JP4517530B2 - Method for producing aqueous potassium hydroxide solution - Google Patents
Method for producing aqueous potassium hydroxide solution Download PDFInfo
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- JP4517530B2 JP4517530B2 JP2001121519A JP2001121519A JP4517530B2 JP 4517530 B2 JP4517530 B2 JP 4517530B2 JP 2001121519 A JP2001121519 A JP 2001121519A JP 2001121519 A JP2001121519 A JP 2001121519A JP 4517530 B2 JP4517530 B2 JP 4517530B2
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Description
【０００１】
【発明の属する技術分野】
本発明は、水酸化カリウム水溶液の製造方法に関する。
【０００２】
【従来の技術】
一般に、水酸化カリウム水溶液は、塩化カリウム水溶液の電解により製造されており、工業用水酸化カリウム水溶液は、濃度４８％のものが標準である。原料として使用される塩化カリウムには、不純物として塩化ナトリウム等の形でナトリウムが含有されている。原料塩化カリウム中のナトリウム含有量（ナトリウム元素換算値。本明細書において同じ。）は３００〜５０００ｐｐｍであるため、原料塩化カリウム中のナトリウム除去を行わないかぎり、ナトリウム含有量が１００ｐｐｍ以下の、濃度４８％水酸化カリウム水溶液を得ることは困難である。
【０００３】
電解により水酸化カリウムを製造するための塩化カリウム水溶液から不純物ナトリウムを除去する方法としては、従来、塩化カリウム水溶液にアンチモン酸を添加してナトリウムを除去する方法（特開昭６１−１００２５号公報参照）、塩化カリウム水溶液にリン酸ジルコニウムを添加してナトリウムを除去する方法（特開平９−２５１１７号公報参照）等が知られている。
【０００４】
これらの方法は、プロセスが煩雑であり、エネルギー消費量も多いという問題があった。特に、塩化カリウム水溶液にアンチモン酸、リン酸ジルコニウム等が添加されると水酸化カリウム中にこれら添加物が混入しがちであり、その除去が困難なことから、得られた水酸化カリウム水溶液は医薬品、食品又は半導体分野向け等には不適であった。
【０００５】
【発明が解決しようとする課題】
本発明は、原料塩化カリウムから効率的にナトリウムを除去し、ナトリウム含有量の少ない水酸化カリウム水溶液を得ることを目的とする。
【０００６】
【課題を解決するための手段】
本発明は、ナトリウム含有量が３００〜５０００ｐｐｍの原料塩化カリウムに、ナトリウム含有量が１５００ｐｐｍ以下の塩化カリウム水溶液又は水を混合して濃度２２〜２８％の粗水溶液とし、前記粗水溶液を温度−５〜１０℃に冷却して固体塩化カリウムを析出させ、析出した固体塩化カリウムを分離して、水に再溶解し、ナトリウム含有量が６０ｐｐｍ以下の飽和塩化カリウム水溶液とし、イオン交換膜電解法により電解して濃度４８％の水酸化カリウム水溶液に換算したときにナトリウム含有量が１００ｐｐｍ以下の水酸化カリウム水溶液を得る水酸化カリウム水溶液の製造方法を提供する。
【０００７】
【発明の実施の形態】
本発明では、原料塩化カリウムと塩化カリウム水溶液又は水とを混合し、濃度２２〜２８％の粗水溶液を作製した後、温度−５〜１０℃まで冷却して固体状態の塩化カリウム（以下、固体塩化カリウムという）を析出させる。この粗水溶液中には、原料塩化カリウムから溶出したナトリウムイオン及び塩化カリウム水溶液又は水に含まれていたナトリウムイオンが存在する。原料塩化カリウム中のナトリウム含有量が３００〜５０００ｐｐｍであり、塩化カリウム水溶液又は水のナトリウム含有量が１５００ｐｐｍ以下であるので、粗水溶液の温度を−５〜１０℃まで冷却した際、塩化カリウムは飽和濃度に達し固体塩化カリウムを生成するが、塩化ナトリウムは飽和濃度より低い濃度となる。その結果、不純物のナトリウムはイオンとして水溶液中に残存する。なお、本明細書では、％、ｐｐｍ、ｐｐｂのいずれも質量換算値である。
【０００８】
本発明では、原料塩化カリウムはナトリウム含有量が３００〜５０００ｐｐｍのものを使用する。ナトリウム含有量が３００ｐｐｍ未満の原料塩化カリウムは、製造方法も難しく高価であるため好ましくない。また、５０００ｐｐｍ超であると、ナトリウムが１００ｐｐｍ以下の４８％水酸化カリウム水溶液を製造することが困難である。原料塩化カリウム中のナトリウム含有量は３００〜１４００ｐｐｍであることが特に好ましい。
【０００９】
本発明では、濃度２２〜２８％の塩化カリウム粗水溶液を作製する。濃度２２％未満であると、塩化カリウム水溶液の固体塩化カリウムを析出する温度が低くなり、冷却等に要する電力が増大するため好ましくない。濃度２８％超であると、固体塩化カリウムを溶解しづらくなるため好ましくない。塩化カリウム粗水溶液の濃度は２６〜２８％が特に好ましい。
【００１０】
本発明では、混合する塩化カリウム水溶液又は水の温度は、０℃〜８０℃が好ましい。温度が０℃未満であると、原料塩化カリウムの溶解の進行が遅くなるので好ましくなく、８０℃超であると、液温が高くなり、扱いにくくなるため好ましくない。温度は５０〜６０℃が特に好ましい。
【００１１】
本発明において、冷却温度は、温度−５〜１０℃にする。冷却温度が−５℃未満であると、塩化カリウムだけでなく塩化ナトリウムも析出しやすくなり、塩化カリウム中のナトリウム含有量が増え、純度が落ちる。また、冷却のためのエネルギーが大きくコスト的に合わない。冷却温度が１０℃超であると、塩化カリウムの溶解度が下がらず、効率よく塩化カリウムを析出させることができない。冷却温度は０℃〜５℃が特に好ましい。
【００１２】
本発明において、固液分離の手段としては、例えば、遠心分離器、水平ベルトフィルタ等の装置を利用する方法、析出した固体塩化カリウムの比重が塩化カリウム水溶液よりも重いことを利用して、冷却槽の構造を、析出した固体塩化カリウムを下部より抜き出し、塩化カリウム水溶液を上部より抜き出す構造とする方法等が挙げられる。
【００１３】
本発明では、冷析工程に供給する塩化カリウム粗水溶液中のカルシウム、マグネシウム又はストロンチウムの含有量は、カルシウム、マグネシウム又はストロンチウムのそれぞれの元素換算値（以下、同じ）でそれぞれ５０ｐｐｂ以下であることが好ましい。これらの元素の含有量が前記の値を超える場合は、冷析工程に供給する前に、塩化カリウム水溶液を陽イオン交換樹脂に通して、カルシウムイオン、マグネシウムイオン又はストロンチウムイオンの２価陽イオンを除去しておくことが好ましい。カルシウムイオン、マグネシウムイオン又はストロンチウムイオンの含有量はそれぞれ２０ｐｐｂ以下が特に好ましい。
【００１４】
陽イオン交換樹脂については、カリウムイオン等の一価イオンよりもカルシウムイオン、マグネシウムイオン又はストロンチウムイオン等の２価陽イオンの方が著しく選択性の高い陽イオン交換樹脂を使用することが好ましい。陽イオン交換樹脂としては、例えば、三菱化学社製の陽イオン交換樹脂ＣＲ−１１等が挙げられる。
【００１５】
本発明において、冷析工程に供給する塩化カリウム粗水溶液は、塩酸を添加することによりｐＨ１〜３とすることが好ましい。ｐＨ３超であると、得られる固体塩化カリウムの結晶が結晶水を含み、飽和塩化カリウム水溶液を作製するための濃度管理が難しくなるので好ましくなく、ｐＨ１未満であると、塩酸を大量に使用すること、装置材質にフッ素樹脂ライニング等の高価な材料を必要とすることから好ましくない。
【００１６】
本発明では、固体塩化カリウムは、水に溶解してナトリウム含有量が６０ｐｐｍ以下の飽和塩化カリウム水溶液とし、イオン交換膜電解法により電解して水酸化カリウム水溶液を製造する。塩化カリウム水溶液のナトリウム含有量が６０ｐｐｍ超であると、本発明における効果が得られないため好ましくない。電解槽から直接得られる水酸化カリウム水溶液の濃度は２８〜５４％が好ましい。水酸化カリウム水溶液の濃度は４８〜５０％が特に好ましい。水酸化カリウム水溶液は濃度４８％換算でナトリウム含有量が１００ｐｐｍ以下のものが得られる。
【００１７】
本発明では、冷析工程で得られた固体塩化カリウムを水に溶解させて電解する工程までの間に、さらに、次の処理を行う場合は、水酸化カリウム水溶液のナトリウム濃度をさらに減少させることができる。以下、この方法を本発明の第２の態様という。
【００１８】
前記固体塩化カリウムを、ナトリウム含有量が６０ｐｐｍ以下の塩化カリウム水溶液又は水と混合して、精製された固体塩化カリウムを含むスラリを形成させることが好ましい。使用する塩化カリウム水溶液は、いずれの濃度のものでも使用できる。塩化カリウム水溶液又は水のナトリウム含有量が６０ｐｐｍ超であると、本発明における効果が得られないため好ましくない。
【００１９】
得られたスラリの水相には、固体塩化カリウムから溶出したナトリウムイオン及び前記塩化カリウム水溶液又は水に含まれていたナトリウムイオンが存在する。このスラリ操作により、固体塩化カリウムに含まれている塩化ナトリウムが水相へ溶出する。スラリの水相において、塩化カリウムは飽和濃度に達するが、塩化カリウム水溶液又は水のナトリウム含有量が６０ｐｐｍ以下であることから、塩化ナトリウムは飽和濃度より低い濃度になり、固体塩化カリウム中の塩化ナトリウムは水相へ溶出し、固体塩化カリウム中のナトリウム成分がさらに除去できる。
【００２０】
スラリは固体濃度１０〜９０％が好ましい。固体濃度が１０％未満であると、生産効率が極めて悪いため好ましくない。固体濃度が９０％超であると、固相と液相の接触が不充分なため満足な洗浄効果が得られず、好ましくない。固体濃度は、７０〜９０％が特に好ましい。なお、固体濃度とは、スラリ中に存在する固体としての濃度であり、スラリの水相に溶解している溶質の量は含まれない。
【００２１】
前記スラリを固液分離することにより精製塩化カリウムが固体として得られる（以下、精製塩化カリウム固体という）ことが好ましい。精製塩化カリウム固体中のナトリウム含有量は、前記固体塩化カリウム中のナトリウム含有量の５０％以上が除去されることが好ましい。固液分離は遠心分離器、水平ベルトフィルタ等により行うことが好ましい。
【００２２】
本発明の第２の態様では、塩化カリウム水溶液又は水を混合してスラリとして固液分離する際、温度０℃〜５０℃とすることにより、原料塩化カリウム中のナトリウム含有量をさらに除去できるので好ましい。塩化カリウム水溶液又は水は温度０℃〜３０℃で混合することが特に好ましい。スラリを混合する温度が３０℃超であると、母液への塩化ナトリウムの溶解度が高くなるので好ましくなく、温度が０℃未満であると、冷却エネルギーが必要となり、コスト的にも好ましくない。スラリを混合する温度は０℃〜１０℃が特に好ましい。
【００２３】
本発明の第２の態様において、精製塩化カリウム固体は、さらに、塩化カリウム水溶液又は水と混合してスラリとし、固液分離する操作を複数回繰り返すことにより、ナトリウム含有量をより低減できるのでさらに好ましい。
【００２４】
精製塩化カリウム固体を水に溶解した後、ナトリウム含有量が４５ｐｐｍ以下の飽和塩化カリウム水溶液とし、イオン交換膜電解法によって電解して水酸化カリウム水溶液を製造することが好ましい。水酸化カリウム水溶液は濃度４８％換算でナトリウム含有量が７５ｐｐｍ以下のものが得られることが好ましい。
【００２５】
本発明の第２の態様において、スラリを固液分離した後の分離母液は、原料塩化カリウムを溶解する前のナトリウム含有量２０００ｐｐｍ以下である塩化カリウム水溶液又は水に、さらに、原料塩化カリウム中から溶出したナトリウムが含有されている。この分離母液は、スラリの溶解又は一般工業用水酸化カリウム水溶液の原料として使用することが好ましい。
【００２６】
【実施例】
以下に本発明の実施例（例１、２、３）及び比較例（例４）を示す。結果をまとめて表１に示す。各例において、水酸化カリウム水溶液中のナトリウム含有量は原子吸光分析法（標準添加法）により測定した。なお、濃度Ｃ％の水酸化カリウム水溶液のナトリウム含有量がＡｐｐｍである場合、濃度４８％の水酸化カリウム水溶液に換算したナトリウム含有量Ｂｐｐｍは、式（Ｂ＝Ａ×４８／Ｃ）により算出した。
【００２７】
[例１]
ナトリウム含有量４２６０ｐｐｍの原料塩化カリウム１０ｋｇに、ナトリウム含有量が０ｐｐｍの水２８ｋｇを添加し、水溶液の温度を５０℃まで上げて、濃度２６％の塩化カリウム粗水溶液３０Ｌを得た。この粗水溶液をイオン交換樹脂（商品名：陽イオン交換樹脂ＣＲ−１１、三菱化学社製、以下同じ）によりカルシウムイオン、マグネシウムイオン、ストロンチウムイオン等の２価陽イオンを除去し、各イオンが２０ｐｐｂ以下とした後、水溶液の温度を５℃まで冷却し、固体塩化カリウムを析出させ、固液分離し、固体塩化カリウム１１００ｇを得た。得られた固体塩化カリウムを純水に溶解し、濃度２６％の塩化カリウム水溶液とした後、この得られた塩化カリウム水溶液を電解（イオン交換膜電解法、電流密度４ｋＡ／ｍ2、電解槽温度９０℃、淡塩水濃度１８％、以下同じ）し、濃度３２％の水酸化カリウム水溶液を得た。
【００２８】
[例２]
例１と同じ塩化ナトリウム粗水溶液を、例１と同様にしてイオン交換樹脂により２価陽イオンを除去した後、濃度１７％塩酸を添加して、水溶液のｐＨを２とした。次に、前記水溶液の温度を５℃まで冷却し、固体塩化カリウムを析出させ、固液分離し、固体塩化カリウムを１１００ｇ得た。得られた固体塩化カリウムをナトリウム含有量が０ｐｐｍの純水に混合、撹拌し、固体濃度８０％のスラリとした後、固液分離し、精製塩化ナトリウム固体１１００ｇを得た。得られた精製塩化カリウムを純水に溶解し、濃度２６％の塩化カリウム水溶液とした後、例１と同様にして電解し、濃度３２％の水酸化カリウム水溶液を得た。
【００２９】
[例３]
ナトリウム含有量１２２０ｐｐｍの原料塩化カリウム１０ｋｇに、ナトリウム含有量０ｐｐｍの水２８ｋｇを添加し、水溶液の温度を５０℃まで上げて、濃度２６％の塩化カリウム粗水溶液３０Ｌを得た。この粗水溶液を、例１と同様にしてイオン交換樹脂により２価陽イオンを除去した後、濃度１７％塩酸を添加し、水溶液のｐＨを２とした。次に、水溶液の温度を５℃まで冷却し、固体塩化カリウムを析出させ、固液分離し、固体塩化カリウム１１００ｇを得た。得られた固体塩化カリウムをナトリウム含有量が０ｐｐｍの純水に混合、撹拌し、固体濃度８０％のスラリとした後、固液分離し、精製塩化ナトリウム固体９３０ｇを得た。この得られた精製塩化カリウムを純水に溶解し、濃度２６％の塩化カリウム水溶液とした後、例１と同様にして電解し、濃度３２％の水酸化カリウム水溶液を得た。
【００３０】
[例４（比較例）]
ナトリウム含有量４２６０ｐｐｍの原料塩化カリウム１０ｋｇに、ナトリウム含有量０ｐｐｍの水２８ｋｇを添加し、水溶液の温度を５０℃まで上げて、濃度２６％の塩化カリウム粗水溶液３０Ｌを得た。以下、例１と同様にして、イオン交換樹脂により陽イオンを除去した後、電解法により濃度３２％の水酸化カリウム水溶液を得た。
【００３１】
[例５（比較例）]
ナトリウム含有量４３０ｐｐｍの原料塩化カリウム１０ｋｇに、ナトリウム含有量０ｐｐｍの水２８ｋｇを添加し、水溶液の温度を５０℃まで上げて、濃度２６％の塩化カリウム粗水溶液３０Ｌを得た。以下、例１と同様にして、イオン交換樹脂により陽イオンを除去した後、電解法により濃度３２％の水酸化カリウム水溶液を得た。
【００３２】
【表１】
表中の単位はいずれもｐｐｍであり、記号は下記のとおり。
ただし、ｅの単位のみ％。
ａ：原料塩化カリウム中のナトリウム含有量、
ｂ：精製塩化カリウム中のナトリウム含有量、
ｃ：陽イオン交換樹脂による精製後の飽和塩化カリウム水溶液中のナトリウム含有量、
ｄ：得られた水酸化カリウム水溶液中のナトリウム含有量、
ｅ：得られた水酸化カリウム水溶液の濃度、
ｆ：濃度４８％に換算した場合の水酸化カリウム水溶液中のナトリウム含有量。
【００３４】
【発明の効果】
本発明により、ナトリウム含有量の少ない水酸化カリウム水溶液を製造できる。また、本発明の方法により得られる水酸化カリウム水溶液は、医薬品、食品及び半導体分野向け等の用途にも好適に使用できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an aqueous potassium hydroxide solution.
[0002]
[Prior art]
In general, an aqueous potassium hydroxide solution is produced by electrolysis of an aqueous potassium chloride solution, and an industrial aqueous potassium hydroxide solution having a concentration of 48% is standard. Potassium chloride used as a raw material contains sodium in the form of sodium chloride as an impurity. Since the sodium content in the raw material potassium chloride (sodium element equivalent value; the same in this specification) is 300 to 5000 ppm, the concentration of the sodium content is 100 ppm or less unless sodium removal in the raw material potassium chloride is performed. It is difficult to obtain a 48% aqueous potassium hydroxide solution.
[0003]
As a method for removing impurity sodium from an aqueous potassium chloride solution for producing potassium hydroxide by electrolysis, a conventional method is to remove sodium by adding antimonic acid to an aqueous potassium chloride solution (see JP-A-61-10025). ), A method of removing sodium by adding zirconium phosphate to an aqueous potassium chloride solution (see JP-A-9-25117), and the like.
[0004]
These methods have problems that the process is complicated and the energy consumption is large. In particular, when antimonic acid, zirconium phosphate, or the like is added to an aqueous potassium chloride solution, these additives tend to be mixed into the potassium hydroxide, and the removal thereof is difficult. It was unsuitable for food or semiconductor fields.
[0005]
[Problems to be solved by the invention]
An object of this invention is to remove sodium efficiently from raw material potassium chloride, and to obtain potassium hydroxide aqueous solution with little sodium content.
[0006]
[Means for Solving the Problems]
In the present invention, a raw material potassium chloride having a sodium content of 300 to 5000 ppm is mixed with a potassium chloride aqueous solution or water having a sodium content of 1500 ppm or less to obtain a crude aqueous solution having a concentration of 22 to 28%. Cooled to -10 ° C to precipitate solid potassium chloride, separated solid potassium chloride was separated and redissolved in water to obtain a saturated potassium chloride aqueous solution having a sodium content of 60 ppm or less, and electrolysis by an ion exchange membrane electrolysis method Thus, a method for producing an aqueous potassium hydroxide solution is provided which obtains an aqueous potassium hydroxide solution having a sodium content of 100 ppm or less when converted to an aqueous potassium hydroxide solution having a concentration of 48%.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, raw material potassium chloride and a potassium chloride aqueous solution or water are mixed to prepare a crude aqueous solution having a concentration of 22 to 28%, and then cooled to a temperature of −5 to 10 ° C. to form solid potassium chloride (hereinafter referred to as solid). (Referred to as potassium chloride). In this crude aqueous solution, there are sodium ions eluted from the raw material potassium chloride and sodium ions contained in the aqueous potassium chloride solution or water. Since the sodium content in the raw material potassium chloride is 300 to 5000 ppm and the sodium content of the aqueous potassium chloride solution or water is 1500 ppm or less, the potassium chloride is saturated when the temperature of the crude aqueous solution is cooled to -5 to 10 ° C. The concentration is reached to produce solid potassium chloride, but sodium chloride is below the saturation concentration. As a result, the impurity sodium remains in the aqueous solution as ions. In addition, in this specification, all of%, ppm, and ppb are mass conversion values.
[0008]
In the present invention, raw material potassium chloride having a sodium content of 300 to 5000 ppm is used. Raw material potassium chloride having a sodium content of less than 300 ppm is not preferred because the production method is difficult and expensive. If it exceeds 5000 ppm, it is difficult to produce a 48% aqueous potassium hydroxide solution containing 100 ppm or less of sodium. The sodium content in the raw material potassium chloride is particularly preferably 300 to 1400 ppm.
[0009]
In the present invention, a crude potassium chloride aqueous solution having a concentration of 22 to 28% is prepared. If the concentration is less than 22%, the temperature for depositing solid potassium chloride in the aqueous potassium chloride solution is lowered, and the electric power required for cooling is increased, which is not preferable. If the concentration exceeds 28%, it is difficult to dissolve solid potassium chloride, which is not preferable. The concentration of the crude potassium chloride aqueous solution is particularly preferably 26 to 28%.
[0010]
In the present invention, the temperature of the aqueous potassium chloride solution or water to be mixed is preferably 0 ° C to 80 ° C. If the temperature is lower than 0 ° C., the progress of dissolution of the raw material potassium chloride is slow, which is not preferable. If the temperature is higher than 80 ° C., the liquid temperature becomes high and is difficult to handle. The temperature is particularly preferably 50 to 60 ° C.
[0011]
In the present invention, the cooling temperature is set to -5 to 10 ° C. When the cooling temperature is less than −5 ° C., not only potassium chloride but also sodium chloride is liable to precipitate, the sodium content in the potassium chloride increases, and the purity decreases. Moreover, the energy for cooling is large and is not suitable for cost. When the cooling temperature is higher than 10 ° C., the solubility of potassium chloride does not decrease, and potassium chloride cannot be precipitated efficiently. The cooling temperature is particularly preferably 0 ° C to 5 ° C.
[0012]
In the present invention, as a means for solid-liquid separation, for example, a method using a device such as a centrifugal separator, a horizontal belt filter, or the like, cooling using the fact that the specific gravity of the precipitated solid potassium chloride is heavier than the aqueous potassium chloride solution. For example, the tank may be structured such that the precipitated solid potassium chloride is extracted from the lower part and the aqueous potassium chloride solution is extracted from the upper part.
[0013]
In the present invention, the content of calcium, magnesium or strontium in the potassium chloride crude aqueous solution to be supplied to the cooling process is 50 ppb or less in terms of elemental values of calcium, magnesium or strontium (hereinafter the same). preferable. When the content of these elements exceeds the above values, before supplying to the crystallization process, a potassium chloride aqueous solution is passed through a cation exchange resin, and a divalent cation of calcium ion, magnesium ion or strontium ion is added. It is preferable to remove it. The content of calcium ion, magnesium ion or strontium ion is particularly preferably 20 ppb or less.
[0014]
As for the cation exchange resin, it is preferable to use a cation exchange resin in which a divalent cation such as a calcium ion, a magnesium ion, or a strontium ion is significantly more selective than a monovalent ion such as a potassium ion. Examples of the cation exchange resin include cation exchange resin CR-11 manufactured by Mitsubishi Chemical Corporation.
[0015]
In this invention, it is preferable that the potassium chloride crude aqueous solution supplied to a cooling process shall be pH 1-3 by adding hydrochloric acid. If the pH exceeds 3, the resulting solid potassium chloride crystals contain water of crystallization, which makes it difficult to control the concentration to produce a saturated aqueous potassium chloride solution. If the pH is less than 1, a large amount of hydrochloric acid should be used. This is not preferable because an expensive material such as a fluororesin lining is required for the device material.
[0016]
In the present invention, solid potassium chloride is dissolved in water to form a saturated potassium chloride aqueous solution having a sodium content of 60 ppm or less, and electrolyzed by an ion exchange membrane electrolysis method to produce a potassium hydroxide aqueous solution. If the sodium content of the aqueous potassium chloride solution is more than 60 ppm, the effect of the present invention cannot be obtained, which is not preferable. The concentration of the aqueous potassium hydroxide solution obtained directly from the electrolytic cell is preferably 28 to 54%. The concentration of the aqueous potassium hydroxide solution is particularly preferably 48 to 50%. A potassium hydroxide aqueous solution having a sodium content of 100 ppm or less in terms of a concentration of 48% is obtained.
[0017]
In the present invention, when the next treatment is performed before the step of dissolving the solid potassium chloride obtained in the cooling process in water and performing electrolysis, the sodium concentration of the aqueous potassium hydroxide solution is further reduced. Can do. Hereinafter, this method is referred to as a second aspect of the present invention.
[0018]
The solid potassium chloride is preferably mixed with a potassium chloride aqueous solution or water having a sodium content of 60 ppm or less to form a slurry containing purified solid potassium chloride. The potassium chloride aqueous solution to be used can be used at any concentration. It is not preferable that the sodium content of the aqueous potassium chloride solution or water exceeds 60 ppm because the effects of the present invention cannot be obtained.
[0019]
The aqueous phase of the resulting slurry contains sodium ions eluted from solid potassium chloride and sodium ions contained in the aqueous potassium chloride solution or water. By this slurry operation, sodium chloride contained in the solid potassium chloride is eluted into the aqueous phase. In the aqueous phase of the slurry, potassium chloride reaches a saturation concentration, but the sodium content of the aqueous potassium chloride solution or water is 60 ppm or less, so sodium chloride is lower than the saturation concentration, and sodium chloride in solid potassium chloride. Elutes into the aqueous phase and the sodium component in the solid potassium chloride can be further removed.
[0020]
The slurry preferably has a solid concentration of 10 to 90%. A solid concentration of less than 10% is not preferable because production efficiency is extremely poor. If the solid concentration is more than 90%, the contact between the solid phase and the liquid phase is insufficient, and a satisfactory cleaning effect cannot be obtained, which is not preferable. The solid concentration is particularly preferably 70 to 90%. The solid concentration is a concentration as a solid present in the slurry, and does not include the amount of solute dissolved in the aqueous phase of the slurry.
[0021]
It is preferable that purified potassium chloride is obtained as a solid by solid-liquid separation of the slurry (hereinafter referred to as purified potassium chloride solid). The sodium content in the purified potassium chloride solid is preferably such that 50% or more of the sodium content in the solid potassium chloride is removed. Solid-liquid separation is preferably performed by a centrifuge, a horizontal belt filter, or the like.
[0022]
In the second aspect of the present invention, when the aqueous solution of potassium chloride or water is mixed and subjected to solid-liquid separation as a slurry, the sodium content in the raw material potassium chloride can be further removed by setting the temperature to 0 ° C. to 50 ° C. preferable. The aqueous potassium chloride solution or water is particularly preferably mixed at a temperature of 0 ° C to 30 ° C. If the temperature at which the slurry is mixed is more than 30 ° C., the solubility of sodium chloride in the mother liquor increases, which is not preferable. If the temperature is less than 0 ° C., cooling energy is required, which is not preferable in terms of cost. The temperature at which the slurry is mixed is particularly preferably 0 ° C to 10 ° C.
[0023]
In the second aspect of the present invention, the purified potassium chloride solid is further mixed with an aqueous potassium chloride solution or water to form a slurry, and solid-liquid separation is repeated a plurality of times, so that the sodium content can be further reduced. preferable.
[0024]
It is preferable to prepare a potassium hydroxide aqueous solution by dissolving a purified potassium chloride solid in water and then forming a saturated potassium chloride aqueous solution having a sodium content of 45 ppm or less and electrolysis by an ion exchange membrane electrolysis method. The aqueous potassium hydroxide solution preferably has a sodium content of 75 ppm or less in terms of a concentration of 48%.
[0025]
In the second aspect of the present invention, the separation mother liquor after the slurry is separated into solid and liquid is added to a potassium chloride aqueous solution or water having a sodium content of 2000 ppm or less before dissolving the raw material potassium chloride, and further from the raw material potassium chloride. Contains eluted sodium. This separated mother liquor is preferably used as a raw material for slurry dissolution or general industrial potassium hydroxide aqueous solution.
[0026]
【Example】
Examples of the present invention (Examples 1, 2, and 3) and comparative examples (Example 4) are shown below. The results are summarized in Table 1. In each example, the sodium content in the aqueous potassium hydroxide solution was measured by atomic absorption analysis (standard addition method). In addition, when the sodium content of the potassium hydroxide aqueous solution of concentration C% is Appm, the sodium content Bppm converted to the potassium hydroxide aqueous solution of concentration 48% was calculated by the formula (B = A × 48 / C). .
[0027]
[Example 1]
28 kg of water having a sodium content of 0 ppm was added to 10 kg of raw material potassium chloride having a sodium content of 4260 ppm, and the temperature of the aqueous solution was raised to 50 ° C. to obtain 30 L of a 26% concentration potassium chloride aqueous solution. From this crude aqueous solution, divalent cations such as calcium ion, magnesium ion, strontium ion and the like are removed with an ion exchange resin (trade name: cation exchange resin CR-11, manufactured by Mitsubishi Chemical Co., Ltd., hereinafter the same), and each ion is 20 ppb. After the following, the temperature of the aqueous solution was cooled to 5 ° C. to precipitate solid potassium chloride, and solid-liquid separation was performed to obtain 1100 g of solid potassium chloride. The obtained solid potassium chloride is dissolved in pure water to make a 26% concentration aqueous potassium chloride solution, and the obtained potassium chloride aqueous solution is electrolyzed (ion exchange membrane electrolysis, current density 4 kA / m 2 , electrolytic cell temperature). 90 ° C., fresh salt water concentration 18%, the same shall apply hereinafter) to obtain a potassium hydroxide aqueous solution having a concentration of 32%.
[0028]
[Example 2]
After removing divalent cations from the same aqueous sodium chloride solution as in Example 1 with an ion exchange resin in the same manner as in Example 1, hydrochloric acid with a concentration of 17% was added to adjust the pH of the aqueous solution to 2. Next, the temperature of the aqueous solution was cooled to 5 ° C. to precipitate solid potassium chloride, and solid-liquid separation was performed to obtain 1100 g of solid potassium chloride. The obtained solid potassium chloride was mixed with pure water having a sodium content of 0 ppm and stirred to obtain a slurry having a solid concentration of 80%, followed by solid-liquid separation to obtain 1100 g of purified sodium chloride solid. The obtained purified potassium chloride was dissolved in pure water to give a 26% strength aqueous potassium chloride solution, and then electrolyzed in the same manner as in Example 1 to obtain a 32% strength aqueous potassium hydroxide solution.
[0029]
[Example 3]
28 kg of water with a sodium content of 0 ppm was added to 10 kg of raw material potassium chloride with a sodium content of 1220 ppm, and the temperature of the aqueous solution was raised to 50 ° C. to obtain 30 L of a crude potassium chloride aqueous solution with a concentration of 26%. In this crude aqueous solution, divalent cations were removed with an ion exchange resin in the same manner as in Example 1, and then 17% hydrochloric acid was added to adjust the pH of the aqueous solution to 2. Next, the temperature of the aqueous solution was cooled to 5 ° C. to precipitate solid potassium chloride, and solid-liquid separation was performed to obtain 1100 g of solid potassium chloride. The obtained solid potassium chloride was mixed with pure water having a sodium content of 0 ppm and stirred to obtain a slurry having a solid concentration of 80%, followed by solid-liquid separation to obtain 930 g of purified sodium chloride solid. The obtained purified potassium chloride was dissolved in pure water to give a 26% strength aqueous potassium chloride solution, and then electrolyzed in the same manner as in Example 1 to obtain a 32% strength aqueous potassium hydroxide solution.
[0030]
[Example 4 (comparative example)]
28 kg of water with a sodium content of 0 ppm was added to 10 kg of raw material potassium chloride with a sodium content of 4260 ppm, and the temperature of the aqueous solution was raised to 50 ° C. to obtain 30 L of a crude potassium chloride aqueous solution with a concentration of 26%. Thereafter, in the same manner as in Example 1, after removing cations with an ion exchange resin, an aqueous potassium hydroxide solution having a concentration of 32% was obtained by electrolytic method.
[0031]
[Example 5 (comparative example)]
28 kg of water with a sodium content of 0 ppm was added to 10 kg of raw material potassium chloride with a sodium content of 430 ppm, and the temperature of the aqueous solution was raised to 50 ° C. to obtain 30 L of a 26% strength potassium chloride crude aqueous solution. Thereafter, in the same manner as in Example 1, after removing cations with an ion exchange resin, an aqueous potassium hydroxide solution having a concentration of 32% was obtained by electrolytic method.
[0032]
[Table 1]
The unit in the table is ppm, and the symbols are as follows.
However, only the unit of e is%.
a: Sodium content in raw material potassium chloride,
b: sodium content in purified potassium chloride,
c: sodium content in saturated aqueous potassium chloride solution after purification with cation exchange resin,
d: sodium content in the obtained aqueous potassium hydroxide solution,
e: concentration of the obtained potassium hydroxide aqueous solution,
f: Sodium content in aqueous potassium hydroxide solution when converted to a concentration of 48%.
[0034]
【The invention's effect】
According to the present invention, an aqueous potassium hydroxide solution having a low sodium content can be produced. Moreover, the potassium hydroxide aqueous solution obtained by the method of the present invention can be suitably used for applications such as those for pharmaceuticals, foods and semiconductors.
Claims (4)
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5556014A (en) * | 1978-10-16 | 1980-04-24 | Sanuki Enso Kk | Production of potassium chloride |
| JPS5565372A (en) * | 1978-11-10 | 1980-05-16 | Asahi Glass Co Ltd | Electrolyzing method of aqueous potassium chloride solution |
| JPS5967379A (en) * | 1982-10-07 | 1984-04-17 | Nippon Soda Co Ltd | Electrolytic method of aqueous potassium chloride solution |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5556014A (en) * | 1978-10-16 | 1980-04-24 | Sanuki Enso Kk | Production of potassium chloride |
| JPS5565372A (en) * | 1978-11-10 | 1980-05-16 | Asahi Glass Co Ltd | Electrolyzing method of aqueous potassium chloride solution |
| JPS5967379A (en) * | 1982-10-07 | 1984-04-17 | Nippon Soda Co Ltd | Electrolytic method of aqueous potassium chloride solution |
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