NO145054B - PROCEDURE FOR THE PREPARATION OF CHLORED ESTATE DERIVATIVES - Google Patents

Description

The present invention generally relates to manufacturing

of chlorinated ethylene derivatives, especially vinyl chloride. Closely related to this is also the synthesis of chlorinated solvents of ethylene, chlorine and/or hydrogen chloride. Among such solvents are the highly chlorinated ethenes such as tetrachloroethene, which are produced by a method where the ethene and/or partially chlorinated ethanes undergo one or more steps of catalytic oxyhydrochlorination with hydrogen chloride and oxygen.

Vinyl chloride is produced by various processes

from ethylene, elemental chlorine and/or hydrogen chloride whereby in most cases a cracking step is used where ethylene dichloride is thermally cracked in the gas phase under pressure to vinyl chloride and the by-product hydrogen chloride. The latter is recovered through an oxyhydrochlorination step in which the hydrogen chloride is reacted with further ethylene and oxygen to produce dichloroethanes which in turn are recycled to the cracking step. In many pro-

sessions, a direct chlorination step is also used where ethylene and elemental chlorine are reacted in the liquid phase to produce dichloroethanes which are then cracked into vinyl chloride.

In all these known solvent and monomer processes, the relevant steps comprising direct chlorination, oxyhydrochlorination and/or cracking are not 100% selective for the formation of the desired chlorinated hydrocarbon end products,

and as a result of this, quite large amounts of unwanted chlorine-containing by-products are obtained in the form of complex mixtures which, with varying composition, contain from chloroform or ethyl chloride to trichloroethanes and trichloroethenes, tetrachloro-

ethanes, hexachloroethanes, hexachlorobutadiene etc, as well as aromatics

connections. These unwanted chlorine-containing by-products obviously cause economic and ecological waste problems.

It would therefore be desirable to have a process for the production of chlorinated derivatives of ethylene and chlorinated solvents of ethylene5 chlorine and/or hydrogen chloride where the generated heat energy is utilized in the process and the production of unwanted chlorinated by-products of hydrocarbons is essentially eliminated or does not occur expressed in the end result due to the reuse of the waste products in the process.

It has been shown that the above-mentioned disadvantages of the previously known processes can be avoided or substantially remedied through the present process whereby unwanted chlorinated hydrocarbons as by-products are recovered for new use in the form of hydrogen chloride which is essentially free of elemental chlorine and chlorinated hydrocarbons, and which hydrogen chloride is reintroduced to the process for the production of chlorinated ethylene derivatives. In addition, the internal heat energy of the raw by-products is recovered and used for the process by preheating the raw material flow and the intermediate product flow. The waste products are transferred to a stream of combustion gases which essentially only contain carbon oxides, water, inert gases and hydrogen chloride.

US patent no. 3,453,07 3 describes recovery of the halogen content in higher chlorinated hydrocarbons and chlorinated methanes by passing these over an acid-type catalyst at elevated temperatures together with water and oxygen. According to this patent, water is essential and it is stated that the amount of water supplied to the system must at least be a stoichiometric amount. Larger amounts of water can also be used, whereby amounts of water that exceed the stoichiometric amount moderate and serve as a diluent for the reaction. According to the patent, water is used because the necessary hydrogen must be obtained,

in addition to the hydrogen included in the hydrocarbons, for the transfer of chlorine to hydrogen chloride, while water, on the other hand, is not used in the present method.

The terms "chlorinated ethylene derivatives" and "ethylene chloride synthesis" mean the various processes and manufactured products whereby ethylene is reacted with elemental chlorine and/or hydrogen chloride in one or more steps to produce a compound of the type chloroethylene or chloroethane, such as vinyl chloride, vinylidene chloride, ethyl chloride, 1,1-dichloroethane, 1,2-dichloroethane, ,v trichloroethanes, trichloroethenes, tetrachloroethanes, perclpretene and .f , many others. Accordingly, the ethylene chloride synthesis includes any of the steps direct chlorination of ethylene or ethylene chloride derivative, oxyhydrochlorination of ethylene or ethylene chloride derivatives whereby ethylene or a chlorinated ethylene derivative is transferred to products with a higher chlorine content, as well as cracking (dehydrochlorination) or recrystallization of the chlorinated ethylene derivatives for the production of those with a higher chlorine content.

According to the present invention, there is

brought a process for the production of chlorinated ethylene derivatives, in particular vinyl chloride, comprising an oxyhydrochlorination step where chlorine-containing by-products are burned in a catalytic combustion reactor to form mainly hydrogen chloride which is returned to the oxychlorination step and made to react with oxygen and ethylene or a chlorinated „ . ethylene derivative, and this method is characterized by the fact that unwanted chlorinated ethylene derivatives and other by-products are separated from a stream in the process, this stream is injected into the body of a combustion catalyst where the catalyst has a surface area of of at least 50 m /g and contains 10-50 wt. 450°C whereby a mixr^ ;

ing of hot combustion gases is achieved as in the essence; • - - ri{i contains hydrogen chloride and is essentially free of both. elemental chlorine and chlorohydrocarbon material, and that the mixture ■ of gases is returned to the oxyhydrochlorination step.

The catalyst bed can either be solid or fluidized, i.e. fluidized with air. The catalyst layer is kept for- ;

step by step in the temperature range 35O-400°C.

In the catalytic layer, the waste materials are burned and transferred to a stream of combustion gases which essentially only contain carbon oxides, water, inert gases and, importantly, hydrogen chloride. The contact time for the waste materials with the catalytic layer is 10 -50 seconds. Cata- . ;: the lysator causes at the temperatures used a in the /_-■- <. 5 essentially complete combustion of chlorinated hydrocarbons • : in the waste stream, but limits the combustion so that the hydrogen atoms are re-bonded to the chlorine atoms in the hydrogen chloride. This enables the production of an eri gas stream which is practically free of elemental chlorine. Elemental chlorine is not desirable and the formation of elemental chlorine must be avoided as much* as possible. As complete a combustion as possible is also important as the presence of chlorinated hydrocarbons in the combustion gases also tends to increase by-product formation tinder the oxyhydrochlorination step. In preparing the catalysts which is used in the present method, CrfNO^)^ • 9^ 2° or CrCl^ 6H2O is dissolved in distilled water and the solution is added to the support, i.e. either A^O^. The wet-impregnated catalyst support is then dried in hot air and calcined for about 16 hours at a temperature of 540° C. The catalyst is then sieved through a sieve of 80 to 325 mesh and is ready for use in the process.

The waste products are gasified after they have entered the carbon catalyst bed and are then burned, exactly on it_

described, regulated manner. Nor direct injection of the liquid by-product stream, which is often viscous and tar-like and contains substances such as suspended coal. affect

the catalytic layer adversely, and also does not affect the fluidization in an unfavorable direction. Feeding of waste materials to the carbon catalyst layer can be easily achieved using standard equipment such as gear pumps, mechanical displacement pumps and the like. With

due to the temperatures used in the present process, as described above, there are many conventional materials that can be used for recording the carbon catalyst layer, which can withstand the corrosive environment.

The pressure used in the bed of combustion catalyst according to the present invention is not decisive. For example, the catalytic combustion reaction can be carried out at atmospheric pressure, particularly when the combustion gases are not fed directly to the oxyhydrochlorination step or reaction. When the gases are fed in in this way, they must be compressed to the same pressure as prevails in the oxyhydrochlorination reactor, as the oxyhydrochlorination reaction is normally carried out above atmospheric pressure. Consequently, it is desirable to keep the gases in the combustion layer at a pressure in the range of 0.17 - 1.05 MPa overpressure and

preferably in the range of 0.28 - 0.6° MPa overpressure. In most

in this case the pressure should be kept exactly slightly higher than the pressure in the oxyhydrochlorination step so that the combustion gases do not need to be pressurized. When carrying out experiments with regard to testing the present catalytic combustion reaction and using a simulated waste stream, it is of course acceptable and convenient to use atmospheric pressure as there is no need for pressure equipment.

Combustion catalysts used according to the present invention contain, as mentioned, 10-50% by weight, based on the total weight of the catalyst, Cr20^ and 90-50% by weight

Al^O^- The catalysts used must have a high surface area, namely of at least 50 m<2>/g. The most active catalysts of this type are those with a surface area of 175 - 600 m 2 /g. It has been found that the most useful combustion catalyst for the present process contains pores with an average size in the range of 30-60 Å in diameter. The preferred catalysts contain approx. 20% Cr2°3 and 80% Al^ O^ and has a surface area in the range 175 - 550 m /g.

The catalyst components used are common

in the trade. When using a fluidized bed, e.g.

especially A^O^ with the random, broad particle size distribution required for good fluidization, namely with some, possibly none, particles smaller than 20 µm or larger than approx. 200 pm and where the largest amount of the particles is in the range of 40 - 140 ym in mean diameter, common in

the trade. Very small particles, or the finest grain fractions, which have a mean diameter below approx. 20 jams should be avoided as they are too easily lost from the reactor. Likewise, large particles with a mean diameter greater than approx. 200 pm is avoided as these are too difficult to fluidize. It is obvious that according to the nature of the present process the catalytic material should not be brittle and should be resistant to the greatest extent possible.

The corrosive action in the catalytic combustion chamber or reactor is very mild in the present process. Common heat exchange coils made of common material and of common design are introduced into the carbon catalyst bed where they serve either as steam-producing tubes or as preheating tubes for raw material or intermediate product inputs to the process for the production of chlorinated ethylene derivatives. Even in such cases, in the production of chlorinated ethylene derivatives where only 3 - 8% of the original ethylene input is transferred to by-products, the annual savings in heat energy are considerable. Furthermore, as the present process can operate at low temperatures, combustion gases formed can be fed directly to the oxy-hydrochlorination reaction without intermediate cooling.

As pointed out earlier, the present invention can be carried out with the catalyst in fluidized form and with the use of air as a fluidizing agent or gas. When such a catalyst system is used, the air must be used in sufficient quantity and at a feed rate that not only completely fluidizes the catalytic bed, but is also sufficient for the supply of enough oxygen for the regulated combustion of hydrocarbons in the waste streams (the by-product streams). To guarantee complete combustion of the waste streams, at least 2 mol of oxygen (Og) must be supplied per moles of carbon (Cg) in the waste stream. However, to guarantee sufficient oxygen supply to

a sufficient amount of air is fed into the fluidized bed catalyst bed so that 2.5 to 10.0 moles of oxygen are present per

moles of carbon in the waste stream. When supply quantities are used that give more than approx. 10.0 mol of oxygen per moles of carbon in the waste stream, this results in reduced capacity and catalyst loss and, which is of greater importance, increases the risk of oxidation of the hydrogen chlorides to elemental chlorine, which must be avoided as previously mentioned. When the air supply rates deliver less than approx. 2.0 mol of oxygen per moles of carbon, only 80 - 85% of complete combustion is achieved. The best air supply rates are therefore such that 2.5 - 5.5 mol of oxygen are introduced per moles of carbon in the byproduct stream. The above feed rates can also be used when using a fixed catalyst bed, although in some cases a slight adjustment may be necessary to obtain the best yields.

The contact times for the waste substances or by-products and the catalyst in the reactor can vary considerably without the efficiency of the combustion being affected too much. When using a reactor with a fluidized bed, contact sides are operated for between 5 and 50 seconds, as one should

remember that only approx. half of the calculated contact time represents the real contact time between the gases and the layer. This is because for the rest of the time the gases are in the •

free spaces above the bed in the catalyst release and cyclone separation section of the reactor. Good results are achieved when the contact time is in the range of 10 - 50 seconds. When using a fixed catalyst bed, the best contact times are 5-25 seconds.

As previously mentioned, the most significant variables in the present catalytic combustion process are the reaction temperature and the catalyst's catalytic effect. When e.g. reaction temperature is less than J00°C, complete combustion cannot be achieved within acceptable contact times. If the reaction temperature exceeds 450°C, the combustion reaction is far too powerful and results in the oxidation of part of the hydrogen chloride to elemental chlorine, which is naturally unfortunate and should be avoided.

It has been shown that most metal chlorides and metal oxides have a certain catalytic effect when they are used separately in the combustion reaction, but to varying degrees. The difficulty with most of these compounds when they are used

is that they act as Deacon catalysts and consequently transfer or relocate at least part of the amount of chlorine in the waste products while forming new polychlorinated hydrocarbons, some of which are more resistant to oxidation.

When such metal catalysts are therefore used, the combustion gases usually contain considerable amounts of polychlorinated and cross-linked by-products. The catalyst used, on the other hand, exhibits the desired catalytic activity and the combustion gases thus produced contain very little and, under optimal conditions, practically no elemental chlorine and essentially no chlorinated hydrocarbons. Furthermore, the catalysts are cheap and robust against contamination with unburned carbon and the trace metal content from the by-products.

By-product streams that are separated in different fractionation steps in many syntheses for chlorinated ethylene contain up to 1-2% by weight of ferric chloride as an impurity.

In the carbon catalyst layer, iron chlorides and the like are oxidized to finely divided iron oxides and these are transported out of the carbon catalyst layer with the combustion gases and separated in the cyclones. The small amounts of iron oxides that remain in the catalyst layer have no visible harmful effect on the catalyst layer's effect. Nor did small amounts of iron oxides transported out of the combustion reactor and into the following oxyhydrochlorination step appear to affect the oxyhydrochlorination catalyst normally located on an aluminum support. The only adverse effect, if any, of the use of combustion gases produced by the present process,

in the oxyhydrochlorination step, there is a very small reduction in capacity due to increased loading of inert gases from the combustion gases in the oxyhydrochlorination feed.

When using the process according to the present invention in connection with a fluidized bed, the combustion reactor with the solid granulated catalyst is first introduced.

After the introduction of air or fluidization, the catalytic layer expands so that it fills the reactor's internal volume. The bed catalyst layer is fluidized in this way before introducing the waste by-product stream. This flow is introduced into the reactor at a level just above the bottom air intake. Preferably, the waste stream is supplied to the reactor through a water-cooled nozzle which prevents evaporation and/or charring of the substances before they come into contact with the catalyst in the bed.

The present invention shall be explained in more detail in

light of the following examples where all quantity ratios and percentages are on a weight basis where nothing else is mentioned.

EXAMPLE I

In this example, a catalyst of chromium chloride on aluminum oxide was produced. The prepared catalyst contained 20 weight percent Cr^O^ and 80 weight percent AlgO^ and had a surface area of 220 m/g. The catalyst was filled with a fluidized bed which was maintained at atmospheric pressure. A simulated mixture of chlorinated hydrocarbons was prepared and fed into the reactor at a rate (amount) of 1.5 ml/hour.. One also introduced

air in the reactor. in a quantity of 5»24 l/hour and in this way fluidized the catalytic layer. The supply rate for the mixture was adjusted so that a contact time between the mixture and the catalyst of 18 seconds was obtained. The oxygen/carbon ratio (in the form of Cg) was 2.85 and the hydrogen/chlorine ratio equal to 1.309. The temperature in the reactor was set at 0°C and later increased to 375°C. Data with regard to supplies and turnover can be found in the following table:

The carbon balance of the reaction was 95 - 121% and the chlorine balance in the form of hydrogen chloride equal to 85 - 109%•

The outgoing gases from the reactor top were analyzed in a chromatograph. The composition of exiting gases at 375°C was as follows:

This means that one achieved the essentials

100 fo conversion or recycling to hydrogen chloride. Exit gas stream was ready for use, as produced, in an oxyhydrochlorination step.

EXAMPLE II

The same procedure as in example I was followed,

with a catalyst consisting of 20% Cro0o and 80 fo Alo0o and

2 / ■ J -> surface area equal to 220 m /g. The reactor pressure was maintained at atmospheric pressure and the reaction temperature at 375°C. The same mixture of chlorinated hydrocarbons as in example I was used and the mixture was fed into the reactor in an amount of 2.0 ml/hour. Air was fed into the bottom of the reactor at a rate of 8.51 l/hour. The supply rate for the mixture was such that a contact time between the mixture and the catalyst equal to 11.2 seconds was obtained. The oxygen/carbon ratio (in the form of C^) was 3>2. Data with regard to supply and turnover can be found in the table:

The carbon balance for the reaction was 100.37% °g the chlorine balance, as hydrogen chloride, equal to 97»3% • The carbon conversion (in the form of Cg) was 80.69% °S the oxygen conversion equal to 30.74. %.

This example shows the sensitivity of the catalyst

with regard to the contact time. When the contact times were lowered from 18 seconds to 11.2 seconds, the conversion was reduced to 80.69 As can be seen from Table II, most of the unreacted compounds were cis- and trans-1,2-dichloroethene. This is because they are formed from 1,1,2-trichloroethane, which occurs in high concentration in the incoming stream.

EXAMPLE III

The procedure from example I is repeated, but a catalyst consisting of 20% Cro0o and 80% is used

AlgO^ with surface area 220 m/g. Reactor pressure was maintained

at atmospheric pressure and the reaction was carried out at 350°C« The mixture of chlorinated hydrocarbons was fed to the reactor in

a quantity of 1.5 ml/hour and the air introduced into the bottom of the reactor in a quantity of 5>24 l/hour. The mixture feed rate was such that a contact time of 18 seconds was achieved for the mixture/catalyst. Oxygen/carbon ratio (in the form of Cg)

was 2.71" and the hydrogen/chlorine ratio was 1.23. Data with regard to supply and turnover can be found in the following table. One should note that the simulated mixture used by

departs somewhat from the previous examples.

The carbon balance for the reaction was 32.63 - 94»45 f° and the chlorine balance in the form of hydrogen chloride 99»54 - 102.8%.

EXAMPLE IV

In this experiment, the procedure from example III was followed with the same catalyst and reactor pressure, but with a reaction temperature of 375°C. The supply rate for the mixture was 1.5 ml/hour and for air 5>24 l/hour. The supply rate for the mixture was such that a mixture/catalyst contact time of 18 seconds was obtained. The composition again deviates somewhat from the previous examples. The oxygen/carbon ratio (in the form of Cg) was 2.225) and the hydrogen/chlorine ratio equal to 1.475" Data with regard to supply and turnover can be found in the following table:

The carbon balance of the reaction was 95 > 9 f° °g the chlorine balance as hydrogen chloride equal to 100.38 f°> The oxygen conversion was 60.27 One should especially note that in both examples III and IV the conversion of all components in the simulated mixture or by-product stream was complete or equal to 100 fo.

EXAMPLE V

In this example, the catalyst contained 20 weight percent CrgO^ and 80 weight percent AlgO^ and was used in a fluidized bed reactor where the pressure was 0.52 MPa overpressure. A simulated mixture of chlorinated hydrocarbons was prepared, with the following composition:

The mixture was then fed into the reactor. Likewise, air was supplied to the reactor at a sufficient rate to fluidize the catalytic layer. The supply rate for the mixture was such that a mixture/catalyst contact time of 12 seconds was obtained. With this mixture, 4 tests were carried out at varying temperatures, with the following results:

o

With reference to table VI, the combustion gas samples were analyzed with a gas chromatograph and the results were used to calculate a total material balance. The carbon turnover was calculated through the ratio of CO and COg to the total amount of outgoing carbon. The hydrogen and chlorine turnovers were calculated by comparing the amounts of unreacted hydrocarbons with corresponding known amounts in the feed, based on the feed, the composition and the total amount of carbon out. As no Clg was found in the outgoing mixture, all chlorine was transferred to HC1 and all hydrogen was transferred to HC1 or HgO. Oxygen in the form of HgO was added in measured quantities as Og, CO and COg. Comparison between these totals and the amount that was calculated in the feed mixture with the measured amount of nitrogen produced an oxygen balance that enabled checking of the calculated data. The figures show that the oxygen balance was good.

EXAMPLE VI

In this example, several experiments were conducted using the same simulated mixture of chlorinated hydrocarbons used in Example V as well as the same catalyst and reaction conditions as in Example V with the exception that the contact time between the mixture and the catalyst was .18 seconds instead of ' 12 seconds. Seven experiments were carried out with varying temperatures, with the following results:

The oxygen balance was good, which indicates that the calculated data were acceptable.

The present invention thus provides a new and improved method for handling unwanted chlorinated by-products which are normally obtained from the production of cleared ethylene derivatives, for example the production of vinyl chloride. The catalytic oxidation according to the present invention also includes recovery of chlorine found in the waste products,

in the form of hydrogen chloride, which can then be used in the oxyhydrochlorination step in the production of chlorinated ethylene derivatives.

Hitherto, hydrogen chloride has been extracted from the unwanted chlorinated by-products by combustion using methane as fuel. However, this method is expensive and not reliable. Moreover, such a process is very impractical as the cost of recycling is more than five times higher than the market price of hydrogen chloride. , Present process<*>s. on the other hand, it is economical as it does not require additional fuel, which significantly reduces recycling costs. The present new method is also advantageous as the temperatures used make it possible to extract heat for the production of steam or for preheating supplied streams in the production of chlorinated ethylene derivatives. A further advantage of the present process is the fact that essentially no elemental or free chlorine is formed, which causes only negligible corrosion of the equipment. Additional advantages of the present invention will be apparent to those skilled in the art.

Claims (3)

1. Process for the production of chlorinated ethylene derivatives, in particular vinyl chloride, comprising an oxyhydrochlorination step where chlorine-containing by-products are burned in a catalytic combustion reactor to form mainly hydrogen chloride which is returned to the oxychlorination step and made to react with oxygen and ethylene or a chlorinated ethylene derivative, characterized by that unwanted chlorinated ethylene derivatives and other by-products are separated from a stream in the process, this stream is injected into a combustion catalyst bed where the catalyst has a surface area of at least 50 m 2/g and contains 10-50 wt% Cr203 and 90-50 wt% Al ^ O^ t air is blown into the layer together with the flow, the layer is kept at a temperature of 300-450°C whereby a mixture of hot combustion gases is obtained which essentially contains hydrogen chloride and is essentially free of both elemental chlorine and chlorohydrocarbon material, and that the mixture of gases is returned to the oxyhydrochlorination step. 2. Method according to claim 1, characterized in that the carbon catalyst layer is held at a pressure of 0.17-1.05 MPa overpressure. 3. Method according to claim 1, characterized in that the current is brought into contact with the combustion catalyst layer for a period of 10-50 seconds.