DE2044623C3 - Process for the production of isoprene - Google Patents

Description

35

It is known that isobutene and formaldehyde can be converted into 4,4-dimethyl-1,3-dioxane in the presence of acidic catalysts to condense and this product in the presence of phosphoric acid or phosphate containing Catalysts split into isoprene, formaldehyde and water.

For example:

The method of the French Petroleum Institute, described in Erdöl und Kohlen, 15, pp. 274-282 and 348-352 (1962), a method carried out in Russia described in Zh. Vses. Khim. Obshchesi 14 3 S 313 to 319 (1969), DT-AS 12 71 106 and ei] method of the paint factories Bayer AG ₁ DT-A: 12 33 880 and Belgian patent 7 35 564.

In the processes mentioned, the reaction of isobutene with formaldehyde is converted into 4,4-dimeth> l m-dioxane in the presence of dilute sulfuric acid or of acidic ion exchangers as a catalyst carried out while the cleavage of 4,4-Dimethyi m-dioxane to isoprene, formaldehyde and water it Presence of phosphoric acid or acidic phosphates, which may be supported on carriers follows. In this reaction it is necessary to use both volatile acid and the reaction products supplement as well as the thermal conversion in the phosphates and in the phosphoric acid increasing free acidity by phosphoric acid introduced into the cleavage.

According to DT-AS 12 71 106 and DT-AS 18 13 354 he follows the post-dosing by adding 0.02 bi; 0.06 percent by weight or 0.001 to 0.1 percent by weight orthophosphoric acid (based on the included set amount of steam) with the steam added to the cleavage, or according to Belgian patent specification 7 35 564 by adding phosphoric acid esters z. B. 0.1 to 0.2 weight percent tri-iso-butyl phosphate based on the amount of feed, together with the dioxane feed, especially advantageous, dissolved in this homogeneously.

In the processes described, a number of products are produced during the production of 4,4-dimethyl-m-dioxane of by-products, some of which are extremely water-soluble and not volatile in steam, so that they also when wiping off water and water vapor Products for concentrating the circulating acid remain in solution.

When working with sulfuric acid as a catalyst these products become with continuous operation when concentrating the acid (separation of the water introduced with the aqueous formaldehyde solution) is steadily enriched. This enrichment is only possible up to the concentration at which coking occurs. So it must be some of the acid continuously removed from the cycle and replaced with fresh acid. The destruction or processing this product is technically very complex,

When working with acidic ion exchangers as a catalyst for the production of 4,4-dimethylm-dioxane from isobutene and formaldehyde (DT-AS 32 33 880) you can find these difficulties with dei Circumvent the circulation of the catalyst by mechanically separating the catalyst and sewage makes. From the practically acid-free wastewater obtained in this way, according to French Patent specification 15 54 005 the water-soluble organic products by complete evaporation isolated and according to Belgian patent 7 35 564 together with the dioxane feedstock: in the Cleavage can be used and used beneficially for isoprene production.

In addition to the use of sulfuric acid or acidic ion exchangers in the manufacture of the 4,4-Dimethyl-m-dioxane is known to react isobutene with formaldehyde, other mineral acids, z. B. orthophosphoric acid to be used as a catalyst.

E. Arundale and L A. M i k e s a show that

Reviews 51, p. 508 (1952) that when 8% orthophosphoric acid is used, moderate yields of 4,4-dimethyl-Sr (referred to in the tables below as 4,4-Dm-DX) are obtained with higher results, while with "use of? Ϊ orthophosphoric acid at low temperatures can improve the yield., and lead out, S use of phosphoric acid is always better-Fr Jbn ™" than the use of sulfuric acid r? D ^ USA patent specification 29 97 480 teaches in Scr manner that it is necessary to use higher phosphorus ions (in the Berekh Wn 15 to 25 GeanzaweWn and when using 85 ⁰ C as a catalyst not to over-STrSn U ^ on your part a sufficient acidity in Reitonsgernisch and on the other hand to avoid etching of the dioxane. Similarly, ^^ patent 33 90 059 teaches that one can produce 4-dimethyl-m-dioxane at concentrations of 5 to 25 percent by weight of onophosphoric acid, that fb is necessary / higher temperatures, at them

i ₅ recovery of the water-soluble by-products dissolved in them and recovered together with the 4,4-dimethyl-m-dioxane to maintain the acidity of the catalyst of the dioxane cleavage stage in this.

The recovery of the by-products dissolved in the aqueous phase is possible when using liquid Mineral acids as catalysts for the implementation the first stage cannot be carried out without further ado evaporation of the aqueous phase would result in the according to the previously known methods required amounts of acid, for. B. 5 to 35% sulfuric acid or 15 to 75% phosphoric acid, based on the total weight of the solution (see British patent specification 8 25 034, p. 2, lines 102 to 108), further enrich and for chemical change, usually for Resinization of the polyglycol-like by-products lead Therefore, for example, in French patent specification 15 54 005, p. 1, right column, second Paragraph, stated that one is responsible for carrying out the enrichment of polyglycols in the sewage

..n- ! _- £ "; ,, -. Aon ir

En on the aqueous amount of formaldehyde, with good difficulties. On the other hand, yields can be produced and that it is possible, of course, to use the acidic or water-soluble by-products of the synthesis by means of concentrates

mmm

ρ "7uk" u " ^A d £, phosphoric acid, ad ^ yf, ansh" s, e ", ng jjnd D, ox.nspal ton ™ * _cakti

shä | «s" eat

, feeds and can be used to break through Phosphorus acid content of formaldehyde solution removed from water vapor and obtained by condensation ester

7 _e J.ndunger ^ ^ _{def techn}

13S 5M / 595 A ^ fI. I 1962), called

ssr »- '» · ■ ■■> ■ "—- - -

costume, ζ. Β. predominantly silica-containing catalysts.

In principle, the process can be carried out as follows: In a tank cascade, formaldehyde and isobutene, which is used in the form of an isobutene-containing C ₄ fraction, are reacted in the liquid phase. The formaldehyde conversion will expediently be carried out as quantitatively as possible and the isobutene will be used in excess and the remaining C ₄ mixture will be separated off after the reaction. Intensive mixing of the two phases is essential for the catalytic reaction. The design of the boiler cascade can be any, you can use reaction loops or other reaction vessels instead of the boiler. At the concentration of phosphoric acid of 0.01 to 1.5 percent by weight used according to the invention, a pressure is applied which is so high that the reaction mixture is kept in the liquid phase. The reaction temperature is 90 to 180, preferably 120 to 16O ⁰ C.

After the reaction, the two phases are separated. _{The unreacted C 4} mixture is separated off from the organic phase by distillation and the crude 4,4-dimethyl-m-dioxane obtained as the bottom product of this column is passed on to the cleavage reactor together with all by-products formed during its formation.

The aqueous phase of the separator is evaporated to obtain the phosphoric acid and other reaction products still contained therein and the distillation bottoms are introduced into the pipe together with the crude dioxane. Before or after evaporation of the aqueous phase, you can purify, for. B. by extraction, perform, where you can use the C ₄ mixture used in the reaction as the extractant.

For the catalytic cleavage of 4,4-dimethyl-1,3-dioxane to isoprene, formaldehyde and water using the catalyst management according to the invention are all conceivable embodiments, e.g. B. fixed bed, moving bed and fluidized bed, possible. Preferably the inventive method is carried out in a fluidized bed, with the on the catalyst Deposited coke is burned off in a regenerator and the catalyst is continuously in the Circle is led. A carrier impregnated with phosphoric acid, preferably silica, is used as the catalyst used. It is not actually necessary to soak the catalyst beforehand, as it slowly increases with it which charges the circulating phosphoric acid. However, since this process takes a long time it makes sense to use a carrier that has already been soaked in phosphoric acid. The cleavage reaction will at temperatures of 200 to 400 ° C., preferably 250 to 350 ° C., carried out. To facilitate the split as well as to better maintain the state of the vortex steam can also be injected into the reactor.

The reaction products leave the cleavage reactor and are condensed in a known manner. At the When working in a fluidized bed, a system of cyclones is expediently used to initially generate the Separate catalyst. The cooling and condensation of the reaction products is expedient carried out in a quench system. The condensed reaction products separate into two Phases: an upper organic and a lower aqueous phase. In the aqueous phase is now the Phosphoric acid discharged from the cleavage system, which is circulated together with that also in the aqueous Phase contained formaldehyde is returned to stage 1 as a catalyst.

The upper phase of the reaction products after the cooling system is carried out in a manner known per se Distillation worked up to obtain pure isoprene. Non-condensable parts, e.g. B. isobutene, can be liquefied by compression.

According to the invention, phosphoric acid is thus circulated over both for stages 1 and 2 of the process Steps led.

The process according to the invention will be explained in more detail with reference to the following examples which illustrate the process However, in no way restrict the individual forms of implementation and only for clarification serve.

example 1

In a stirred autoclave with a volume of 0.71, 151 g of 37 weight percent formaldehyde solution with various additions of phosphoric acid and 200 g of a C ₄ hydrocarbon mixture with a content of 46.5 volume percent isobutene were stirred at various temperatures. After 1 hour in each case, the stirrer was switched off and after it was switched off

cool the excess Q-hydrocarbons relaxed via a gas pipette (for analysis) and a gas meter for volume measurement. The residue was then separated into an aqueous and an organic phase and both products by gas chromatography examined. Table 1 shows the results.

Example 2

In the test arrangement as in Example 1, 151 g of 37 weight percent formalin solution and 200 g of a Q mixture with a content of 46.5 % isobutene were used for 20 minutes at different temperatures and with different phosphoric acid contents.

stirs. The procedure was then as in Example 1. The results are shown in Table 2.

Table 1 temperature
° C pressure
aiii H ₃ PO ₄ in the
formaldehyde
solution
Weight percent Formaldehyde-
sales volume Isobutene
sales volume Dioxane selectivity based on:
implemented implemented
Formaldehyde isobutene 62.9%
62.5%
68.7%
66.7% attempt
No. 140
130
130
120 35
30th
31
23 0.28
0.28
0.56
0.56 97.9%
90.6%
96.3%
86.2% 67.9%
56.2%
63.8%
48.8% 78.1%
76.8%
80.3%
67.2% 1
2
3
4th

Table 2

attempt temperature pressure H ₃ PO ₄ in the Formaldehyde- Isobutene Dioxane selectivity based on: Formaldehyde- sales volume sales volume solution implemented implemented Formaldehyde isobutene No. ⁰ C atü

110
110
130
140
140
170

19th
22nd
26th
32
40
58

Example 3

1.13% 0.56% 0.28% 0.28% 0.14% 0.14%

56.7% 54.4% 62.5% 88.9% 72.7% 94.0%

29.6%
30.5%
36.5%
57.5%
44 9 «/

63.5%

68.2% 67.3% 62.8% 69.0% 79.5% 71.3%

73.3% 67.3% 63.6% 59.7% 72.3% 59.2%

a) 4,4-Dimethyl-1,3-dioxane production

The experimental set-up for continuous production of 4,4-dimethyl-1,3-dioxane is shown in the attached FIG. 1 shown.

Through a stirred tank cascade of 7 tanks with a total volume of 20.4 liters, of which the tanks (1 to 3) and (4 to 6) were created by each triple chambering of two larger tanks, were under a pressure of 29 atm and at Temperatures of 130 ^° C. in the kettles (1 to 3), 135 ^° C. in the kettles (4 to 6) and 137 ^° C. in the kettle (7) per hour with a content of 12.1 kg of 37% formaldehyde (20) of 0.24 percent by weight of phosphoric acid as a catalyst and 12.9 kg of a cracked C _{4 cut} (18) which has been freed from butadiene by extractive distillation and has a content of 6.1 kg of isobutene. In addition, 2.0 kg of water were used to rinse the stuffing boxes of the stirrer.

Behind the last stirred tank there was a separator (8) in which the reaction mixture was separated into a ·? organic (12) and an aqueous phase (13) was separated.

The organic phase was drawn off into a distillation column (9) and in 9.4 kg / hour of a C _{4 cut} (14) at the top of the column with a

Table 3

Content of 28.51% i-butene and 6.32 kg / hour of a crude dioxane mixture (15) with a content of 82.0% 4,4-dimethyl-1,3-dioxane at the bottom. The aqueous phase (13) from the separator was distilled in a vacuum column (10). The following were obtained at the bottom: 1.1 kg / hour of an organic residue (16) which contained 1.8% phosphoric acid and at the top a distillate (17) which is used to remove 4,4-dimethyl-1,3-dioxane and tert-butanol was extracted in an extraction column (11) with the C _{4 cut} (18) serving as the feedstock. After the extraction, 10.1 kg of waste water (19) were obtained from the extractor with a residual formaldehyde content of 1.36 kg / hour. The result of the reaction was therefore:

Formaldehyde conversion 69.7%

Isobutene conversion 56.1%

Dioxane selectivity (based on formaldehyde) 75.9%

Dioxane activity (based on

total converted isobutene) 72.5%

Dwell time in the cascade 37 minutes

In the same experimental set-up, four further series of experiments were carried out under the same reaction conditions whose characteristic data are summarized in Table 3.

attempt Formalde H ₃ PO ₁ - Isobutene shape Isobutene Raw dioxane Content of selectivity 4,4-D-m-DX hydrometer additive mission aldehyde- sales volume crowd 4.4 Dm DX related to related to coll. mission sales volume coll. shape Isobutene row aldehyde

12.4 kg / h 0.12%

with 4.6 kg related to

HCHO Form

(100%) aldehyde

11.95 kg / h 0.5%
with 4.42 kg relative to
HCHO form (100%) aldehyde

15.0 kg / h 0.48%
with 4.50 kg
HCHO
(100%)

15.0 kg / h
with return formal content
4.48 kg
HCHO
000%)

0.48%

12.9 kg / h 49.7% - 5.0 kg / h 82.9%

C ₄ mixture

with 5.94 kg

Isobutene

12.9 kg / h 79.5% 70.3% 7.54 kg / h 80.5%

C ₄ mixture

with 5.94 kg

Isobutene

15.1 kg / h 75.4% 54.3% 6.76 kg / h 82.0%

C ₄ mixture

with 7.02 kg

Isobutene

13.1 kg / h 75.8% 57.8% 6.15 kg / h 82.3%

C ₄ mixture

with 6.1 kg

HCHO

(100%) 93.8;

77.2%

82.4% 69.5%

77.6% 64.1%

60? 608 / 14i

ίο

Table 4

Experiment with use of dioxane - Dioxane
Mix sales isoprene Isobutene formaldehyde
solution with
Formaldehyde-
concentration Η ,, ΡΟ, -Κοηζ.
in the back
formaldehyde-
solution Higher boiling
Products 2 11.0 kg / h raw 96.3%
Dioxane + 1.0 kg / h
Evaporation residue
with 0.7% H ₃ PO ₄ 3.65 kg / h 0.7 kg / h 11.25 kg / h
with 21.4%
formaldehyde 0.01% 1.42 kg / h 3 11.0 kg / h raw 97.6%
Dioxane + 0.3 kg / h
Λ vapor residue
with 1.8% H ₃ PO ₄
+ 0.7 kg / h return
lead product
the split 3.65 kg / h 0.4 kg / h 11.16 kg / h
with 20.3%
formaldehyde 0.01% 1.39 kg / h

b) Dioxane cleavage

The cleavage of the 4,4-dimethyl-1,3-dioxane prepared according to a) was in the attached Fig. 2 described experimental apparatus carried out.

The reactor (I) of the experimental plant consisted of a pipe 80 mm in diameter and 1300 mm in length. At the top, the pipe was extended over a length of 600 mm to a diameter of 135 mm. At the bottom the reactor was conically contracted, and there was a nozzle (2) for the use of steam. Immediately above the cone was a laterally arranged nozzle with a steam nozzle for activation (3) for the catalyst feed via a downpipe (4) from the regenerator (5). A water-cooled nozzle (6) for introducing the dioxane feed mixture was used 300 mm above the inlet connection for the catalyst. In the lower part of the reactor, the incoming from the regenerator having a temperature of 580 to 61O ⁰ C catalyst was charged with 3.2 kg per hour of water vapor held by the nozzle in the fluidized state and mixed with colder catalyst in the reactor. To improve the running-in of the catalyst, 400 to 600 g of activation steam were blown in every hour through nozzle (3).

Through the insert nozzle for the dioxane mixture (6), 12 kg of the crude dioxane obtained according to a) and containing 0.2 percent by weight of tri-isobutyl phosphate were injected cold into the reactor every hour. The temperature in the gap part of the reactor was 300 to 310 ⁰ C, the pressure 0.2 to 0.3 atm. Immediately after the spraying, the dioxane evaporated and the cleavage began. The catalyst and the cleavage products rose to the top of the reactor and separated in the upper, enlarged part of the reactor.

The catalyst passed through a stripping zone (7) in which the catalyst drained off with an amount of steam of 0.5 kg / h was stripped from the reactor and was in the pneumatic lift (8) in promoted the regenerator. There the coke was burned off and the catalyst for the cracking reaction required heat supplied.

The gaseous cleavage products were first placed in a cyclone for the separation of catalyst dust (9) and from there into a cooling and compression system (10) in which the products are known per se Way were cooled and liquefied.

After all, the individual products were rolled into one Worked up distillation system. An additional 2.0 kg of washing water was passed through the cleaning system fed to the cleavage process.

After working up, you got:

Isoprene 3.40 kg / h

Isobutene 0.40 kg / h

A formaldehyde solution containing 19% formaldehyde
and 0.01% free phosphoric acid .... 11.0 kg / h
Dioxane and other products for

Return 1.0 kg / h

High polymers and other by-products "! 0.33 kg / h

The dioxane conversion was 96.3%.

The results of two further series of tests are given in Table 4.

For this purpose 2 sheets of drawings

Claims (5)

Patent claims: 1. Process for the preparation of isoprene by reacting isobutene or an isobutene-containing Q-hydrocarbon mixture with formaldehyde in a molar ratio of 1: 1 to 2 in aqueous solution at elevated temperature in the presence of phosphoric acid as a catalyst to give 4,4-dimethyl-m-dioxane in one first stage, separation of the reaction mixture obtained in this way into an organic phase containing 4,4-dimethyl-m-dioxane and an aqueous phase containing by-products and phosphoric acid and cleavage of the 4,4-dimethyl-m-dioxane in the presence of a supported catalyst containing phosphoric acid at elevated levels temperature in a fluidized bed reactor in a second stage, characterized in that one carries out the reaction of the first stage in the presence of 0.01 to 1.5 percent by weight of orthophosphoric acid, based on the amount of formaldehyde, at a temperature of 90 to 18O ⁰ C, the aqueous phase obtained is evaporated to enrich the by-products dissolved in it and the phosphoric acid, then end the 4,4-dimethyl-m-dioxane formed in the first stage together with the phosphoric acid-containing by-products obtained as evaporation residue during the evaporation of the aqueous phase for carrying out the second stage of the cleavage in the ^{fluidized bed reactor operating at 200 to 400 0} C in liquid form and if appropriate, the phosphoric acid-containing formaldehyde solution discharged during the cleavage by steam and obtained by condensation is returned to the first reaction stage. 2. The method according to claim 1, characterized in that the implementation of the first stage in The presence of 0.1 to 0.5 weight percent orthophosphoric acid is carried out. 3. Process according to Claims 1 and 2, characterized in that the reaction of the first stage is carried out at a temperature of 120 to 160 ^° C. 4. Process according to claims 1 to 3, characterized in that the cleavage of the 4,4-m-dioxane is performed to isoprene at a temperature of 250 to 35O ⁰ C. 5. Process according to Claims 1 to 4, characterized in that the from the first stage according to Separation of the organic phase remaining aqueous phase before evaporation of a pre-cleaning is subjected to extraction.