DE4103667A1 - Dry chlorination of PVC at specified temp. with irradiation - in 14-chamber fluid-bed reactor with specified residence time, back-mixing ratio and temp. for each chamber - Google Patents

Abstract

Process is for the dry chlorination of PVC in a multi-chamber fluid-bed reactor at 55-100 deg. C with a reaction gas contg. 0.18-0.66 kg Cl/kg gas and a radiation dose of 10-30 krad/hr. The PVC is chlorinated in a 14-chamber reactor with residence times as follows: (a) in chamber 1, 30-45 mins., in chambers 2, 3 and 4, residence times in the ratio 0.7:0.4:0.4 w.r.t. 1.0 in chamber 1, (b) in chambers 5-3, the same residence times as in chamber 4, (c) in chambers 9-13, a residence time which is in the ratio 1:0.3 w.r.t. that in chamber 1, and (d) in chamber 14 a residence time which is in the ratio 1:0.35 w.r.t. that in chamber 1; the degree of back-mixing established in the various chambers, as expressed by the ratio between the ratio of reaction mass to mass throughput and the ratio of the area of apertures to the area of chamber partitions in the height of the fluid bed, is 200-1200 in chambers 1-8 and 1200-2000 in chambers 9-13. USE/ADVANTAGE - The process is useful for the prodn. of PVC-C contg. 64-69 wt.% Cl; the invention provides a simplified continuous process for the prodn. of PVC-C with high thermal stability and a narrow range of Cl distribution, without sintering of the PVC-C particl

Description

The invention relates to a method for dry chlorine tion of polyvinyl chloride and is used for the production of chlorinated polyvinyl chloride (PVCC) containing chlorine between 64 and 69 wt .-% applied.

The dry chlorination process has due to its continuous operation in recent years he significantly gained importance. In dry chlorine tion is the PVC in solid form with chlorine gas, the ge diluted with inert gas if necessary, continuously in a fluidized bed or fluidized bed reactor under irradiation exposure to chlorine levels between 64 and 69 % By weight chlorinated. To be in continuous chlorination tion of vinyl chloride polymers a product quality with good performance properties to it range, the following requirements will be imposed on the procedure posed:

• long mean residence times of the reaction mixture,
• - adaptation of the chlorination parameters to the changing reactivity of the PVC during chlorination,
• - narrow residence time spectrum,
• - Underpressure of degradation processes,
• - Avoiding temperature peaks in the reaction product mass.

The realization of these requirements should be a chlo tured end product with high thermal stability and Guaranteed grain homogeneity, so that the Thermoplastic processing carried out easily can be.  

It was intended to compact reactors designed for To solve this problem.

However, fluidized bed reactors have the disadvantage that the PVC in the chlorination an extremely wide Ver time spectrum is subject. This will worsen the properties in terms of thermal stability and the chlorine value distribution of the chlorinated end products, and adversely affect the application technology Properties off.

To avoid this, in DE-AS 16 45 097 a Ver drive and a device for the chlorination of vinyl chloride polymers described, wherein the chlorination u. a. in several successive reaction zones, which correspond to several successive stages, is carried out. This corresponds to a reaction zone a reactor that ver with a stimulus and cooling system see, an irradiation device, an on direction for continuous feeding of the PVC part Chen, a device for introducing chlorine gas and Inert gas and to whirl up the particles and withdrawal facilities for the PVCC and unreacted Chlorine gas, hydrogen chloride formed and gege if necessary, the inert gas. The reactor chambers are as a paralleleleptide with circular, quadrangular or formed with a hexagonal base. It can too several reactors cascade and / or parallel to be arranged one another, the reactors through a product line are connected to each other. The after Part of this solution consists in the fact that He range of products required for good product properties Chlorine distribution a higher number of reactors to one Cascade must be interconnected. This high equipment costs caused enormous costs. also is the technological vote of each process stages very complicated and the effort to hassle  Handling the radiation sources (UV lamp) is very high. Furthermore, in DE-AS 16 45 097 a method before beaten, in which by adhering to the process parameters (Chlorine partial pressure, temperature) the PVCC in each process a chlorine limit value is assigned. Each one of them successive chlorination stages is intended to one constant chlorine limit of the PVCC. This Ver way of creating a process-friendly Chlorine value spectrum leads to economically unsatisfactory Chlorination times and mass flow rates. Already at one one-stage process control is a chlorination time of approx. 3 to 12 hours required. Through the process management inevitably arise long and different ver times of PVC / PVCC particles in the reactor after Partial effects on the thermal stability of the PVCC to have.

From DD-PS 1 48 188 is a reactor for carrying out radiation-chemical reactions known. This reactor is as an annular, hollow cylindrical multi-chamber vortex Bed reactor formed, all chambers a ge common channel for the supply of gas and one own common channel for the exhaust gas. The single ones Reactor chambers are the same in their base area. in the free interior and outer circumference are tubes for the Radiation sources arranged. To avoid a short Final flow from chamber to chamber were the separation walls so far over the fluidized bed surface, that a solids transport over this largely from closed is. To that with usual Mehrkammerwirbel Bed reactors occurring very wide range of residence narrow, the chamber openings are called overflow and Underflow trained. In practice, it turned out that this reactor has a number of disadvantages. So is in the strongly exothermic reaction, especially in  the first reactor chambers, which complicates heat dissipation, so that it often comes to sintering of the PVC powder. The additional removal of the heat of reaction by cooling Although installations showed positive effects on the temperature leadership in the chambers, but led to disturbances of the We Behverhaltens, which also sintered PVC pul verse entails. In addition, the cleaning of the Reak tor complicated by the cooling fixtures. Another after part is the long lingering of the reaction material in the Reactor chambers in which, for reasons of inertia the chlorinated PVC higher temperatures can be adjusted have to. This leads to a thermal damage of the PVCC and there appear hornifications of the powder grains, the lead to problems in further processing.

To exclude sintering of the PVCC grains is from DE-OS 23 24 908 known, the chlorination under Set of a conventional pigment, which has a low Affinity for chlorine, perform. This will achieved a uniform chlorination and the pigments have a sintering-preventing effect. As pigments carbon black and titanium oxide are proposed. This method is technically-economically very complicated, since the continuous Liche dosage of fine-grained pigments is complicated. In addition, the pigments cause additional costs and for some applications, pigmentation is uner wishes.

Furthermore, it has already been proposed (patent application WP C 08 F / 2 70 241 5), the openings in the chamber separation wall surfaces to be specially dimensioned and the reactor functionally interconnect the chambers so that the Chlo in three stages and min at least three reactor chambers are run through. In each Process stage become different reaction parameters  adjusted to the reaction conditions accordingly to adapt to the product characteristics. So becomes the one Setting the temperature of the installation additional cooling Installations proposed and in the first process stage the installation of distribution systems for feeding inert Gas recommended.

In practice, however, it turned out that this method has some disadvantages. The heat dissipation, especially in the first process zones, is in spite of the installation additional Cooling devices still too low, so that continue the Ge drive a thermal damage to the PVCC product part exists. When using PVC with high reactivity If fluctuations occur in the reaction temperature curve, the formation of sintering of the PVCC particles being able to lead. The maintenance of the reactor is in Follow the complicated geometric design very much consuming. The relatively long lingering of the reaction good in reactor chambers with high reaction temperature adversely affects the quality of the product.

The aim of the invention is the technical and economic Her reduce operating costs, to combine maintenance times and improve product quality.

The object of the invention is a method to provide dry chlorination of polyvinyl chloride, this is a simplified technological process allows running during the continuous Chlorination process no sintering of the PVCC particles occur and that leads to PVCC products with a tight chlorine distribution and high thermal stability.

According to the invention the object is achieved in that the polyvinyl chloride in a reactor with 14 reactor Chambers is chlorinated, taking in the individual chambers  the following residence time is set:

• - in the first chamber, 30 to 45 minutes,
• - in the second, third and fourth chamber a Residence time, which is related to the residence time in the first chamber such as 1: 0.7: 0.5: 0.4,
• - in the fifth, sixth, seventh and eighth Chamber the same residence time as in the fourth Chamber,
• - in the ninth, tenth, eleventh, twelfth and three tenth chamber each have a residence time, which is to the residence time in the first chamber such as 1: 0.3 behaves and
• - In the fourteenth chamber, a residence time, the to the residence time in the first chamber like 1: 0.35 behaves;

and in the reactor chambers a different Rückver mixture, expressed by the ratio of the quotient the reaction mass to mass throughput to the quotient the area of the openings to the chamber partition wall surface in Fluidized bed height, which is set in each of the Chambers one to eight 200 to 1200 and in each of the Kam between nine and thirteen is between 1200 and 2000.

The Vor required for carrying out the method direction consists of a multi-chamber fluidized bed reactor with fourteen chambers, either as a reactor out is formed or consists of two to three segments. The Radiation sources may vary depending on the geometry of the reactor (straight, L- or U-shape /) on one or both sides of the reac be arranged.

The adjustment of the chamber-specific residence times can be realized by various ways, for. B. by choosing the reactor chamber base areas at the same Fluidized bed height and / or by different vortex  layer heights in the individual reactor chambers when sliding chamber surface.

Just as important for the aspired success of the inventor According to the invention, compliance with the angege reverse remixing ratios. To set the Required remixing ratios are each Kam mennennwand provided with an opening, which as sub run trained and variably adjustable in size is.

With the procedure according to the invention could over surprisingly, the problem of heat dissipation during the Chlorination without complicated chamber installations satisfying be resolved, so that technological-related disorders no longer cause sintering of the PVC powder, especially in lead the first reactor chambers.

Unexpected is also the fact that in the known Process always occurred thermal damage on Product could be largely avoided. The after produced the chlorination process according to the invention Vinyl chloride polymers have a high thermal stability on and the otherwise observed cornification of the powder grains could be significantly reduced.

Essential for the success of the procedure is the number of Reactor chambers. From studies with reactors clotting The chamber number showed that the products obtained with continuous chlorination a very broad chlorine have distribution and for that reason for a lot number of applications were not suitable. In the result Complex attempts could solve this problem with a Chamber number of 14 for conventional types of PVC satisfying ge be solved. An increase in this number of chambers showed no further beneficial effects on the constriction of the  Chlorine distribution, however, increase the cost of the reac peat production significantly.

Compliance with the specified residence times for the PVC / PVCC in the individual chambers plays an important role Roll. If z. B. the residence time of 30 min in the Kam mer 1 and consequently also the residence time in the other Chambers below, so can a sufficient heat dissipation was not guaranteed in the strongly exothermic reaction be done and there are often sintering of the PVCC powder on, especially in the first chambers. At egg ner dwell more than 45 min in the chamber 1 and the from this derived residence times in the remaining chambers is already a thermal and radiation damage of the PVCC powder, resulting in a lower Ther stability.

It has also proved necessary that Ver the time of the product in the last reactor chamber is greater than in the previous chamber. If the Ver time of the product in this chamber, in which the Product discharge from the reactor is realized showed Subsequent reactions of the product in subsequent Pro zeßstufen.

Will depend on the above backmixing ratios gave way, especially in the first reactor chambers, so are at higher remix ratios often Inhomo in the Chlorierverlauf in individual chambers to be care and with smaller remixing ratios problems with the distribution of chlorine occur again. For the process according to the invention, it is immaterial whether the remixing ratios in the stated Be rich for all chambers are the same or different.

The invention will be described below by several examples to be purified.

For the experiments, a mass PVC with a K value of 60 and a porosity of 26% used.

The experiments are carried out in a fluidized bed reactor leads. The reactor has a width of 300 mm and is in divided into fourteen chambers. The length of each Reak Torkammern is given in the table below. The Fluidized bed height is set the same for all chambers. On both longitudinal sides of the reactor are tubes for blasting sources arranged such that a for all chambers uniform radiation field with a dose rate of 12 krd / h. The reactor walls and the chamber separation Walls are designed as tempering surfaces.

Chamber no. length in mm 1 500 2 350 3 250 4 200 5 200 6 200 7 200 8th 200 9 150 10 150 11 150 12 150 13 150 14 170

example 1

The reactor chambers have a fluidized bed height of 400 mm.

The reactor is continuously a PVC amount of 37 kg / h fed. The chlorine content in the reaction gas is 0.51 kg / kg set.  

The residence time, the remixing ratio and the Temperatures in the individual chambers are as follows set.

After a residence time of 3 hours and 1.5 minutes 40 kg / h of PVCC powder are discharged from the reactor. On the withdrawn product, a mean chlorine content of 0.657 kg / kg is determined. Furthermore, the grain-specific chlorine distribution width is determined. The procedure is as follows:
The PVCC powder is placed in a solvent mixture of defined density. The density of the mixture corresponds once to a chlorine content of the PVCC powder of 1% below the average chlorine content and in a second measurement, a chlorine content of 1% above the mean chlorine content of the PVCC powder. For both measurements, the sediment is determined quantitatively and the mass difference is given as the chlorine distribution width. In addition, the thermal stability according to Meixner (TGL 20427/02) and the grain disintegration during processing are determined on the PVCC powder. For this purpose, the chlorinated PVC with 0.02 kg / kg parts of a tribasic lead sulfate and 0.005 kg / kg calcium stearate is mixed to a dry blend and kneaded in a measuring kneader at a temperature of 190 ° C and 30 rev / min for 5 min.

Subsequently, the plasticized PVCC piece is inserted Thin section manufactured and light microscopically the part undigested PVCC powder grains determined. The individual values are in the angege after the examples Benen table listed. Further, over a period of time Room of 240 h the chlorination evaluated.

Example 2

The reactor chambers have a fluidized bed height of 600 mm up. The reactor is continuously a PVC men ge supplied from 37 kg / h. The chlorine content in the reaction Gas is set to 0.51 kg / kg. The residence time, the Remixing ratio and temperatures in the one individual chambers are set as follows.

After a residence time of 4 hours and 32.25 minutes who out of the reactor 42 kg PVCC powder per hour gen. On the withdrawn product is a medium chlorine content of 0.664 kg / kg. The further evaluation takes place analogous to Example 1. The values are in the after Bei play specified table listed.

Example 3

The reactor chambers have a fluidized bed height of 600 mm on. The reactor is continuously a PVC amount of Fed 42 kg / h. The chlorine content in the reaction gas is on 0.66 kg / kg. The residence time, the Rückver Mixing ratio and temperatures in each Kam are set as follows.

After a residence time of 4 hours and 2 minutes will be discharged 48 kg of PVCC powder per hour from the reactor. On the withdrawn product is a mean chlorine content of 0.668 kg / kg. The further evaluation of the example takes place analogously to Example 1. The values are in the listed in the examples.

Example 4

The reactor chambers have a fluidized bed height of 800 mm. The reactor is continuously a PVC men fed from 75 kg / h. The chlorine content in the reaction Gas is set to 0.51 kg / kg. The residence time, the Remixing ratio and temperatures in the one individual chambers are set as follows.

After a residence time of 3 hours and 1.5 minutes from the reactor 86 kg of PVCC powder per hour discharged. The withdrawn product becomes a medium Chlorine content of 0,662 kg / kg determined. The further off Valuation is analogous to Example 1. The values are in the table given in the examples leads.

Example 5

The reactor chambers have a fluidized bed height of 400 mm. The reactor is continuously a PVC men ge supplied from 32 kg / h. The chlorine content in the reaction gas is set to 0.51 kg / kg. The residence time, the Remixing ratio and temperatures in the one individual chambers are set as follows.

After a residence time of 3 hours and 31.75 minutes 37 kg of PVCC powder per hour are discharged from the reactor carried. On the withdrawn product is a medium chlorine content of 0.659 kg / kg. The further evaluation takes place analogously to Example 1. The values are in the listed in the examples.

Example 6

Under the same conditions as in Example 2, single with an increased radiation dose of 26 krad / h and a chlorine content in the reaction gas of 0.25 kg / kg Chlorinated PVC of the same type.

After a residence time of 4 hours and 32.25 minutes become from the reactor 40.5 kg of PVCC powder per hour carried. On the withdrawn product is a medium chlorine content of 0,661 kg / kg. The further evaluation takes place analogously to Example 1. The values are in the listed below.

On the prepared according to Examples 1 to 6 PVCC Pul the following property values were determined:

Comparative Example 1

Under the same conditions as in Example 1, single with a shortened by a factor of 0.74 residence time of the PVC / PVCC in the reactor chambers 1 to 14 is PVC the same type chlorinated. The reactor is hourly 50 kg PVC supplied.  

After a residence time of 2 hours and 14.3 minutes 58 kg of PVCC powder are discharged every hour, with a mean chlorine content of 0.648 kg / kg. The Be The course of the chlorination showed that the heat did not dissipate pro in the individual reactor chambers blemeless was dominated and the chlorination several times be interrupted by the formation of sintered bodies had to.

The results obtained are in the after comparison Examples listed in the table below.

Comparative Example 2

Under the same conditions as in Example 3, PVC chlorinated, only with the difference that in the Reactor chambers 1 to 13 a constant remixing ratio of 3000 is set.

The chlorination showed that in a single reaction temperature increases occurred several times and this only by intensive cooling of the corresponding Chamber could be intercepted. This went through the Total chlorination is less stable. At the withdrawn product a mean chlorine content of 0.666 kg / kg was determined. The determined values of thermostability, the chlorine distribution and the proportion of undistorted PVCC par are significantly worse than the product, which was chlorinated according to Example 3.

The results are in the according to the comparative examples listed in the table below.

Comparative Example 3

A PVC type used as in the other examples is chlorinated in an 8-chamber fluidized-bed reactor according to DD-PS 1 48 188 fol gender dimensions:
Outer diameter 600 mm, inner diameter 200 mm. The Do sisleistung is 12 kra / h.

The reactor chambers have a fluidized bed height of 400 mm. Of the 8 reactor chambers have the first 7 chambers an equal footprint. The last chamber has a reduced area of 50%. The reactor is hourly a PVC amount of 10 kg guided. The residence time, the remixing ratio and the temperature in each chamber will be like follows set.

After a residence time of 4 hours and 30 minutes who from the reactor out 12 kg of PVCC powder per hour carry. The chlorine content of the withdrawn product is 0,662 kg / kg. During the chlorination Temperaturer occurred Increases in individual chambers, the only by inten sive cooling of the corresponding chambers are intercepted could. It has also been observed that the PVCC powder for After-reaction tends, which in subsequent process steps Ver sintering resulted. The values for the thermo stability, chlorine distribution and grain digestion in the following table. The evaluation leaves recognize that by the 8-Kammerfahrweise he averaged property values have worsened and so on the performance characteristics of the PVCC powder considerably ge are reduced.  

At the Herge according to Comparative Examples 1 to 3 PVCC powders have the following properties values determined:

In summary, it can be estimated that after he inventive chlorination PVCC products with a very good thermal stability and the PVCC Powder has very good processing properties. except This showed that the chlorination process was essential has higher stability.

Claims (2)

Process for the dry chlorination of polyvinyl chloride in a multi-chamber fluidized bed reactor at temperatures of 55 ° C to 100 ° C and chlorine content in the reaction gas of 0.18 kg / kg to 0.66 kg / kg and a radiation dose between 10 krad / h and 30 krad / h, characterized as by that the polyvinyl chloride is chlorinated in a reactor with 14 reactor chambers, wherein in the individual chambers, the following residence time is set:

• in the first chamber 30 to 45 minutes, in the second, third and fourth chambers a residence time which corresponds to the residence time in the first chamber such as 1: 0.7: 0.5: 0.4,
• - the same residence time in the fifth, sixth, seventh and eighth chamber as in the fourth chamber,
• - in the ninth, tenth, eleventh, twelfth and tenth three chambers each have a residence time which corresponds to the residence time in the first chamber as 1: 0.3 and
• in the fourteenth chamber, a residence time which corresponds to the residence time in the first chamber, such as 1: 0.35;

and in the reactor chambers a different Rückver mixture, expressed by the ratio of the quotient the reaction mass to mass throughput to the quotient the area of the openings to the chamber partition wall surface in Fluidized bed height, which is set in each of the Chambers one to eight 200 to 1200 and in each of the Kam between nine and thirteen is between 1200 and 2000.