US1557660A - Method of making anhydrous magnesium chlorides - Google Patents

Description

Patented Oct, 20, 1925.

UNITED STATES:

PADI. COT'I'RINGER ANI)l WILLIAM R. COLLINGS, OF MIDLAND, MICHIGAN, ABSIGNORS4 PATENT OFFICE.

T0 THE DOW CHEMICAL COMPANY, 0F MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN.

METHOD 0F MAKING .ANHYDBOUS MACNESIUM CHDORIDIB.

Application led. March 10, 1921. Serial Fo. 451,199.

To all whom z't may concern.'

Be it known that we, PAUL COTTRINGER and WILLIAM R. CoLLINGs, citizens of the United States, and residents of Midland, county of Midland, State of Michigan, have jointly invented a new and useful Improvement in Methods of Making Anhydrous Magnesium Chlorides, of which the following is a specification, the principle of the invention being herein explained, and the best mode in which we have contemplated apf plying that principle so as to' distinguish it from other inventions. The published methods for the production of anhydrous magnesium chlo-ride (MgCl2), up to a very recent date at least, will be found very well summarized in Gmelin-Krauts Handbuch der anorganischen Chemie (1909) II 2, p. 420. In the same connection, the well known dificulties encountered in the production of the waterfree salt are recited, the principal such diiculty being that thc normal heXa-hydrate will melt and form a solution in its Water of crystallization at a relatively low temperature, and dehyrationl of the resultant solu-- tion must be carried on at a very slight increase in temperature and with extreme caution if decomposition of the salt is to be avoided. The present improved method for the production of the anhydrous salt has as its object ,the avoidance of this particular diiculty, and also provides for the more ready and convenient handling of the material during the preliminary stages of dehydration; as well as for the economical use of hydrochloric acid gas which is used to drive off the last remaining waterof crystallization. .v To the accomplishment of the foregoing and related ends the invention then consists of the steps hereinafter fully described and particularly pointed out in the claims, the annexed drawing and the following description settingr forth in ldetail one mode of carrying out the invention, such disclosed mode constituting, however, but one of various ways in which the principle of the invention may be used.

In said annexed drawing Fig. 1 is a more Ior less diagrammatic view of an improved apparatus suitable for carrying out the partial dehydration of the material 1n questlon, and Fig. 2 1s a snrnilar vlew of an applaratus specially designed for carryln out t e final stage of dehydration',

in whic a current of hydrochloric acid gas is employed, as indicated above.

The apparatus as shown in Fig. 1 comprises as its rinci al element a shelf dryer 1, through w 1ch t e material is passed successively from the u per to the lower shelves 2 in well un erstood manner by means of shovels or plows 3 carried on .a rotating shaft 4. The material to be treated is fed into the upper end of the dryer by means of asuitable ho per 5 and is discharged at the lower end) throu h an outlet 6. Likewise connectedwith suc lower end of the dryer is a duct 7 through which flue gases or products ofv combustion directly received from a gas or oil burner or from a. furnace burning coal or other solid fuel are admit-ted to the interior of the dryer,

through which they circulate in a general upward direction, finally escaping lthrough an exit duct 8. Connected with said duct 7 is a valve controlled branch d'uct or opening 9, whereby outside air may be admitted in a regulated amount and mixed withthe` aforesaid liue gases so as to lower the temperature of the latter when 'admited to the-dryer. The dimensions of the apparatus and the temperature and rate of supply of the Hue gases thus tempered with outside air regulat-ed so that the highest temperat re encountered by -the material at the lo er or exit end of the dryer will not rise .abo e 350 6, the transfer of such portion of the partially dehydrated product being indicated by a line l0 with direction arrow only. Where the highest tem erature encountered by the material is 350 egrees centigrade, as just stated, such partially dehydrated prod- 'uct will consist mainly of rdihydrate (MgCl2.2I-I,O), which has a fusion point above 360 degrees centigrade, and theamount of this product diverted for use in mixing with the normal hexa-hydrate will be approximately one half of t-he latter. lVhere such partially dehydrated product is mixed in amount approximately as stated, with the normal hydrate, the mixture may be immediately subjected to a temperature of approximately 115 degrees indicated above as the temperature of the' heating gases as discharged from the apparatus, without any of the harmful effects that would result. were the normal hydrate by itself subjected to such temperature.

It will be noted that the foregoing procedure is distinguished from that disclosed in German Patent No. 51,084, dated March 16, 1889. In the first place, in our improved process, :it is not the completely dehydrated chloride that is thus adinixcd with the n'o-rmal hydrate, and in the second place,` in our process, such admixt-ure is simply made with. both materials in solid formwithout, in other Words, fusing the normal hydrate, and then stirring in the dihydrate which results in the production of a hard cake that requires to be broken up before it can be passed through the drying apparatus. The anhydrous product is 4too valuable to warrant its use in any large commercial way for thus admixing with the normal hydra-te and it apparently was never realized that the partially dehydrated product might prove cffective in the same manner to render the normal salt. amenable to ordin-ary methods of drying. K

The portion of partially dehydrated salt, (most if not all in the form ofthe dihydrate) that isdelivered from the shelf dryer in excess of that returned in thefashiion just described to be passed through a second time, is thereupon transferred either continuously or Aintermittently to an externally heated rotary drum dryer 12 for treatment in what may be regarded as a second stage of the process. A current of hydrochloric Iacid gas 1s continuously passed through said dryer 12 as it rotates, such gasbeing derived initially from any suitable source. The circuit of the gas includes one or more towers through which snlphuric acid of proper strength is passed, either in the samedirection or counter to the current of hydrochloric -acid gas, so as to remove therefrom substantially all traces of water. ln the illustrative form of .apparatus lshown in Fig. 2, two such towers 1? are thus included 1n the circuit 14. through which the hydrochloric acid gas is caused to flow by means ot a pump 15, suitable valves being provided whereby .such fiow of gas can be diverted from one to the other tower 13.215 desired. A sutlicient body of sulphuric acid is kept circulating through the particular tower that happens to be thus in use and such circulation continued until the sulphuric acid reaches a density of approxmately 60 degrees B aum, whereupon t-he hydrochloric acid gas is switched to the other tower where lanother portion of sulphuric acidof proper strength to remove the water from'the. gas is ready to be circulated. A concentra-tor 16 is connected with the. pipes 17 whereby the circulation of sulphuric acid is thus maintained in the respective towers 13, so that such acid |after absorbing the maximum amount of water that a dcsirable may be concentrated and the acid then returned foil use-ove; again, as will be readily understood.

The circulation of the hydrochloric acid gas may thus be continued as long as found necessary to effect the dehydration of any particular hatch of partially dehydrated magnesium chloride in drum 12, or by proriding suitable means for continuously feeding such chloride to and removing same from said drum, the circulation of the hydrochloric acid gas may be continued indefinitely. Where the chloride is dried in batches the temperature in said rotary drum 12 will be gradually raised from approximately 200 degrees to approximately 500 degrees centigrade, the higher temperature being necessary to insure the complete driving oft" of the water of crystallization, while if continuous operation is to be secured the partially dehydrated chloride is introduced at one end of the drum, which end is maintained at the lower temperature just indicated, and such temperature gradually increased lengthwise of the drum until at its other, discharge .end the higher temperature is reached.

4By means of the foregoing steps and 'apparatus it is possible to prepare anhydrous magnesium chloride at a much lower cost than has heretofore been possible, the hulk of the water of crystallization being driven off by ordinary air drying and only the last stage requiring the use of hydrochloric acid gas. The latter moreover is used over and over again without material loss save such as may occur due to leakage and the like. It will be understood, of course, that the process is not limited to any precise degree of dehydration being reached at the end of the first stage` since hydrochloric acid gas will be effective to remove water of crystallization in excess of two molecules, but the .drying in the first stage is preferably carried to as near this point of dehydration as possible for reasons of economy. 1f the process be carried out with the temperature ranges as hereinbefore described, the product.. resulting from the first stage will be substantially all-in the dihydrate form.

Other modes of applying the principle of our invention may be employed instead of the one explained, change beim.r made as regards the steps herein disclosed. provided lift) those stated by any ofthe following claims or their .equivalents be employed.

We claim:

1. In a method of making anhydrous magnesium chloride, the steps which consist in intermixin partially dehydrated magnesium chloride with the normal hydrated salt, both in solid form, and then directly heating the mixture at a temperature sufliciently elevated to drive-off water of crystallization.

2. In a method of making anhydrous magnesium chloride, the steps which con-- sist in intermixing a quantity of the dihydrate salt with the normal h drated salt, both in solid form, and then irectl heating the mixture at a temperature su ciently elevated to drive oi' water of crystallization. 3. In a, method of making anh drous magnesium chloride, the ste s whic consist in intermixing partially ehydrated magnesium chloridewith the normal h drated salt,

both in solid form, and then 'directly heating the mixture through a temperature range gradually increasing from approxi.

mately 115 to approximately 350 degrees centigrade.I

4. In a method of making anhydrous magnesium chloride, the steps which consist in intermixin a quantity of ,the dihydrate salt with the normal h drated salt, both in solid form, and then irectly heating the mixture through a temperature range gradually increasmg from approximately 115 to approximately 350 degrees centigrade.

5. In a method of making anh drous magnesium chloride, the steps whic consist in intermixin a quantity of the dihydrate salt with t e normal hydrated sa t,

driving olf water of crystallization from the resulting mixture until it reaches approximately the dihydrate stage, and returning a portion of the product for use over again 1n the receding steps.

6. In a method of making anh drous magnesium chloride, the steps whic consist in vdrivin `ofi' a portion of the water of crystallization from the normal hydrated salt by a current of gases of cumbustion, and regulating the temperature of such gases by admixing air at normal temperature therewith. I

7. In a methbd of making anh drous lnagnesium chloride, the steps whic consist(in. driving off a portion of the water of crystallization from the normal hydrated salt by moving the latter in opposed direction against a current of gases of combustion, and re ulating the temperature of such gases by atnixing air at normal temperature therewith.

8. In a method of making anhydrous magnesium chloride the steps which consist in driving ol a portion of the water of crystallization from the normal h' drated salt by moving the latter in oppose direction against a current of gases of combustion, regulating the temperature of such gases by admixing air at normal temperature therewith, and returning a portion of' the product for use over again in the preceding steps.

Signed at Midland, Mich., this 4th day of March, 1921.

PAUL eo'r'rRiNGi-JR. l WILLIAM R. COLLINGS.

Images