Background technology
Potassium carbonate is an important basic raw material for inorganic chemicals. It was successfully developed and put into industrial production in my country in the early 1970s. At that time, it was mainly used in the purification of synthesis gas in synthetic ammonia plants. It can also be used When used as chlorine-free potassium fertilizer, the demand is small. After the 1980s, the demand for potassium carbonate in my country has grown rapidly, and its applications have become increasingly widespread: it is widely used as a decarbonization agent for fertilizers in the chemical industry, and as a scavenger for hydrogen sulfide and carbon dioxide in industrial gases; Anti-aging agent for rubber; widely used in the glass industry to manufacture computer monitors, TV picture tube glass shells, electronic tubes, precision glassware and various special glasses for decoration; in agricultural production, it is a good chlorine-free potassium fertilizer, which contains The carbonate radical is the raw material for photosynthesis of plants and has a loosening effect on the soil; in addition, potassium carbonate is also widely used in welding rods, inks, photographic chemicals, polyester, explosives, tanning, electroplating, ceramics, building materials, crystal, Production of potassium soaps and pharmaceuticals.
Production methods
Potassium carbonate is produced by the plant ash method, Lubrand method, electrolysis method, and ion exchange method. wait. The plant ash method is the oldest method, which is extracted from plant ash burned from various plant shells (such as cottonseed shells, tea seed shells, tung seed shells, and sunflower seed shells). The plant ash contains soluble potassium carbonate, potassium sulfate, potassium chloride, etc. Salt can be separated by precipitation and filtration. This method is rarely used due to low product quality, uneconomical, and limited by the source of raw materials. The Lubulan method is to mix potassium sulfate with coal powder and lime, and then reduce and roast it to obtain Black ash (containing burned products such as potassium carbonate and calcium sulfide) is leached, filtered, evaporated, and carbonized to obtain potassium bicarbonate, which is then filtered and calcined to obtain the product. This method has been replaced by other methods due to the long process flow and other reasons. Replaced; the electrolysis method is to electrolyze the potassium hydroxide solution obtained by electrolyzing potassium chloride, carbonize it with carbon dioxide in a carbonization tower, evaporate it through a multi-effect evaporator, filter it to obtain potassium bicarbonate, and then calcine it to obtain the product. This method is because Raw materials are easily available, potassium utilization is high, and no three wastes are produced, so it is widely used. However, it consumes a lot of power and has high equipment requirements. The investment in ion membrane electrolyzer equipment costs a lot of tools and the capital recovery cycle is long, resulting in high product costs; ion membrane electrolyzer equipment The exchange method uses cation exchange resin to exchange with potassium chloride, and then uses ammonium bicarbonate to elute into a dilute potassium bicarbonate solution. The product is obtained through multi-effect evaporation, carbonization, crystallization, separation, and calcination. The product of this method has good quality and the process flow is Short, but only suitable for small-scale production. The raw material potassium chloride is usually chemically pure or industrially pure, and the cost is high. Since cation exchange resins often use sodium-type ion exchange resins, there will also be resin exchange capacity and potassium ion exchange rate. It is not high, the dosage of potassium chloride is large, and the consumption is large.
Preparation method
(1) Primary brine refining: send the raw potassium salt to the salt tank, add water to form a saturated solution at a temperature of 50~60°C For crude brine, add KOH solution to the crude brine until the Mg2+ concentration in the crude brine is less than 5ppm. Add a small amount of FeCl3 solution until the color of the crude brine changes to earthy yellow, then add no more. Then add KKO3 solution until the Ca2+ concentration of the crude brine is less than 5ppm. , let stand, filter, and obtain primary brine and salt mud respectively;
(2) Secondary brine refining: filter the primary brine through a membrane filter, and then send the filtrate into the chelating resin tower to obtain Refined brine, and pass it into the brine storage tank;
(3) Preparation of the potassium liquid: Prepare the refined brine in the brine storage tank into a potassium chloride solution with a weight concentration of 2% as the potassium liquid;
(4) Ion exchange reaction: 732 sodium type cation exchange resin is selected in the ion exchange tower, and the upper potassium liquid is counter-currently flowed into the ion exchange tower. The upper potassium flow is 0.028L.min-1, and the sodium Type cation exchange resin is converted into potassium type resin. Experiments have proven that the potassium ion exchange rate can reach 93%;
(5) Elution reaction: Use ammonium saturated NH4HCO3 solution as the eluent, and follow the The flow flows into the ion exchange tower. The ammonium supply flow rate is 0.030L.min-1. The potassium resin is converted into ammonium resin. The molar ratio of the amount of ammonium to the amount of potassium in step ⑷ or step ⑹ is 1.13:1. After elution Obtain a mixed solution of potassium bicarbonate and ammonium bicarbonate;
(6) Resin regeneration reaction: Countercurrently flow the upper potassium liquid into the ion exchange tower, backwash the ammonium resin, and convert the ammonium resin into potassium resin, repeat steps ⑸ and step (6) multiple times;
(7) Evaporation and concentration: The mixed solution of potassium bicarbonate and ammonium bicarbonate obtained in step ⑸ is heated to a temperature of 120~150°C. Evaporate and concentrate, using water as the reference density. When the relative density of the solution is 1.576, stop heating;
(8) Spray granulation: Spray granulate the solution obtained in step ⑺ to obtain potassium carbonate product.
