DE2308665A1 - High temp. exothermic reaction - regulated using multiple recycling of reacted prod. in thermal exchange - Google Patents

Abstract

TheParent Patent describes an exothermic reaction process where heat from the reacted mixt. is transferred to the incoming raw mixt. in parallel flow along the entire length of the reactor; the raw mixt. may be diluted with reacted mixt. In the Patent of Addn, the reacted mixt. is recycled several times, with intermediate cooling, the quantity continuously removed being equal to the raw feed rate.

Description

"Process for carrying out exothermic reactions with a high starting temperature" (Addition to patent application P 20 16 323.9-41) Subject of the main patent. ... ... (patent application P 20 16 323.9-41) is a method for carrying out exothermic Reactions with a high start temperature, the fresh reaction mixture being replaced by heat exchange is brought to the required starting temperature with fully reacted mixture and Before the start of the reaction, preheating may take place, which is characterized by this is that the entire reacted mixture with fresh reaction mixture on the entire length of the reaction space with indirect heat exchange in cocurrent the reactor is passed, the fresh reaction mixture optionally with reacted mixture can be diluted.

Another subject of the main patent is a direct current reactor for Carrying out exothermic reactions with a high starting temperature, consisting of two pipes arranged concentrically to one another, which is characterized by that the supply of the reactants at the entrance of one of the two tubes and the outlet is at the other end of the same tube, this outlet in each case reconnected to the beginning of the other tube and the discharge for the reacted Mixture is arranged at the end of this other tube.

As described, this reaction system is suitable for reactions which have a starting temperature which is below that temperature which would occur with complete heat exchange of the product streams entering in parallel. It will be a sufficiently complete one. Sales at the end of the first heat exchanger pass and extensive temperature equalization between the product flows at the end of the Assuming a reactor.

In order to meet these conditions, depending on the type of reaction the temperature level, the throughput, the degree of dilution and catalytic Reactions vary the catalyst concentration. A dilution can be used here both by the excess of a reaction component as well as by cooled Finished product (see main patent. ... ... patent application P 20 16 323.9-41, example 5) to be effected, if necessary, the level of the occurring maximum temperature to limit the portable wet.

The present additional invention sets itself the task, including such more exothermic reactions using the principle of the direct current reactor where it seems disadvantageous to directly use the raw material mixture dilute. The reasons may be that the diluent is undesirable reacts or the reaction as a result of reduced residence time and reduced concentration the reactant runs insufficiently, so that otherwise an enlargement of the reactor. would be required.

In the manufacture of such products there is a risk that the thermal load limit is exceeded and the product becomes unusable. This load limit is to be determined empirically as a function for each reaction of temperature and time. In most cases, that turns out to be very short-term thermal loads are harmless with regard to a reduction in quality, as already in the main patent. ... ... (patent application P 20 16 323.9-41) on the basis of Figure 2 and in the D? -PS 1 255 653 detailed is explained. In order to keep the period of time for this high temperature load as short as possible, Proposed in the DT-PS, the heat exchange medium that the reaction components surrounds to be divided into separate, independently controllable zones or better not to be separated and to use an evaporating medium, its temperature through Pressure control is regulated. However, this means that only one corresponding Temperature can be controlled. Obviously, this is where the difficulty arises. on the one hand to have to preheat to the starting temperature, on the other hand after starting remove the heat of reaction from the reaction without exceeding the permissible temperature limit to exceed, and in addition to achieve an approximately quantitative conversion.

It has now been found that these strongly exothermic reactions are elegant can be performed if that is at the end of the first heat exchanger pass largely reacted mixture by means of a pump in parallel passage on the temperature-compensating Page turned over several times and in the meantime before the respective re-entry is cooled to a temperature T1 (Figure 1a). Thereby TE as well as the circulation ratio n matched to the system; n means the mass ratio of the throughput of the second (Q2) for throughput of the first heat exchange passage (Q1).

This measure provides the process claimed in the main patent an additional degree of freedom. Because the one on the temperature-compensating side led current must be controlled separately, it is also easily possible here, to use a foreign medium (Figure 1b).

The heat exchange area between the parallel flows is opposite the main patent if necessary enlarged that instead of the concentric arranged double pipe a heat exchanger with a larger effective surface, e.g. a tubular heat exchanger or a plate heat exchanger is used.

In order to avoid inefficiently high pressure losses, it is for the purpose of moderate, the ratio of the cross sections of the heat exchange passages according to the relation align the throughput quantities and their material constants.

In the following 7 examples, the reaction processes are shown as temperature and conversion functions shown over the reaction pathways (Figures 2 to 4). The examples are selected and summarized in such a way that the influences of the parameters are relative can compare to each other. Plate heat exchanger elements are sometimes used, which are easy to take apart. In this way it is possible to adjust the plate spacing to vary and to adapt to the respective reactions to be carried out. The frame housing is pressure-resistant. When cooling with the reaction product, the heat exchange surfaces need not to be designed for the absolute system pressure, as they are only the relatively small ones Record the pressure level of the circulation pump in accordance with the dynamic pressure loss have to.

On the other hand, two are arranged concentrically to one another Pressure-resistant pipes with unequal free cross-sections used (jacket pipe).

Since it is difficult to attach a large number of thermal sensors is, the data generated by the computer are used to display the curves reproduced. The results agreed with the experience gained experimentally match.

The curve examples show what high heat tones according to Examples 6 and 7: PEG 600 + 77 ethylene oxide PEG 4000 + approx. 2100 WE can be mastered and how extremely sensitive the reaction conditions can be adapted to the reactants. For the individual case it is possible to coordinate the variables: temperature, circulation ratio, throughput, catalyst concentration and the type of temperature-compensating medium so that the desired requirements of high throughput, high accumulation ratio and the maximum temperature to be limited are not only alternatively, but simultaneously taking into account the priorities are met.

According to operational experience, there is a very strong exotherm Reactions (Examples 4 to 7) that that reaction procedure is preferred, whose Sales take place as evenly as possible so that deviations from the rules are not exceeded the limited limit values (e.g. maximum temperature). The direct current principle has the major advantage over all previously known reaction procedures that it regulates in a balancing manner, since the heat transfer is directly proportional to the is the locally adjusting temperature difference.

This additional invention makes it possible, for example, to use phenol with unsaturated Hydrocarbons to alkylphenols at a higher rate than the main patent To implement temperature level faster or e.g. fatty alcohols at lower temperatures to alkoxylate. The production of polyalkylene glycols is particularly interesting, which are obtained in high molecular weight by connecting such reactor systems in series as desired will.

A major advantage of the process is that in the continuous Reaction, if necessary, the catalyst concentration to (10% of the discontinuous applied areas can be lowered. This effect is important for processing from polyglycols to polyurethane foams or as pharmaceutical goods. Not implemented Traces of alkylene oxides are generated continuously, e.g. by means of a thin-film evaporator removed.

The process for the production of products is of particular importance which should be produced continuously and a limited maximum temperature may not exceed during production, because at higher product temperatures By-products or decomposition products must be feared, which are difficult to analyze analytically detectable, but can be detrimental from an application point of view.

In the case of continuous production over several reaction stages intermediate products can optionally be deducted in a meaningful way. Each resulting The uses and reaction conditions can advantageously be calculated using a computer steer.

Example 1: A plate heat exchanger is used as the reactor; the Plates are 0.34 m wide and spaced on the side of the responsive Medium of 5 mm and on the temperature-compensating side of 10 mm. The length of the panels is 1000 mm individually. They are connected in series in pairs. In FIG. 2, running meters are given as the abscissa. The reactor becomes one-sided with 100 kg of a mixture of 2 moles of ethylene oxide and 1 mole of lauryl alcohol and one Catalyst content of 0.069% Na + charged in the form of NaOH. The functions of the Temperature on both sides of the heat exchanger and the conversion over the distance reproduced.

After leaving the 30 m long reaction section at 1330C, this opens up > 99% fully reacted product in a circuit which, according to scheme Figure 1 a, means Pump is led via a cooler to the parallel passage of the reactor. The inlet temperature is set to 100 ° C. The heat exchange reversal occurs after approx. 3 running meters. That The temperature maximum occurs at approx. 22 running meters at 14900.

By the end of the reaction section, conversion is practically complete and temperature compensation achieved. The system pressure is determined by regulating the product withdrawal held at 15 atm.

Example 2: For comparison, compared to Example 1 under otherwise the same conditions, the inlet temperature of the circulating liquid is lowered to 950C and the catalyst concentration increased to 0.086% Na +. It turns out as expected an almost identical conversion curve, but despite the higher temperature level the maximum temperature the same at 1490C '(Figure 2).

Example 3: In comparison to Examples 1 and 2, under otherwise the same conditions, the calibration temperature to 1000C and the catalyst content set to 0.081 /. There is a temperature increase of up to 18700.

Example 4: A pressure-resistant jacket pipe of 500 m is used as the reactor Length used with diversions. The clear diameter of the inner tube is 8 mm, the wall thickness 2 mm; the clear diameter of the outer tube is 25 mm. The inner tube is with 100 kg of a mixture of 1 mole of polyethylene glycol of the middle Molecular weight 600 and 20 moles of ethylene oxide in the presence of 0.115% Na + in the form of the polyelycolate charged at 200C. After passing through the inner tube, the Product is pumped in parallel flow through the outer pipe with a circulation ratio of 12: 1 and sensed to 1400C before each entry. The temperatures that are set and sales are shown in FIG.

Example 5: By way of comparison, example 4 is otherwise identical Conditions increased the inlet temperature in the jacket to 1600C and the catalyst concentration decreased to 0.057 Na +. The result is a very similar conversion curve to that in the example 4 (Figure 3) and despite the 20 ° C higher temperature level, the same maximum temperature of 207 ° C at about 270 running meters.

Example 6: A jacket pipe according to Example 4 is used. However the product is withdrawn as a finished product after leaving the inner tube.

The outer pipe is charged with condensate separately (FIG. 1b). It a polyglycol with an average molecular weight of 4000 is produced from such a product of average molecular weight 600 due to the addition of ethylene oxide. As Eatalysats serves 0.17 ffi Na + in the form of polyglycolate. The circulation ratio - here the amount Condensate per amount of product produced - is 10: 1. The heat exchange is condensate side operated above the saturation vapor pressure of water (approx. 34 at), so that none substantial evaporation occurs. The inlet temperature T1 is 1900C. at 410 running meters, the maximum temperature of 23800 is reached. Temperature and Sales profile are shown in FIG. After leaving the reactor, the Xonde set is through Relaxation cooled and fed back to the inlet by means of a pump. The at Approx. 1900C relaxed steam is made available for other purposes and the shortfall supplemented in the form of fresh condensate.

Example 7: Compared to Example 6, under otherwise identical conditions the catalyst content increased to 0.287% Na +, the inlet temperature T1 on the Condensate side lowered to 18000 and the circulation ratio increased to 20: 1. In this way a maximum temperature of 2070C is maintained and a very uniform conversion per running meter is achieved (FIG. 4).

Claims (3)

Patent claims: 1. Process for carrying out exothermic reactions with a high starting temperature according to patent. ... ... (patent application P 2v 16 323.9-41), the fresh reaction mixture by heat exchange with the fully reacted mixture to the required starting temperature is brought and, if necessary, preheating takes place before the start of the reaction, with the indicator that the entire reacted mixture with fresh reaction mixture over the entire length of the reaction chamber with indirect heat exchange in direct current is passed through the reactor, the fresh reaction mixture optionally can be diluted with fully reacted fish so that it can be used c hn e t that the exhausted mixture on the temperature-compensating heat exchanger side recirculated several times, cooled in the meantime and only the raw materials supplied The corresponding proportion of the quantity is withdrawn as an in-house product, 2. Same-atom reactor for carrying out exothermic reactions with a high starting temperature according to claim 2 of the main patent (patent application P 20 16 323.9-41), characterized in that that instead of the concentrically arranged tubes heat exchangers with relative larger surface can be used. 3. DC reactor according to claim 2, characterized in that the free cross-sections of the heat exchanger passages are different from one another.