Abstract
The invention relates to a method for preparing high-purity magnesium oxide by pyrolysis of magnesium chloride. The method includes the following steps: (1) After dissolving salt lake hydrochlorite or old brine, B2O3 and SO2-4 are removed to obtain a mass concentration of 29 to 29 32% magnesium chloride solution; (2) After pre-concentrating the magnesium chloride solution, spray it into the pyrolysis reactor through the nozzle, where the decomposition temperature is 500~650°C, the pressure is -80~-20Pa, and the decomposition time is 1~5s Decompose under the conditions to obtain the pyrolysis product magnesium oxide and pyrolysis tail gas; (3) The pyrolysis product magnesium oxide is sequentially hydrated to remove impurities, washed, filtered and then roasted to obtain high-purity magnesium oxide with MgO>99.0%. The invention has simple process, low cost, high raw material decomposition rate, short decomposition time, high thermal efficiency and full utilization of heat.
Description
A method for preparing high-purity magnesium oxide by pyrolysis of magnesium chloride
Technical field
The present invention relates to a method for preparing high-purity magnesium oxide in the technical field of inorganic chemicals, and in particular, to a method for preparing high-purity magnesium oxide by pyrolysis of magnesium chloride using salt lake hydrochlorite (brine) as raw material.
Background technology
Magnesium oxide is mainly used as a raw material for the preparation of ceramics, enamels, refractory crucibles and refractory bricks. It is also used as a polishing agent, adhesive, filler for coatings and paper, and an accelerator and activator for chloroprene rubber and fluorine rubber; and After mixing magnesium chloride and other solutions, magnesium oxide water can be made. It is used as an antacid and laxative in medicine, for gastric acidosis and duodenal ulcer disease; in the chemical industry, it is used as a catalyst and a raw material for manufacturing magnesium salts.
MgO≥99.0% is called high-purity magnesium oxide, which is mainly used to produce high-purity magnesia, high-purity magnesium hydroxide flame retardant, silicon steel grade magnesium oxide, fused magnesium oxide single crystal, high-purity fused magnesium oxide, nanoscale magnesium oxide and oxide Magnesium whiskers and other special magnesium oxide series products.
Divided by the raw materials used, there are currently several methods for producing magnesium oxide:
1) Natural magnesite calcined. The main component of magnesite is MgCO3, which is calcined at a certain temperature to become magnesium oxide. The reaction equation is as follows:
MgCO3＝MgO+CO2↑
In this method, impurities in the raw materials will be brought into the product. Due to the limitations of the raw materials, the MgO content of the product is 92 to 97%, which cannot meet the requirements of high-purity magnesium oxide.
2) Dolomite carbonization method. After dolomite is calcined, it undergoes hydration, carbonization, separation, pyrolysis and roasting to obtain magnesium oxide. The reaction equation is as follows:
CaMg(CO3)2＝CaO+MgO+2CO2↑
CaO+MgO+2H2O＝Ca(OH)2+Mg(OH)2
Ca(OH)2+Mg(OH)2+CO2＝Mg(HCO3)2+CaCO3↓
2Mg(HCO3)2+H2O＝MgCO3·Mg(OH)2·H2O+3CO2↑
MgCO3·Mg(OH)2＝2MgO+2H2O↑+CO2↑
The product obtained by this method is of good quality, but the process is complicated and the product cost is high.
3) Magnesium chloride (bischite, seawater and old brine) method. Magnesium chloride reacts with alkali or salt (NaOH, CaOH, NH3·H2O, Na2CO3, NH4(HCO3)2) to produce magnesium hydroxide or basic magnesium chloride, which decomposes to obtain magnesium oxide and magnesium chloride is thermally decomposed to produce magnesium oxide. There are mainly lime method, ammonia method and ammonium carbonate method.
① Lime method
After calcining limestone, the hydrated Ca(OH)2 reacts with magnesium chloride to produce Mg(OH)2, which is then roasted to obtain magnesium oxide. The process includes limestone, ash milk preparation, magnesium hydroxide precipitation, solid-liquid separation, magnesium hydroxide light burning and other process processes. The reaction equation is as follows:
CaCO3＝CaO+2CO2↑
MgCl2+CaO+H2O＝Mg(OH)2↓+CaCl2
2Mg(OH)2＝2MgO+2H2O↑
This method has a simple process flow and low production cost, but it has the disadvantages of poor filtration performance of magnesium hydroxide during the production process, high requirements for raw materials, and difficulty in obtaining high-quality products.
② Ammonia method
The basic principle of the ammonia method is the same as that of the lime method or dolomite method, except that ammonia water with weak alkalinity is used as a precipitant, that is, ammonia or ammonia water reacts with brine to generate magnesium hydroxide, and then magnesium hydroxide is lightly calcined into magnesium oxide.
The obvious advantages of the ammonia method are that the generated Mg(OH)2 has high crystallinity, fast sedimentation rate, easy filtration and washing, and easy control and removal of impurities, which is conducive to improving product quality, but the yield is low and the cost is high.
③ Carbon ammonium method
This method uses ammonium bicarbonate or sodium carbonate to react with magnesium chloride to generate magnesium carbonate, and magnesium carbonate is thermally decomposed to generate magnesium oxide. The advantages of this method are small equipment investment, high product purity and high yield, but the cost of raw materials is high, the value of by-products is low, and the process technology is poor.
④ Pyrolysis method
Magnesium chloride is pyrolyzed to produce magnesium oxide and HCl. The reaction equation is as follows:
MgCl2+H2O＝MgO+2HCl↑
The method has a simple process, does not require other raw materials in the production process, and has high product quality, but the pyrolysis process control is relatively complex and the pyrolysis energy consumption is relatively high.
Invention content
The technical problem to be solved by the present invention is to provide a method for preparing high-purity magnesium oxide by pyrolysis of magnesium chloride with a simple process and low cost.
In order to solve the above problems, a method for preparing high-purity magnesium oxide by pyrolysis of magnesium chloride described in the present invention comprises the following steps:
(1) After dissolving salt lake water bischofite or old brine, barium chloride and boron adsorption special resin are used to remove B2O3 and SO2- 4. Obtain a magnesium chloride solution with a mass concentration of 29-32%; wherein 15-20g of barium chloride is consumed for every kg of bischofite or old brine;
(2) Pre-concentrating the magnesium chloride solution obtained in step (1) to a mass concentration of 38-41% and a solution temperature of 80-90°C, spraying it into a pyrolysis reactor through a nozzle at a flow rate of 55-61L/h, and contacting it with a gas at a temperature of 1200-1500°C under a nozzle pressure of 0.3-1.0MPa; decomposing it under the conditions of a decomposition temperature of 500-650°C, a pressure of -80–20Pa, and a decomposition time of 1-5s, to obtain a pyrolysis product of magnesium oxide and a pyrolysis tail gas containing magnesium oxide dust at a temperature of 400-480°C, the main components of which are HCl, H2O, CO2 and N2;
The magnesium oxide settles into the product silo at the bottom of the pyrolysis reactor;
The pyrolysis tail gas is discharged from the upper gas outlet of the pyrolysis reactor. After gas-solid separation, the solid settles into the product silo at the bottom of the pyrolysis reactor. The gas temperature drops to 280-380°C and contacts with the magnesium chloride solution obtained in step (1) in the pre-evaporator to reduce the gas temperature to 90-110°C. At the same time, the magnesium chloride solution is concentrated to a mass concentration of 38-41% and a temperature of 80-90°C; the gas exiting the pre-evaporator is absorbed in the hydrochloric acid absorption system to obtain by-product hydrochloric acid;
(3) The pyrolysis product magnesium oxide is hydrated, impurity-removed, washed, and filtered, and then roasted at 650-800°C to obtain high-purity magnesium oxide with MgO>99.0%.
The salt lake bischofite in step (1) refers to MgCl2·6H2O produced as a by-product after potassium is extracted from the salt lake.
The old brine in step (1) refers to a MgCl2 solution containing 33% by mass of MgCl2.
The nozzle in step (2) is a pressure type or a centrifugal type.
The pyrolysis reactor in step (2) is a spray reactor.
Compared with the prior art, the present invention has the following advantages:
1. Since the high-temperature tail gas generated by decomposition is contacted with the concentrated magnesium chloride solution for heat exchange and evaporation, the concentration and temperature of the magnesium chloride solution are not only increased, but also the temperature of the gas is reduced, so that the heat is effectively utilized, thereby reducing the production cost.
2. Since the pyrolysis reactor used in the present invention is a spray reactor, and the reactor is equipped with three fuel burners, the thermal efficiency is effectively improved.
3. Compared with other pyrolysis methods, the decomposition time of magnesium chloride is short and the decomposition rate is as high as 96.0-99.2%.
4. The process of the present invention is simple and easy to implement. The obtained high-purity magnesium oxide can be used as an ideal raw material for producing magnesium compound products such as high-purity magnesia, high-purity magnesium hydroxide flame retardant, silicon steel grade magnesium oxide, electrical grade magnesium oxide and magnesium oxide whiskers.
Specific implementation method
Example 1 A method for preparing high-purity magnesium oxide by pyrolysis of magnesium chloride, comprising the following steps:
(1) After dissolving salt lake bischofite with water, barium chloride and boron adsorption special resin are used to remove B2O3 and SO2-4 respectively to obtain a magnesium chloride solution with a mass concentration of 29-32%; wherein 15-20g of barium chloride is consumed per kg of bischofite.
(2) The magnesium chloride solution obtained in step (1) is concentrated in a pre-concentration container to a mass concentration of 38-41% and a solution temperature of 80-90°C, and then sprayed into a pyrolysis reactor through a pressure nozzle at a flow rate of 55L/h. Under the action of a nozzle pressure of 0.3MPa, it contacts with a gas at a temperature of 1200-1500°C; decomposition is carried out under the conditions of a decomposition temperature of 500°C, a pressure of -60Pa, and a decomposition time of 1-5s to obtain a pyrolysis product of magnesium oxide and a pyrolysis tail gas containing magnesium oxide dust at a temperature of 400-480°C, the main components of which are HCl, H2O, CO2 and N2; the decomposition rate of magnesium chloride is 96.18%.
The magnesium oxide settles into the product silo at the bottom of the pyrolysis reactor.
The pyrolysis tail gas is discharged from the upper gas outlet of the pyrolysis reactor. After gas-solid separation, the solid settles into the product silo at the bottom of the pyrolysis reactor. The gas temperature drops to 280-380°C and contacts with the magnesium chloride solution obtained in step (1) in the pre-evaporator to reduce the gas temperature to 90-110°C. At the same time, the magnesium chloride solution is concentrated to a mass concentration of 38-41% and a temperature of 80-90°C. The gas exiting the pre-evaporator is absorbed in the hydrochloric acid absorption system to obtain hydrochloric acid as a byproduct.
(3) The pyrolysis product magnesium oxide is hydrated to remove the water-soluble impurities NaCl and KCl therein to obtain Mg(OH)2 slurry; the Mg(OH)2 slurry is filtered and washed by a plate-frame filter to obtain a filter cake; the filter cake is placed in a roasting furnace and roasted at 650-800°C to obtain high-purity magnesium oxide with MgO>99.0%.
Example 2 A method for preparing high-purity magnesium oxide by pyrolysis of magnesium chloride, comprising the following steps:
(1) After dissolving the old brine with water, barium chloride and boron adsorption special resin are used to remove B2O3 and SO2-4 respectively to obtain a magnesium chloride solution with a mass concentration of 29-32%; wherein 15-20g of barium chloride is consumed per kg of old brine.
(2) The magnesium chloride solution obtained in step (1) is concentrated in a pre-concentration container to a mass concentration of 38-41% and a solution temperature of 80-90°C, and then sprayed into a pyrolysis reactor through a centrifugal nozzle at a flow rate of 55L/h. Under the action of a nozzle pressure of 0.5MPa, it contacts with a gas at a temperature of 1200-1500°C; decomposition is carried out under the conditions of a decomposition temperature of 500°C, a pressure of -80Pa, and a decomposition time of 1-5s to obtain a pyrolysis product of magnesium oxide and a pyrolysis tail gas containing magnesium oxide dust at a temperature of 400-480°C, the main components of which are HCl, H2O, CO2 and N2; the decomposition rate of magnesium chloride is 97.47%.
The magnesium oxide settles into the product silo at the bottom of the pyrolysis reactor.
The pyrolysis tail gas is discharged from the upper gas outlet of the pyrolysis reactor. After gas-solid separation, the solid settles into the product silo at the bottom of the pyrolysis reactor. The gas temperature drops to 280-380°C and contacts with the magnesium chloride solution obtained in step (1) in the pre-evaporator to reduce the gas temperature to 90-110°C. At the same time, the magnesium chloride solution is concentrated to a mass concentration of 38-41% and a temperature of 80-90°C. The gas exiting the pre-evaporator is absorbed in the hydrochloric acid absorption system to obtain by-product hydrochloric acid.
(3) The pyrolysis product magnesium oxide is hydrated to remove the water-soluble impurities NaCl and KCl therein to obtain Mg(OH)2 slurry; the Mg(OH)2 slurry is filtered and washed by a plate-frame filter to obtain a filter cake; the filter cake is placed in a roasting furnace and roasted at 650-800°C to obtain high-purity magnesium oxide with MgO>99.0%.
Example 3 A method for preparing high-purity magnesium oxide by pyrolysis of magnesium chloride, comprising the following steps:
(1) Dissolving salt lake bischofite with water, and then using barium chloride and boron adsorption special resin to remove B2O3 and SO2- 4respectively, to obtain a magnesium chloride solution with a mass concentration of 29-32%; wherein 15-20g of barium chloride is consumed per kg of bischofite.
(2) The magnesium chloride solution obtained in step (1) is concentrated in a pre-concentration container to a mass concentration of 38-41% and a solution temperature of 80-90°C, and then sprayed into a pyrolysis reactor through a pressure nozzle at a flow rate of 61L/h. Under the action of a nozzle pressure of 0.5MPa, it contacts with a gas at a temperature of 1200-1500°C; decomposition is carried out under the conditions of a decomposition temperature of 550°C, a pressure of -35Pa, and a decomposition time of 1-5s to obtain a pyrolysis product of magnesium oxide and a pyrolysis tail gas containing magnesium oxide dust at a temperature of 400-480°C, the main components of which are HCl, H2O, CO2 and N2; the decomposition rate of magnesium chloride is 98.85%.
The magnesium oxide settles into the product silo at the bottom of the pyrolysis reactor.
The pyrolysis tail gas is discharged from the upper gas outlet of the pyrolysis reactor. After gas-solid separation, the solid settles into the product silo at the bottom of the pyrolysis reactor. The gas temperature drops to 280-380°C and contacts with the magnesium chloride solution obtained in step (1) in the pre-evaporator to reduce the gas temperature to 90-110°C. At the same time, the magnesium chloride solution is concentrated to a mass concentration of 38-41% and a temperature of 80-90°C. The gas exiting the pre-evaporator is absorbed in the hydrochloric acid absorption system to obtain by-product hydrochloric acid.
(3) The pyrolysis product magnesium oxide is hydrated to remove the water-soluble impurities NaCl and KCl therein to obtain Mg(OH)2 slurry; the Mg(OH)2 slurry is filtered and washed by a plate-frame filter to obtain a filter cake; the filter cake is placed in a roasting furnace and roasted at 650-800°C to obtain high-purity magnesium oxide with MgO>99.0%.
Example 4 A method for preparing high-purity magnesium oxide by pyrolysis of magnesium chloride, comprising the following steps:
(1) After dissolving the old brine with water, barium chloride and boron adsorption special resin are used to remove B2O3 and SO2-4 respectively to obtain a magnesium chloride solution with a mass concentration of 29-32%; wherein 15-20g of barium chloride is consumed per kg of old brine.
(2) The magnesium chloride solution obtained in step (1) is concentrated in a pre-concentration container to a mass concentration of 38-41% and a solution temperature of 80-90°C, and then sprayed into a pyrolysis reactor through a centrifugal nozzle at a flow rate of 61L/h. Under the action of a nozzle pressure of 0.5MPa, it contacts with a gas at a temperature of 1200-1500°C; decomposition is carried out under the conditions of a decomposition temperature of 600°C, a pressure of -53Pa, and a decomposition time of 1-5s to obtain a pyrolysis product of magnesium oxide and a pyrolysis tail gas containing magnesium oxide dust at a temperature of 400-480°C, the main components of which are HCl, H2O, CO2 and N2; the decomposition rate of magnesium chloride is 99.04%.
The magnesium oxide settles into the product silo at the bottom of the pyrolysis reactor.
The pyrolysis tail gas is discharged from the upper gas outlet of the pyrolysis reactor. After gas-solid separation, the solid settles into the product silo at the bottom of the pyrolysis reactor. The gas temperature drops to 280-380°C and contacts with the magnesium chloride solution obtained in step (1) in the pre-evaporator to reduce the gas temperature to 90-110°C. At the same time, the magnesium chloride solution is concentrated to a mass concentration of 38-41% and a temperature of 80-90°C. The gas exiting the pre-evaporator is absorbed in the hydrochloric acid absorption system to obtain hydrochloric acid as a byproduct.
(3) The pyrolysis product magnesium oxide is hydrated to remove the water-soluble impurities NaCl and KCl therein to obtain Mg(OH)2 slurry; the Mg(OH)2 slurry is filtered and washed by a plate-frame filter to obtain a filter cake; the filter cake is placed in a roasting furnace and roasted at 650-800°C to obtain high-purity magnesium oxide with MgO>99.0%.
Example 5 A method for preparing high-purity magnesium oxide by pyrolysis of magnesium chloride, comprising the following steps:
(1) Dissolving salt lake bischofite in water, and then using barium chloride and boron adsorption special resin to remove B2O3 and SO2-4 respectively, to obtain a magnesium chloride solution with a mass concentration of 29-32%; wherein 15-20g of barium chloride is consumed per kg of bischofite.
(2) The magnesium chloride solution obtained in step (1) is concentrated in a pre-concentration container to a mass concentration of 38-41% and a solution temperature of 80-90°C, and then sprayed into a pyrolysis reactor through a pressure nozzle at a flow rate of 61L/h. Under the action of a nozzle pressure of 0.8MPa, it contacts with a gas at a temperature of 1200-1500°C; decomposition is carried out under the conditions of a decomposition temperature of 600°C, a pressure of -28Pa, and a decomposition time of 1-5s to obtain a pyrolysis product of magnesium oxide and a pyrolysis tail gas with a temperature of 400-480°C and containing magnesium oxide dust whose main components are HCl, H2O, CO2 and N2; the decomposition rate of magnesium chloride is 99.11%.
The magnesium oxide settles into the product silo at the bottom of the pyrolysis reactor.
The pyrolysis tail gas is discharged from the upper gas outlet of the pyrolysis reactor. After gas-solid separation, the solid settles into the product silo at the bottom of the pyrolysis reactor. The gas temperature drops to 280-380°C and contacts with the magnesium chloride solution obtained in step (1) in the pre-evaporator to reduce the gas temperature to 90-110°C. At the same time, the magnesium chloride solution is concentrated to a mass concentration of 38-41% and a temperature of 80-90°C. The gas exiting the pre-evaporator is absorbed in the hydrochloric acid absorption system to obtain by-product hydrochloric acid.
(3) The pyrolysis product magnesium oxide is hydrated to remove the water-soluble impurities NaCl and KCl therein to obtain Mg(OH)2 slurry; the Mg(OH)2 slurry is filtered and washed by a plate-frame filter to obtain a filter cake; the filter cake is placed in a roasting furnace and roasted at 650-800°C to obtain high-purity magnesium oxide with MgO>99.0%.
Example 6 A method for preparing high-purity magnesium oxide by pyrolysis of magnesium chloride, comprising the following steps:
(1) After dissolving the old brine with water, barium chloride and boron adsorption special resin are used to remove B2O3 and SO2- 4 respectively to obtain a magnesium chloride solution with a mass concentration of 29-32%; wherein 15-20g of barium chloride is consumed per kg of old brine.
(2) The magnesium chloride solution obtained in step (1) is concentrated in a pre-concentration container to a mass concentration of 38-41% and a solution temperature of 80-90°C, and then sprayed into a pyrolysis reactor through a centrifugal nozzle at a flow rate of 58L/h. Under the action of a nozzle pressure of 1.0MPa, it contacts with a gas at a temperature of 1200-1500°C; decomposition is carried out under the conditions of a decomposition temperature of 650°C, a pressure of -20Pa, and a decomposition time of 1-5s to obtain a pyrolysis product of magnesium oxide and a pyrolysis tail gas containing magnesium oxide dust at a temperature of 400-480°C, the main components of which are HCl, H2O, CO2 and N2; the decomposition rate of magnesium chloride is 99.20%.
The magnesium oxide settles into the product silo at the bottom of the pyrolysis reactor.
The pyrolysis tail gas is discharged from the upper gas outlet of the pyrolysis reactor. After gas-solid separation, the solid settles into the product silo at the bottom of the pyrolysis reactor. The gas temperature drops to 280-380°C and contacts with the magnesium chloride solution obtained in step (1) in the pre-evaporator to reduce the gas temperature to 90-110°C. At the same time, the magnesium chloride solution is concentrated to a mass concentration of 38-41% and a temperature of 80-90°C. The gas exiting the pre-evaporator is absorbed in the hydrochloric acid absorption system to obtain hydrochloric acid as a byproduct.
(3) The pyrolysis product magnesium oxide is hydrated to remove the water-soluble impurities NaCl and KCl therein to obtain Mg(OH)2 slurry; the Mg(OH)2 slurry is filtered and washed by a plate-frame filter to obtain a filter cake; the filter cake is placed in a roasting furnace and roasted at 650-800°C to obtain high-purity magnesium oxide with MgO>99.0%.
The pyrolysis reactors in the above-mentioned Examples 1-6 are all spray reactors developed by the Institute of Salt Lakes, Chinese Academy of Sciences.
Salt lake water bischofite refers to MgCl2·6H2O produced as a byproduct after potassium is extracted from salt lakes.
Old brine refers to a MgCl2 solution containing 33% MgCl2 by mass.