DE2016323C3 - Process for carrying out exothermic reactions with a high starting temperature - Google Patents

Description

The invention is a method for carrying out exothermic reactions with high Start temperature, the fresh reaction mixture being increased by heat exchange with the fully reacted mixture the required starting temperature is brought, and preheating, if necessary, before the start of the reaction takes place, which is characterized in that the entire reacted mixture with the fresh reaction mixture over the entire length of the reaction space with indirect heat exchange is passed in cocurrent through the reactor, the fresh reaction mixture optionally can be diluted with fully reacted mixture.

There are reactions which are exothermic, but relatively high starting temperatures for their initiation require. Therefore, in many cases, catalysts are used to generate the excitation energies and thus to lower the reaction temperatures, often at the same time the equilibrium of the reaction is shifted noticeably in the desired direction. Nevertheless, there are reactions for which none have yet or no sufficiently effective catalysts have been found, or the use of such Should be avoided because of the economic wedge or because of other disadvantages.

Exothermic reactions with heat levels of > 10 Kcal / mole, such as when opening double bonds or three rings as well as with Halogenation reactions occur due to equimolecular mixtures of the reaction components sometimes temperature increases in the liquid phase, depending on the specific heat of the reaction products, from some KKTC; this is particularly disadvantageous if for the reaction in question a relatively high starting temperature is required and the heat of reaction must be dissipated.

In principle, this can be done directly through the reaction medium or indirectly through heat exchange surfaces be discharged, in the form of specific

ίο heat or heat of vaporization.

If the operating conditions permit, it is customary to dilute the reaction components, wherein the diluent be inert or the excess of a reaction component or the Can represent reaction product. The latter is z. B. in German Patent 843 842, page 2, Lines 81 to 97 described.

Equally, the heat of reaction can also be an excess in the form of heat of evaporation

so reaction component can be discharged, as is the US Pat. No. 3,117,998, p. 2, line 33 et seq proposes the production of polypropylene glycol.

Furthermore, the heat of reaction can be in the form of

specific heat can be indirectly dissipated by means of relatively high circulating quantities of a coolant. When using solid alkali dialysis with a defined reaction space, the raw material mixture may be suitable as a heat exchanger, the temperature of which is regulated outside the exchange zone (Swiss Patent specification 145 140). A foreign medium can also be used as a heat exchanger are, according to processes for the addition of alkylene oxides to hydroxyl-containing organic Compounds (German Patent 735 418, p. 2, line i8 ff.). The desired constancy of the heat bath is achieved even better if an evaporating coolant is used whose evaporation temperature is controlled by maintaining pressure (British Patent 736 991, U.S. Patent 2 988 572, German interpretative document 1 255 653).

The processes of these principles are based on the same task, a reaction temperature to maintain, on the one hand for the conduct of the reaction, on the other hand for the stability of the Reactants, quality of the reaction products or the technical design of the equipment Represents limit value. The difficulty is to get the limit for maximum space-time yield safe to use. It is necessary that there are technically caused fluctuations in the controlled variables be included.

The indirect heat exchange can be carried out using a countercurrent heat exchanger connected upstream of the reaction vessel can be achieved, wherein the fully reacting hot reaction product is used to the Bring raw material mixture in countercurrent to the required starting temperature. The latter procedure will often used for liquid media, e.g. B. in the production of glycol by the addition of Ethylene oxide in water (see Ost-Rassow. Chem. Technologie, 27th edition, pp. 1104 to 1105) and is only suitable as long as the adiabatic temperature increase remains below about 150 "C. Nevertheless, it still exists the disadvantage of such a process is that when the raw mixture is heated in countercurrent a very narrow temperature range must be maintained, within the limits of which the reaction is sufficient starts quickly, d. H. gets going, but

not yet passed through in the heat exchanger and to a large extent, reaching undesirably higher levels Temperatures reacted. Recognizing this difficulty it has also already been proposed to arrange additional heat exchange surfaces in the reaction part to be able to heat or cool from outside if necessary (see Ullmann, Encyclopedia of Technical Chemie, 3rd Edition, 3rd Vol., 1953, pp. 137 and 138). This measure is uneconomical and controls hardly feasible because of the phase shift.

It has also been proposed to carry out exothermic reactions in tubular reactors, as in the German Auslegeschrift 1 061 764 is described for the production of alkylene glycols or their Monoethers in order to avoid backmixing, which leads to the formation of undesirable higher degrees of polymerization to lead.

AU of these known processes include the need to propose dk Reaktionskomponenen: heat and quickly dissipate the heat of reaction sufficiently. In some cases, the processes are spatially separated, in some cases a heating medium is used that is kept at an approximately constant mean temperature level that is suitable for both preheating the reaction components and cooling the reaction mixture. As a result, only a relatively unsatisfactory temperature difference is available for both heating and cooling. In order to still be able to dissipate the heat to a technically sufficient extent, very large amounts of coolant are circulated or heat baths with boiling liquids are used, the boiling temperature of which is regulated by setting the corresponding saturation vapor pressure.

The present application is now concerned with the task of finding a system which is able to heat up very quickly with as little technical effort as possible and at the moment of use the strongly exothermic reaction to cool intensively. The amount of heat to be dissipated per unit of time amounts to:

Product leads in direct current, so that Functions of the • 'heat exchanger ^, and de gliding in a "direct current re * Kioi

convicted. . _{71ir through}

A preferred cocurrent reactor for

Execution of the ^ ™ _{nzenlri sch according to} the invention in principle - from two ' ^m * ^e * f " ¹ ^ _n » jacket pipe, arranged pipes - im, folp: nden ^. ^

called _, which «> arranged jmd last "Mixture in e.nes de," tubes rrtt;

Pipe flows through and this as

lUerFi ^

shown. It consists of
the inner tube 1 and the
over the nozzle 3 tnit
the outer tube 2 en, leaves

will.

| J _{emisch got} in 4 Sd

I. Ta t

Tu, = Te + Tau

30th

β = A-FJ7-

F- \ T

where Q is the amount of heat, / the unit of time, A: the heat transfer, F the exchange area, AT the temperature difference, \, and \ ₂ the heat transfer coefficients at the phase interfaces Product ^ -r pipe and pipe ■ * -? ■ heat bath, c / the pipe wall thickness and / represents the thermal conductivity of the pipe wall. It is easy to see from this that the improvement in the heat transfer coefficient \ ₂ in the case of evaporative cooling can only contribute little to the acceleration of heat dissipation, provided that * i is relatively small and cannot be improved. In contrast, AT is directly proportional to the equation. Therefore, a way was sought to self-regulate as large a .17 "as possible with turbulent flow within the reaction section. It has now been found that this technically desirable condition is almost reached and the reaction can be made to a high degree isothermally and therefore also more safely , if one means with the help of heat exchange a fresh and fully reacted thereby:

Ta initial temper,

Tad adiabatic temperature increase,

Tf. Endtemperauir.

Dew temperature protection.

The adiabatic temperature increase Tad for a given heat tone depends essentially on the degree of dilution and the specific heat of the reaction mixture. The radiated heat Tau \ o will be kept small in terms of maximum energy recovery through appropriate insulation. In the following considerations it will therefore

neglected.

In the F i g. 1 and 2, in which the cocurrent and countercurrent mode are compared with the same throughputs for the case of glycol production from ethylene oxide and water, the temperature profile is plotted over the reaction volume passed through, with Fiel corresponding to the ratios given in the references mentioned. In the countercurrent procedure, the raw material mixture in the section A is heated, that is heat exchanged against the fully reacted reaction product, m area B react the mixture in the range C - this is · when mirrored area A shown - heat is given off in exchange for A. It can be seen from this that the transition A - * ■ B takes place in a defined manner, in that the raw material mixture leaves the countercurrent heat exchanger and enters the reactor. Since the reaction rate constant increases progressively with the temperature, a relatively large reaction volume must be made available as a reactor, because the reaction that has just started can initially develop only slowly. F 1 g. 2 shows the temperature curve in a direct current reactor. Part A shows the heat exchange, which is significantly shorter than in FIG. 1. The raw material mixture is initially heated by exchanging

specific heat. When the start-up temperature Tu overlay ^{1 is} exceeded, the heat of reaction is additive up to point Λ '. The intersection point X represents the turning point for the temperature curve of the raw material gene a and the minimum for the temperature curve of the reaction product b . The heat exchange is reversed. In part B the shark piantcil of the actual reaction takes place. At the end of this distance, the temperature maximum is formed as part of the greatest turnover per running meter. The maximum at point) 'arises because the reaction rate decreases proportionally to the depletion of the reaction components, but increases with the temperature in the sense of a disproportionate function. Part C is used for extensive temperature compensation. The repeated passage of the reaction product in the jacket tube also serves to complete the reaction.

The reversal of the heat exchange at point A 'has the prerequisite that the reaction starts, d. h .. that

7 ".υ =

Ta τ

T _n is. If Tm > T _n

Part A will be very short. The transition from part A to part B depends exclusively on the reversal of the heat exchange. This is an essential feature of the invention. In the conventional process, the amount of heat necessary to start the reaction is supplied empirically. Process disruptions due to even slight fluctuations in the ■ control of raw material supply, temperature, etc. can easily lead to the reaction "falling asleep" or "running away". In order to bring such extreme reaction conditions back into equilibrium, the heat exchange tubes installed in the reactor must be operated with steam or with cooling water.

The process just described using the example of glycol preparation can be used for production of products that arise exothermically from their components and a rclatix high starl performance require. In this way gas reactions can be carried out, e.g. B. the chlorination of Methane: the larger area of application is in the field of reactions in the liquid phase, e.g. B. Alkylation with olefins, continue the implementation of Epoxides, such as ethylene oxide, propylene oxide, butylene oxide, Epichlorohydrin and others with compounds with active hydrogen such as water, alcohols, phenols. Ammonia and amines or phosphorus oxychloride.

The method according to the invention offers the following compared to the stated prior art Benefits:

The reaction management achieved by means of the described direct current converter avoids regulatory uncertainties and ensures the stability of the system according to equation i. The spatial extent of zones A ₁ B and C is self-regulating according to the selected reaction conditions, which results in fundamental advantages over the previously practiced processes.

The Raum-Zcit-Ausheutc is among otherwise comparable Conditions several times as great as with the Cicgcnstrom-Fahrwcisc. because the heating zone is very is short. At the end of the reaction path, relative periods of time occur, their height can be controlled. This ideally requires an acceleration of the reaction that is otherwise isothermal would have to fade out very slowly as a result of the depletion of reaction components. As a result, can also the post-reaction space can be kept very small, especially since the converted product through the repeated parallel guidance also gains time in order to be able to react completely with certainty. the Product quality is ensured by short response times

ίο improved in most "cases.

For homogeneously catalyzed reactions it is usually desirable to use little catalyst without the Having to increase the temperature. With the help of the proposed reactor, it is due to the flexibility of the Components are possible within wide limits, two of the three variables - throughput, maximum Temperature and applied catalyst concentration - to vary.

Since the reaction components in the reactor described mil relatively high speeds the pipes are guided, there is an extremely favorable heat exchange. At the same time it becomes largely avoided that remixings take place; Mixtures between proportions different The progress of the reaction can lead to a reduction in quality or an undesirable distribution spectrum. As a result of the reaction procedure according to equation I, the reaction product falls, in contrast to the countercurrent procedure, with a relatively high final temperature. This is especially true with such reactions of importance, in which a distillation downstream is, as for example in the alkylation of phenols with olefins or in the reaction of alkylene oxides !! with water, alcohols. Ammonia or amines to form low molecular weight products. In In such cases, the reaction solution as hot as possible is sent directly through a multi-air steam generator relax.

Make sure that parts A, B and C are identical in terms of equipment! it. to vary the capacity of the reactor according to the modular principle. In this way, the question of short-term capacity expansion is continuously possible, using all components that have already been invested. The effort for metrological regulation and control functions is also significantly smaller than with the countercurrent mode of operation.

example 1

In a jacket tube with a total length of 200 m, a diameter of the inner tube 50 mm and a diameter of the outer tube of 50 mm, ethylene oxide is reacted with water in a volume ratio of 1: 7 using NaOH as a catalyst. The heat exchanger is designed as a package of horizontally arranged tubes with corresponding deflections; the package is isolated on the whole. A preheating temperature of 160 ° C. is set. The product leaves the reactor at 220.degree. C. The alcohol and water are mixed in the inner tube. the reaction solution passed in the jacket tube. When the reactor is started up, the system is filled with water at ^ 200 C. At a throughput of 2000 l / h oxide, the heat exchange returns to approximately (ι lfdin of the jacket pipe to the ^{Tempcraturniavimuni:.} M inner pipe is achieved after about 120 1fdm, it howl at 22 ^l) is C. After 150Ifdm a Um> atz in the inner tube of J? ¹ ^. *) ",, reached. The Tcmner.iturverlaui is in I i e. 4 wicdcnieeebcn.

If one proceeds in the same way, but chooses a throughput of 3200 l / h oxide, the reversal of the heat exchanger is achieved at around 100 lfdm. After 200 linear meters of the conversion 98 is ¹ Y _n - The remaining 2 ° / ₀ are implemented in the cladding tube guide. The corresponding heat tone of 1.3 ° C is not important for the heat exchange.

Example 2

Propylene oxide is reacted with water in a volume ratio of 1: 4 in a jacket tube with a total length of 100 m, an inner tube diameter of 65 mm and an outer tube diameter of 100 mm. The arrangement of the heat exchanger corresponds to the example 1. It is catalyzed with KOH and set a preheating temperature of 120 ⁰ C. The product leaves the reactor at 210.degree. With a throughput of 1600 l / h propylene oxide, the heat exchange is reversed after 35 running meters. The maximum temperature is reached after 60 running meters in the amount of 230 ^° C.

Example 3

Using a technical apparatus according to Example 1, ethylene oxide is reacted with methanol in a volume ratio of 1:10. The preheating temperature is 150 ⁰ C. As the catalyst KOH is used. The product leaves the reactor at about 220.degree. After 180 running meters, a conversion of> 99.9% is achieved.

Example 4

In a copper jacket tube with a length of 6 m, a clear diameter of the inner tube of 6 mm, a clear diameter of the outer tube. of 10 mm with a wall thickness of 1 mm, ethylene oxide is reacted with tributylphenol in a molar ratio of 1.8: 1. The raw materials are mixed at room temperature and fed into the jacket pipe. Before being put into operation, the reactor is preheated to 150 ° C. using a reaction solution. KOH or NaOH is used as a catalyst. The reaction starts immediately _{e; n} ß _e j _CMEM flow rate of 2 l / h of ethylene oxide occurs a complete conversion.

Re- '15

In a jacket tube of the dimensions according to Example 4, phosphorus oxychloride is mixed with ethylene oxide

¹ S in a ratio of 1: 3 converted to tris - (/? - chloräthyi) phosphate. The temperature rise caused by the heat of reaction is reduced accordingly by diluting the raw materials with 8 times the amount of finished product. At an initial temperature of 20 ⁰ C to a final temperature of 80 ° C is achieved in consideration of the Ab-radiant heat. _{TiCl 4 is} used as the catalyst. Complete conversion is achieved at a throughput of 3 l / h of ethylene oxide.

Example 6

In a jacket tube according to Example 4, pheno is reacted with a mixture of λ- and /? - butylene to give tri-sec-butylphenol. _{BF 3} serves as the catalyst. The raw materials are mixed with the 2,5fachcn volume ^{of the} reaction products ⁵ and introduced at room temperature in a pre-heated to 180 ⁰ C reactor. Complete conversion is achieved at a throughput of 2 l / h of butylene.

1 sheet of drawings

3 »« «1/336

Claims (4)

Patent claims: 1. A method for carrying out exothermic reactions with a high starting temperature, the Fresh reaction mixture is brought to the required temperature by exchanging heat with the mixture that has reacted out is brought and, if necessary, preheating takes place before the start of the reaction, thereby characterized in that the entire reacted mixture with the fresh reaction mixture over the entire length of the reaction space with indirect heat exchange in cocurrent the reactor is passed, the fresh reaction mixture optionally with fully reacted Mixture can be diluted. 2. Gleichsiromreaktor for carrying out exothermic reactions with a high starting temperature, consisting of two tubes arranged concentrically to one another, characterized in that the feed (3) of the reactants at the entrance of one of the two tubes (2) and the Exit (4) is at the other end of the same tube, this exit always at the beginning of the other pipe connected again (6) and the discharge line (7) for the fully reacted mixture on The end of this other tube is arranged. 3. DC reactor according to claim 2, characterized in that the same from individual parts that can be assembled in a modular manner 4. DC reactor according to claim 3 and 4, characterized in that the same is hairpin-shaped is guided horizontally and insulated together as a package.