SU458123A3 - The method of producing isoprene - Google Patents

Description

Evaporation of the liquid starting product occurs first in the reactor. To supply the heat required for the reaction, the catalyst circulation between the regenerator and the two-stage reactor is set so that the total amount of heat required for evaporation, superheating and splitting of the starting product is introduced with the catalyst at the incoming catalyst temperature of 500-700 ° C. The catalyst and the reaction products are conducted from the bottom upward through the two reaction stages. The preferred residence time for the cleavage products is 0.5-3 seconds.

The catalyst preferably has an average grain diameter of 0.2-2.0 mm. During the reaction, polymer-like products that are deposited on the catalyst as coke-like products are preferably burned out in a regenerator at 500–700 ° C, in a usual manner in a fluidized bed, with a hot gas containing an excess of oxygen.

When carrying out the cleavage reaction, it turned out that the process is much more profitable: the amount of water vapor is significantly reduced, special measures for introducing the reaction heat into the cleavage zone are not necessary.

The drawing shows the technological scheme of the implementation of the proposed method.

In reactor 1, preferably without packing, the crude 4,4-dimethyl-1,3-dioxane on the catalyst containing phosphoric acid is decomposed into isoprene, water and formaldehyde. Splitting occurs at 200-400 ° C, preferably at 250-350 ° C. The fluidized catalyst and precursors are raised upward in the reactor.

The catalyst flows through overflow 2 and to separate the organic compounds contained in it, it is stripped off with water vapor in the stripper 3 and fed into the ascent pipe 4. The reaction products exit from the top of the reactor as steam and are released from the lean catalyst in the cyclone 5.

The crude starting material for cleavage is introduced into the reactor, preferably in liquid form. Various forms of implementation are suitable for this, it is preferable to inject the liquid product into the fluidized bed through several nozzles 6. This injection unit is, however, not at the bottom of the reactor, but located at a considerable distance, for example, 1 m from the bottom, in the zone where the temperature is kept uniform, close to the reaction temperature. At the bottom of the reactor is an injection nozzle 7.

Directly above the water vapor inlet (i.e., at the bottom of the reactor) a superheated catalyst is introduced with a temperature of 500-700 ° C (via line 8). The hot catalyst brings the heat required for the cleavage reaction completely or most to the reaction zone, i.e. the supplied water vapor has a cleavage temperature and serves to dilute the cleavage product and maintain the fluidized bed in the pre-mixing part 9. The hot catalyst is introduced into a reactor in a known manner, and it is advisable to use several inlet points distributed evenly over the reaction space. Adding "lively steam (on line

10) at the points of entry, the catalyst is loosened and the incoming quantity can be adjusted. Catalyst insertion points should not necessarily be located on the outside of the reactor, but can be carried out

through the reactor top. In principle, various forms of implementation are possible.

In the mixing part 9 of the reactor, between the introduction of the catalyst or the addition of water vapor and the place of supply of the split raw dioxane, located above, the freshly heated hot catalyst is agitated intensively with the catalyst in the fluidized state with water vapor and the temperature is equalized. The catalyst, passing upward in the fluidized state, reaches the feed point of the raw dioxane only after the heat applied is evenly distributed. Preferably, in liquid form, the injected crude dioxane is evaporated directly upon injection, with higher boiling parts precipitating onto the catalyst. Vaporous products quickly rise, the residence time is 0.1-6 seconds,

preferably 0.5-3.0 seconds. The splitting of the reaction product can be varied within wide limits, the proportion of splitting is more than 90%. The required heat for the reaction is provided by a hot catalyst (500-700 ° C) entering at the bottom and leaving the reactor at the top. The catalyst circulation can be adjusted depending on the heat demand of the reaction. Due to the evaporation of dioxaia and an increase in the volume of the reaction product (1 mole of isoprene, 1 mole of water and 1 mole of formaldehyde are formed from 1 mole of dioxane), the vapor velocity in the cylindrical reactor from bottom to top increases greatly. In order to obtain a uniform fluidized bed, it is advisable that the part of the reactor where only water vapor is used for the turbulence is accordingly reduced in diameter (mixing part 9). In addition, it is advisable reactor

correspondingly, an increasing degree of cleavage is slightly broadened and at the top, by means of stronger expansion, embed a "calming zone." The catalyst leaving the reactor is

riser pipe 4 is introduced into regenerator 11 located above the reactor. According to the location of the regenerator, various means can be applied to transport the catalyst from the reactor to the regenerator, and vice versa.

The form of the fluidized bed provides for a regenerator without any build-in. Due to high temperatures, the regenerator is lined by direct heating with a flame placed in a fluidized bed or indirect heating with an oxygen-containing flue gas. The regenerator is maintained at a temperature of 500-700 ° C, it is heated by a flame, high in it, directly in the fluidized bed. A portion of the required heat during the cleavage reaction is obtained by roasting the carbon deposits on the catalyst itself. The vortex state of the regenerator is maintained by blowing a hot, oxygen-containing gas (but line 12). The residence time is chosen so that a portion of the carbon deposits on the catalyst is annealed: it is 10-20 minutes and depends on the regeneration temperature.

From a hot regenerator, the catalyst is fed, if necessary, through a buffer vessel, back into the reactor via line 8. With the regenerator located preferably above the reactor, the hot catalyst can be reintroduced into the reactor by a free fall, if necessary adjusted by a damper.

As a catalyst for the cleavage reaction, all inorganic or organic materials that have sufficient abrasion resistance for the fluidized bed, which withstand the temperature load in the reactor and especially in the regenerator, and can be impregnated with phosphoric acid or phosphoric acid containing compounds, are suitable. These can be, for example, alumina, silicic acid, aluminosilicates, or graphite.

These inorganic fluid bed materials are preferably used in spherical form. The size of the grains depends on the device of the reactor.

Preferred is an average particle diameter of 0.3-3.0 mm. During turbulence, a known attrition occurs, i.e. the individual catalyst grains become smaller and can be continuously removed from the system with a cyclone (on line 13) and replaced with fresh catalyst.

Compounds which, under the reaction conditions, cleave phosphoric acid, for example triethyl phosphate, tri-nbutyl phosphate, tri-iso-butyl phosphate, can also serve as the active component of the catalyst.

In addition to the organic esters of phosphoric acid and polyphosphoric acids, o-phosphoric acid is used.

with the reaction products, small amounts of phosphoric acid are carried away from the system during the reaction. Therefore, it is advisable to add the appropriate amounts of phosphoric acid or phosphornuc, acidic substances. This continuous feed can be carried out at various points in the system. One particularly preferred embodiment of the process is the addition of catalytic substances directly to the crude dioxane.

Products released as vapor from the reactor are separated in cyclone system 5 from

carried catalyst, as well as from catalyst dust. This separation is carried out in a known manner, with the catalyst carried back to the cleavage system, while the catalyst dust is finally removed from the system via line 13.

Catalyst-free vapor products are liquefied by known methods such as cooling, quenching by mixing with a cold product or compression, and then fed to further processing through line 14. The resulting highly pure isoprene is used, for example, to produce rubber.

Example. The reactor consists of a pipe with a diameter of 80 mm and a length of 1300 mm. From bottom to top, the tube is conically expanded to a diameter of 135 mm over 600 mm. Bottom reactor

conically constricted and there is a steam injection nozzle. Directly above it is a pipe for introducing a hot catalyst through the downstream pipe from the regenerator. 300 mm higher than introductory

the catalyst nozzle is placed in a water-cooled nozzle to inject the initial dioxane mixture. The reactor has a lower part in which there is only steam and a catalyst supplied from the regenerator, and a part for production

maintaining a splitting reaction at the top is long about 1000 mm.

Hourly 3 weight is blown into this reactor from the bottom. including water vapor at EPA and through the catalyst located in the water inlet

nozzle once again 0.3-0.4 weight. hours / hour steam for mixing the injected catalyst.

Through a water cooled nozzle located above the catalyst mixing zone

injected hourly in liquid form 12 wt. including mixtures of raw dioxane, obtained by the reaction of the exchange decomposition of isobutenes with formaldehyde, from the products of recycling of the splitting process and waste

evaporation of wastewater upon receipt of dioxane. The mixing ratio of these components is 8 wt. h. raw dioxane, 1 wt. including recycled products and 1 wt. including evaporation residues.

The temperature of the catalyst coming from the regenerator at the lower end of the mixing zone is 700 ° C, the amount introduced is about 21 kg / hour. The temperature in the splinter part is already set at the inlet of dioxane. composition