GB2120225A - Chlorine production - Google Patents

Abstract

A method for the preparation of chlorine which comprises contacting a gaseous mixture containing hydrogen chloride and oxygen at elevated temperature with a catalyst comprising a copper salt supported on titania.

Description

SPECIFICATION Catalytic process This invention relates to a catalytic process and more particularly to a process for the catalytic conversion of hydrogen chloride to chlorine.

The Deacon process in which chlorine is produced by the catalytic oxidation of hydrogen chloride is well known. In the process, a gaseous mixture containing hydrogen chloride and oxygen is passed over a catalyst at an elevated temperature. Catalysts that have been proposed include heavy metal salts, especially cupric chloride, optionally in admixture with other salts such as potassium and lanthanum chlorides, on an inert support such as alumina, silica gel or pumice.

It has now been found that this reaction is catalysed very effectively by a copper salt supported on titania.

In particular it has been found that high conversions of hydrogen chloride to chloride are obtained at lower temperatures than is the case when the catalyst comprises a copper salt supported on a conventional carrier such as silica gel.

Thus, according to the invention, there is provided a method for the preparation of chlorine which comprises contacting a gaseous mixture containing hydrogen chloride and oxygen at elevated temperature with a catalyst comprising a copper salt supported on titania.

The catalyst may be prepared by impregnating the titania with an aqueous or non-aqueous solution of a copper salt followed by removal of the solvent. Particularly useful results in terms of low temperature activity have been obtained using catalysts in which a copper salt is supported on freshly precipitated titania.

The preferred copper salt is a chloride or oxychloride which may be deposited on the titania initially or may be formed in situ by depositing another copper compound on the titania and subsequently converting it to the chloride or oxychloride by treatment with hydrogen chloride.

The copper content of the catalyst is suitably within the range of from 1 to 25% by weight based on the total catalyst including carrier.

The conversion of hydrogen chloride to chlorine is further enhanced if the catalyst contains a rare earth metal salt, such as lanthanum chloride, and an alkali metal salt, such as potassium chloride, in addition to the copper salt. The atomic ratio of the rare earth metal to copper is suitably in the range 1:10 to 10:1 and the atomic ratio of alkali metal to copper is suitably in the same range. Excellent conversions may also be obtained using catalysts containing both a copper and a manganese salt with further improvements when a rare earth metal salt and an alkali metal salt are also present.

The catalyst may be employed in fixed, moving orfluidised beds of the appropriate size.

The oxygen employed in the process of the invention may be introduced in the form of pure oxygen or as an oxygen-containing gas such as air. The hydrogen chloride/oxygen molar ratio is suitably in the range 6:1 to 2.1, preferably about 4:1.

The most suitable reaction temperature depends upon the particular catalyst being employed but it is usually within the range 300-500"C, especially 350-450"C. Su ita ble pressures are atmospheric or slightly higher.

The invention is illustrated but not limited by the following Examples.

Example 1 A catalyst was prepared from freshly precipitated titania with an atomic ratio of Cu: K: La Ti of 1:1:1:10 using the following method: 4.33 g of La(NO3)2.7H2O were dissolved in 100 ml of water and mixed with 113 ml of a 15% aqueous solution of TiCI4. 65 ml of 25% ammonium hydroxide solution were added to give a white precipitate which was filtered off and washed with distilled water. A solution was made up containing 2.416 g of Cu(NO3)23H2O and 1.011 g of KNO3 dissolved in 30 ml of water and this was mixed with the freshly separated precipitate.After allowing to stand overnight, the excess liquid was evaporated off and the material dried at 120"C. Overnight calcination at 500"C gave a dark green granular material which was ground to 30-60 mesh size and packed into a 6.3 mm O.D. stainless steel tube to give a 10 cm bed length. This reactor tube was surrounded by a controlled tube furnace and the catalyst was chlorinated for 1 hour at 400"C in a stream of HCI. Deacon activity was then assessed by passing a mixture of air (5 ml)min) and HCI (4 ml/min) over the catalyst held at a fixed temperature in the range 200-550"C and determining the concentration of chlorine in the exit gas stream.The exit gas was analysed by passing into a solution of (excess) potassium iodide together with an appropriate amount of 0.1 N sodium thiosulphate and "Thyodene" indicator and timing the period required to reach the blue end point. The results are summarised in Table 1. For comparative purposes, similar combinations of copper, potassium and lanthanum were prepared supported on silica gel and fumed silica.

The silica gel supported catalyst was prepared by the method given in US Patent No. 3,260,678. A solution was made up containing 6.707 g CuCl2.2H2O, 6.684 g LaCl3.7H2O and 2.859 g KCI in 54 ml of distilled water and poured onto 50 g of silica gel (4-6 mesh, "Gallenkamp"). After standing overnight, excess water was evaporated on a hot plate and the material was dried at 120"C. Prior to testing, the catalyst was pretreated in air for 3 hours at 250 C.

The fumed silica supported catalyst was prepared by a non-aqueous solvent technique. 200 g of Cu Cl were shaken vigorously with 470 ml acetonitrile. 220 ml of the resulting solution were mixed with 20.4 g fumed silica (CABOSIL 5M), a further 90 ml acetonitrile added and the mixture was allowed to stand overnight. Excess solvent was removed in a rotary evaporator and the material was dried for 6 hrs at 1 000C in a vacuum oven. A solution of 6.23 g KCI and 5.10 LaCI3 in 160 ml formic acid was then mixed in and after standing overnight the material was dried again as before to give a pale brown material.

From the experimental results it may be seen that the titania based catalyst gave improved low temperature conversion of HCI at an equivalent copper loading.

Example 2 The effect of adding potassium, lanthanum and manganese to the catalyst is illustrated in Table 2.

Catalysts were prepared as in Example 1 but adding 4.2 ml of a 50% solution of Mn(NO3)2.6H2O to the freshly precipitated titania for Cu:K:La:Mn-Ti(1 :1:1:1:10) and then omitting the potassium and lanthanum components to give Cu:Mn:Ti(1 :1:10). The same testing procedure was adopted as in Example 1, the results showing that while TABLE 1 % of HCI feed converted Temperature Catalyst 250 300 350 400 450 500 Cu:K:La:Ti 1:1:1:10(6% Cu) 0.8 3.2 23.8 51.6 36.0 35.0 Cu:K:La:Si Silica Gel (8%Cu) - 2.7 17.0 35.5 37.9 35.1 Cu:K:La:Si Fumed silica (23% Cu) - - 20.5 39.5 46.7 34.8 TABLE 2 2 % of HCI feed converted Temperature "C Catalyst 300 325 350 400 425 450 Cu:Mn:Ti not 1:1:10(7% Cu) 1.0 rec 5.8 25.0 32.7 49.3 Cu:K:La::Ti 1:1:1:10 (6% Cu) 3.2 11.9 23.8 51.6 39.8 36 Cu:K:La:Mn:Ti 1:1:1:1:10(5%Cu) 3.1 15.9 34.3 51.7 61.9 45.6 the presence of potassium and lanthanum in Cu:K:La:Ti gives superior low temperature performance to the Cu:Mn:Ti system, the presence of all three components in Cu:K:La:Mn:Ti (1:1:1:10) gives an additional improvement over a wider range of temperature.

Example 3 The performance of some titania supported catalysts prepared by other methods is summarised in Table 3. Fumed titania supported materials were prepared from Titanoxid P.25 (Degussa) by impregnating (separately) with solutions of KCI, LaCl3.7H2O and CuCI in non-aqueous solvents and removing excess solvent with a rotary evaporator and drying under vacuum at 80"C. Catalyst (a) was prepared by impregnating 18.7 g of fumed titania with 3.16 g KCI in 21 ml formic acid, 0.44 g of LaCl3.7H2O in 5 ml formic acid and 0.43 g CuCI in 50 ml acetonitrile. In catalyst (b), 18.82 g titania was impregnated with 24.1 g CuCI, 6.65 g KCI and 8.2 g LaCl3.7H2O. Catalyst (c) was prepared from a Tilcom E (Tioxide) support by the same method, impregnating 50 g of titania with 1.74 g of CuCI in 35 ml acetonitrile and 0.815 g LaCl3.7H2O and 0.23 g KCI in 35 ml formic acid.

TABLE 3 % of HCI feed converted Temperature C Catalyst 300 350 375 400 425 450 Cu:K:La (a) on Fumed Titania (1.2% Cu) 0.9 2.6 6.0 6.8 9.0 14.2 Cu:K:La (b) on Fumed Titania (23% Cu) 2.8 48.6 51.0 43.2 43.3 37.3 Cu:K:La (c) on Tilcom E (5% Cu) 1.3 17.5 46.4 50.2 58.1 51.3 Cu:K:La:Ti (d) (1:1:1:10)(6%Cu) 3.2 23.8 47.8 51.6 39.8 36.0

Claims (7)

1. A method for the preparation of chlorine which comprises contacting a gaseous mixture containing hydrogen chloride and oxygen at elevated temperature with a catalyst comprising a copper salt supported on titania.

2. A method according to Claim 1 wherein the copper salt is a chloride or oxychloride.

3. A method according to Claim 1 or Claim 2 wherein the catalyst additionally contains a rare earth metal salt and an alkali metal salt.

4. A method according to any one of the preceding claims wherein the catalyst additionally contains a manganese salt.

5. A method according to any one of the preceding claims wherein the temperature is within the range 300-500"C.

6. A method according to Claim 5 wherein the temperature is within the range 350-450"C.

7. A method according to Claim 1 substantially as hereinbefore described with reference to the foregoing Examples.