PROCESS FOR THE COMBINED PREPARATION OF CHLORINATED HYDROCARBONS AND A CARBONATE OF AN ALKALI METAL

Abstract: In the combined production of chlorinated hydrocarbons by oxychlorination of olefins in liquid phase and a carbonate of an alkali metal by carbonation of an alkali metal chloride use is made of an aliphatic amine as a chlor-transferring agent in recycle operation. The amine should have hyd­ rogen-free carbon atoms in the α-position and exhibit a specified low decomposition rate. The preferred amine is t-butyl amine.

Description: Process for the combined preparation of chlorinated hrdr0ddrbons and a carbonate of an alkali metal The invention relates to both the preparation of chlorinated hydrocarbons and the preparation of a carbonate of an alkali metal, the two preparations being intercoupled as it were, use being made in either case of one and the same auxiliary material. The term carbonate as used herein refers to both carbonate and bicarbonate. A process for such a combined preparation is disclosed in US 4 256 719. This known process comprises the process steps mentioned in the introductory part of claim 1, the auxiliary material generally being an aliphatic amine having a boiling point below about 100 C. Such a combined preparation is also reported in Research Disclosure of September 1980, p. 365. It has been found that in actual practice the use of the amines named in said disclosures, particularly the trimethylamine (ism) resxliaended therein, is subject to rather undesirable limitations. These limitations are mainly bound up with the stability of these amines under the conditions of the reaction. The object of combining the chlorination process (step a) with the soda process (step b) is to make it possible for the amine auxiliary material to keep serving its purpose in the two processes without any aE- preciable loss. Loss of amines as a result of deccuasition, however, cannot altogether be avoided, so that also when use is made of IMk the oxidative regeneration of the chlorination liquid must be carried out at a considerably lower temperature (about 500C) than the chlorination (about 100 C). Of course, also for the stripping of IMA the temperature must not be chosen too high. Nevertheless, even at relatively low thermal levels loss of TMA as a result of decomposition cannot altogether be prevented. Apart from this inevitable loss the maintenance of various temperature levels in the chlorination cycle is necessarily attended with the energy wasting procedure of repeated cooling and heating. It has now been found that for the purpose envisaged use can be made of a considerably stabler type of amines. The invention consists in that in the afore-mentioned known process use is made of an amine having exclusively hydrogen-free carbon atoms in the apposition and a k lower than 0,01 mm a The symbol k stands for the first order reaction rate constant in a alkalinity under standard conditions and is a measure of the rate of amine decomposition. Amines of this type appear to be sufficiently stable to be safely exposed to higher temperatures than permitted with the previously known amines without being subject to decomposition. This has the great advantage that the regeneration of the chlorinating liquid also may be carried out at elevated temperature, including the stripping of the amine recovered. As a result, the entire chlorination cycle can, if desired, be kept at the same temperature level. Examples of suitable a-hydrogen-free amines include 2rnino-2-methyl propane (t-butylamine), di-t-butylamine, 2-amino-2Hmethyl propanol 1, and 2,2,6,6-tetramethyl piperidine. Preference is given to t-butylamine (IBA). In view of their considerably better thermal stability, hcnxrzer, there is no need for the a-H-free amines to have a boiling point below 100 C, provided that there is sufficient evaporation in the stripping section. The favourable effect of a-H-free carbon atoms on the stability of the amines will be apparent, int.al., from the following table, in which is is a measure of the rate of amine decomposition under standard conditions.* EMI3.1 <tb> <SEP> amine <SEP> ka <SEP> <SEP> tempera- <SEP> number <SEP> <tb> <SEP> (min-1) <SEP> ture <SEP> C <SEP> of <SEP> &alpha; ;-H's <SEP> <tb> trimethylamine <SEP> 0,135 <SEP> 80 <SEP> 9 <tb> diethylamine <SEP> 0,29 <SEP> 83 <SEP> 4 <tb> diisopropylamine <SEP> 0,042 <SEP> 80 <SEP> 2 <tb> t-butyiarnine <SEP> 0,0007 <SEP> 90 <SEP> 0 <tb> 2 <SEP> amino <SEP> 2 <SEP> methyl <SEP> propanol <SEP> 1 <SEP> 0,0035 <SEP> 88 <SEP> O <SEP> <tb> 2,2,6,6-tetramethyl <SEP> piperidine <SEP> 0,0013 <SEP> 84 <SEP> 0 <tb> * Test solution : 25 ml adiponitrile 0,65 moles/kg CuCl2.2 ag. 2,2 moles/kg amine HC1 0,275 moles/kg OCI 0,5 moles/kg amine 0,225 moles/kg 12 Heat the solution to 800-900C, add amine, maintain at temperature and determine change in alkalinity (by amine decomposition) with time by potentianetric analysis and calculate from it the first order reaction rate constant ka. The chlorinating liquid is a substantially non-aqueous system containing a suitable organic solvent. Various solvents may be used, as is also mentioned in US 4 256 719. With the use of the present a-H-free amines the choice of the solvent is partly influenced by the higher temperature that can be employed. As examples of suitable solvents may be mentioned N-methyl pyrrolidone, tetramethylene sulphone, 3-methyl tetramethylene sulphone, adiponitrile and pyrrolidone-2. The use of the a-H-free amine TBA leads to good results, especially when the solvent employed is N-methyl pyrrolidone. The process of the invention will be further described in the following example. The example gives a stepwise illustration of the preparation by the process of the invention of EDC from ethylene and of soda from sodium chloride. For the combined preparation envisaged the various process steps are, evidently, intercoupled in actual practice by circulation of process flows. Example The experiments for regeneration (step c) and chlorination (step a) were successively carried out in the same reactor. The preparation of carbonate (step b) was conducted in a separate experimental set-up. 1. Regeneration/chlorination - Preparation of chlorinating liquid and oxidation In a 2-1 glass reactor fitted with a stirrer a mixture was pre pared from 99 g of cuprous chloride, 219 g of t-butylamine hydro chloride (TBA.HCl), 63,5 g of iodine, 20 g of water and 598,5 g of 1 methyl 2-pyrrolidone ANMP). The mixture was heated to 100 C, after which through an inlet tube to below the level of the liquid air was introduced at a rate of 54 standard litres per hour (2,4 moles/h), a pressure of 600 kPa being maintained in the reactor. The speed of the stirrer had been so chosen that the reaction speed decreased after about 115 minutes, at which moment 700 mmoles of TB-A had formed and the air feed was stopped. - TBA stripping The TBA formed was partly stripped in vacuo (4-7 kPa) with a nitrogen stream at a rate of about 150 standard litres per hour. After about 60 minutes half of the TBA formed wats stripped and for the greater part condensed at -300C. The off-gas from the condenser was washed free of TBA with dilute HC1 in an absorber. The TBA (about 350 mmoles) left in the contents of the reactor was subsequently neutralized with 37%-hydrochloric acid. - Ethylene chlorination In the same reactor chlorination was conducted at 1000C and 300 kPa by introducing ethylene through an inlet tube extending to below the level of the liquid. After about 60 minutes the reaction was stopped, at which moment about 350 mmoles of 1,2-dichloro ethane (etc) had formed. - EDC stripping Next, the EDC formed was stripped with nitrogen (about 150 stank dard litres per hour) in vacuo at 1OQOC and renxnnxd from the stripping gas by condensation at -300C. - Restoring of reactor contents Finally, the contents of the reactor were restored to their original specification by adding about 350 moles of TBA.HCl and sane NMP which had escaped during stripping. The afore-described cycle was re-started with oxidation and was carried out ten times in all to lead to practically identical results. 2. Preparation of carbonate A 250-ml flask was charged with an aqueous solution saturated at 200C and made up of 1,27 g of NaHCO3, 29,7 g of Naci and 31,8 g of 'IBA.HC1 in 120 g of water. CD2 was introduced at a rate of 87 mmoles/h through an inlet tube extending to below the level of the liquid. A gas mixture of nitrogen (1170 mmoles/h) and TBA (61 mmoles/h) was introduced through a second inlet tube. In the off-gas the amount of TBA which had not been taken up was measured by absorption in an acid solution which was kept at a con stant pH by titration with acid. After 93,5 minutes the experiment was stopped, at which moment 84 moles of TBA had been taken up by the solution and a crystal sed- ment had formed. The crystal mass was filtered off and dried to the air to 7,7 g containing 81,9% by weight of NaHCO3. The crystals were washed once with water to free them of inyBlrities introduced by the adhering mother liquor and dried at 100 C to yield 4,4 g of crystals containing 95% by weight of sodium carbonate and bicarbonate. To the remaining mother liquor were added 84 mmoles of NaC1 and 84 innoles of water. The salt crystals slowly dissolved with stirring at room temperature and a floating crystal was formed. After 2 hours practically all NaCl had dissolved. The crystals formed were filtered off and dried to the air to yield 11,2 g con- taining 78,5 % by weight of TBA.HC1. Again a single washing with water and drying at 1000C yielded 7,5 g of crystals containing 96% TBA.HC1. The residual mother liquor had the same composition as the solution with which the experiment was started.

Claims: CLAIMS 1. A process for the combined preparation of chlorinated hydrocarbons and a carbonate of an alkali metal comprising the steps of a. chlorinating an olefinic hydrocarbon with a substantially nonr aqueous chlorinating liquid containing iodine and cupric and/or ferric chloride; b. converting an alkali metal chloride by carbonatation into carbo nate with the aid of an aliphatic amine as alkaline material, with formation of the amine hydrochloride as byproduct; c. regenerating the chlorinating liquid used in step a. with the amine hydrochloride formed in step b. as chlorine source in the presence of oxygen or an oxygen-containing gas, and returning the amine recovered to step b.; ; characterized in that use is made of an amine having exclusively hydrogen-free carbon atans in the cr-2?osition and a kar as defined herein, lower than 0,01 min-l 2. A process according to claim 1, characterized in that use is made of t-butylamine. 3. A process according to claim 2, characterized in that the chlorinat ing liquid substantially contains as solvent N nettyl pyrrolidone. 4. A process according to claim 1, characterized in that the steps a. and b. are carried out at practically the same temperature level. 5. A process according to claim 1, characterized in that it is used for the combined preparation of 1,2-dichloroethane and soda from ethylene and sodium chloride.

Inventors: ALBERS, JAN
Applicants: AKZO N.V.
Application year: 1983
Main classification: C07C17
IPC codes: C07C19, C07C67, C07C17, C01D7