DE2042055A1 - Process for the production of high purity isoprene - Google Patents

Description

2042055 FARBENFABRIKEN BAYER AG

LEVE RKUSEN- Bayerwerk patent department

Dä / Rö 2% Aug, 1970

Process for the production of high purity isoprene

The invention relates to a process for the production of high-purity isoprene and the device used for this purpose.

It is known to use 4,4-dimethyl-1,3-dioxane if necessary together with the by-products formed during its production in the presence of phosphoric acid or phosphate-containing Catalysts split into isoprene, formaldehyde and water.

Preferred embodiments for the cleavage reactor are either a fixed bed reactor (O.B. Litvin, K.S. Solov'en, K, A. Jakovlev, Z. vses. chim. Obsc. 14, (1969) No. 3, S. 313-319} DAS 12711o6), a moving bed reactor (F. Coussement and M. Hellin in petroleum and coal, natural gas, Petrochemie 15, 274-282 (1962) or a fluidized bed reactor (Acc. Patent 735,564, HoIl. O.S. 69o94o8).

When working in a fixed bed or in a moving bed, it is necessary to use the product in vapor form and if possible to be used pre-distilled in the reactor and the heat required for the reaction by adding superheated

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Steam or by means of heat supplies built into the reactor in a known manner, such as jacket heaters or heating pipes, bring in. At the same time, in order to achieve a long service life for the catalyst, the formation of coke must be carried out Suppress the addition of large excesses of inert gas (water vapor or nitrogen) (see German Auslegeschrift I27II06.

These measures require large amounts of water vapor that after the reaction are condensed and, as waste water, the process also entails considerable work-up costs burden. Since the entire feed must be distilled and pre-evaporated, the energy costs are considerable.

When working in a fluidized bed with continuous regeneration and reactivation of the catalyst, on the other hand, a higher degree of coking can be allowed on the catalyst and thus considerably lower the steam requirement of the reactor. In addition, after the in the BeIg. Patent specification 735 564 described procedure to dispense with a distillation of the feedstock and the crude Dioxane mixture, as is the case in the production from formaldehyde and isobutene-containing C ^ cuts after separation of the C ^ hydrocarbons are obtained in liquid form in the reactor feed in. This feed is expediently above the steam supply (cf. DAS 1192186). By this measure uses the stripping effect (stripping of removable organic components) of the steam, in order to prevent cleavage products with the heat transfer medium passed through the reactor from top to bottom from the Reactor to be discharged.

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This staggered arrangement of steam and product feeds is also used in the method described in the appendix. Patent specification 735 564 is described, of advantage, since without the streaking effect of the steam in the lower part of the reactor quickly from Dead spaces at the bottom of the reactor from growing with polymers and coked products and no more circulation is possible. The disadvantage of this method of operation is that when adding the circulating hot, regenerated catalyst with the permissible temperature is limited to values that are not significantly above the reaction temperature of 25o - 300 ° C may be, since Otherwise there is an increased formation of coke and by-products (iso-pentenes which are undesirable for the polymerization, which are distillative cannot be separated from the isoprene). Since the coke, on the other hand, burned down at temperatures above 500 ° C must be, a cracking system using a fluidized bed can only be achieved with considerable yield losses operate.

It has now been found, surprisingly, that highly pure Isoprene in good yield from the cleavage of 4,4-dimethyl-1,3-dioxane in the presence of phosphoric acid or phosphate-containing catalysts at elevated temperature obtained when a continuous cycle is carried out between a regenerator and a two-stage reactor Catalyst containing phosphoric acid or acidic phosphates for introducing the heat required for the cleavage at 5oo - 7oo ° C in a first stage of the reactor, holds there with water vapor in the fluidized state and with already The catalyst located in the reactor is premixed or cooled to the cracking temperature of 2oo - 4oo ° C and then crude 4,4-dimethyl-m-dioxane in the one above

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feeds second vortex zone.

The cleavage is preferably carried out at 25 ° -35 ° C.

Erflndungsgeiafiß so one känii r & hsa 4,4-dimethyl-m-dioxane at a temperature of 2oo - 4oo, preferably 25o - 35o ° C columns, supplying the heat of reaction with the at 5oo 7oo ^'J C heated by burning of the polymers catalyst. By using a two-stage reactor, side reactions caused by overheating of the input or end product are avoided. The catalyst cooled in the first fluidized bed zone causes the very selective cleavage of the feedstock to isoprene. Crude 4,4-dimethyl-1,3-dioxane is preferably sprayed with a nozzle device above the first reactor stage together with the by-products formed in small amounts during its preparation from isobutene and formaldehyde in the presence of acidic catalysts, such as tert-butanol , 3-methylbutene-3-01-1, 3-methylbuten-2-ol-1, 3-methylbuten-1-ol-i, 3-methylbutenediol-1, and other enolic or glycol-like compounds, higher-boiling condensation products of 4,4 -Dimethyl-1,3-dioxane with formaldehyde, some of which are present as water-soluble polyglycols or alcohols and are isolated, for example, by evaporation of the aqueous phase.

The composition of the crude dioxane used for the process according to the invention is not critical. For example, raw products such as those obtained according to German Auslegeschrift 1233 88o and Belgian patent specification 708 799 can be used. The crude dioxane can be fed to the cleavage zone in either gaseous or liquid form.

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The evaporation of the liquid feedstock then only takes place in the reactor. To introduce the heat of reaction preferably the catalyst circuit between the regenerator and the two-stage reactor adjusted so that the entire heat required for evaporation, superheating and cleavage of the feedstock with the catalyst at one temperature of the incoming catalyst of 500 - 700 ° C is introduced. Preferably in the invention Process Catalyst and reaction products passed cocurrently from bottom to top through the two reaction stages. The preferred residence time for the cleavage products is between 0.5 - 3 seconds.

The catalyst preferably has an average grain diameter of 0.2-3.0 mm. The during the reaction on the Polymers deposited as coke-shaped products are preferably stored in a regenerator at temperatures burned from 500 - 700 ° C in the usual way in a fluidized bed with an oxygen excess containing heating gas.,

When the cleavage reaction is carried out in the manner according to the invention, there is therefore a considerable improvement in the Economic efficiency of the process: The amount of water vapor is considerably reduced, special measures for introduction the heat of reaction in the cleavage zone are no longer required.

The execution of the method is described in more detail with reference to the attached FIG.

In a reaction space (1), which is mainly free of internals, crude 4,4-dimethyl-i, 3-dioxane (DX)

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catalytically to a phosphoric acid-containing catalyst Isoprene, water and formaldehyde split. The cleavage takes place at temperatures of 200-4oo ° C, preferably at 25o - 35o ° C. The fluidized catalyst and feedstocks rise in the reactor in direct current upwards.

The catalyst runs off via an overflow (2) and becomes for the separation of adhering organic constituents with steam in a stripper (3) and gets into the lift system (4). The reaction products exit in vapor form at the top of the reactor and are in a cyclone (5) of freed entrained catalyst before they get to the usual condensation and work-up (15).

The crude feedstock obtained from the reaction of isobutene and formaldehyde for the cleavage is preferably introduced into the reactor in liquid form. Various known embodiments are suitable for this purpose; The liquid product is preferably injected into the fluidized bed through a number of nozzles (6) evenly distributed over the reactor. This Sinspritzaggregate are but non as fluidized bed reactors usual - at the bottom of the reactor, but ir> siaoa considerable distance, eg 1 m from the ground in a Ζα-χβ, is ^ ler uniform, already close to the reaction temperature lying temperature prevails. At the bottom of the reactor there are injection nozzles (7) - a wide variety of technical designs can also be used here - for the water vapor required for the cleavage at a temperature of 150 ° -500 ° C. (preferably 25 ° -35 ° C.). Immediately above this addition of steam (that is to say at the bottom of the reactor) the superheated catalyst is introduced at 50 ° -70 ° C. (13).

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The hot catalyst brings the heat of reaction for the Cleavage wholly or largely into the reaction scene, i.e. the water vapor becomes with the temperature of the The fission itself is blown in and only serves to dilute the fission products and maintain the Fluidized bed in the upstream mixing part (9). He is called Catalyst is fed to the reactor in a manner known per se, expediently several evenly Inlet points distributed over the reaction space can be used. By measures known per se, such as the addition of "Activation steam" (8), the catalyst is loosened at the inlet points and can thus within certain limits its feed rate can be regulated. The entry points for the catalyst does not necessarily have to be arranged on the outside of the reactor, but can instead pass through from above the reactor can be carried out. In principle, all conceivable embodiments are possible.

According to the invention, in the premixing zone (9) between the catalyst inlet or water vapor addition and the welter at the top of the feed point for the crude dioxane to be cleaved, the freshly incoming hot catalyst with the one in the reactor The fluidized catalyst is intensively mixed by the steam and a temperature equalization is brought about. The catalyst, which migrates upwards in the fluidized state, therefore reaches the point of addition for the crude dioxane only after the temperature peaks have dissipated and the heat introduced has been evenly distributed.

The crude dioxane, which is preferably injected in liquid form, evaporates immediately upon injection, with higher-boiling components being deposited on the catalyst. The steam transport

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: ni £ 3n products walkway quickly upward, the residence time beträft o _r 1 - β sec, preferably o, 5 - 3, ο sec The cipa'Ltiiiig ler reaction products can be obtained by the choice of..

as well as the reaction temperature in a wide range, preferably the cleavage rate is more air S * ..- fi ~ The heat requirement of the reaction is applied by hot catalyst (500 ° - 700 ° C) which enters the bottom (13) and leaves the reactor at the top (2). The catalyst circulation can be adjusted according to the heat requirement of the reaction.

Due to the evaporation of the dioxane and the increase in volume the reaction products (1 mole of dioxane produces 1 mole of isoprene, 1 mole of water and 1 mole of formaldehyde) the steam velocity would increase sharply from bottom to top in a cylindrical reactor. To get an even To achieve fluidized bed, it is therefore expedient in the procedure according to the invention, the part of the reactor, in which only steam is used for the turbulence, to reduce the diameter accordingly (9). In addition, it is expedient to close the reactor slightly towards the top in accordance with the progressing cleavage rate expand and build in a calming zone (1o) for the catalytic converter at the very top by means of a strong extension which the catalyst can overflow (2). The reactor is basically an empty container, but there are others too Embodiments, e.g. with internals known per se to avoid large gas bubbles, are possible.

After stripping, the catalyst emerging from the reactor is introduced into a regenerator (11) via (4). This regenerator is conveniently located above

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of the reactor. However, this arrangement is not absolutely necessary; rather, other arrangements can also be used can be selected in which the regenerator is arranged e.g. to the side or below the reactor. According to the Arrangement of the regenerator can be used in various ways to move the catalyst from the reactor into the Transport the regenerator and back again. This can be done e.g. by pneumatic conveying, simple mechanical Conveyance, e.g. screws, paddle wheels, or by means of conveyor belts.

The regenerator is preferably also designed as a fluidized bed, but other embodiments are also possible, e.g. a moving bed, can be used in principle. The preferred embodiment of the fluidized bed includes a regenerator without any internals. Because of the high temperatures, this regenerator is expediently lined with brick. By direct heating with flames immersed in the fluidized bed or indirect heating with oxygen-containing flames Flue gas or other measures, a temperature of 500 - 700 ° C is maintained in the regenerator. A part the heat required is generated during operation of the cracking system according to the invention by burning off the on the catalyst The fluidized state in the reactor is preferred maintained by blowing in hot, oxygen-containing gases (12), but in principle inert gases can also be used or use steam for this. The residence time is chosen so that all resin components on the catalyst are burned, it is preferably 10-20 minutes, it depends on the regenerator temperature.

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The hot regenerator becomes the catalyst - possibly over a buffer vessel - fed back to the reactor at the bottom in the manner according to the invention (13). Here you can use the corresponding Manner, the measures described for introducing the catalyst into the regenerator are applied. at The preferred arrangement of the regenerator above the reactor, the hot catalyst in free fall - if necessary still controlled by a slide - fed back to the reactor.

Suitable as a catalyst for the cleavage system according to the invention all inorganic or organic materials that have sufficient abrasion resistance for the fluidized bed, withstand the temperature load in the reactor and especially in the regenerator and deal with phosphoric acid or phosphoric acid Let substances soak. Examples include: aluminum oxides, silica, aluminum silicates or graphite.

These inorganic materials are preferably used in spherical form for the fluidized bed. The grain size depends on the design of the reactor and, within certain limits, a mean particle diameter ύοώ ü ,, 3 - 3, c- iaa. During the "vortex", a certain amount of abrasion occurs, i.e. the individual catalyst grains become smaller. This undersized grain can be continuously withdrawn from the cyclone system (14) and replaced by fresh contact.

Phosphoric acid or compounds containing phosphoric acid serve as the actual catalyst for the process according to the invention or compounds under the reaction conditions

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conditions splitting off phosphoric acid * Such compounds are e.g. in Ulimann's encyclopedia of techn. Chemistry, Vol. 13, S. 594/595 (ed. 3, 1962) mentioned. Examples are triethyl phosphate, tri-n-buthyl phosphate and tri-iso-buthyl phosphate cited.

In addition to organic phosphoric acid esters and polyphosphoric acids, preference is given to the process according to the invention Phosphoric acid used.

During the reaction, the reaction products become phosphoric acid discharged from the system in small quantities. It is therefore advisable to use appropriate amounts of phosphoric acid " or give in phosphoric acid-releasing substances. These continuous addition can take place at various points in the system. A particularly preferred embodiment in the process according to the invention is the addition of these catalytic substances directly to raw dioxane.

The products emerging from the reactor in vapor form are separated from entrained contact and contact dust in a system of cyclones (5). This separation is carried out in a manner known per se, the entrained catalyst being returned to the cracking system, while the catalyst dust is finally removed from the system (14). λ The vaporous products from which the catalyst has been removed are liquefied using known measures such as cooling, quenching or compression and then fed to further processing (15). The high-purity isoprene obtainable by the process is used, for example, for the production of rubber.

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ras inventive method is explained in detail in the following example in a special embodiment:

i) 6 i L · "U j; v J." i

The: i.eactor consisted of a tube (see Fig. 1) with a diameter of 80 mm and a length of 1,3oo mm. Above that, the pipe was conically widened to a length of 600 mm to a diameter of 135 mm. At the bottom the reactor was conically contracted and there was an injection nozzle for water vapor. Immediately above this was a laterally arranged nozzle for introducing the hot contact via a downpipe from the regenerator. A water-cooled nozzle for introducing the dioxane feed mixture was attached 300 mm above the inlet connection for the catalyst. The reactor consisted of a lower part, in which only steam and catalyst from the regenerator were present, and the actual gap part above with a length of about 1,000 mm.

3 parts by weight of steam at a temperature of 300 ° C. per hour were blown into this reactor from below and again 0.3-0.4 parts by weight / h through a nozzle introduced into the inlet nozzle at the inlet of the catalyst Steam added to activate the catalyst inlet.

By the water-cooled one arranged above the catalyst mixing zone Nozzle were every hour 12 parts by weight of a mixture of a crude dioxane, as in the implementation of Isobutene is obtained with formaldehyde, from recycle products from the cleavage and from the evaporation residue Wastewater from dioxane production is sprayed in as a liquid.

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The mixing ratio of the three specified components was 8 parts by weight of crude dioxane, 1 part by weight of recycle products and 1 part by weight of evaporation residue.

The temperature of the contact flowing in from the regenerator at the lower end of the catalyst mixing zone was 700 ° C, the amount supplied was approx. 21 kg / h.

The temperature in the actual cleavage part, which was already set at the entry point of the dioxane, was 275 ° G. The pressure in the cleavage reactor was about 0.2 atm.

The cleavage products were separated from the contact in the upper, expanded part of the reactor, via a quench and compression system cooled in a known manner, liquefied and analyzed by gas chromatography. The following were received every hour:

3 »o4 parts by weight of isoprene

1.8 parts by weight isobutene

2.2 parts by weight formaldehyde (100 % calculated)

2.2 parts by weight of higher-boiling products.

The content of undesired isopentenes in isoprene was 0.28%.

Example 2 (for comparison)

In a reaction tube, as described in Example 1, in which, however, the crude dioxane does not pass through a nozzle attached laterally above a catalyst mixing zone, but together with the steam through a two-fluid nozzle which has a central opening for dioxane and an annular gap for

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the steam input possessed, from below into the inlet level of the was injected into a hot contact Catalyst inlet temperature of approx. 500 ° C and a catalyst circulation rate between reactor and regenerator of approx. 45 kg / h and an added amount of steam of 4 parts by weight / h only 6-7 parts by weight of the dioxane mixture described in Example 1 are injected without the Reactor sticky due to heavy buildup of coke at the catalyst inlet point. Even so, the content was undesirable isopentenes between 0.5 and 0.6 in isoprene.

It can be seen from the comparative example that even when the dioxane mixture is sprayed in directly, the temperature reaches 500.degree Catalyst byproduct and coke formation were significantly increased, albeit with a much higher steam load than worked in Example 1.

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Claims (6)

2 O 4 2 O Γ 5 Patent claims ( 1. Process for the production of high-purity isoprene by cleavage of 4,4 ~ dimethyl ~ 1,3-dicxane in the presence of: phosphoric acid or phosphate-containing catalysts at elevated temperature, characterized in that one between a regenerator and a two-stage Reactor in a continuous cycle phosphoric acid or acid phosphate-containing catalyst to incorporate the heat required for the cleavage at 500 -? 00 ° C in a first stage of the reactor, there is kept in a fluidized state with steam and is already in the reactor chem catalyst to the cracking temperature of 200 - 400 ⁰ C, or premixing and then cooled crude 4,4-dimethyl-1,3-dioxane in the thereabove second fluidized zone feeds. 2. The method according to claim 1, characterized in that the cleavage at 250 - 350 ⁰ C is carried out. 3. The method according to claim 1 and 2, characterized in that the heat required for the cleavage is wholly or partially by burning off the polymeric compounds deposited on the catalyst. 4. Process according to Claims 1 to 3, characterized in that the catalyst is circulated according to the heat requirement the cleavage reaction stops. 5. Process according to Claims 1 to 4, characterized in that the residence time of the cleavage products in the second Holds reaction level between 0.5 and 3 seconds. 6. Process according to Claims 1 to 5, characterized in that there is a spherical catalyst with a medium Grain diameters of 0.2 - 3 mm are used. Le A 13 221 - 15 - 2 0 9 810/1831 ^{BAD 0RielNAL} Device for carrying out the process according to Claims 1 to 6, characterized in that a two-stage Reaction space used, consisting of a catalyst mixing space in the heated catalyst from the regenerator is mixed with the catalyst at reaction temperature by swirling with steam and one above located reaction space in the nozzle devices 4,4-dimethyl-1,3-dioxane together with at his Production of by-products formed, optionally after their isolation from the aqueous reaction phase 4,4-Dimethyl-1,3 dioxane production, fed in, evaporated and is split into isoprene. Le A 13 221 - 16 - 209810/1831 - -. . ■ ORiGWALlNSPECTED