DE10036603A1 - Process for the production of monochloroacetic acid in microreactors - Google Patents

Abstract

The invention relates to a method for the selective production of chlorination products of formula (I), wherein R1 and R2, independently of each other, represent H, Cl or R1 or R2 represents COOH or R1 and R2 together form a group C=O and R3 represents H, a phenyl or benzyl radical which can optionally be substituted with up to 5, especially up to 3 radicals from the following group: CH3, F, Cl, CN; CH2X(X=Cl, Br, OH), by reacting compounds of formula (II) with chlorine gas at a temperature > 140 DEG C, especially a temperature of between 160 and 220 DEG C, preferably at a temperature of between 170 and 190 DEG C, this reaction being carried in a microreactor.

Description

The present invention is in the field of selective manufacture of Monochloroacetic acid from acetic acid and chlorine gas in a microreactor, the Formation of dichloroacetic acid compared to the known processes drastically is reduced.

According to the acetic acid chlorination process customary in the prior art Monochloroacetic acid are acetic acid and acetic anhydride along with a recycled distillate from acetic acid, acetyl chloride, monochloroacetic acid, Dichloroacetic acid and hydrogen chloride gas submitted, with acetic anhydride Hydrogen chloride gas reacted immediately to form acetyl chloride.

This mixture is in bubble column reactors, so-called chlorination towers, pumped and into this at a pressure of about 3.5 bar abs. and a temperature in the range of 115 to 145 ° C chlorine gas. Because of the changing The composition of the returned distillate fluctuates the reaction mixture in particular the acetyl chloride portion in relatively broad Limits.

The composition of the reaction mixture is usually approx. 38.5% Acetic acid, 11.5% acetic anhydride (this corresponds to about 20% acetyl chloride) and about 50% chlorine gas. The chlorine gas is metered in so that a maximum of 0.1% on the head Escape unused chlorine gas again.

After passing through the bubble columns, the crude acid is separated off and at approx. 150 mbar and approx. 80 ° C initially freed from low boilers by distillation. At a Acetic acid conversion of 85%, the composition of the raw acid is approx. 85% Monochloroacetic acid, approx. 11.5% acetic acid and 3.5% dichloroacetic acid.  

The monochloroacetic acid still containing dichloroacetic acid must be removed dichloroacetic acid (DCE) either by complex crystallization processes or via an expensive heterogeneously catalyzed hydrogen reduction with palladium Catalysts are cleaned up to lower DCE contents.

The object of the present method is therefore an economical method for To provide production of monochloroacetic acid which allows Obtain monochloroacetic acid in high yields with good selectivity and which at the same time the formation of dichloroacetic acid as a by-product is less than with the methods known in the prior art.

The object is achieved by the present invention and relates to a method for acetic acid chlorination, especially for the production of monochloroacetic acid, by reacting acetic acid with chlorine gas at a temperature <140 ° C, especially at a temperature in the range of 160 to 220 ° C, preferably in Range of 170 to 190 ° C, the reaction being carried out in a microreactor becomes.

In the present process, acetic acid and chlorine gas are compared 0.8: 1 to 0.95: 1, preferably in a ratio of 0.85: 1 to 0.90: 1 and acetyl chloride in Range from 1 to 50%, preferably in the range from 10 to 30% continuously Temperatures of <140 ° C implemented in a microreactor. Instead of Acetyl chloride, acetic anhydride and hydrogen chloride gas can also be used.

The control of the required flows and the addition of the liquid reactants is preferred over precision piston pumps, centrifugal pumps or Tumble piston pumps and computer-controlled controls. The The reaction temperature is monitored via integrated sensors and with the help of Regulation and a thermostat monitored and controlled.

The chlorine gas is supplied via a pressure reducer and a shut-off valve from pressurized gas containers. The associated volume flow is indicated by a suitable variable area flowmeter.  

The reaction mixture is made up of one, preferably at temperatures in the range from 170 to 190 ° C tempered, preferably by means of a pump dosed into the microreactor.

The exhaust gas and the product come together from the microreactor downstream separator tank. The fill level of the separation tank is recorded by means of a magnetic float guided in a separate tube and regulated. If the upper limit is reached, the downstream one opens Solenoid valve thus the system pressure through the flowing product mixture is not influenced if possible.

The operating pressure of the system, which is in the range of 1 to 10 bar, especially 5 to 8 bar is in addition to the pressure set for the chlorine supply regulated by throttling the escaping product gas flow.

With the method according to the invention it is possible to use the Removal of the dichloroacetic acid formed as a by-product is required extensive work-up of the reaction mixture, for example by Crystallization or heterogeneously catalyzed hydrogen reduction.

Microreactors are for example from EP-A-0 688 242 and US-A-5,811,062 known. These microreactors are made up of a variety of stacked and interconnected platelets built up whose surfaces are micromechanically generated structures that are in their Interacting form horizontal reaction spaces to make each one desirable perform chemical reactions.

Such microreactors are, however, for carrying out reactions between gaseous and liquid reactants are unsuitable because the reactants are in cannot mix enough in the horizontal reaction spaces.

The microreactors used for the process according to the invention Microcapillary reactors, micro bubble column reactors or microdroplet reactors in  Question. The use of microcapillary reactors is for the manufacture of Monochloroacetic acid preferred.

In the case of microcapillary reactors, the reaction mixture is reduced to one with micro grooves provided plate and the chlorine gas in the gas space above added. The back wall of the plate is used to remove the heat of reaction. The advantages of the microcapillary reactor are particularly simple Liquid dosing, as well as in the separate management of the phases, so that none additional components for separating the phases are necessary. thin Liquid films enable good heat control and intensification the exchange of materials through short diffusion distances.

An example of a reactor which can be used for the production of monochloroacetic acid is described in Fig. 1.

The central component of the microreactor is a fluid guide plate ( 1 , Fig. 1). The plate holds the reacting liquid on its surface in special capillary grooves using capillary forces. It has a thickness ( 1 a) of 1000 microns to 4000 microns, preferably from 1500 microns to 3000 microns. It contains open capillary grooves in which liquid threads are created. These capillary grooves have a width ( 1 b) of 500 μm to 2000 μm, preferably 1000 μm to 1500 μm and a depth ( 1 c) of 200 μm to 500 μm, preferably from 300 μm to 400 μm. The webs ( 1 d) between two adjacent capillary grooves have a width of 100 μm to 300 μm, preferably from 150 μm to 200 μm.

In the exemplary embodiment shown in FIG. 2, it is assumed that the microreactor according to the invention consists of five structured plates, a base plate ( 22 ), an intermediate plate ( 6 ), and a cover plate ( 12 ) and two fluid guide plates ( 1 ). The two fluid guide plates ( 1 ) are each installed between two of these plates and are sealed on the back, for example by O-rings. The feed lines ( 2 ), ( 8 ) and ( 15 ) are also preferably sealed by O-rings.

Not shown are guide pins and screws which seal the plates compress.

The fluid guide plate ( 1 ) rests on an intermediate plate ( 6 ) or the base plate ( 22 ) through which the fluid reactant is fed to the reactor via the feed line. This is connected to a bore ( 3 ) which opens into the distribution channel ( 4 ), which ensures uniform flow distribution. A flow restriction is provided between the distribution channel ( 4 ) or the liquid collection channel ( 7 ) and the reaction chamber ( 5 ). Such a constriction can e.g. B. can be achieved in that the microstructured fluid guide plate ( 1 ) is pressed against the intermediate plate ( 6 ) and the resulting microchannels throttle the flow of the fluid reactant. After the liquid has passed this constriction, it comes into contact with the gaseous reactant. This contact lasts as long as the fluid reactant runs down the microcapillary grooves of the fluid guide plate ( 1 ).

The gaseous reaction partner flows in an analogous manner via the gas guide line ( 8 ) and the branching bore ( 9 ) into the gas distribution channel ( 10 ). These holes can be closed on the outer wall of the housing by means of screws ( 14 ). The flow path of the gas is provided with narrow points ( 11 ) which are formed by the fluid guide plate ( 1 ) and an intermediate plate ( 6 ) and / or the cover plate ( 12 ).

Since the gas volume flow can exceed that of the liquid by several orders of magnitude, the reaction chamber ( 5 ) is designed with a correspondingly larger width than the microchannels on the fluid guide plate ( 1 ). This could have an unfavorable effect on the mass transfer in the gas phase. Therefore, the reaction chamber ( 5 ) is preferably equipped with ramps ( 13 ), which are arranged in particular offset from one another, which improve the mass transfer.

The liquid and gas are applied and distributed via horizontal Distribution channels and can be won from the same side or from the opposite Sides of the reactor. The liquid and gaseous components of the  Reaction mixtures can be used together or from one another via horizontal channels be discharged separately.

If working under pressure, the webs ( 18 ) serve to prevent the reaction plate 1 from bending. So pressures from 1 to 10 bar can be applied.

The reaction conditions (thread thickness, Concentration, temperature, pH values, flow rates).

The rear side of the fluid guide plate ( 1 ) can be cooled or heated, a liquid or gaseous heat transfer medium flowing in channels of 0.5 to 2 mm in width. The supply of the heat transfer medium takes place via a feed line ( 15 ) and bores ( 16 ) which branch off to the individual reaction plates ( 1 ). The heat transfer medium is removed via the heat transfer manifold ( 19 ), bores ( 20 ) and the outlet line ( 21 ). The interaction of the heat transfer channel ( 17 ) with the heat transfer channels ( 23 ) results in a good flow uniform distribution of the heat transfer medium, especially if the supply line ( 15 ) and the outlet line ( 21 ) are arranged diagonally in the intermediate plate ( 6 ), which is for the sake of clarity in Fig was. 2 not shown.

Temperature control of the reaction layer from the rear by liquid or gaseous media in a temperature range of 70 to 300 ° C, preferably from 160 to 200 ° C, possible.

Through internal parallelization, ie the connection of several individual reactors in one reaction block, the amount converted can be increased to the technically relevant range. A reactor is created by combining a base plate ( 22 ) with a fluid guide plate ( 1 ) and a cover plate ( 12 ). By adding an intermediate plate ( 6 ) and a further fluid guide plate ( 1 ), an additional reactor module is created (see FIG. 2). The liquid and gaseous reactants are each fed via a common feed line and distributed evenly among the individual reaction units.

The liquid or gaseous phases collected are also discharged via a common line. This creates a modular reaction system with a freely scalable number of intermediate plates ( 6 ) and fluid guide plates ( 1 ).

The system used according to the invention can be made of metal, glass, ceramic, Plastic, semiconductor materials or combinations thereof, preferably made of tantalum, graphite, ceramic or glass fiber reinforced Polytetrafluoroethylene (PTFE).

The use of microreaction technology in the method according to the invention enables many advantages in reaction management. So condition the little ones Dimensions high heat transfer coefficients for optimal Reaction management can be used. Furthermore, the generation is great specific phase interfaces an intensification of the mass exchange is achieved. Thin liquid films cause a more homogeneous concentration distribution as well small diffusion paths and thus an acceleration of the mass transport in the Liquid phase.

The process according to the invention allows the production of monochloroacetic acid with high selectivity. The dichloroacetic acid content can be Acetic acid conversions from <85% to <0.1%, preferably <0.05% (500 ppm) be lowered.  

Examples example 1

The reaction is carried out in a microreactor according to FIG. 2. An intermediate plate ( 6 ) was used. The base, cover and intermediate plates are made of graphite, the fluid guide plate ( 1 ) from tantalum.

dimensions

Fluid guide plate: length 30 cm, width 10 cm, thickness 2000 µm,
Capillary grooves: width 1500 µm, depth 300 µm,
Bars: width 150 µm

Acetic acid and 15 mol% acetyl chloride are continuously added together Microcapillary reactor supplied. There is a throughput of 45 g / min of liquid set. The temperature is adjusted to 180 ° C. Chlorine gas is at one Passed overpressure of 5 bar in direct current so that a share in the exhaust gas flow falls below 0.1% chlorine. The exhaust gas and the product will be led together from the microcapillary reactor into a separating tank, liquid and gaseous phase separated there. By reacting with water acid chlorides and anhydrides still present in the liquid crude acid implemented the free acids. The hydrogen chloride formed is removed. The The proportion of monochloroacetic acid in the liquid reaction product is about 85%. The unreacted acetic acid (11-12%) is at 150 mbar and 80 ° C distilled off. The proportion of dichloroacetic acid is less than 0.05%. Another Cleaning is therefore not necessary.

Example 2

The reaction is carried out in a microreactor according to FIG. 2. Three intermediate plates ( 6 ) were used, that is, a triple parallel arrangement. The base, cover and intermediate plates are made of graphite, the fluid guide plate ( 1 ) from tantalum.

dimensions

Fluid guide plate: length 30 cm, width 10 cm, thickness 2000 µm,
Capillary grooves: width 1500 µm, depth 300 µm,
Bars: width 150 µm

Acetic acid and 20 mol% acetyl chloride are continuously added together Microcapillary reactor supplied. A throughput of 100 (2.50 (!)) G / min Liquid adjusted. The temperature is adjusted to 170 ° C. Chlorine gas is at an excess pressure of 4 bar in counterflow. The exhaust gas and that Product are removed as described under 1), separated and worked up. The The proportion of monochloroacetic acid in the liquid reaction product is about 85%. The The proportion of dichloroacetic acid is less than 0.1%. A further cleaning is therefore not necessary.

Example 3

The reaction is carried out in a microreactor according to FIG. 2. An intermediate plate ( 6 ) was used. The base, cover and intermediate plates are made of graphite, the fluid guide plate ( 1 ) is made of tantalum.

dimensions

Fluid guide plate: length 30 cm, width 10 cm, thickness 2000 µm,
Capillary grooves: width 1500 µm, depth 300 µm,
Bars: width 150 µm

Acetic acid and 10 mol% acetyl chloride are continuously added together Microcapillary reactor supplied. There is a throughput of 50 g / min of liquid set. The temperature is adjusted to 190 ° C. Chlorine gas is at one Overpressure of 6 bar passed through in direct current. The exhaust gas and the product are discharged, separated and worked up as described under 1). The amount  Monochloroacetic acid on the liquid reaction product is about 90%. The amount dichloroacetic acid is less than 0.05%. Further cleaning is therefore not necessary.

Comparative example Processing of the crude acid I emerging from the last bubble column Processing of the crude acid I by melt crystallization

Before the raw acid I (composition approx. 85% monochloroacetic acid, approx. 3.5% Dichloroacetic acid, approx. 11% acetic acid, remainder: HCl, acetyl chloride etc.) Melt crystallization can be purified, the crude acid I still in Vacuum at about 80 ° C and about 150 mbar freed from low boilers by distillation. This gives the so-called crude acid II, which is then obtained by melt crystallization is cleaned.

The crude acid II with about 3.5% dichloroacetic acid is at about 85 ° C in one of the Crystallizer driven, cooled to 26 ° C within approx. 8 h, approx. 3 h tempered and then melted for about 4 hours. Here fall about 65% Crystallizate (finished monochloroacetic acid) with a dichloroacetic acid content of approx. 1% and about 35% mother liquor.

Processing of crude acid I by palladium-catalyzed hydrogen reduction

The crude acid I can be purified directly without prior removal of the low boilers become. For this, the crude acid I (composition 86.1% Monochloroacetic acid, 2.5% dichloroacetic acid and 11.1% acetic acid) at approx. 130 ° C and approx. 30 NL / h hydrogen at approx. 0.5 bar hydrogen overpressure several hydrogenation towers with fixed catalyst bed (1% Pd / C) passed (residence time a total of approx. 2 h). With fresh catalyst, a crude acid with a Composition of 85.6% monochloroacetic acid, 0% dichloroacetic acid and 14.3% acetic acid, a crude acid with a used catalyst Composition of 88.9% monochloroacetic acid, 0% dichloroacetic acid and  Obtained 11.8% acetic acid. The crude acid must then still be at approx. 80 ° C and approx. 150 mbar are freed from low boilers by distillation.

Claims (9)

1. A process for acetic acid chlorination by reacting acetic acid with chlorine gas at a temperature in the range <140 ° C, characterized in that the reaction is carried out in a microreactor. 2. The method according to claim 1, characterized in that the microreactor a microcapillary reactor, a micro bubble column reactor, or a Is microdroplet reactor. 3. The method according to claim 2, characterized in that the reactor Microcapillary reactor. 4. The method according to any one of the preceding claims, characterized characterized in that the acetic acid chlorination at a pressure in the range of 1 to 10 bar is carried out. 5. The method according to any one of the preceding claims, characterized characterized in that the dichloroacetic acid content with acetic acid conversion <85% <0.1%, in particular <0.05%. 6. The method according to any one of the preceding claims, characterized characterized that the reaction in a microreactor made of tantalum, graphite, Ceramic, glass fiber reinforced PTFE or combinations of these materials consists. 7. The method according to any one of the preceding claims, characterized characterized that the ratio of acetic acid and chlorine gas in the range of 0.8: 1 to 0.95: 1. 8. The method according to any one of the preceding claims, characterized characterized that several single reactors in one reaction block are connected in series.   9. The method according to any one of the preceding claims, characterized characterized in that the reaction conditions over optionally in Microreactor integrated sensors can be detected and controlled.