DE2135158C3 - Process for the production of isoprene - Google Patents

Description

To meet the increasing demand for isoprene as a starting material for the production of synthetic rubber and the like, a method is desired that enables isoprene to be easily converted into high To produce purity and in good yield. For this purpose, the direct production (one-step process) proposed by condensation of isobutylene and formaldehyde due to the simplified procedure. For this one-step procedure are several catalysts, e.g. B. aluminum oxide, silicon dioxide-aluminum oxide, cadmium phosphate, Phosphoric acid-chromium oxide (or chromium hydroxide), phosphoric acid-manganese oxide (or Manganese hydroxide), known. However, these known catalysts have the following disadvantages:

1. Low conversion of formaldehyde (i.e. ratio of the amount of converted formaldehyde the amount of formaldehyde used).

2. Poor yield of isoprene based on converted formaldehyde.

Since these known processes are inevitably formed by carbon compounds during the condensation reaction are poisoned, the conversion of formaldehyde increases in the course of the reaction time off quickly. In other words, when the known catalysts are used, the regeneration must be carried out by burning off the catalysts to remove the carbon compounds at very short intervals be repeated. This frequent regeneration is undesirable from a technical point of view.

It has now surprisingly been found that the abovementioned disadvantages are eliminated when a solid catalyst is used, the silica and a bismuth component contains

The invention accordingly provides a process for production that can be carried out on an industrial scale of isoprene in high purity and in high yield with a long service life of the catalyst.

The invention relates to a method for the production of isoprene, which is characterized in

ίο that isobutylene is reacted with formaldehyde in the vapor phase in the presence of a solid catalyst containing silicon dioxide and a bismuth component.
The solid catalyst used in the process according to the invention is prepared by combining a silicon component with a bismuth component and heating the resulting mixture.
Suitable silicon components are, for example, silicon dioxide (e.g. silica xerogel, silica hydrogel, silica sol, crystalline silicon dioxide), silicic acid salts (e.g. potassium silicate and sodium silicate), silicon halides (ζ. B. silicon tetrachloride and silicon tetrafluoride), silicic acid esters (ζ. Tetraethylorthosilicate), other compounds that can easily be converted into the silicon component, and clay minerals containing such compounds.
Suitable bismuth components are, for example, bismuth oxide (e.g. bismuth trioxide and bismuth pentoxide), bismuth hydroxide [ζ. Β BiO (OH) and Bi (OH) ₃ ], bismuth acid and its salts (e.g. ortho bismuth acid, sodium bismuthate, potassium bismuthate and ammonium bismuthate), bismuth halides, ammonowismuth or its partial hydrolysates (e.g. bismuth pentachloride, bismuth trichloride oxychloride, bismuth ammonium chloride) , bismuth salts with inorganic acids or the corresponding basic bismuth salts (eg. as bismuth nitrate, bismuth sulfate, and basic bismuth sulfate), bismuth carbonate, and basic bismuth carbonate, Wismutchalcogenide (z. B. bismuth sulphide, bismuth selenide and bismuth telluride), organic bismuth compounds (eg. B. CH ₃ BiCl ₂ ), bismuth salts with organic acids

(e.g. bismuth pyrogallate), bismuth alcoholates [e.g. B. Bi (OC ₂ Hg) ₃ ], bismuth rhodanate and metallic bismuth.

The two components are mixed or reacted by methods known per se put together, z. B.

1. by mixing an aqueous solution of the silicon component with an aqueous solution the bismuth component, whereby gelation of the two components takes place,

2. Impregnation of one component with an aqueous solution of the other component,

3. ion exchange,

4. by physical means with the help of a ball mill, a kneader, etc.,

5. Uniform vapor deposition of a bismuth compound on silicon dioxide and

6. Mixing an organic bismuth compound with an organosilicon compound and hydrolysis of the mixture obtained.

If a compound other than silicon dioxide is used as the silicon component, or if not bismuth oxide, but a different one

Wisrnutverbindungen used as bismuth component it is advisable to mix the two components with an aqueous solution an inorganic acid (e.g. hydrochloric acid and sulfuric acid and / or by heating in the presence to hydrolyze oxygen.

The ratio of the bismuth component to the silicon dioxide in the solid catalyst can be within of a wide range, but is usually about 0.001: 1 to 1: 1, preferably about 0.01: 1 to 0.6: 1, with a ratio of about 0.01: 1 to 0.1: 1, calculated as the atomic ratio of Bismuth to silicon, is particularly preferred.

The components combined in this way are then brought to a temperature of about 40 to 1000 ° C, preferably about 180 to 800 ° C, heated. Heating is usually done in the presence of air, Inert gases (e.g. nitrogen and carbon dioxide), oxygen, hydrogen, water vapor or mixtures of these gases. It is preferred in the presence of oxygen or oxygen-containing gases heated. Since the condensation reaction between isobutylene and formaldehyde generally occurs carried out at a temperature above about 180 ° C it is not absolutely necessary to use the catalyst for the reaction before using it heat.

The solid catalyst prepared in this way contains silica and a bismuth component. The bismuth component in the solid catalyst can be in the form of elemental metal, ions or compounds containing bismuth, e.g. B. oxides, hydroxides or transition stages between these compounds, but at least part of the bismuth component is in the form of its oxide, e.g. B. as Bi ₂ O., before.

The solid catalyst used according to the invention can also be used as a further component of at least one of the elements Al, P, B, W, Fc, Ti, Zr, V, Cr, Mo, Mn, Co, Ni, Cu, Ag, Cd, Mg, Ca, Tl, Sn, Pb, Rb, Cs, Sr, Ba, Nd ₁ In and Te contained in an amount equivalent to a weight ratio of minor ingredient to silica of about 0.0001: 1 to 0.5: 1, calculated as Atomic ratio of the corresponding element or elements to silicon. The addition of aluminum is particularly recommended from the standpoint of the service life of the solid catalyst.

The above-mentioned elements can be added as minor components before they are combined the silicon component with the bismuth component or after combining these both components. These elements can be the catalyst, for example in the form of the appropriate Nitrates, halides, sulfates, salts with organic acids (e.g. acetic acid), ammonium salts or other common compounds can be added.

The quantitative ratio of the secondary constituents to silicon dioxide in the solid catalyst is preferably at about 0.001: 1 to 0.2: 1, calculated as the atomic ratio of the corresponding element or of the corresponding elements to silicon. The addition of the secondary constituents can be as mentioned above Procedure.

At least some of the elements present as minor components in the solid catalyst are in the form of the corresponding oxide, e.g. B. as Al ₂ O ₃ , P ₂ O ₅ , B ₂ O ₃ , WO ₃ , Fe ₂ O ₃ , TiO ₂ , ZrO ₂ , V ₂ O ₅ , Cr ₂ O ₃ , Mo ₃ , MnO ₂ , Co ₀ O ₃ , NiO, CuO, Ag ₂ O, CdO, MgO, CaO, Tl ₂ O, SnO ₂ , PbO, Rb ₂ O, Cs ₂ O, SrO, BaO, Nd ₂ O ₃ , Ia ₂ O ₃ and TeO ₈ , before.

The production of isoprene according to the invention takes place through the condensation reaction between Isobutylene and formaldehyde in the vapor phase in the presence of the catalyst described above. The

ίο molar ratio of isobutylene to formaldehyde can be varied depending on the reaction conditions, but the isobutylene is preferably in excess, ζ. B. in an amount of more than 3 moles per mole of formaldehyde is used. These two starting materials are usually reacted in the vapor phase at a temperature of more than 180.degree. C., preferably about 250 to 330.degree.
The residence time of the reactants, ie of the isobutylene and formaldehyde over the acidic catalyst, can also be varied as a function of the other reaction conditions, but is preferably in the range from about 0.1 to 100 g / hour. per mole of reactants at about 0.5 to 20 atmospheres. The reaction can be carried out at normal pressure, reduced pressure or increased pressure, but to achieve high isoprene production it is advisable to work at slightly increased pressure.

Certain substances can be added to the reaction system as diluents for the starting materials that do not interfere with the reaction. Examples of suitable inert gaseous compounds are Water vapor, methanol, nitrogen, air, carbon dioxide and paraffinic hydrocarbons (e.g. Methane, ethane and propane). The presence of water vapor is particularly desirable, as this results in it a sudden drop in the activity of the kiftalyser prevented and the isoprene yield based on converted formaldehyde is increased.

If the activity of the solid catalyst in terms of conversion and selectivity after a long reaction time has decreased sharply, the catalyst is regenerated by being in the presence of air, oxygen or steam is heated, whereupon it can be used again in the condensation reaction can.

The catalyst can be in the form of a fixed bed, a fluidized bed, a moving bed or the like.

used, however, is the use as a fixed bed in a system in which multiple reactors are used and switched to a fresh bed after deactivation of the catalyst, on most advantageous.

The reaction product is condensed or absorbed in a suitable solvent and in isolated in a known manner by fractionation or by other conventional methods. Not implemented Isobutylene and unreacted formaldehyde can be separated and used as starting materials in the condensation reaction can be recycled.

In the manner described above, isoprene becomes high in conversion and in high yield and formed in a very high purity of more than 99%.

In the following examples, the conversion and the isoprene yield are average values in the stated Response time indicated.

example 1

Sodium silicate (Na ₂ O nSiO. - xH ₂ O; SiO, 28 to 30%, Na ₂ O 9 to 10%, surface 450 mVg, pore volume 0.80 cc / g, mean specific weight 0.48 g / cc, average pore diameter 71 A) is neutralized and gelled with sulfuric acid, washed with water to remove the sodium and dried at 100.degree. The SUicaxerogel obtained in this way is crushed and sieved. 500 g of the sieve fraction from 0.84 to 4 mm are added to 1.21 3N hydrochloric acid, which contains 106.5 g of bismuth trichloride and 8.2 g of aluminum trichloride. The mixture is left to stand at room temperature for 1 day with constant stirring. It is then transferred to an evaporation dish, where it is evaporated to dryness on a water bath at 100 ° C. for 5 hours, during which the water and hydrogen chloride gas are evaporated. The dry residue is kept at 400 ° C. for 2 hours in a stream of air containing water vapor, a solid catalyst being obtained.

15 parts by weight of the solid catalyst prepared in this way are placed in a tubular reactor filled. Isobutylene (50.49 parts by weight) and gaseous formaldehyde, which is obtained from a 40% strength aqueous formaldehyde solution has been evaporated (9.65 parts by weight / hour), are at 300 ° C in the Reactor introduced. The reaction is 10 hours

ίο carried out at normal pressure. The isoprene formed is cooled and isolated in liquid form, while unreacted formaldehyde and water vapor separated by absorption in water. Isoprene is more than 99% pure

obtained by fractionation of the isolated product

The conversion of formaldehyde and the selectivity to isoprene in the reaction described above are given below as mean values for each 2 hours.

Time after the start of the reaction, hours 0 to 2 2 to 4 4 to 6

6 to 8

8 to 10

Mean value for 10 hours

Formaldehyde conversion,%
Selectivity to isoprene,%

93.2
52.8

90.2
80.8

88.8
78.5

86.9
77.9

90.98
72.96

Example 2

In 100 g of sodium silicate (Na ₂ O · nSiO "· xH"O; SiO ₂ 26 to 30%, Na ₂ O 9 to 10%, surface 450m ^z / g, pore volume 0.80 cc / g, mean specific weight 0, 48 g / cc, mean pore diameter 71 A), 5.00 g of sodium bismuthate are dispersed. 1.02 g of neodymium carbon atdecahydrate are evenly suspended in the mixture. The mixture is converted into a gel by adding 200 ml of 3N-orthophosphoric acid, whereupon the same 3N-phosphoric acid is gradually added until no more carbon dioxide is evolved. The gel obtained is washed with water until no more sodium ion is detected and dried at 100 ° C. for 12 hours. It is then heated to 350 ° C. for 2 hours while air containing ammonia is passed through, forming a solid catalyst.

The reaction between isobutylene and formaldehyde is 10 hours below those mentioned in Example 1 Conditions using the solid prepared in the manner described above Catalyst carried out. The following results are obtained:

Formaldehyde conversion 85%

Isoprene yield 75%

Isoprene purity over 99%

Example 3

1 kg of commercially available silica xerogel (SiO ₂ 99.5%, Na ₂ O 0.25%, Al ₂ O ₃ 0.15%, CaO 0.05%; sieve fraction 0.84 to 4 mm) becomes a solution of 48, Put 5 g bismuth nitrate in 200 ml 6 η-nitric acid. The mixture is evaporated to dryness on a water bath.

Separately, 4.23 g of silver dihydrogen phosphate are added to about 200 ml of water, whereupon 30 ml of an aqueous 3N NH ₃ solution are added to form a solution. To this solution

the dry residue described above is given. The mixture obtained is described in the above Way again evaporated to dryness. By introducing air containing water vapor, the dry residue is gradually heated until the temperature has reached 500 ° C. At this The residue is held at temperature for 2 hours, a solid catalyst being formed.

The reaction between isobutylene and formaldehyde is 10 hours below that in Example 1 p Conditions using the catalyst prepared in the manner described above accomplished. The following results are obtained:

Formaldehyde conversion 85%

Isoprene yield 71%

Isoprene purity over 99%

Example 4

_{500 ml of an aqueous 2N NH 3} solution are added to a solution of 128 g of bismuth trichloride in 500 ml of 2N hydrochloric acid, basic bismuth chloride being precipitated. The precipitate is filtered off and 500 g of granular Silicaxeroe, el and 100 ml of water are added. The mixture is kneaded in a ball mill for 12 hours. The gel obtained is dried and crushed and the fraction .0.84 to 4 mm is sieved off. This sieve fraction is kept in a stream of air at 400 ° C. for 5 days, a solid catalyst being obtained.

The reaction between isobutylene and formaldehyde is 10 hours under the ee in Example 1

mentioned conditions using the solid prepared in the manner described above Catalyst carried out. The following results are obtained:

Formaldehyde conversion 82%

Isoprene yield 77%

Isoprene purity over 99%>

Example 5

1000 ml of 2η hydrochloric acid, which contains 256 g of bismuth trichloride and 45 g of iron (III) chloride, are gradually added to 2500 g of silica sol containing 20 percent by weight of SiO _2. While stirring, this mixture is _{adjusted to pH 8 by adding an aqueous 3N NH 3} solution, whereby the gel formation is completed. The gel is dried and comminuted and the 0.84 to 4 mm sieve fraction is sieved and heated to 500 ° C. for 2 hours in a stream of air containing water vapor, a solid catalyst being formed.

The reaction between isobutylene and formaldehyde is 10 hours below those mentioned in Example 1 Conditions using the solid catalyst prepared as described above accomplished. The following results are obtained:

Formaldehyde conversion 92%

Isoprene yield 72%

Isoprene purity over 99%

Example 6

1 kg of sodium silicate (Na "O-nSiOv * H ₂ O; SiO ₂ 28 to 30 _{%, Na 2} O 9 to 10% "Surface area 450 m ² / g," pore volume 0.80 cc / g, mean specific weight 0.48 g / cc, mean pore diameter 71 A), which has been diluted with 6 l of water, a sol being formed. The sol is adjusted to a pH of about 3 and the sol is heated to 100 ° C. for 3 hours, a gelatinous hydrogel being formed. Cut the hydrogel into cubes approximately 8 cm x ¹ with a knife and wash with deionized water until no more sodium ion is detected. The hydrogel is added to 5 l of an aqueous 0.1 N silver nitrate solution and the mixture is kept at room temperature for 12 hours. The solution is drained from the hydrogel, which has been ion-exchanged for silver ions in this way. It is washed with water, dried and mixed with 32.5 g of powdered yellow tungstic acid. The mixture is ground for 12 hours in a ball mill, the powder obtained in this way is added to 500 ml of an aqueous solution containing 5.0 g of oxoboric acid, and the mixture is evaporated to dryness in an evaporator dish.

50 ml of silica sol containing 20 percent by weight SiO and 1.5 l of water are added to the residue. The mixture is dried for 10 hours at 100 ^° C., ground and the fraction 0.84 to 4 mm is sieved off. The granules are heated in a stream of air containing water vapor for 6 hours at 350 ° C., a solid catalyst being contained.

The reaction between isobutylene and formaldehyde is 10 hours below those mentioned in Example 1 Conditions are carried out whereby the following results are obtained:

Formaldehyde conversion 95%

Isoprene yield 75%

Isoprene purity over 99%

Example 7

1000 g of a silica sol containing 20 percent by weight of SiO ₂ ,

Contains 64.6 g of bismuth nitrate, 5.0 g of aluminum nitrate, 13.5 g of iron (III) chloride and 2.3 g of 85% strength aqueous orthophosphoric acid solution. The mixture is adjusted to a pH of about 8 by gradually adding an aqueous 3N NH ₃ solution with stirring, whereby the gel formation is completed. The gel obtained is dried for 15 hours at 100 ° C., the 0.84 to 4 mm fraction is grinded and heated! 3 hours in a stream of air containing water vapor at 400 ° C., a solid catalyst being formed.

The reaction between isobutylene and formaldehyde is 10 hours below those mentioned in Example 1 Conditions carried out using the catalyst prepared in the manner described above. The following results are obtained:

Formaldehyde conversion 91%

Isoprene yield 76%

Isoprene purity over 99%

Claims (4)

Patent claims: 1. A process for the production of isoprene, characterized in that isobutylene Reacts with formaldehyde in the vapor phase in the presence of a solid catalyst, which contains silica and a bismuth component. 2. The method according to claim 1, characterized in that it is carried out with a catalyst in which the ratio of the bismuth component to silicon dioxide is about 0.001: 1 to 1: 1, preferably about 0.01: 1 to 0.6: 1, calculated as the atomic ratio of bismuth to silicon. 3. The method according to claim 1 and 2, characterized in that one is with a solid catalyst works, which also as a further component of at least one of the elements Al, P, B, W, Fe, Ti, Zr, V, Cr, Mo, Mn, Co, Ni, Cu, Ag, Cd, Mg, Ca, Tl, Sn, Pb, Rb, Cs, Sr, Ba, Nd, Contains In and Te in an amount equal to a weight ratio of the minor ingredient to silicon dioxide from about 0.0001: 1 to 0.5: 1, calculated as the atomic ratio of the corresponding Element or the corresponding elements to silicon. 4. The method according to claim 1 to 3, characterized in that the solid catalyst Al as contains subordinate component.