EP0103819B1 - Process for treating chlorination residues - Google Patents

Description

The invention relates to a process for the treatment of chlorination residues.

Particularly in the case of high-temperature chlorinations, such as those used for the production of carbon tetrachloride and / or perchlorethylene from C ₁ to C ₃ hydrocarbons or partially chlorinated hydrocarbons with 1 to 4 carbon atoms, mixtures are formed as undesirable residues which essentially contain perchlorinated compounds, especially hexachlorobenzene , as well as hexachloroethane and hexachlorobutadiene.

The disposal of these residues is problematic both for reasons of environmental protection and from a technical and economic point of view: hexachlorobenzene, the main component of these residues, is persistent and would, if released to the environment, accumulate through bioaccumulation. These residues are therefore often deposited in officially approved underground landfills. This type of disposal is unsatisfactory, however, because 5-20% by weight of the chlorine used is lost with these residues, depending on the course of the reaction in the chlorination process.

On the other hand, the disposal of these residues by incineration, if possible with the recovery of the chlorine content, presents considerable technical difficulties. It assumes that these residues are in a well-dosed and therefore flowable state. These residues are only melted at temperatures above approx. 230 ° C. They are extremely corrosive and moreover difficult to handle because of their high melting point. Attempts to bring these residues into solution are subject to narrow limits, since such a treatment only makes sense if the combustion product does not produce too large amounts of water in addition to the desired hydrogen chloride, which means that the hydrogen chloride is only obtained as relatively worthless hydrochloric acid. Furthermore, high proportions of carbon dioxide and carbon monoxide or even soot are undesirable as combustion products and would make a disposal process by incineration uneconomical.

These chlorination wastes are also poorly soluble. For example, a chlorination residue with a typical composition of about two thirds hexachlorobenzene and one quarter hexachlorobutadiene only dissolves in the solvent, which is suitable in terms of its chemical constitution, to only 7.5% by weight. Only about 1% by weight is soluble in 1,2-dichloroethane.

DE-B-1228232 proposes a process in which chlorinated hydrocarbon residues are first dissolved in a suitable chlorine-free or low-chlorine hydrocarbon and the mixture is then atomized in a heated incinerator. This process is also reported in DE-B-2540178. There it is pointed out that this and other combustion processes, e.g. recommend the use of heating oil to increase the flammability, are only suitable for liquid and therefore of course easy-to-dose products that do not contain any noteworthy solid particles and do not tend to cake and resinification.

The object of the invention was to find a process for the treatment of chlorination residues, the chlorination residues being intended to be brought into a flowable state at more moderate temperatures than would be required to melt these residues. Furthermore, it was an object of the invention to obtain preparations which can be burned in such a way that the concerns of environmental protection are safeguarded and at least the majority of the chlorine can be obtained at a reasonable cost as dry, for example hydrogen chloride suitable for oxychlorination.

It has now been found that tar-like chlorinated hydrocarbons, which are obtained as by-products in the pyrolysis of dichloroethane to give monomeric vinyl chloride and in the workup of the pyrolysis products or crude 1,2-dichloroethane from the direct and / or oxychlorination of ethylene, as solvents to appropriate treatment of chlorination residues. Hydrocarbons with a low aromatic content in the boiling range 160 to 300 ° C were also found as alternative solvents.

The invention _{relates to} a process for the preparation of chlorination _{residues of the empirical} formula C _S - _ö Cl _5.8.6.0, characterized in that these chlorination _residues are brought into solution at temperatures of 100 to 180 ° C in hydrocarbons containing chlorine and oxygen, which have a weight ratio of hydrogen : Chlorine 0.028 to 0.06: 1, an oxygen: carbon weight ratio of 0.0038 to 0.0089; 1 and have an atomic ratio of carbon: hydrogen of 1: 1.1 to 1.9 and / or in hydrocarbons which boil in the range from 160 to 380 ° C. at 0.1 MPa and an atomic ratio of carbon: hydrogen of 1 : 1.85 to 2.0, the Hengen ratios being chosen so that a liquid preparation is obtained which has a weight ratio of hydrogen: chlorine of 0.028 to 0.05 l.

The proportion of chlorination residues in the preparation is preferably 20 to 50% by weight.

genügt, wobei t die Temperatur in °C ist und x den Anteil an Chlorierungsrückständen, ausgedrückt in Gew.-%, bezogen auf das Gesamtgewicht der Zubereitung, bedeutet. Das Korrekturglied ± 5 gibt die Toleranzgrenze für die optimale Temperaturführung wieder.It is further preferred to adjust the temperature in the treatment process so that the relationship

is sufficient, where t is the temperature in ° C. and x is the proportion of chlorination residues, expressed in% by weight, based on the total weight of the preparation. The correction element ± 5 shows the tolerance limit for the optimal temperature control.

Furthermore, the ratio of hydrogen to chlorine in the preparation is preferably 0.028 to 0.04: 1.

The preparation is carried out in the technically reasonable range from 0.12 to 0.5 MPa abs. carried out. However, higher pressures can be used if desired.

• C_5-6Cl_5,8-6,0

darstellen lassen. Ein Wasserstoffanteil, der bei der erfindungsgemäßen Zubereitung in Rechnung zu stellen wäre, fehlt praktisch vollständig.The residues to be processed according to the invention are intrinsically undesirable by-products which arise in chlorination processes, in particular in high-temperature chlorinations, as described above. These are mixtures which consist of at least 95% by weight, but mostly practically 100% by weight, of perchlorinated products. The main components are hexachlorobenzene, hexachlorobutadiene and hexachloroethane. Furthermore, the chlorinated hydrocarbons per se desired in the chlorination process can also be present in the mixture to a small extent. Correspondingly, these chioration residues have a chemical composition which is a good approximation of the empirical formula

• C _5-6 Cl _5.8-6.0

show. A proportion of hydrogen that would have to be taken into account in the preparation according to the invention is practically completely absent.

• I C_3.0-3,5H_4,0-5,5Cl_2,6-3,6O_0,01-0,02
• sowie durch die Summenformel
• 11 C_2,0-2.5H_3,0-3,5Cl_2,4-3,0O_0,01-0.015

wiedergegeben werden. Entsprechend weisen diese Chlorierungsrückstände ein Gewichtsverhältnis von Wasserstoff : Chlor von 0,028 bis 0,06 : 1, ein Gewichtsverhältnis von Sauerstoff : Kohlenstoff von 0,0038 bis 0,0089 : 1 und ein Atomverhältnis von Kohlenstoff : Wasserstoff von 1 : 1,1 bis 1,9 auf.The hydrocarbons containing oxygen and chlorine which are used according to the invention for the treatment of the chlorination residues are obtained in the pyrolysis of dichloroethane or in the preparation of the pyrolysis products and in crude 1,2-dichloroethane from the direct and / or oxychlorination of ethylene. These are tar-like mixtures whose chemical composition is based on the empirical formula

• IC _3.0-3.5 H _4.0-5.5 Cl _2.6-3.6 O _0.01-0.02
• as well as by the empirical formula
• 11 C _2.0-2.5 H _3.0-3.5 Cl _2.4-3.0 O _0.01-0.015

are reproduced. Accordingly, these chlorination residues have a hydrogen: chlorine weight ratio of 0.028 to 0.06: 1, an oxygen: carbon weight ratio of 0.0038 to 0.0089: 1, and a carbon: hydrogen atomic ratio of 1: 1.1 to 1 , 9 on.

The tar-like compositions of formula 1 are obtained in the first processing stage of the pyrolysis products, in which the pyrolysis products are quenched after leaving the pyrolysis furnace. The lower-carbon compositions of the formula are obtained as distillation residues in the treatment stage in which, after the low boilers and the desired monomeric vinyl chloride have been separated off, the 1,2-dichloroethane which has not been converted in the pyrolysis is recovered together with crude 1,2-dichloroethane from the direct and / or oxychlorination of ethylene becomes.

The tar-like mixtures mentioned often still contain solids, such as coke and metal chlorides. It is therefore expedient to filter them, for example, using heated fine filters before use in accordance with the invention. As an alternative to this, the preparations which already contain the chlorination residues to be prepared can also be filtered before being metered into the incineration plant.

Examples of the alternative use of chlorinated hydrocarbons from the boiling range 160 to 380 ° C at 0.1 MPa abs., Which still have a carbon-hydrogen atom ratio of 1: 1.85 to 2.0, are kerosene and heavy and light heating oils, their aromatic content is below 10% by weight.

The processing agents mentioned above can be used individually or in a mixture. Since the tar-like processing agents are intrinsically undesirable by-products in the production of ionomer vinyl chloride and are best disposed of by burning anyway, it is preferred to use these tar-like mixtures as processing agents. It is possible within this preferred embodiment of the method, e.g. To balance the carbon / hydrogen / chlorine balance of the preparation, use smaller amounts of hydrocarbons from the boiling range 160 to 380 ° C.

The chlorination residues can be brought into solution in a manner known per se, for example in pressure vessels which are provided with retractors. In principle, it does not matter in which order the components are added. The residence time of the preparations should expediently be limited to approximately 10 hours, since otherwise the release of hydrogen chloride can lead to pressure increases in the containers which exceed the sensible range of approximately 0.5 MPa in absolute terms. In principle, you can work both continuously and discontinuously.

The chlorination residues prepared according to the invention can finally be fed to combustion devices known per se. A suitable combustion process is described for example according to DE-OS 28 27 761.

The process according to the invention succeeds in treating chlorination residues, in particular those which occur in high-temperature chlorination processes, in such a way that they can be burned in an environmentally friendly manner. Furthermore, the chlorine content present in the residues can at least for the most part be obtained as reusable dry hydrogen chloride, which can be fed to oxychlorination, for example. The process according to the invention is particularly valuable as a disposal process within the composite production technology used in the chemical industry, since in addition to the chlorination residues mentioned, the tars produced in the production of vinyl chloride can also be disposed of at the same time.

The invention will now be explained in more detail by means of examples and comparative examples:

example 1

• 2,0 Gew.-% Perchlorethylen
• 4,7 Gew.-% Hexachlorethan
• 23,9 Gew.-% Hexachlorbutadien
• 69,4 Gew.-% Hexachlorbenzol

In a high-temperature chlorination process for the production of perchlorethylene, 125 kg of residues of the following composition were obtained per hour.

• 2.0% by weight perchlorethylene
• 4.7% by weight hexachloroethane
• 23.9% by weight hexachlorobutadiene
• 69.4% by weight hexachlorobenzene

These chlorination residues fell under operating conditions in the residue concentrator at 270 ° C and 0.26 MPa abs. Pressure in the molten state. They contained 22.7% by weight of carbon and 77.3% by weight of chlorine. Every 8 hours, 1000 kg of these residues were emptied into a 4 m ³ transport wagon which was heated with 0.6 MPa steam and equipped with a propeller stirrer driven by compressed air. All parts in contact with the product were made of stainless steel.

• 28,58 Gew:-% Kohlenstoff
• 3,67 Gew.-% Wasserstoff
• 67,64 Gew.-% Chlor
• 0,11 Gew.-% Sauerstoff und
• 250 kg eines Kohlenwasserstoffs der Siedefraktion 180 bis 220° C mit einem Atomverhältnis Kohlenstoff: Wasserstoff = 1 : 1,95 versetzt. Die beiden letztgenannten Zusätze wiesen die Temperatur der umgebenden Atmosphäre auf, während die Gesamtzubereitung auf einer Temperatur von 150°C gehalten wurde. Am Ende des Abfüllvorganges befanden sich im Wagen 2233 kg eines Gesamtgemisches, dessen Anteil an Chlorierungsrückständen 43,8 Gew.-% betrug. Das Gewichtsverhältnis von Wasserstoff : Chlor betrug 0,035 : 1. Der Druck über dem Gemisch lag anfänglich bei etwa 1 050 MPa und stieg bis zur Beendigung des Abfüllvorganges auf ca. 0,22 MPa absolut an. Es wurde eine Lösung erhalten, wobei der Lösevorgang sich zeitlich im gleichen Rahmen abspielte, wie das Zusammenfließenlassen der Komponenten.

During the 20-minute filling process, the molten residues flowed into this car through a pipe with a throughput of 3000 kg / hour. The chlorination residues were in the filling tube with 3600 kg of a liquid, tar-like composition from a vinyl chloride production, which had the following analytical data:

• 28.58 wt: -% carbon
• 3.67% by weight of hydrogen
• 67.64 wt% chlorine
• 0.11% by weight of oxygen and
• 250 kg of a hydrocarbon of the boiling fraction 180 to 220 ° C with an atomic ratio of carbon: hydrogen = 1: 1.95. The latter two additives had the temperature of the surrounding atmosphere while the overall preparation was kept at a temperature of 150 ° C. At the end of the filling process there were 2233 kg of a total mixture in the car, the proportion of chlorination residues of which was 43.8% by weight. The weight ratio of hydrogen: chlorine was 0.035: 1. The pressure above the mixture was initially about 1050 MPa and rose to about 0.22 MPa in absolute terms until the filling process was completed. A solution was obtained, the dissolution process taking place in the same time frame as the confluence of the components.

The chlorination residues prepared in this way could then be fed into an incineration plant in a well dosed manner.

Example 2

• Die Beheizung des Transportwagens wurde mit 0,22 MPa abs. Dampf betrieben. Zu 1000 kg Chlorierungsrückständen der gemäß Beispiel 1 beschriebenen Zusammensetzung wurden mit einem Durchsatz von 3000 kg/Stunde 9000 kg eines flüssigen, aus einer Vinylchlorid-Produktion stammenden, teerartigen Gemisches der folgenden Zusammensetzung:
  • 24,49 Gew.-% Kohlenstoff
  • 2,86 Gew.-% Wasserstoff
  • 72,45 Gew.-% Chlor
  • 0,20 Gew.-% Sauerstoff
  
  gegeben. Nach ca. 20 Minuten wurde eine Lösung erhalten, deren Anteil an Chlorierungsrückständen 25 Gew.-% betrug. Die Temperatur der Zubereitung wurde auf 121°C gehalten. Das Gewichtsverhältnis von Wasserstoff: Chlor in der Zubereitung betrug 0,029 : 1. Der Druck über der Zubereitung stieg von anfänglich 1 bar absolut auf 0,3 MPa absolut an.

The procedure according to Example 1 was repeated with the following changes:

• The heating of the trolley was with 0.22 MPa abs. Steam operated. To 1000 kg of chlorination residues of the composition described in Example 1 were added at a throughput of 3000 kg / hour 9000 kg of a liquid, tar-like mixture from a vinyl chloride production of the following composition:
  • 24.49 wt% carbon
  • 2.86% by weight of hydrogen
  • 72.45 wt% chlorine
  • 0.20 wt% oxygen
  
  given. After about 20 minutes a solution was obtained, the proportion of chlorination residues being 25% by weight. The temperature of the preparation was kept at 121 ° C. The weight ratio of hydrogen: chlorine in the preparation was 0.029: 1. The pressure above the preparation rose from an initial 1 bar absolute to 0.3 MPa absolute.

An easily metered preparation was obtained which was fed into an incineration plant.

Comparative Example 1

10 g of chlorination residue of the composition described in Example 1 and 10 g of hydrocarbon, the atomic ratio of carbon: hydrogen of which was 1: 1.33, were introduced into a glass bomb tube. After melting, the temperature was raised to 200 ° C. The mixture did not dissolve.

Example 3

10 g - chlorination residues of the composition described according to Example 1 and 40 g of the tar-like mixture described in Example 1 originating from a vinyl chloride production were placed in a glass bomb tube (analogous to Comparative Example 1). After the bomb tube had melted, the temperature was raised to 110 ° C. There was a complete dissolution of the chlorination residues.

Claims (4)

1. Process for treating chlorination residues of the molecular formula C_5-6Cl_5.8-6, characterised in that these chlorination residues are dissolved at temperatures of from 100 to 180° C in hydrocarbons, containing chlorine and oxygen, that have a weight ratio of hydrogen:chlorine of from 0.028 to 0.06:1, a weight ratio of oxygen:carbon of from 0.0038 to 0.0089:1 and an atomic ratio of carbon:hydrogen of 1: from 1.1 to 1.9 and/or in hydrocarbons that have a boiling point in the range of from 160 to 380°C at 0.1 MPa (absolute pressure) and an atomic ratio of carbon:hydrogen of 1: from 1.85 to 2.0, the amounts being so chosen that a liquid preparation is obtained which has a weight ratio of hydrogen:chlorine of from 0.028 to 0.05:1.

2. Process according to claim 1, characterised in that the proportion of chlorination residues in the preparation is from 20 to 50 % by weight.

3. Process according to at least one of claims 1 and 2, characterised in that the weight ratio of hydrogen:chlorine in the preparation is from 0.028 to 0.04:1.

4. Process according to at least one of claims 1, 2 and 3, characterised in that the temperature during the treatment is so adjusted that-it satisfies the relationship

t being the temperature in °C and x being the proportion of chlorination residues, expressed in percent by weight, based on the total weight of the preparation.