalysts isoprene, as well as isobutylene and formaldehyde can be obtained from high-boiling byproducts in a comparatively high yield. The yield of isoprene in converting high-boiling byproducts ranges from 22 to 23%, formaldehyde -- 25% and isobutylene -- 7%. The method according to the invention permits the complete processing of high-boiling byproducts without discharging any fraction thereof due to recycle of unconverted heavy components contained in the starting products and heavy reaction products. The method may be effected using standard equipment employed in isoprene production from formaldehyde and isobutylene.

The process may be conducted in a continuous manner.

The method according to the invention is effected as follows.

For splitting high-boiling byproducts the use was made of an installation comprising an evaporator, two reactors, conventional condensation apparatus, cooling apparatus, apparatus for catching light fractions, for receiving gas and liquid products.

For the conduct of the process the temperature and rate of delivery of starting products are selected to ensure a sufficient rate of the process so as to make it more economical and, on the other hand, so as to eliminate the development of undesired secondary conversions. In addition, the secondary conversions are hindered by diluting the reaction mixture with steam so that an excessive amount of water should be fed into the installation for normal operation of the both reactors.

Starting high-boiling byproducts and water in a selected weight ratio are fed by means of a metering pump into a heated evaporator. Then the resulting vapours are fed into a reactor containing aluminum oxide, wherein the mixture is catalytically split at a preselected temperature. The resulting vapour mixture is then admitted into a reactor charged with calcium-phosphate catalyst for further catalytic conversion and then into the condensation and receiving apparatus. As a result, a reaction mixture is obtained which contains isoprene, isobutylene and formaldehyde. The liquid and gaseous products thus obtained are measured, separated and analyzed.

With continuous operation of the installation two reactor systems are used which are alternately switch-over for processing the starting products and for regeneration of the catalysts. The desired products are isolated from the reaction mixture by known methods, such rectification, and the residue is recycled for secondary processing together with the starting high-boiling byproducts.

The present invention will be better understood from the following specific examples.

EXAMPLE 1

30 g of aluminum oxide were charged into the first reactor. 60 g of calcium-phosphate catalyst were charged into the second reactor. The conditions of high-boiling by-products splitting, which are carried out under atmospheric pressure, are given in Table 5 and the resulting products yields are given in Table 6.

TABLE 5______________________________________CONDITIONS OF PROCESSING HIGH-BOILINGBYPRODUCTS OVER ALUMINUM OXIDE ANDCALCIUM PHOSPHATE CATALYSTSReactorin the flow Temperature in Rate of feed-direction of the catalyst High-boiling ing high-boil-high-boil- column, .degree. C. byproducts/ ing byproductsing byprod- mid- bot- water weight g/h per 1 gucts vapours top dle tom ratio of catalyst______________________________________1st reactorwith alumi-num oxide 253 243 280 1:2 2.02nd reactorwith calciumphosphatecatalyst 317 324 340 1:2 1.0______________________________________ TABLE 6__________________________________________________________________________YIELDS OF PRODUCTS IN SPLITTING HIGH-BOILING BYPRODUCTSOVER ALUMINUM OXIDE AND CALCIUM-PHOSPHATE CATALYSTSUNDER THE CONDITIONS SHOWN IN TABLE 5Starting high-boiling byproducts Yield of Content products in the Reaction mixture % of mix used Reaction products obtained conver- for tests, Organic Aqueous Gas, Total, sion ofComponents g Components layer,g layer,g g g Converted g byproducts1 2 3 4 5 6 7 8 9 10 11__________________________________________________________________________ Carbon dioxide 2.27 2.27 2.27 1.42 Carbon oxide 0.55 0.55 0.55 0.84 Isobutylene 5.92 -- 6.22 12.14 12.14 7.59 Amylenes 1.38 -- -- 1.38 1.38 0.86 Isoprene 34.47 -- 1.46 35.93 35.93 22.46 Methanol 2.76 9.92 -- 12.68 12.68 7.92 Trimethylcarbinol 0.40 2.69 -- 3.09 3.09 1.93Unsaturated Unsaturated 2.14 2.06 -- 4.2 0.53 0.33alcohols 3.67 alcohols C.sub.5C.sub.5 Methylenetetra- hydropyran 1.62 1.03 -- 2.65 2.65 1.66 Methylhydropyran 10.52 0.90 -- 11.42 11.42 7.15 p-Xylene 0.30 -- -- 0.30 0.30 0.19 Dimethylidoxane 2.99 3.14 -- 6.13 6.13 3.84 Methylvinyldioxane 0.57 -- -- 0.57 0.57 0.36Methylbutandiol ethers Methylbutandiol -- 0.94 -- 0.94 1.74 65.0 -- -- 2.68 ethers 0.32 -- 0.32 0.32 0.20Pyran alcohol 4.41 Pyran alcohol 0.26 1.26 -- 1.52 2.89 65.5 -- --Methylbutandiol 21.96 Methylbutandiol 0.38 2.11 -- 2.49 19.47 89.0 -- --Dioxane alcohol 7.52 Dioxane alcohol 0.70 0.67 -- 1.37 6.15 81.6 -- --ethers ethersDioxane alcohol 5.37 Dioxane alcohol 0.47 0.49 -- 0.96 4.41 82.1 -- --formals formalsDioxane alcohols 67.70 Dioxane alcohols 0.47 0.27 -- 0.74 66.96 98.5 -- --Total of unidentified Total of unidentifiedcompounds 6.18 products 7.47 1.92 -- 9.39 48.5 3.21 4.55Heavy unidentified Heavy unidentifiedproducts 58.33 products 4.05 -- -- 4.05 54.28 93.0 -- --Total of high-boiling Formaldehyde 2.16 38.0 -- 40.16 -- -- 40.16 25.1byproducts 177.82Water 362.18 Water 0.57 382.88 -- 383.45 -- -- 21.27 13.29 Losses -- -- 1.3 1.3 0.81Total 540.00 Total 79.6 448.6 10.5 540.0 155.90 89.5 155.90 100.0__________________________________________________________________________

It is clear from the above-given data that only 4.2 g of unsaturated alcohols or 4.2/540 100 = 0.78 w.% are present in the reaction mixture (organic and water layers). The quantity cannot have any appreciable effect on the results by a rectification even if all unsaturated alcohols react with formaldehyde.

At the same time, the resluts given above show that by the method according to the invention about 90% of high-boiling byproducts are converted with the following yields of desired products:

isoprene -- 22.4% of converted high-boiling byproducts, formaldehyde -- 25.1% of converted high-boiling byproducts, isobutylene -- 7.5% of converted high-boiling byproducts.

In addition, the following products are obtained which may be used for conversion into desired products at isoprene plants:

methyldilydropyran -- 7.1% dimethyldioxane -- 3.8% methanol -- 7.9% trimethylcarbinol -- 1.9%, so that additional yields of isoprene, formaldehyde and isobutylene are obtained which were not taken into account in this Example.

EXAMPLE 2

30 g. of aluminum oxide were charged into the first reactor and 60 g. of calcium-phosphate catalyst were charged into the second reactor. The conditions of processing high-boiling byproducts, which was carried-out at atmospheric pressure, are given in Table 7, and the resulting products yields are given in Table 8.

TABLE 7______________________________________CONDITIONS OF PROCESSING HIGH BOILINGBYPRODUCTS OVER ALUMINUM OXIDE ANDCALCIUM-PHOSPHATE CATALYSTSReactor Rate ofin the flow Temperature in feedingdirection of the catalyst High-boiling high-boilinghigh boil- column, .degree. C byproducts byproductsing byprod- bot- water weight g/h per 1 gucts vapours top middle tom ratio of catalyst______________________________________1st reactorwithaluminumoxide 268 255-256 290 1:1 1.02nd reactorwithcalcium-phosphatecatalyst 338 344 360 1:2 0.7______________________________________ TABLE 8__________________________________________________________________________YIELDS OF PRODUCTS IN SPLITTING HIGH-BOILING BYPRODUCTSOVER ALUMINUM OXIDE AND CALCIUM-PHOSPHATE CATALYSTSUNDER THE CONDITIONS SHOWN IN TABLE 7 Yield of products % ofStarting high-boiling byproducts Conver- Content Reaction mixture sion of of mix- Reaction products obtained high-boil- ture used Organic Aqueous Gas, Total, Converted ing by-Components for tests Components layer,g layer,g g g g % g products1 2 3 4 5 6 7 8 9 10 11__________________________________________________________________________ Carbon dioxide -- -- 2.16 2.16 2.16 1.32 Carbon oxide -- -- 0.73 0.73 0.73 0.45 Isobutylene 3.74 -- 9.20 12.94 12.94 7.93 1.38 Amylenes 1.38 -- 1.38 0.85 Isoprene 35.66 -- 2.38 38.04 38.04 23.35 Methanol 3.59 4.35 7.94 7.94 4.27 Trimethylcarbinol 0.31 3.16 3.47 3.47 2.63Unsaturated Unsaturated alco-alcohols 5.38 hols C.sub.5 2.51 1.14 3.65 1.73 32.2 -- --C.sub.5 Methylenetetrahy- dropyran 1.58 -- 1.58 1.58 0.97 Methylhydropyran 10.39 2.70 13.09 13.09 8.03 p-Xylene 0.29 0.29 0.29 0.18 Dimethyldioxane 2.56 2.96 5.52 5.52 3.38Methylvinyldioxane 1.01 Methylvinyldioxane 0.85 -- -- 0.85 0.16 15.9 -- --Methylbutandiol ether 2.79 Methylbutandiol and Trimethylcarbi- -- 2.85 2.85 -- -- 0.06 0.04 nol etherPyran alcohol 5.08 Pyran alcohol 0.54 3.16 3.70 1.38 27.2 -- --Methylbutandiol 21.27 Methylbutandiol 0.36 0.78 1.14 20.13 95.0 -- --Dioxane alcohol 10.75 Dioxane alcohol 2.36 3.57 5.93 4.82 44.8 -- --ethers ethersDioxane alcohol for- 6.96 Dioxane alcohol 0.41 1.14 1.55 5.41 77.8 -- --mals formalsDioxane alcohols 87.49 Dioxane alcohols 0.67 1.86 2.53 84.96 97.0 -- --Total of unidenti- 13.66 Total of unidentified 11.58 3.63 15.21 -- -- 1.55 0.95fied compounds productsHeavy unidentified 50.30 Heavy unidentified 5.86 -- 5.86 44.44 88.5 -- --compounds compoundsFormaldehyde 2.94 Formaldehyde 4.36 39.49 43.85 40.91 25.10Total of high-boil-ing byproducts usedin test 207.63Water 422.37 Water 0.5 447.41 447.91 25.54 15.65 Losses -- -- -- 7.83 7.83 4.80Total 630.0 Total 89.5 518.2 14.47 630.0 163.03 82.5 163.03 100.0__________________________________________________________________________

The content of unsaturated alcohols in the final mixture is also negligible 3.65/630 100 = 0.52% which cannot appreciably lower the yield of isoprene on rectifying liquid reaction products due to chemical reactions.

The degree of conversion of high-boiling byproducts is more than 80%.

The yields of the desired products are as follows:

isoprene -- 23.3% of converted high-boiling byproducts,

formaldehyde -- 25.1% of converted high-boiling byproducts,

isobutylene -- 7-9% of converted high-boiling byproducts

In addition, the following products which are processed at isoprene plants into desired products are obtained:

methyldihydropyran -- 8.0% dimethyldioxane -- 3.4% methanol -- 4.8% trimethylcarbinol -- 2.6%

All remaining products may also be recycled for further processing into isoprene, formaldehyde and isobutylene.

Claims

1. A method of processing high-boiling byproducts obtained at the first stage of isoprene production by the dioxane method into isoprene, isobutylene and formaldehyde comprising catalytically splitting said byproducts in the vapour phase in the presence of water with a weight ratio therebetween of 1:1+2, respectively, at 250.degree.-290.degree. C over aluminium oxide as catalyst to obtain a vapour mixture; catalytically splitting said vapour mixture over calcium-phosphate catalyst at 315.degree.-360.degree. C to obtain a reaction mixture containing isoprene, isobutylene and formaldehyde.