CA1266682A - Preparation of methyl isopropyl ketone and isoprene - Google Patents

Abstract

Abstract of the Disclosure: Methyl isopropyl ketone and isoprene are prepared by converting a pivalaldehyde con-taining reaction mixture over a zeolite catalyst at ele-vated temperatures, the said reaction mixture being ob-tained by hydroformylation of isobutene or of an isobu-tene-containing C4 cut.

Description

- 1 - O.Z. 0050/37882 Preparation of methyl isopropyl ketone and isoprene The earlier application EP 85105768 (Laid-Open Application 0,162,387), proposed the preparation of ke-tones by isomerization of aldehydes at up to 600C ;n the presence of zeolites as catalysts.
In this procedure, pure pivalaldehyde (2,2-di-methylpropanal) was converted to methyl isopropyl ketone according to equat;on (1).
CH3 ~ zeOlite H3C 11 CH~--F--~ CH C--CH3 ( 1 ) CH~ H H3C
Furthermore, the earlier application EP 85105766 (Laid-Open Application 0,162,385) proposed the prepara-tion of dienes by dehydration of aldehydes at elevated temperatures, using zeolite catalysts. lsoprene was ob-tained by converting pivalaldehyde, 2-methylbutanal or 1S 3-methylbu~anal according to equation (2) ~ CH3 o ., I ~
H3C--f--C~ \

~ \ ~eolite CH3--~H2--fH--c ~ CHz=fH--c=cH2 ~2) CH3--fH~CH2--C~

Since industrial processes frequently give mix-tures of isopentanals which may contain further compo-nents, such as n-alkanals, tertiary alcohols, hydrocar-bons and/or water, it is an object of the present inven-tion to prepare methyl ;sopropyl ketone and isoprene starting from industr;al reaction mixturesr without side reactions between the various components taking place.

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- 2 - O.Z~ 0050/37B82 We have found that this object is achieved, and that methyl isopropyl ketone and isoprene are advanta-geously prepared by converting p;valaldehyde over a zeo-lite catalyst at elevated temperatures, ;f a hydrofor-mylation mixture of isobutene or of an isobutene-con-taining C4 cut is used for the conversion.
Suitable starting mixtures for the process are obtained by hydroformylation of isobutene or isobutene-containing C~ cuts under catalysis by a carbonyl com-plex of a metal of group 8 of the Periodic Table, undersuperatmospheric pressure and at elevated temperatures, by a conventional method~ for example according to W.J. Schneider, Chemiker-Zeitung 96 (t972) 7, 383-387 or J.E. Knap, N.R. Cox and W.R. Privette, Chem. Eng. Pro-gress 62 (1966) 4, 74-78. To achieve high contents of methyl isopropyl ketone, the aldehydes, such 35 n-butyr-aldehyde, n-valeraldehyde, 2-methylbutanal and 3-methyl-butanal, which are present, in addition to pivalalde-hyde, ;n the crude reaction mixture from the hydrofor-mylation, can be removed completely or partly before theconversion over the zeolite. Preferably reacted start-ing mixtures are the mixtures obtained after hydrofor-mylation of the isobutene and complete or partial re-moval of the 3-methylbutanal. Any tert-butanol which Z5 may be present ;n the reaction mixture has no effect on the react;on; it is dehydrated completely and with high selectivity to give isobutene according to equation (3) ::
:: :
fH~zeolite H3C\
CH3-CI-OH /C=CH2 (3)

3 H3C
and the isobutene is advantageously separated off from the resulting isoprene and ;s reused, for example, for the hydroformylation step.
; The catalystsr in particular aluminosilicate, borosilicate and iron s;licate zeolites of the pentasil ' ~,., :
' - 3 - O.Z. 0050/37882 type, which have been proposed in the earlier applica-tion EP 85105768, are advantageously also used for the conversion of the crude reaction mixtures described, which as a rule contain from hO to 95~ by weight of pival-aldehyde~ Surprisingly, no side reactions, such as al-dol condensation or oligomerization, are observed. The process described in the earlier applicat;on ;s therefore not restr;cted to the use of pure substances as start;ng components and, starting from industrial product mix-tures, gives h;gh select;vities and convers;ons coupledw;th long catalys~ lives. Expensive isolation and Puri-fication of the starting substances are therefore dis-pensed with.
The aluminosilicate zeolite is prepared, for ex-ample, from an aluminum compound, preferably Al(OH)3 or Al2(S04)3, and a silicon component, preferably ~inely divided silica~ in an aqueous amine solution, in particular in 1,6 hexanediamine, 1,3-propanediamine or triethylenetetramine solution, with or w;thout the addi-tion o~ an alkali metal or alkaline earth metal, at from 100 to 220C under autogenous pressure. Such zeolites include the isotactic zeolites described in German Laid-Open Application ~OS 3,006,471. The resulting alumino-silicate zeolites have an SiO2/Al203 ratio of from 25 10 to 40,000, depending on the choice of the amounts o~
; starting materials. The aluminosilicate zeolites can also be prepared in an etherial medium, such as diethyl-ene glycol dimethyl ether, ;n an alcoholic medium, such as methanol or butane-1,4-diol, or in water.
The borosilicate zeolite is synthesized, for ex-ample, at from 90 to 200C under autogenous pressure, by reacting a boron compound, eg. H3~03, with a sllicon compound, preferably finely div;ded silica, in an aqueous amine solution, in particular in 1,6-hexanediamine, 1,3-propanediamine or triethylenetetramine solution, ~ith c~r without the addition of an alkali metal or alkaline earth metal. In this reaction, it is possible to use, .

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- 4 - O.Z. 0050/37882 instead of an aqueous amine solution, an etherial solu-tion~ for example with diethylene glycol dimethyl ether as the solvent, or an alcoholic solution, for example with hexane-1,6-diol as the solvent.
The iron silicate zeolite is obtained, for ex-ample, from an iron compound, preferably Fez(S04)3 and a silicon compound, preferably finely divided silica, in an aqueous amine solution, in particular 1,6-hexanediamine, with or without the addition of an alkali metaL or alka-line earth metal, at from 100 to 200C under autogenous pressure.
The aluminosilicate, borosilicate and iron sili-cate zeolites prepared in this manner can be isolated, dried at from 100 to 160C~ preferabLy 110C, calcined at from 450 to 550C, preferably 500C, and then molded with a binder in a ratio of from 90:10 to 40:60% by weight to give extrudates or pellets. Suitable binders are various aluminas, preferably boehmite, amorphous aluminosilicates having an SiO2/Alz03 ratio of from 25:75 to 95:5, preferably 75:25, silica, preferably finely divided SiO2, mixtures of finely divided SiO2 and finely div;ded Alz03, finely divided TiO2 and clay.
After the molding procedure, the extrudates or pellets are dr;ed at 110C for 16 hours and calcined at 500C
for 16 hours. Such catalysts can be particularly ad-vantageously prepared by molding the isolated alumi-nosilicater borosilicate or iron silicate zeolites directly after drying, and subjecting them to caLcinat-ion only after the molding procedure. The catalyst ~hich has been molded to give extrudates can be con-verted to fluidizable material having a particle size of from 0.1 to 0.5 mm by milling and screening. How-ever, the aluminosilicate, borosilicate and iron sili-~ cate zeolites can also be used in pure form, without a ; 35 binder, as extrudates or pellets~ This molding pro-cedure is carried out w;th the addition of extrudation or peptization assistants, su-h as hexaethylcellulose, ~ ~ ' - S - O.Z. 0050/37882 stearic acid, potato starch, form;c acid, acetic acid, oxalic acid, nitric acid, ammonia, amines, silicoesters, graphite or a mixture of these. If~ because of its method of preparation, the zeolite is not in the catalytically preferred acidic H form but in, for example, the Na form, the latter can be converted completely or partially to the desired H form by ion exchange with ammonium ions followed by calcination, or by treatment with an acid.
To increase the selectivity, the li'fe and the number of possible regenerations, it is sometimes advan-tageous to modify the zeolites. ~''In a suitable metho~
of modify;ng the catalysts, for example, the unmolded or molded zeolite may be subjected to ;on exchange or impregnated with an alkali metal tunless the alkali form of the zeolite is obtained in the synthesis), ~ith an alkaline earth metal, such as Ca or Mg, or with an earth metal such as B or Ti. It ;s particularly advantageous to dope the zeolite w;th a transition metal, such as Mo, W, Fe, Zn or Cu, a noble metal, such as Pd, and a rare earth metal, such as Ce or La.
In practice, such modified catalysts are pre-pared, for example, by initially taking the molded pen-tasil zeolite in a r;ser tube and passing, for example, an aqueous or ammoniacal solution of a halide or nitrate of the metals described above over the said zeolite at from 20 to 1û0C. Ion exchange of this type can be effected with~ for example, the hydrogen, ammonium and alkali metal forms of the zeolite. Metals can be applied to the zeolites, for example, by impregnating the zeolite material with, for example, a halide, a nitrate or an :
oxide of the metals described above, in aqueous, alco-holic or ammoniacal sol~tion. 8Oth ion exchange and im-pregnation are followed by one or more drying steps and, if desired, repeated calcination.
~ ; ~35 An example of a specific procedure is as follows:
`~ tungstic acid (HzW04) or CetN03)3 . 6H20 is dissolved ~ in ~ater, and the solution is then used to impregnate : : :
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- 6 - O.Z. 0050/37882 the extruded or unextruded zeolite for a certain t;me (about 30 minutes). The supernatant solution is freed from water ;n a rotary evaporator, after which the ;m-pregnated zeolite is dried at about 150C and calcined at about 550C. This impregnat;on process can be carried out several times in succession in order to ob-tain the desired metal content.
It is also possible, for example, to prepare an ammoniacal Pd(N03)2 solution and to suspend the pure zeo lite powder in this solut;on for about 24 hours at from 40 to 100C, while stirring. After it has been fil-tered off, dried at about 150C and calcined at about 500C, the zeolite material obtained in this manner can be further processed, with or without a binder, to give extrudates, pellets or fluidizable material.
The zeolite present in the H form can be sub-jected to ion exchange by a method in which the zeolite in the form of extrudates or pellets is initially taken in a column and, for example, an ammonia~al Pd(N0~)2 solution is circulated over it at slightly elevated tem-peratures of from 30 to 80C for from 15 to 2û hours.
The zeolite is then washed thoroughly with water, dried at abou~ 15ûC and calcined at about 550C.
In the case of some metal-doped zeolites, after-treatment with hydrogen is advantageous.
- In another possible method of modification, ~he zeolite material, molded or unmolded, ;s subjected to a treatment with an acid, such as hydrochlor;c acid, hydrofluoric acid or phosphoric acid and/or with steam.
This procedure is advantageously carried out, for example, as follows: the zeolite powder, before being molded, is treated with 0.001 - 2 N, preferably 0.05 - 0.5 N, hydro-fluoric acid for from 1 to 3 hours under reflux. The pro-duct is filtered off, washed thoroughly, dried at from 100 to 160C and then calcined at from 400 to 550C. It may fur~hermore be advantageous to treat the zeolite with hydro-chlor;c acld lfter the zeolit~ has been molded tith e binder.

:, - 7 - O.Z. 0050/3788Z
To do this, the zeolite is treated, for example, for from 1 to 3 hours at from 60 to 80C with a 3 - 25%
strength hydrochloric acid, after which it is washed thoroughly, dried at from 100 to 160C and calcined at from 400 to 550C. The zeolite may also be modified by applying a phosphorus compound, such as trimethyl phosphate.
If the ~eolite catalyst becomes deactivated, which may occur in the process of the invention as a re-sult of coking, the said catalyst can be regenerated ina simple manner by burning off the coke depos;t with air or with an air/N2 mixture at from 400 to 550C, pre-ferably 500C, with the result that the catalyst re-gains its initial act;vity.
The activity of the catalyst can furthermore be adjusted to give optimum selectivity with respect to the desired product by precoking.
In general, the ca~alyst can be used either as 2 - 4 mm extrudates, as tablets of 3 - 5 mm diameter, as powders having particle sizes of from û.3 to 0.5 mm or as a fluidizable catalyst of 0.1 - 0.5 mm particle size.
Isomerization or dehydration of the aldehydes over the zeolites can be carr;ed out in the liquid phase at, for example, from 30 to 300C~ The reaction ;s preferably carried out in the gas phase at from 100 to 600C, in particular from 250 to 500C. The space velocity (WHSY) ;s from 0.1 to 20, preferably from 0.5 to 5, kg of mixture per kg of catalyst per hour. The procecs can be carried out batchwise or continuously, under atmospheric or superatmospheric pressure, for ex-ample in a continuous-flow reactor or a fluidized-bed reactor.
~ The flow diagram of the process is shown ;n the draw;ng. in th;s diagram, the starting mixture is fed via l;ne 1 into reactor 2. The products are passed v;a l;ne 3 into the f;rst distillation column 4, in which :

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- 8 - 0.Z. 0050/37882 isoprene and, ~here relevant, isobutene are separated off via the top (line 5). The bottom products are passed via line 6 into the second dist;llat;on column 7, where the methyl isoproPyl ketone is separated from the remain-; 5 ;ng product and recovered via line 8. The bottom pro-ducts of the second dist;llation can be recycled via line 9 or removed via line 10.
`~ Methyl isopropyl ketone is predominantly used as an intermediate for the pre~paration of drugs, herbi-cides and indigo dyes (Fischer synthesis), while iso-prene is employed for the preparation of cis-1,4-poly-isoprene. Other possible uses are described in Ullmanns Encyclopadie der technischen Chemie, 4th edition (1977), VolO 14, page 198, and Vol. 13, pages 385 and 386.
EXAMPLES
The catalyst used was prepared in a hydrothermal synthesis from 640 9 of SiO2 (f;nely divided silica), 121 9 of H~903 and 8000 g of an aqueous hexanedia-mine solution tweight ratio of the components of the mixture 50:50) at 170C under autogenous pressure in a stirred autoclave. The crystalline reaction product was filtered off, washed thoroughly, dried at 100C
for 24 hours and then calcined at 500C for 24 hours to give a borosilicate zeolite of the pentasil type, which contained 94.2% by weight of SiO2 and 2.3~ by weight f ~23 This zeolite was converted to 2 mm extrudates, which were dried at 100C and calcined at 500C for 24 hours.
The experiments were carried out under isother-mal conditions in a tube reactor having a catalyst vol-ume of 1û0 mL and an internal diameter of 2 cm.
The reactor was thermostated in a salt bath. The reaction mixture was vaporized in an upstream evaporator at 120C and passed in gaseous form, at from 400 to 450C and at a WHSV of 1 - 2 h 1, over the zeolite catalyst. The reaction products were condensed, and - collected in cold traps. They were identified and :'~6~
- 9 - O.Z. 0050/37882 determined quantitatively by conventional methods, for example by distillation, gas chromatography (GC) or coupled GC-MS.

A mixture containing 75.8~ by weight of pival-aldehyde and 17.5~ by weight of tert-butanol as well as 3.5~ by weight of isovaleraldehyde and 3.2% by weight rlf C~ hydrocarbons was used as the starting mixture, and the results summarized in Table 1 were obtained.
TA~LE 1 Temperaturecoc] 400 450 450 ~HSV Ch 1] 1 1 2 Conversion with respect to pivalaldehyde, in %96.2 95.3 96.1 15 Selectivity 1) %
Methyl isopropyl ketone 79.5 60.9 68.7 Isoprene 18.7 36.7 27.2 Total selectivity 98.Z 97.6 95.9 1~ based on pivalaldehyde converted.

Z0 In all 3 experiments, the tert-butanol was con-verted to isobutene with 85 - 90% selectivity.

For Examples 4 to 7, the reaction mixture used consisted of 48.5% by weight of pivalaldehyde, 13.2% by weigh~ of 3-methylbutanal, 20.0% by weight of tert-but-anol and 13.4% by ~eight of r,-butyraldehyde, the remain-der being trimethylpentane, dimethylhexane and water.
The experimental results obtained with this mixture are summarized in Table 2.

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, - 10 - O.Z. 0050/37882 TA~LE 2 Temperature ~C] 400 450 400 450 WHSV ~h '] 1 1 2 2 Conversion in %
Pivalaldehyde 96.3 96.3 96.2 96.3 3-Methylbutanal 45.9 58.Z 22.7 44.4 ` Pentanals 85.5 88.2 80.5 85.2 Selectivity ~
Methyl isopropyl ketone 1) 72.9 60.7 78.9 66.9 Isoprene 2) 2205 31.1 16.9 26.6 Total selectiv;ty 95.4 91.8 95.8 93.5 '' based on pivalaldehyde converted 2) based on pentanals converted The tert-butanol present in the starting mixture was dehydrated to isobutene with 85 - 88% selectivity, the conversion being 100%.

Example 8 comprises a long-term experiment carried out using the same reaction mixture as in Examples 4 to 7. The experimental conditions chosen were 400C and WHSV = 2 h 1. Table 3 reproduces the experimental re-sults of 4 mass balance periods.

25 Mass balance period 1 2 3 4 . . . ~
Conversion in %
P;valaldehyde 96.9 97.0 97.0 97.0 Isovaleraldehyde 33.9 33.3 24.5 24.8 ~ pentanals 83.4 83.4 81.5 81.6 Selectivity %
Methyl isopropyl ketone 1) 77.6 76.6 76.2 76.0 Isoprene Z) 19.3 21.0 21.2 21.0 Total selectivity 96.9 97.6 Y7.4 97.0 T;me on stream h 23 24 Z4 29 . . .
1) based on pivalaldehyde converted 2) based on pentanals converted :

~ O.Z. 0050/37882 The tert-butanol present in the starting mixture was converted to isobutene with 85 - 90% selectivity, the conversion being 100X.

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Claims (3)

- 12 - O.Z. 0050/37882 We claim:-

1. A process for the preparation of methyl isopropyl ketone and isoprene by converting pivalaldehyde over a zeolite catalyst at from 30 to 600°C, wherein a hydro-formylation mixture of isobutene or of an isobutene-con-taining C4 cut is used for the conversion.

2. A process as claimed in claim 1, wherein the hydroformylation products of isobutene or of an isobu-tene-containing C4 cut are converted, after complete or partial removal of the 3-methylbutanal.

3. A process as claimed in claim 1, wherein the conversion is carried out in the gas phase at from 100 to 600°C.

Drawing.