IL45373A - Process for the production of chlorine and magnesia from magnesium chloride - Google Patents

Description

45373/2 Process for the production of chlorine and magnesia from magnesium chloride This Invention relates to an Improved process for the production of chlorine from magnesium chloride. More specifically, t relates to direct production of chlorine and magnesia by thermal oxidation of partially hydrated magnesium chloride.

The most widespread method 1n use for the manufacture of chlorine Is the electrolysis of sodium chloride, which produces caustic soda as a byproduct; however, 1n view of the fact that the demand for caustic soda does not Increase as fast as that for chlorine, 1t has been considered desirable to develop methods for production of chlorine which do not Involve the co-production of caustic soda. Such methods generally consist of the oxidation of hydrogen chloride gas by means of a r or oxygen. These methods are quite feasible, some having reached commercial Implementation, and have the advantage of requiring considerably less energy than the afcresald electrolytic process, but have a serious disadvantage, I .e. , that they require some Intermediate catalytic action to obtain acceptable yields of product. For example, a copper chloride catalyst may be used, but this entails costly volatility losses , or use may be made of reactions such as the formation and subsequent decomposition of nltrosyl chloride, but such reactions can lead to corrosion problems , and to pollution problems resulting from the evolution of oxides of nitrogen.

Furthermore, hydrogen chloride 1s not a primary product: 1t 1s a byproduct of organic chlorl nations of the type R-H + Cl2 ♦ RC1 + HC1 (1 ) where R Is any organic radical , or of inorganic reactions such as production of alkali metal sulphates from the corresponding chloride, 1n accordance with 2MC1 «■ H2S04 + M2S04 + HC1 (2) where M Is an alkali metal cation. Consequently, any method of production of chlorine using hydrogen chloride as feed, 1s to be regarded as a supplement, rather than as an alternative, to the currently-practiced electrolytic process .

It Is therefore desirable to provide a novel method for productj^i of chlorine which uses as feed an easily available chloride-containing substance, and does not require catalysts or Intermediate reagents , while maintaining the low-energy advantage of the aforesaid hydrogen chloride oxidation processes.

An attractive primary source for large-scale manufacture of chlorine would be magnesium chloride, which 1s a wldely-occurlng naturally found substance, generally In the form of aqueous brines. Such brines frequently contain other dissolved salts , but by known methods of partial evaporation and crystallization, and, possibly, also cooling to below ambient temperature, a separation may be effected whereby 1s obtained either a liquid phase being an aqueous solution of essentially magnesium chloride and a solid phase consisting of the other salts contained 1n said brine, or a solid phase consisting esse-tlally of hydrated magnesium chloride and a liquid phase being an aqueous solution of the other salts contained 1n said brine.

The reaction of anhydrous magnesium chloride with oxygen or air to form chlorine and magnesia, 1n accordance with the equation 2MgCl2 + 02 * 2MgO + 2C12 (3) Is in fact known from the literature, being reported, for example, by: elley K.K. "Energy Requirements and Equilibria 1n the Dehydration, Hydrolysis and Decomposition of Magnesium Chloride (Chan. & Met. Engineering, 1944) , but the known difficulties 1n the complete dehydration of hydrated magnesium chloride, make th s approach unattractive. It should be noted that the above reaction (3) has been ncorporated Into US Patent No. 3 323 871 for production of chlorine; however, the process claimed 1n said patent does not use magnesium chloride as a feed material at all , 1t 1s merely one of the many HC1 oxidation processes referred to above, the steps 1n this case being partial hydrochlor nation of magnesia at one temperature, followed by oxidation of the MgO/MgCl2 mixture with oxygen at a different temperature, to form chlorine 1n accordance with equation (3) above, the MgO obtained being recycled. Thus the said Similarly, the thermal decomposition of magnesium chloride monohydrate to form hydrogen chloride and magnesia. In accordance with the equation MgCl2.H20 ·* MgCl2 + HgO ·* MgO ·► 2HC1 (4) 1s known* being also reported by Kelley. This reaction requires quite high temperatures for Its completion, e.g. , at a temperature as high as 700°C, the gases contain only about 90¾ mole of HC1 , corresponding to only about 82% conversion of MgCl2 to MgO, but 1t nevertheless would be feasible to produce gaseous hydrogen chloride by said thermal decomposition. Hydrogen chloride thus obtained could then be oxidised to chlorine by one of the known processes for accompl ishing said oxidation, but as stated hereinbefore HC1 oxidation processes require some Intermediate reaction with Its attendant problems.

However, 1t has now been observed that In both reactions (3) and (4) there 1s an Increase In the number of gaseous molecules , consequently the extent of conversion In both reactions will be enhanced by the presence of Inert gases. Accordingly, combination of the two reactions (3) and (4) suc that both occur at the same time, 1s to the mutual advantage of each, In that the chlorine and oxygen or reaction (3) serve as "Inert gases" for reaction (4) , while the HC1 and HgO of reaction (4) serve as " nert gases" for reaction (3) . For example, oxidation of anhydrous magnesium chloride by oxygen at 627°C gives an equilibrium conversion of 81.92, I .e. , 81 .9% of the chloride content of magnesium chloride 1s converted to chlorine 1f stoch ometrlc quantities of reagents are used, whereas 1f the magnesium chloride used contains 5Ϊ by weight of water, while the ratio of oxygen to magnesium chloride 1s unchanged, the equilibrium conversion of chloride to chlorine rises to about 942 In view of the simultaneous hydrolysis reaction (4) by which magnesium chloride 1s converted to HC1 , 1t 1s seen that practically all of the chloride content of the MgCl9 In the feed leaves 1n gaseous form, as chlorine and HC1 , while the solid product practically pure magnesia, apart from any Impurities such as other chloride salts associated with the magnesium chloride starting material . In practice, the kinetics of reaction (4) are quicker than those of reaction (3) , so that Initially most of the HgO content of the magnesium chloride feed will react with the equivalent amount of magnesium chloride to form MgO and HC1 , while the reaction of the remaining MgCl2 with oxygen takes longer to be completed.

Thus according to the present Invention there Is provided a method for the production of chlorine and magnesia from magnesium chloride comprising reacting partially hydrated magnesium chloride having a water content by weight of up to 16¾ at a temperature of between 500*C and 700°C with a gaseous stream havi g an oxygen content of at least 20Ϊ whereby there Is produced a gaseous product comprising chlorine and HC1 and a solid product consisting essentially of magnesia.

The magnesia obtained 1s a useful by-product, but whereas In the conventional electrolytic process 1t 1s essential to be able to sell all the by-product -caustic soda- at a reasonable price, otherwise the cost of the chlorine would be prohibitively expensive, n the process described herein the sale of the by-product magnesia , though desirable, s not essential for the economic success of the process , due to the considerably lower energy requirements In this process , than 1n the aforesaid electrolytic process. Disposal of unwanted magnesia - which Is not corrosive and 1s far less reactive than caustic soda - should present no great difficulties , so that the possible nability to sell al l the by-product magnesia should not hinder the widespread adoption of the process described herein.

The discovery that It Is possible to produce chlorine and magnesia n high yield by oxidation of partial ly hydrated magnesium chloride which contains a high percentage, up to 16% by weight, of water, Is unexpected and probably the main reason why the prior art dealt with the reaction of anhydrous magnesium chloride with oxygen or air to form chlorine despite the Furthermore 1t would be expected that most of the chlorine present would convert to HC1 1n the presence of water and that all the water would react n accordance with equation (4) . Surprisingly It was Instead found that 1n the process of the present Invention using partially hydrated magnesium chloride a higher ratio of Cl2 to HC1 was obtained than would have been expected from the thermodynamics of the reaction and that apparently a large percent of the ewater present does not participate In the reaction.

Thus the method of the present I vention provides a novel and unexpectedly effective method for the production of ch orine In high yields from the easily available chloride containing magnesium chloride.

Both reactions (3) and (4) are endothermlc, so that heat needs to be supplied to the device 1n which the proposed process Is carried out. The supply of heat may be direct or Indirect; If direct firing of fuel 1s used, the presence of large volumes of combustion gases wi l Increase the equilibrium conversion to chlorine, but will decrease the actual rate of reaction due to the lower concentration of oxygen, and wi l result 1n a low concentration of chlorine 1n the exit gas stream, thus requiring expensive separation operations, consequently 1t 1s preferable to use Indirect heating. Devices for carrying out high -temperature gas-sol 1d reactions which require Indirect heating are available commercially, e.g. , the 1nd1rect-heat rotary cal dner, described In Perry's Chemical Engineers Handbook (5th Ed. (1973) pp. 2Θ-44 to 2Θ-46) . As the fuel-burning section of the device 1s separated from the reaction section, any available form of fuel may be used, and there Is no risk of contamination of the chlorine gas stream by sulphur dioxide resulting from combustion of any sulphur contained In the fuel .

The device used may be of the horizontal , rotary type, the gravity moving -bed type, or the multiple-hearth type, and the reaction gas flow may be In co-current, counter-current, or cross-flow with respect to the magnesium chloride movement through the reaction device.

The oxygen-bearing gaseous stream may, as stated above, contain as little as 20ft oxygen by weight and thus the use of atmospheric air Is quite feasible. However, the use of a gas with such a low oxygen conte^ 1s not preferred, as such a mode of operation would result 1n a reduced rate of reaction due to the low prevalent concentration of oxygen , would nvolve the handl ing of large volumes of gases , and would entail a ihlgh work of separation of chlorine from the gaseous product produced, consequently the gas to be used should preferably be tonnage oxygen, containing more than 90% O^, which may be readily purchased, or produced on site. The supply of oxygen-bearing gas should preferably not be less than that dictated by the stochlo-metry of the equation MgCl2 + bH20 + J(l-b)02 * MgO + 2bHCl + (l-b)Cl2 (5) where b 1s the molar ratio of water to magnesium chloride, but advantageously excess oxygen is used, so as to accelerate the rate of reaction. The upper limit of the ratio of oxygen to magnesium chloride Is set by the cost of handling large volumes of gases , and of separating chlorine from the product gases both of which ncrease with a rise 1n said ratio, and It Is recommended that the said ratio shall not exceed 3 moles of oxygen per mole MgClg.

The range of possible temperatures of operation are set by the following considerations: 1 ) Below about 500°C , the rate of reaction falls to unsatisfactory values; 2) Above about 700°C, there 1s a risk of meting of the partial ly dehydrated magnesium chloride; and 3) The equilibrium In the reaction 4HC1 + 02 ^=± 2C12 + 2H20 (6) tends to the Increased formation of HC1 with rising temperature.

Consequently, the temperature of operation should be In the range 500-700°C, preferably 550-650eC. The operation may be carried out Isothermally, or there may be a temperature gradient rising n the direction of MgO formation.

The gaseous product produced by the method of the present Invention and consisting of chlorine, HC1 , and excess atmospheric gases, may may be used as such for organic Dechlorinations , e.g. , of ethylene to }ψ2 d1chloro-e thane, or of benzene to monochlorobenzene, In which cases all three major components of said mixture - chlorine, HC1 and excess oxygen - are effectively made use of. Alternatively the gas may be used to produce bromine from bromide-bearing brines which may contain some divalent manganese, n which case the chlorine alone Is active component, but the presence of HC1 helps to avoid the possible formation of nsoluble MnOg which could hinder the smooth running of the bromine production plant, and the atmospheric gases may assist 1n displacement of the bromine from the sa d brine.

Al ternatively, the gaseous mixture may be treated so as to obtain each component separately. For example, It Is possible to absorb the. HC1 content nto a stream of water or weak hydrochloric add, so as to produce a strong add containing at least 301 HC1 by weight, this being a saleable product.

The chlorine component may be obtained, either before or after the said HC1 absorption, by partial liquefaction under pressure, absorption of the residual gaseous chlorine at a low temperature Into a solvent selective for chlorine, such as carbon tetrachloride, and subsequent release of the absorbed chlorine, at a higher temperature. If the residual gas after the aforesaid operations contains a high percentage of oxygen, some of this gas may be recycled.

These, and similar, methods of treatment of chlorine-bearing gases , are known to those skil led In the art, as many have been used, singly or 1n combination, for treatment of the off -gases obtained 1n the electrolytic process for production of chlorine.

In a preferred embodiment of the present Invention the partially hydra ted magnesium chloride used as a starting product of the present method 1s obtained from natural ly occurring sources of magnesium chloride such as sal ine brines or carnal Ute deposits by separating substantially pure magnesium chlorid from said naturally occurring sources and dehydrating said separated magnesium chloride by methods known per se to give a partially dehydrated product having a water content by weight of up to 16%.

Magnesium chloride obtained from said naturally occurring sources can now be dehydrated 1n any suitable device, such as a spray dryer or ^ flu1d1sed-bed dryer, to a residual water content of about 15.8% by weight, this value corresponding to the water content of MgClg.HgO, magnesium chloride monohydrate. If the dehydration Is performed 1n a spray dryer, dehydration to monohydrate proceeds without any decomposition, due to the short residence time, but dehydration to a lower water content will always be accompanied by some decomposition to magnesia. The product of dehydration thus wil l contain at least 80% chlorides of magnesium and of other catlonlc Impurities present , such as sodium, potassium and/or calcium, and wil l contain not more than 16¾ H20, the balance being MgO. A typical product which 1s easily obtained In commercial ly available spray dryers has the analysis (¾) : gCl 2-90 H20-5 MgO-5 , by weight, but these figures are given as an example only.

The partial ly dehydrated magnesium chloride can now be brought Into co- or counter-current contact wi th a gaseous oxidising stream consisting of air, enriched air, or oxygen, at temperatures of 500 to 700°C, under which conditions are obtained a solid product consisti ng of magnesia together with any chloride Impurities , e.g. , chlorides of sodium, potassi um, or calcium, resul ting from Impurities 1n the original magnesium chloride fed to the dehydration step , and a gaseous product consisting of chlorine, HC1 , excess oxygen , and nitrogen or other gases present 1n the said oxidising stream.

This gaseous product can either be used as such or separated nto Its components .

In the U.S. Patent 3 ,275 ,409 there Is described and claimed a process for producing magnesium oxide from a magnesium chloride hydrate-containing starting material which comprises a two-stage operation, the first stage comprising the steps of Introducing said material Into a shaft type chamber In atomized state at a pressure ranging from 5 to 15 at . , passing combustion gases Into said chamber at the same end with the magnesium chloride hydrate containing material at the approximate temperature of 400 to 800°C, said gases carrying said atomized particles lengthwise along said chamber and causing evaporation of excess l iquid therefrom, separating said dried magnesium chloride hydrate from said gases , conveying the magnesium chloride hydrate Into a decomposition chamber, Introducing simul taneously therewith combustion gases at a temperature whereby decomposition occurs 1n a few seconds , and separating substantial ly pure magnesium oxide from the HC1 -containing gases , the temperature of the leavi ng gases being about 900-950°C.

While said patent Involves the production of magnesium oxide from a magnesium chloride hydrate-contai ning starting material by means of a process which differs In several respects from that of the present Invention especially Important 1s the fact that a close perusal of the specification of said patent discloses that In fact magnesium chloride 1s fed Into a spray dryer where It 1s dried I nto magnesium chloride hydrate containing approximately 2to 6 mol s of water. Thus 1t wil l be realized that said patent teaches only dehydration to at most the dihydrate of formula MgCl and then heating to magnesium oxide and HC1 .

In contradistinction to the above process the process of the present Invention relates to partially hydrated magnesium chloride having a water content by weight of up to 16% and preferably of about 2 to 10% and thus Is directed to the monohydrate and mixtures of mono and anhydrous MgCl^.

Thus said patent neither describes nor teaches the process of the present Invention or the advantages thereof.

More specifically an expanded process of the present Invention could be characterized as constituting the following steps : a) separation of magnesium chloride in the form of an aqueous solution or of hydrated crystals , from naturally-occurring sources of same , by the appropriate combination of evaporation, cool ing , crystallization , and filtration; said separated magnesium chloride stream containing not more than 30% and preferably not more than 10% by weight, with respect to MgCl^, b) dehydration of the magnesium chloride obtained n step (a) by kn^j^ means of dehydration, for example . spray drying or ftu1d1sed-bed drying, to a solid product containing not more than 16% and preferably between 2 and 10% HgO by weight, whi le the MgO content should preferably not exceed 10%. Spray drying 1s to be preferred for this step, as 1t enables an output mater4al containing less than 5% each of MgO and H20 to be obtained without difficulty. c) treatment of the partially dehydrated magnesium chloride obtained 1n step (b) , after compaction 1f desired, with a stream of oxygen, air or enriched air containing between 20% and 100% oxygen by weight, 1n a suitable reaction device and at a temperature between 500° and 700°C but preferably between 550 and 650°C, so as to obtain a gaseous stream consisting of chlorine, HC1 , excess oxygen , and other components of 1he gaseous stream fed to this reaction step, and a solid product consisting princi ally of MgO, but possibly containing some undecomposed MgCI^* as well as whatever chloride salt mpurities became associated with the said magnesium chloride during Its passage from step (a) . d) product treatment 1f desired. The gaseous chlorine-bearing stream obtained 1n step (c) may be util ised as such , or may be treated by known process as hereinbefore described, so as to separate the chlorine and/or the HC1 from the other components 1n the said stream with optional recycle of part of the exit gases from said separation, now enriched 1n oxygen, to step (c) , so as to economise on the consumption of oxygen 1n the process described herein. The solid product from step (c) may be treated to obtain refractory grade magnesia by aqueous washing, to remove any residual magnesium chloride and/or other chloride salts, followed, 1f desired, by known steps of drying and/or calcination.

The most common saline Impurities Hkely to be associated with the magnesium chloride obtained as 1n step (a) are chlorides of sodium, potassium, and calcium, sulphates of magnesium and calcium, and bromide ion. The only potassium chloride. It Is known from the literature that potassium ch ^lde has a stabilising effect on magnesium chloride, due to the formation of the anhydrous carnal 11 te double salt CI .MgClg* whereupon the magnesium chloride becomes more resistant to oxidation 1n accordance with equation (3) above, consequently the ratio of potassium to magnesium chloride n the solid feed to step (c) should be well below equlmolar. The presence of other chlorides and sulphates does not reduce the equilibrium yield of the oxidation reaction given 1n equation (3) above, but may reduce the rate of reaction, which, according to Allen & Clark, (J.Appl led Chemistry 16. (1966) pp.327-332) , 1s diffusion-controlled, merely due to the presence of Inert material which can Impede free diffusion. Calcium sulphate will , moreover, contaminate the magnesia obtained 1n step (c) as 1t cannot be removed by aqueous washing as specified 1n step (d) . The presence of bromide has no Inhibiting effect whatsoever on reactions (3) or (4) , but the gaseous product from step (c) will contain bromine, with Its attendant corrosion problems. Consequently, the concentration of Impurities 1n the magnesium chloride obtained 1n step (a) 1s advantageously maintained below 10% by weight of the MgClg content of said material .

The magnesium chloride as obtained from the spray drying operation (b) s generally 1n the form of a fine powder of low bulk density 1n some cases It may be Introduced as such Into the said reaction device, whereas 1n other cases some form of compaction may first be required e.g. , to reduce dust forma tion and carry-over Into the exiting chlorine-bearing gases . Suitable compacting devices are available commercially. It 1s to be understood that all reaction devices and modes of operation satisfying the requirements of this and the preceding paragraphs, fall within the scope of this Invention.

While the Invention will now be described 1n connection with certain preferred embodiments n the fol lowing examples It wil l be understood that 1t Is not Intended to l imit the Invention to these particular embodiments. On the contrary it 1s Intended to cover all alternatives , modifications and equivalents as may be Included within the scope of the Invention as Example 1 Magnesium chloride brine was spray dried and the sol id product havSflg the composition given below was formed Into pellets weighing about 3 gm each. One such pellet was held for 2 hours In a stream of oxygen, obtained from a cylinder of compressed gas. The outgoing gas was passed through a caustic soda trap, the contents of which were analysed, at regular Intervals, for chlorine (as NaOCI ) and total chloride. The following results were obtained, at a working temperature of 650°C: Analyses - weight percent: MgCl2 CaCl Na/ Cl MgO H20 feed material : 88.5 0.3 1.3 5.2 4.7 product 3.2 0.8 3.3 92.7 gases produced: 0 - ÷ hr 195 376 total 797 407 It s seen that 98.5¾ of the MgCl2 1s converted to MgO, that the ratio of chlorine to HC1 1n the exit gases , 1s almost 2:1 , and that the hydrolysis reaction (4) 1s ndeed much faster than the oxidation reaction (3).

Example 2 The experiment of Example 1 was repeated, but using a sample of partially-dehydrated magnesium chloride with a higher HgO and CaClg c<¾tent, and was continued for 3 hours nstead of 2. analyses - weight percent: MgCl2 CaClg Na/KCl MgO Hg0 feed material : 78.3 4.7 4.7 4.3 8.0 product : 0.7 8.6 9.5 81 .2 gases produced: Cl2, mg HCl, mg 1 2 hr 428 39 2 3 80 8 total 684 606 It 1s seen that 1n spite of the higher water content of the feed-more than 10% by weight with respect to Mg Cl2 - the results are similar to those of Ex.1: the conversion to MgO Is 99.1% and the hydrolysis c reaction 1s virtually completed In the first half hour, but the C12:HC1 ratio 1s of course much lower, due to the higher water content of the feed. Example 3 The experiment of Example 1 was repeated, but using a number of pellets, of total weight 10 gm. The following results were obtained: analyses, weight percent: MgCl2 CaCl2 Na/KCl MgO H20 feed material : 87.5 0.2 1.2 5.1 6.0 product : 7.1 0.7 2.2 88.2 1.8 Gases produced: Cl2mg HCl, mg 0 + ½hr 924 794 ¾ - 1 hr 1448 45 1 - lihr 1289 ]j+ 2 hr 533 Total 4274 839 It 1s seen that 95.5% of the gClg Is converted to MgO, that the ratio of chlorine to HCl 1n the exit gases Is 5:1, and that, as in the e h dr i ea i i o t formation It will be evident to those skilled In the art that the Invention 1s not l imited to the details of the foregoing Illustrative embodiments and examples and that the present Invention may be embodied 1n other specific forms without departing from the spirit or essential attributes thereof, and H is therefore desired that the present examples be considered In all respects as Illustrative and not restrictive, reference being made to the appended claims , rather than to the foregoing description, 1n which 1t 1s Intended to claim a l modifications coming within the scope and spirit of the Invention.

Claims (16)

WHAT IS CLAIMED IS: Λ

1. . A nethod for the production of chlorine and magnesia from magnesium chloride comprising reacting partial ly hydrated magnesium chloride having a water content by weight of up to 16% at a temperature of between 500° C and 700°C with a gaseous stream having an oxygen content of at least 202 whereby there 1s produced a gaseous product comprising chlorine and HC1 and a solid product consisting essential ly of magnesia.

2. A method for the production of chlorine and magnesia according to claim 1 wherein said partially hydrated magnesium chloride has a water content of between 2 and 10%.

3. A method for thep"oduct1on of chlorine and magnesia according to claim 1 wherein said gaseous stream has an oxygen content of at least 90%.

4. A method for the production of chlorine and magnesia according to claim 1 wherein the supply of oxygen - bearing gas 1s at least equal to the amount dictated by the stochlometry of the equation MgCl2 + bH20 + (l-b)02 * MgO + 2bHCl + (l-b)Cl2 wherein b 1s the molar ratio of water to magnesium chloride 1n the partially hydrated magnesium chloride.

5. A method for the production of chlorine and magnesia according to claim 1 wherein the reaction 1s carried out at a temperature of between 550°C and 650° C.

6. A method for theproductlon of chlorine and magnesia according to claim 1 comprising the additional prior steps whereby the partially hydrated magnesium chloride used therein 1s obtained from naturally occurring sources of magnesium chloride by separating substantial ly pure magnesium chloride from said natural ly occurring sources and dehydrati ng said separated magnesium chloride by methods known per se to g ve a partial ly dehydrated sol id product having a water content by weight of up to 16%.

7. A method for the production of chlorine and magnesia according to claim 6 wherein magnesium chloride* In the form of hydrated crystals or an aqueous solution 1s separated from said naturally occurring sources by one or more of the operations selected from the group consist ng of partial dissolution , , evaporation, cooling, crystal lization, filtration and washing whereby there Is obtained a magnesium chloride containing up to 30% by weight with respect to MgCl2 of saline Impurities originating from said natural ly-occurring sources.

8. A method for the production of chlorine and magnesia according to claim 7 wherein there 1s obtained a separated magnesium chloride containing up to 10% by weight saline Impurities.

9. A method for the production of chlorine and magnesia according to claim 6 wherein sa d separated magnesium chloride Is dehydrated by spray drying to g ve a solid product having a water content of between 2 and 0%·

10. A method for th eproduct on of chlorine andmagnesla according to claim 1 wherein said gaseous product 1s treated by known means to separate therefrom chlorine, 1n gaseous or l iquid form, and/or HC1 , 1n the form of anhydrous gas , anhydrous 1-1 quid , or aqueous solution, the residual gases from said treatment being discarded to the atmosphere unless their oxygen concentration exceeds that of atmospheric air 1n which case they are either partially recycled or treated by known means to recover part or al l of their oxygen content.

11. A method for th e?roduct1on of chlorine and magnesia according to claim 1 wherein the source of magnesium chloride 1s an end brine from potash processing operations.

12. A method for theproduct on of chlorine and magnesia according to claim 6 wherein said naturally occurring source of magnesium chloride Is a saline brine.

13. A method for the production of chlorine and magnesia according to claim 6 wherein said natural ly occurring source of magnesium chloride 1s a carnal l te deposit.

14. A method for the production of chlorine and magnesia according to m whe ein t e ar ial de drated ma nesium chloride obtained 1s

15. A method for the production of chlorine and magnesia according,., to claim 1 wherein said reaction 1s carried out 1n a reaction device or sequence of devices in such a manner as to enable the gaseous stream flowing through said device or devices to be extracted at one or more Intermediate points and to be treated by known means so as to remove part or all of the HCl formed 1n the Initial stages of the reaction occurring 1n said device or devices , after which treatment the said gaseous stream 1s returned to the said device or devices for completion of the reaction, thereby obtaining In the gaseous product a higher ratio of chlorine to HCl than would be obtained if said intermediate extraction and treatment were not carried out.

16. A method for the production of chlorine and magnesia substantially as hereinbefore described and with reference to the examples. For the Applicants Wolff, Bregman and Go Her By: J* . ,W%