DE3231813A1 - Method of removing enthalpy from gas/liquid suspension reactors - Google Patents

Abstract

In gas/liquid reactors or suspension reactors (3), in which the heat transfer obtained on incorporated heat exchange surfaces is too poor and evaporative cooling is not possible, the gas rate fed in is increased above the level required for the reaction to such an extent that the liquid-laden gas largely transports the enthalpy of reaction out of the reactor. A gas circulation system with a condenser (8) is preferred. The gases which are in the critical region under the conditions prevailing in the reactor are particularly suitable. <IMAGE>

Description

Process for enthalpy removal from gas / liquid and

Suspension reactors The invention relates to a method of implementation exothermic reactions in gas / liquid reactors at elevated pressure and temperature. In particular, it is aimed at the removal of enthalpy in exothermic gas / liquid reactions in gas / liquid reactors or

Suspension reactors.

In "Ullmann's Encyclopedia of Technical Chemistry" is a summary on the removal of the enthalpy of reaction in suspension reactions shown, the Temperature via the reactor jacket, built-in heat exchanger or an external one To regulate circulation. The last option should be omitted if the promotion of the Suspension causes operational difficulties or damages the catalyst. Evaporative cooling is also known for exothermic reactions.

There are restrictions when the heat exchanger bundle is inserted in terms of the maximum in the reactor heat exchange surfaces that can be accommodated; one is with regard to the heat transfer on that of the transport of the product through the flow velocities originating in the reactor. With the known Applications, the heat exchange surface is in direct contact with the suspension; it is therefore a sign of corrosion, as well as a possible formation of crusts or crystals exposed and subject to full operating pressure. Especially with high quality Materials and high operating pressure are stirred systems or systems with external Circulation in use to create flow conditions for good heat transfer between to ensure the suspension and the heat exchanger wall. Such systems are at large reactors very expensive. Agitators are up to 60 bar, with great effort up to about 80 bar, achievable; there are similar limits for those under full operating pressure standing circulation pumps in external heat exchanger systems. It is difficult with the Circulation systems in addition to the high operating pressure when a suspension (the catalyst is often a solid material) and, for reasons of catalyst damage, this upheaval must also be carried out gently.

If external circulation is not possible, the technical implementation be called into question if the required heat exchange surfaces in the reactor are not are to be accommodated. Evaporative cooling is generally used because of the high pressures not possible because the boiling temperatures are too high.

All of these heat exchange systems directly exposed to suspension together is the difficult one Calculation of a large system (scale-up) as well as the high financial and time expenditure involved in the piloting.

The object of the invention is to provide a method for enthalpy removal To develop gas / liquid reactors, in particular from suspension reactors, that even under difficult conditions, such as increased pressure and temperature, a safe removal of the enthalpy of reaction from the reactor is guaranteed. It should In addition, the dimensioning without pilot tests at an early stage on the basis in general recognized calculation bases and on the basis of these technical Design can be proven at an early stage that an economical operation is possible.

The object is achieved by a method in which the amount of inflowing gas that is not or only slightly loaded with the liquid reaction medium is increased over the reaction-related level, preferably 5 to 15 times Amount of the stoichiometric requirement is used.

The amount caused by the reaction excludes that of the reaction kinetic Reasons often used excess of the gas over the stoichiometric Crowd out a. The value is usually in the range of 10%.

In a preferred embodiment, the gas is at least partially Circulated and withdrawn heat from outside the reactor. In doing so, the energy the exothermic reaction can be used to generate useful steam, and the condensed Liquid can be in Temperature range from -15 to 1000C, preferably in the range from 20 to 700C, are fed back into the reactor.

The process of the invention is not based on gas / liquid reactors limited. It can also be used in the same way in suspension reactors, in which, in addition to gaseous and liquid substances, there are also solid substances in which Usually it is the catalysts that are in place.

The process according to the invention works particularly well with gas / liquid material systems perform in which relatively large amounts of liquid under the reaction conditions pass into the supplied gas and these amounts of liquid are reduced by lowering the temperature in a downstream condensation stage at the highest possible temperature let condense out. The first criterion is important for the gas throughput the reactor does not have to become too large, the second for the question of heat recovery at a high temperature level (useful steam generation). If the system basically leaves the Using different solvents too, this should be considered when considering Choice of solvent must be taken into account. Here is the high solubility of the liquid in the gas in general by working in the range of the critical Pressure is given, since in this area the solubility of most substance systems increases far beyond the normal range. It is particularly suitable for a temperature range from 100 to 2500C and at pressures from 60 to 200 bar carbon monoxide, carbon dioxide and ethanol. Carbon monoxide is alone or at least as a component in the cycle gas especially preferred.

The gas mixtures containing carbon monoxide can be further essential Reactants contain hydrogen; here are molar ratios of carbon monoxide to hydrogen from 1: 4 to 20: 1 preferred.

In a further embodiment of the method, this can be in carbon monoxide The gas mixture contained contains molecular oxygen as an essential reactant, wherein molar ratios of carbon monoxide to oxygen from 1: 1 to 50: 1, very particularly from 2: 1 to 25: 1 are preferred.

When performing the procedure, especially when using Carbon monoxide / hydrogen and gas mixtures containing carbon monoxide / oxygen, it can be advantageous to add additional inert gases or to circulate them, to maintain an inert gas level that prevents the formation of explosive mixtures prevented. Particularly suitable inert gases are nitrogen and / or carbon dioxide.

The gas flows introduced into the reactor are preferred in the range of 5 to 15 times the stoichiometrically required mass flow. at certain reactions must be accompanied by undesirable gas fractions when circulating gas is carried out removed from the gas cycle after the gas is fed back into the reactor; such operations are not hindered by the method according to the invention and must also be carried out here in a known manner if necessary.

In principle, of course, the method according to the invention can also be used Heat can be brought out of a reactor when the gas is not at all at the Reaction is involved.

As reactors for carrying out the reaction can in principle all known apparatus for gas / liquid systems can be used. Because of her Simplicity are reactors without internal fittings, such as tube, loop or jet nozzle reactors, preferred. As a rule, an agitator is not required; the ones available Liquid and gas flows introduced into the reactor are large enough a thorough mixing of the reaction space with a sufficiently high energy dissipation density to achieve.

The method according to the invention is suitable for producing aroma table urethanes made from aromatic nitro compounds for the production of hydrocarbons according to Fischer-Tropsch, for the production of lower aliphatic alcohols from carbon monoxide / hydrogen, mix, for the production of aldehydes and alcohols from olefins and carbon monoxide / hydrogen mixtures (Hydroformylation), for carrying out a carbonylation of olefins and / or Acetylenes with carbon monoxide and compounds of the general formula R-OH or R2NH (Reppe synthesis) and for oxycarbonylation, such as the production of carbonic acid esters from carbon monoxide, alcohols and oxygen or the oxycarbonylation of aromatic Amines or ureas with nitro compounds and / or molecular oxygen.

The inventive method has the following advantages: The technical Carrying out gas / liquid reactions with suspension catalyst systems that tend to form crusts becomes possible.

Carrying out the reaction in a large reactor, instead of from Reasons for accommodating the required heat exchange surfaces selected larger Number of smaller reactors becomes possible.

The limitation of the size, which does not apply to the circulating gas heat exchanger enables the enthalpy of reaction to be recovered for the purpose of generating useful steam to a considerable extent.

The design of the reactor is simplified; no mechanical stirrer because energy is dissipated to a sufficient extent in the reactor via the circulating material flows can be. The reactor is getting smaller.

The simple reactor construction without internals makes the use of high-quality special materials, such as explosion-clad composite materials, first possible and thus allows reactions with increased requirements to be carried out the materials used.

When using corrosive suspension systems, the Circulating gas heat exchangers in general simpler material qualities are produced as the heat exchangers in contact with the suspension.

A procedural processing is secured early on Base possible without problems of heat transfer and scale-up in lengthy and having to examine costly pilot plants.

The method according to the invention is shown by way of example in the drawing and described in more detail below. 1 shows the method according to the invention with circulating gas and recirculation of the condensed, cooled liquid; FIG. 2 the prior art method; FIG. 3 shows the method according to the invention in a multi-stage process.

Fig. 1 shows a gas / liquid reaction in a suspension reactor with a solid catalyst. The gaseous components are released through the pipeline 1, the liquid components and the suspended catalyst via the pipeline 2 introduced into reactor 3. The gas exiting from the reactor 4 is via a Washer 5 with the application of washing liquid via the feed 6 of entrained Liquid droplets and catalyst particles cleaned. That with reaction liquid loaded gas passes through the Line 7 in the capacitor 8 and is separated into the liquid phase and gas phase in the downstream phase separator 9. The main amount of the liquid is via the pipeline 10 into a downstream Radiator 11 out, in which the temperature of the cooling liquid in depen dence of the reaction temperature in reactor 3 is set. The pump 12 is the Liquid fed into the reactor 3. The gas produced in the separator 9 is passed through the pipeline 13 into the purification stage 14, in which the gaseous reaction products separated and discharged via the pipeline 15. The cleaned and cooled gas is fed back into reactor 3 via recycle gas compressor 16. The liquid reaction product is withdrawn from reactor 3 via line 17.

In the system according to FIG. 1, for example, nitrobenzene was used as 20 % solution in ethanol reacted with carbon monoxide at 1800C and 90 bar. In the The feed solution contained about 6% by weight of a catalyst system which essentially from fine-grained suspended iron oxide and iron chloride in addition to small amounts Palladium existed.

2.53 kg / h of nitrobenzene and 18.69 kg / h of gas were used. Of the Reactor 3 was a bubble column reactor.

The liquid separated in the separator 9 became smaller Partial flow 6 withdrawn for the washing process in the washer 5. The bulk of the liquid flow was in the heat exchanger 11 to the required Cooled down temperature. The carbon dioxide formed during the reaction left the gas cleaner 14 via the Pipeline 20. In reactor 3 itself, there were no built-in heat exchangers for discharge the enthalpy of reaction of 3.73 kW occurring at 1900C and 90 bar pressure.

The enthalpy of reaction was via the cooler / condenser 8 at high Temperature level pulled out of the system. The capacitor 8 was in contrast the material of the reactor 3 made of cheap carbon steel. The cycle gas consisted of 90% by volume of carbon monoxide; the remainder was essentially carbon dioxide. The total amount of carbon monoxide introduced into the reactor 3 was about 10 times the stoichiometrically required amount of carbon monoxide. The amount of circulating gas was thereby so determined that the heat of reaction to be dissipated is completely removed from the system was, with 70% of the heat of reaction through the phase transition, the remaining 30 % as latent heat of the material flows according to their specific heat capacity and the feed temperatures were removed.

A large technical reactor can be described without problems in the Kind of operated.

The prior art method is shown in FIG. Apparatus parts with the same effect have the same reference numerals as in Fig. 1. There were 7.58 kg / h of nitrobenzene as a 20% solution in ethanol with 6.13 kg / h of carbon monoxide implemented at 1800C and 90 bar.

The catalyst system (6 wt% of the feed solution) essentially passed of iron oxide and iron chloride rid and small amounts of palladium. Due to the reaction, the amount of carbon monoxide was slightly above the stoichiometric requirement (1.2 times the stoichiometry). In the phase separator 9, the gas components Discharged via the pipeline 20 and the liquid components via the pipeline 21.

The enthalpy of reaction to be removed was 10.2 kW; measured heat transfer values were 100 W / m2K with strong fluctuations over time. The installed heat exchange surface (one cooling coil in the reactor) was 58 m2 / m3; taking into account the desired The area required for heat recovery was 52 m2 / m3. Hastelloy came for reasons of corrosion C used.

The specific heat exchange area determined in the test facility cannot be accommodated in a large-scale reactor. For the technical implementation this process is unsuitable for this reaction.

In the apparatus according to FIG. 3, 2.11 kg / h of dinitrotoluene were dissolved reacted with 1.98 kg / h carbon monoxide at 1700C and 140 bar to give toluene diurethane. The liquid to be converted was first of all to the reactor via pipe 25 26 and then via the pipes 27 to 30 into the subsequent reactors 31 to 34 headed. The liquid left the reactor 34 via the pipe 35. Zur Removal of the enthalpy of reaction was a circulating gas stream of 22.83 kg / h over the Pipeline 36 at 600C and a circulating liquid flow of 10.68 kg / h with 400C returned to the reaction stages via pipeline 37. The feed into the reactors took place on the gas side via the feed lines 38 to 42, on the liquid side via the feed lines 43 to 47. The feed into the individual reactors was at the same time via appropriate regulating devices depending on the internal reactor temperature made so that just the reaction enthalpy occurring in the respective reactor was discharged. The recirculated liquid and gas flows were in proportion the enthalpy of reaction in the ratio 1: 0.6: 0.2: 0.14: 0.06 divided between the reactors. The entire circulating gas stream, which was returned via line 36, was there - calculated as carbon monoxide equivalent - at 11.53 times the amount compared to the stoichiometrically required amount of carbon monoxide.

Claims (8)

Claims e method for carrying out exothermic reactions in gas / liquid reactors at elevated pressure and temperature, characterized in that that the amount of the inflowing, with the liquid reaction medium is little or no loaded gas is increased over the reaction-related level, preferably the 5 to 15 times the amount of the stoichiometric requirement is used. 2) Method according to claim 1, characterized in that the gas is at least partially circulated and withdrawn from it heat outside the reactor will. 3) The method according to claim 2, characterized in that the condensed liquid is fed back to the reactor. 4) Process according to Claims 1 to 3, characterized in that the temperature of the streams fed in is lower than the temperature in the reactor. 5) Process according to Claims 1 to 4, modified in that in addition to The liquid and gaseous substances in the reactor also contain solid substances. 6) Process according to Claims 1 to 5, characterized in that a gas is fed in, which under the conditions prevailing in the reactor in the critical Area is present. 7) Process according to Claims 1 to 6, characterized in that the gas is or contains carbon monoxide. 8) Process according to Claims 1 to 7 for the production of urethanes from aromatic nitro compounds, hydrocarbons according to Fischer-Tropsch, lower aliphatic alcohols, aldehydes and alcohols (hydroformylation) and for Carbonylation of olefins and / or acetylenes according to the Reppe synthesis.