Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
  • C01D1/00—Oxides or hydroxides of sodium, potassium or alkali metals in general
  • C01D1/04—Hydroxides
  • C01D1/42—Concentration; Dehydration
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F11/00—Compounds of calcium, strontium, or barium
  • C01F11/20—Halides
  • C01F11/24—Chlorides
  • C01F11/30—Concentrating; Dehydrating; Preventing the adsorption of moisture or caking

Definitions

• This invention relates to a new process for the Z manufacture of solid calcium chloride, and more particularly to a new and improved method for the dehydration of relatively concentrated solutions of calcium chloride.
• the process in commercial operation for the f "manufacture of calcium chloride employs a dilute f liquor as starting point, which is available as a i. by-product of the ammonia-soda process.
• f'jliquor is evaporated in a steam heated or other type of evaporator until a concentration of about 40% to 50% CaCl2 is reached, if desired under 'vacuum, and any deposited solids are removed.
• this solid is fur- .theiwdehydrated by putting it in an oven or by passing it through a rotating drier which is heated either through the walls or by a current of hot air, togive a product containing 7 6 to 78% Caclz.
• This product requires less packing and transport than 70 to 72% CaClz and is also less liable to cake on storage.
• Another method of making a substantially anhydrous product is to spread the ;70%, CaCl-z solution on a conveyor which takes it through a furnace at 350 to 450 C. to
• One object of the present invention is to provide an improved process for the manufacture of 75 to 77% CaClz. Another object is to decrease the amount of heat which must be supplied in the manufacture of commercial calcium chloride, and to provide an improved evaporation process. Yet another object is to provide a, new and useful form of commercial calcium chloride.
• the temperature of this solution is adjusted to about to C.
• the solution is then subjected to conditions in which the partial water vapour pressure above the solution is kept below atmospheric, e. g. is kept at 100 to 400 mm. of mercury, and a large surface area of solution is provided e. g. by spraying the solution down an empty tower.
• the above description represents the optimum case where it is unnecessary to introduce any heat whatsoever, and the only heat precautions which must be taken are that undue losses to the atmosphere must be avoided.
• Another method of operation is to spray an appropriate solution down a tube in which there is an ascending current of air to carry off the water vapour and thus maintain a low water vapour partial pressure.
• This method also gives dry granular calcium chloride.
• the air should be Warm to avoid undue heat losses from the solution, and it may if desired be hot enough to supply some heat to the process.
• the method of providing a large surface area may be by any of the standard methods normally adopted for this purpose, e. g. spraying, exposing as a film, agitating a solution or distributing it on previously produced granular calcium chlo-' ride as carrier for the solution in a creeper mixer.
• spraying exposing as a film
• the time involved in autoevaporation is much less than is normally taken in evaporating calcium chloride solutions or in further dehydrating solid 70% CaCh.
• my invention comprises adiabatic or substantially adiabatic conversion of an appropriately chosen solution into vapour and solid merely by subjecting it to the necessary reduction of partial water vapour pressure.
• this adiabatic process is also an isothermal one.
• the ideal case is represented by the use of about 72% calcium chloride solution at about 170 to 175 C., but there are other conditions within the immediate vicinity of this point where the operation though adiabatic is not isothermal in that some change of the temperature occurs during the autoevaporation.
• solutions can be used containing as much as 75% CaCl at a temperature not exceeding 200 C.
• a lower limit I may use liquor containing 67% calcium chloride with an initial temperature as low as 150 to 160 C., which will autoevaporate adiabatically to give solid calcium chloride by reducing the partial vapour pressure of water down to about 50 mm. of mercury.
• the same eifect can be achieved by starting with 65% calcium chloride solution at a higher temperatures and subjecting it to the same process, but this does not give the same thermal advantage.
• concentrations there is a com aratively restricted range of concentrations in which my process operates without the introduction of any heat.
• 65% to CaClz the preferred concentrations lie between 68% and 72% CaClz, and for the 68% liquor it has been found preferable to start with a temperature between 150 and 170 C., and for the 72% liquor it has been found preferable to start at a temperature between 170 and 180 C.
• a paddle creeper which is open at the top for access of air.
• the paddle creeper contains granular calcium chloride, and a 68% to 72% calcium chloride liquor at a temperature of 150 to 180 C. is fed in at one end of this creeper.
• a pool of liquor thus forms at the feed end, and further along the creeper the contents become mushy and subsequently become dry, and eventually free-flowing granular calcium chloride runs off at the far end.
• I provide a process for producing solid calcium chloride from a highly concentrated solution at an elevated temperature, preferably between 120 and 200 C., by providing a large surface area of the liquor and a low partial water vapour pressure to facilitate vaporisation of the water, and substantially adiabatically allowing the vaporisation to yield solid calcium chloride.
• the solution employed is of a concentration at or near saturation at these temperatures.
• the process may be carried out, for example, by spraying a 67% 'to 72% CaClz solution at 150 to 175 C. into a vacuum, or by spraying a 65% to 70% CaClz solution at 150 to 170 0.
• the characteristic feature of the invention is the substantially adiabatic nature of the operation, thereby avoiding the difficult process of heat this maximum vapour pressure, the heat required a to convert a saturated solution to water vapour and solid calcium chloride dihydrate at the same temperature is nil. In' respect of this vapour pressureof saturated aqueous. solutions, calcium chloride differs from most other inorganic substances.
• the invention also provides a further characteristic feature in the form of the product.
• the process can clearl be carried out as a batch process, but in industrial operation it is much more convenient to carry it out as a continuous process as, for example, in apparatus of the creeper type.
• the process is operated at a relatively low temperature and therefore the attack on materials of which the plant'is con.- structed is not serious.
• mild steel can be used for the construction of the plant, and cast iron is also eminently satisfactory.
• attack on th vessels duringthe present process can readily be avoided by producing a thin layer, of scale on the surface of the vessel and any stirrers or other metallic parts.
• the thin layer of scale may be readil deposited from the solution used in the process by filling the vessels with this solution and causing slight cooling.
• the scale so formed is adherent and permits the manufacture of white calcium chloride.
• Example 1 The apparatus used in this example consists of a vertical tower 3 feet in diameter and 15 feet high, equipped at the bottom with a tray which can be emptied through a doorway, and at-the top with a spray nozzle :fed through a control valve from a stock tank. Apart from these fea tures, the tower is empty and is closed to the atmosphere and connected through a condenser to a vacuum pump. In the process; theabsolute pressure inside'the tower is reduced to 5 lbs. per square inch by means of the vacuum-pump. 'The stock tank is filled with a liquor containing 70% CaGlz, 28% E20 and 2% of sundry impurities principally N aCl, which is at C.
• the control valve is then opened to admit liquor at a rate of 200 litres per hour.
• the liquor may be observed through windows in the walls of the tower and is seen to emerge from the spray nozzle as multitudinous droplets As these droplets fall in the tower they change to a solid. and collect on the tray in the manner of snowfall.
• the liquor feed valve is closed, the vacuum is released, the tray is emptied into a container and the operation restarted.
• the product so obtained is much too hot to handle manually when removed from the tower, and when cold is found to contain 76% CaClz. It has a bulk density of .4 to .5 gram per cc. Microscopically the structure of the solid can be observed to be jagged and shredded.
• Example 2 In this example the apparatus consists of a vertical tower of 5 feet diameter and 30 feet high,
• the spray nozzles are fed by a pump from a stock tank.
• the stock tank is filled with liquor containing 70% CaClz, 28% H20 and the remainder impurities principally NaCl. This liquor is kept at 170 C. and is pumped through the spray nozzles into the tower at a rate of 250 litres per hour.
• simule taneously, air is blown into the bottom of the tower at 180 C. and at a rate of 150 m. per hour, and evacuated from the top along with the water vapour evolved.
• Hot, granular 76% calcium chloride collects on the band conveyor and is removed and packed. It has a bulk density of 0.8 gm. per cc.
• Example 3 The equipment consists of an inclined. trough 2 feet wide and 2 feet deep, fitted with a rotatin paddle mixer, and insulated to prevent undue loss of heat through the walls.
• the liquor ems ployed contains 65% CaClz and 33% B20, and is used at a temperature of 150 C. Air at 150 C. is allowed to circulate freely over the top of the open trough.
• the trough is substantially filled with solid granular calcium chloride (about cwts.), and liquor is then run into the feed end of the trough continuously at a rate of .1 m5 per hour.
• Example 4 solid 75% calcium chloride, which is scraped 017 as flakes on the downgoing side of the drum.
• Example 5 In this example a batch process is, illustrated.
• The'apparatus consists of an open stirred pot which is heated gently. This pot. is half-filled with 70% CaClz liquor. Hot air is blown over the top; of the liquor, which becomes first a slurry and then a moist solid which gradually dries and crumbles. Within an hour a dry freeeflowing granular solid of particle size chiefly between.. 2 mm. and .5 mm. is obtained, containing 76% calcium chloride.
• the process for the manufacture, of solid hydrated calcium chloride from an aqueous solution thereoi whi h comprises heating an aqueous calcium chloride solution of between 60% to 72% calcium chloride content to a temperature of between 120- and 200 0., then providing a large surface area of the heated solution, subjecting the solution to a partial water vapor pressure of less than one atmosphere and allowing the solution to yield solid hydrated calcium chloride by substantially adiabatic evaporation of water.
• a process for the manufacture of solid. hydrated calcium chloride from an aqueous solution thereof which comprises heating an aqueous calcium chloride solution of between 65%. to calcium chloride content to a temperature of to C., and then spraying. he heated solution. into a vacuum to provide a large sur: face area of the. heated solution, allowing the solution to yield solid. hydrated calcium chloride by substantially adiabatic evaporation of water and, thereafter collecting the resultingsolid hydrated calcium chloride.
• a process for the production of solid hydrated calcium chloride from an aqueous solution thereof which comprises heating an aqueous solution of calcium chloride containing between 65 to 70% calcium chloride to a temperature of 150 to 0., providing a large area of the heated solution by spraying the heated solution into a current of air heated to atemperature between 150 to 170 C., and collecting the resulting solid hydrated calcium chloride particles.
• a process for the production of solid hydrated calcium chloride from an aqueous solution thereof which comprises heating an aqueous solution of calcium chloride containing between 60 to 72% calcium chloride. to. a temperature of 120 to 200 0., providing a large area ofthe heated solution by flowing the heated solution onto an agitated bed of granulated. calcium chloride, cir-.- culating air of approximately the same temperature as the heated solution over the agitated bed, and removing particles of solid hydrated calcium chloride from said bed.

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Geology (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
• Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=26239558

Family Applications (1)

Country Status (7)

Cited By (5)

Families Citing this family (3)

Citations (12)

• 1946
  • 1946-03-25 GB GB9116/46A patent/GB612530A/en not_active Expired
  • 1946-03-25 GB GB6243/47A patent/GB612603A/en not_active Expired
• 1947
  • 1947-03-21 US US736423A patent/US2556184A/en not_active Expired - Lifetime
  • 1947-03-22 NL NL131168A patent/NL77144C/nl active
  • 1947-03-25 BE BE472117A patent/BE472117A/fr unknown
  • 1947-03-25 CH CH275158D patent/CH275158A/de unknown
  • 1947-03-25 BE BE472116A patent/BE472116A/fr unknown
  • 1947-03-26 FR FR943963D patent/FR943963A/fr not_active Expired
• 1948
  • 1948-10-27 DE DEP309D patent/DE819689C/de not_active Expired

Patent Citations (12)

Also Published As

Similar Documents