Ammonia soda process - Ammonia soda process

Also known as the Solvay process. A method for producing soda ash (sodium carbonate). It was first developed by E. Solvay of Belgium in 1866. After the First World War, it replaced the traditional Leblanc process, and today all soda ash is produced using this method. The overall reaction is:

2NaCl + CaCO ₃ → Na ₂ CO ₃ + CaCl ₂

The process is shown in the figure below, and consists of the following steps: (1) Production of ammoniacal brine: Raw salt is dissolved in seawater. Since it contains _CaSO4 , _MgSO4 , and MgCl, milk of lime Ca(OH) ₂ is added and first removed as Mg(OH) ₂ (primary purification). Next, the Ca content is precipitated through the waste gas ( _NH3 - _CO2 - _N2 ) from the carbonation tower, and purified brine (secondary purification) is produced in a clarification tank. In recent years, polymeric flocculants such as polyacrylamide have been used to promote precipitation and coagulation. This is allowed to flow down from the top of the ammonia absorption tower and _NH3 (which contains _CO2 and water vapor) is saturated (it generates heat, so it is kept below 60°C). 1 liter of ammoniacal brine contains approximately 260 g of NaCl, 75 g of _NH3 , and 40 g of _CO2 . (2) Carbonation: Brine is gravity-fed from the top of a carbonation tower (Solvay tower) until it is saturated with _CO2 , and _NaHCO3 is precipitated by utilizing the difference in solubility of each salt according to the following equation.

NaCl + NH ₃ + H ₂ O + CO ₂ → NaHCO ₃ (1) + NH ₄ Cl

The necessary _CO2 is obtained by calcining _NaHCO3 and roasting limestone _CaCO3 . A cooling section is installed in the tower to increase the reaction rate by carbonation. The reaction efficiency is expressed as the salt utilization rate _UNa , or the _NH3 utilization rate _UNH3 . In actual operation, _UNa is about 75%. The solution containing the _NaHCO3 crystals is filtered using an Oliver-type rotating cylindrical vacuum filter to separate it from the mother liquor. The cake contains 70% _NaHCO3 . The crystals are washed with water and dried, and then calcined and dehydrated, usually at around 200°C, to produce soda ash (light ash) with an apparent specific gravity of about 0.7.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

ソルベー法ともいう．ソーダ灰(炭酸ナトリウム)の製造法．1866年にベルギーのE. Solvay(ソルベー)が創始した．第一次世界大戦終了とともに従来のルブラン法にとってかわり，現在，ソーダ灰製造はすべてこの方法によっている．全反応は

2NaCl ＋ CaCO₃ → Na₂CO₃ ＋ CaCl₂

で示されるが，ほぼ次の工程からなる．(1)アンモニアかん水(ammoniacal brine，安かん水)の製造：原料塩を海水に溶かし，CaSO₄，MgSO₄，MgClを含むので，石灰乳Ca(OH)₂を加えてまずMg(OH)₂として除き(一次精製)，ついで炭酸化塔の廃ガス(NH₃-CO₂-N₂)を通じてCa分を沈殿させ，清澄槽で精製かん水(二次精製)をつくる．近年は，ポリアクリルアミドのような高分子凝集剤を用いて沈殿凝集を促進している．これをアンモニア吸収塔上から流下させ，NH₃(CO₂と水蒸気を含む)を飽和させる(発熱するから60 ℃ 以下に保つ)．安かん水1 L 中に，約NaCl 260 g，NH₃75 g，CO₂40 g が含まれる．(2)炭酸化：炭酸化塔(ソルベー塔)の上から安かん水を自然流下してCO₂を飽和させ，次式により各塩の溶解度の差を利用してNaHCO₃を沈殿させる．

　　NaCl ＋ NH₃ ＋ H₂O ＋ CO₂ → NaHCO₃(1) ＋ NH₄Cl　　

必要なCO₂はNaHCO₃のか焼と石灰石CaCO₃のばい焼によって得られる．炭酸化で反応率を上げるため，塔に冷却部をもうける．反応効率は食塩利用率 U_Na，あるいはNH₃利用率 U_NH3 で表される．実操業では U_Na ＝ 75％ 程度である．NaHCO₃結晶を含む溶液はオリバー式回転円筒型の真空濾過器などでこして，母液と分離する．ケーキ中にNaHCO₃は70％ 含まれる．結晶を水洗，乾燥後，通常200 ℃ 程度でか焼脱水し，見掛けの比重0.7程度のソーダ灰(軽灰)とする．

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