【発明の詳細な説明】[Detailed description of the invention]
本発明はイオン交換膜電気透析装置における糖
液の脱塩方法に関する。
従来、糖液の脱塩方法としては、例えばイオン
交換樹脂、イオン交換膜、あるいは両者を組合せ
て用いる方法が提案されている。このうちイオン
交換膜を用いる糖液の脱塩方法は、陰陽の電極間
に陽イオン交換膜と陰イオン交換膜とを配して、
脱塩室および濃縮室を構成してなる電気透析槽に
おいて実施される。即ち、このようなイオン交換
膜電気透析槽の脱塩室に糖液を、また濃縮室に電
解質を含有する液、例えば希薄食塩水を流通させ
ながら両極間に直流電圧を印加することによつ
て、該糖液中に存在する塩類（灰分）がイオンと
してイオン交換膜を透過して濃縮液側に移行し脱
塩処理される。
一般に製糖工業では糖液中に塩類（灰分）が多
く存在すると、砂糖結晶化工程において砂糖結晶
の成長が阻害され、また灰分に伴なつて蔗糖が糖
蜜側に移行し、そのため砂糖の回収率を低下させ
たり、あるいは廃糖蜜においても移行した灰分に
よりニガ味を生じとしての使用食用が限定される
などの悪影響がある。従つてこれらの障害を除く
ため塩分の除去方法がいくつか研究され提案され
てきたが、除去能力、経済的な面で有効な手段が
見い出せないのが実状であつた。しかるに近年、
イオン交換膜電気透析法による脱塩処理がクロー
ズアツプされ、製糖工業への適用の研究がさかん
になつてきた。しかしながらかかるイオン交換膜
電気透析装置において糖液の脱塩を実施してみる
と、該糖液中に含有されるイオン化した有機性の
汚染物質により、特に陰イオン交換膜が汚染され
て膜抵抗が、増加するなどの現象を生じる。この
ため、従来の糖液の透析法では槽電圧が上昇して
透析エネルギーの増大や安定した運転の継続が出
来ず、かつイオン交換膜の使用期間が短かいなど
の大きな欠陥を有していた。
これらの対策として一般的なイオン交換樹脂、
限外過、活性炭処理などにより糖液の前処理を
おこなつて不純物を除去した後、電気透析する方
法も提案されているが、これら前処理を実施して
も汚染物質の除去が不充分な場合が多く、また設
備費、再生処理費など経済的に実用上問題が多
い。さらに汚染されたイオン交換膜を薬液洗浄、
逆通電処理等により再生することを考えられる
が、実際上、イオン交換膜の完全な再生は極めて
困難である。例えば特公昭56−38119号には、糖
液をイオン交換膜電気透析により脱塩する方法に
おいて糖蜜を予め弱塩基性陰イオン交換樹脂で処
理することにより、汚染物質を効果的に選択除去
する糖蜜の精製法が提案されている。しかしなが
ら、この方法も工業的には弱塩基性陰イオン樹脂
による処理工程、その再生工程などの前処理を要
するため脱塩工程を煩雑にする問題がある。
本発明者らは、上記の課題に鑑み、イオン交換
膜電気透析槽において糖の酸による転化分解にお
ける糖分損失を極力回避し、糖液を効率よく脱塩
する簡便な方法について鋭意研究を重ねた。その
結果、イオン交換膜電気透析槽において糖液を脱
塩するに際し濃縮液に酸を添加し、望ましくはそ
のPHを４以下に調整することにより、陰イオン交
換膜の汚染が防止され効率的脱塩が可能なること
を知見し、本発明を提供するに至つたものであ
る。本発明の効果が如何なる作用により発揮され
るのか十分には明確でないが、濃縮液側に添加、
存在する水素イオンが陰イオン交換膜を通して脱
塩室側に、拡散、透過するため、この水素イオン
の透過により、脱塩液（糖液）に接した陰イオン
交換膜面ないしは界面において有機性汚染物質の
付着が防止抑制され、ひいては槽電圧の上昇が抑
止されるものと推測している。したがつて本発明
は、濃縮液側に酸を添加して濃縮液PHを一般に４
以下、特に３以下に調整するのが望ましい。用い
る酸としては一般に塩酸、硫酸、硝酸などの無機
酸が好ましく、また酢酸、クエン酸、プロピオン
酸などの有機酸の使用も可能である。濃縮液とし
ては一般に塩化ナトリウム、塩化カリウムなどの
電解質の水溶液が用いられるが、そのほか酸の希
釈水溶液をそのまま用いることも出来る。かかる
濃縮液は、濃縮液自体に酸を連続的または間けつ
的に添加しPHを４以下に調整してもよく、あるい
は系外でPH４以下に調整しながら電気透析槽に給
液してもよい。
本発明の効果をさらに確実に発揮させるために
は、濃縮液のPHを脱塩液のPHより少くとも0.5以
上低く望ましくは２以上低く保持することが好ま
しい。脱塩処理すべき糖液の種類、濃度、温度、
PH等の条件により、濃縮液の最適PH値は変化する
が、濃縮液のPHを一般に４以下にし、かつ、その
濃縮液PH値を脱塩液PH値より0.5以上低く、望ま
しくは２以上低くすることにより、陰イオン交換
膜の有機汚染による槽電圧上昇を防止し、透析槽
の安定運転の継続に好結果をもたらす。
本発明においては濃縮液に酸を添加し、濃縮液
のPHを４以下に調整することにより、脱塩室側液
（糖液）のPHも影響をうけ若干低下する傾向にあ
る。その結果、糖液の電導度が上昇するため、電
気透析による脱塩効率が向上する。このような脱
塩室における糖蜜液のPHを低下させて処理する方
法としては既に特公昭56−39638号が提案されて
いる。しかし特公昭56−39638号に開示されてい
る方法は脱塩側の糖蜜液に酸を存在させて、PHを
0.5〜3.5に調整する方法であつて、本発明の濃縮
液側に酸を存在させて濃縮液のPH調整をおこなう
方法とは本質的に異なる。一般に脱塩室の糖液の
PH調整に用いられた酸は、脱塩処理後にアルカリ
剤により中和され元のPH値にもどされる。従つ
て、調整用の酸およびアルカリの消費量は、処理
コストの面から無視できない値になる。これに対
し、本発明におけるPH４以下に調整した濃縮液
は、脱塩工程に於て繰返し使用しうるため、理論
的には該濃縮液側からイオン交換膜を通して脱塩
側の糖液に移行した酸のみが消費され、中和には
該酸分に相当するアルカリ剤を要するのみであ
る。従つて、本発明は酸の消費量を必要最少限に
節減することが可能になり、それに応じて脱塩後
の糖液を中和するに必要な中和剤も節減できる。
本発明で、脱塩処理により消費される酸使用量
は、糖液の種類、脱塩率、PH値により異なるが一
般に糖液側PH調節法に比べて約1/2〜1/10程度に
削減される。
また本発明によれば、脱塩液の糖液に対して酸
を直接添加する態様でなく、濃縮液に必要最少限
の酸を用いることにより該糖液の転化分解を、可
及的に抑えることが出来る利点がある。普通、糖
液の酸による加水分解を転化といい糖の損失にな
るが、この転化率は添加する酸の種類、糖液の
PH、温度、濃度、接触時間などによつて異なる。
例えば、塩酸、硫酸などの無機酸の転化力は、ク
エン酸や酢酸などの有機酸にくらべて数10倍以上
も強い。また糖液温度を上昇することにより、第
１図からも判るように、糖液濃度を高くしても、
該液の電導度を高めることができ、電気透析の効
率の面からは非常にメリツトが生じるが、反面、
糖液PHが低い場合には糖液温度の上昇で糖液の転
化率は加速的に増大する傾向になるため、糖液の
PHが低い条件での、高温の電気透析法を製糖工業
において採用することは実用上困難である。上記
のように、糖液のPHが低下すると転化率は増大し
糖の損失が生じることになる。例えばPH＝5.1、
BX40、温度50℃の廃糖蜜液を塩酸によりPH調節
し、２時間後の糖の分解転化率はPH＝４、３、２
でそれぞれ0.1％、3.5％、3.0％となり、糖液のPH
を低下させることは糖の分解を著しく促進させる
ことがわかる。このように糖の分解、転化率の面
からみると、糖液のPH値をできるだけ高く維持し
て透析することが望ましく、高温透析では特に重
要である。本発明は脱塩液のPHを本質的に低下さ
せることなく、糖の転化防止の面から非常に有効
である。なお、本発明において脱塩液、即ち糖液
側に酸を添加しPH調整する方法をあわせて用いる
ことは何ら妨げられず、糖の分解転化率、酸使用
量等からみて支障ない場合は適宜用いればよい。
さらに本発明者らは脱塩時の糖液の温度を高め
ることによつて該糖液の希釈度を抑えたまま好ま
しい脱塩が達成できることを見出した。第１図に
示したように、糖液の透析温度を維持することは
糖液の電導度が著しく高くなり、特に糖濃度が高
い状態でも液電導度が高くなり脱塩が容易にな
る。即ち、従来、糖液の脱塩は、20〜35℃の常温
付近での透析が一般的であつたが、本発明では糖
の転化率が非常に低いため、例えば45℃以上の高
温下で、糖液をイオン交換膜電気透析槽に供する
ことが可能であり、脱塩効率の向上を図ることが
出来るとともに、透析槽内における微生物の汚染
（増殖）を防止することが出来る。また高温下に
おいては高濃度の糖液を透析槽に仕込むことが出
来るため、電気透析による脱塩処理後の後工程で
の濃縮エネルギー（主に蒸発工程での蒸気エネル
ギー）が減少し、さらに糖液の粘度低下および高
濃度液仕込による単位固型分あたりの処理液量の
減少によりポンプ、撹拌機などの補機動力も大巾
に減少されて、工業的には極めて有利である。し
たがつて、本発明における糖液温度は、常温でも
もちろん適用可能であるが、高温にするほど望ま
しく、一般に45℃以上、特に50℃以上が好適であ
り、50〜70℃の範囲がよい。
本発明に供される糖液としては灰分（塩類）を
含む糖液であれば特に制限なく、例えば精製糖、
甜菜糖、甘蔗糖などの砂糖工業における糖汁、糖
蜜、洗糖蜜、廃糖蜜のほか甘蜜澱粉などからの澱
粉糖液にも適用可能である。これら糖液は一般に
水で希釈して所定の濃度でイオン交換膜電気透析
槽に供給されるが、本発明においては上記したよ
うに高温下の電気透析が可能であるため、例えば
BX40〜50の高濃度の糖液を供給することが出来
る。
本発明のイオン交換膜電気透析槽は陰陽電極間
に陰陽イオン交換膜をガスケツトを介して交互に
配列し、脱塩室、濃縮室を構成してなるいわゆる
フイルタープレス型電気透析槽であればいずれの
型式も使用できる。これらに用いる陽イオン交換
膜および陰イオン交換膜も一般の市販品が特に制
限なく使用できる。また電気透析法は回分式、部
分循環式、連続式いずれの方式も適用可能であ
り、処理量等の条件により適当に選択すればよ
い。さらに透析槽への電流の印加方法も定電圧
法、定電流法、脱塩液電導度追従法など、いずれ
の方式も適用できるが、電導度追従法が、経済的
で好ましい場合が多い。また運転電流密度は糖液
の種類性状により種々異なるが、電流密度ｉ
（Ａ／ｄm2）、糖液電導度ｋ（ms／cmat25℃）で表
わした場合、ｉ／ｋ＝0.01〜１の範囲が好適であ
る。
本発明において、透析槽に糖液を供給する前に
予め該糖液中に共存する不純物の除去あるいは脱
色のために必要に応じて、例えばプレコード
過、限外過、精密過、イオン交換樹脂処理、
炭酸飽充処理、活性炭処理などを行うことは特に
制限されない。
本発明により脱塩処理された糖液は従来法と同
様に、その用途に応じて一般にアルカリ添加、イ
オン交換樹脂による中和、あるいは濃縮して性状
および成分が調整される。
このように本発明によれば、イオン交換膜電気
透析装置において、濃縮液側に酸を添加し、該液
のPHを４以下に調整するだけの簡便な方法によ
り、イオン交換膜の汚染が防止され、槽電圧の上
昇を抑制し、また糖の分解転化による糖の損失を
最少に押えて、糖液の脱塩処理をおこなうことが
できる。さらに本発明によれば、電気透析による
脱塩処理が連続的な長期運転を可能にし、あるい
はイオン交換膜の使用期間が長いなどの利点ばか
りでなく、高温下での透析を可能にし、電力、蒸
気等の処理エネルギーの低減、蔗糖の転化防止、
使用酸量の低減、微生物増殖の防止など経済的な
面で多くの効果が期待できる。
以下、実施例でもつて具体的に説明する。
実施例 １
精糖工業の２番蜜（BX80）を上水にてBX45
に希釈した糖液を、被脱塩処理液として電気透析
法にて脱塩処理をおこなつた。
電気透析装置としては徳山曹達(株)製TS−220型
を用いて、陽イオン交換膜はネオセプタCL−
25T、陰イオン交換膜はネオセプタAFNの有効
通電面積2dm2のものを20対使用した。脱塩方法
は回分式脱塩法を用い、バツチ当りの糖液の仕込
量は８、透析温度は50℃±２℃に設定した。
濃縮液は0.2Nの食塩水を用い表１に示す各実験
条件のPH値に塩酸を添加して調節した。添加した
塩酸濃度は、設定PH値に応じて１〜5Nの範囲のも
のを適宜使用した。電流の印加方法は脱塩液の電
導度に従つて電流値を設定する、電流−電導度の
追従方式を用い、全脱塩過程においてｉ／ｋ＝
0.15（ｉ＝電流密度Ａ／ｄm2、ｋ＝脱塩液電導度
ms／cm）とした。また脱塩液および濃縮液の膜
面流速は各々６cm／secであつた。表１に示すよ
うにNo.１、２、３、４、５、６は濃縮液をPH調節
しており実施例で、No.７は脱塩液側をPH調節した
比較例である。実験結果からわかるように、濃縮
液を塩酸添加によりPH調節をおこない、特にPH値
を４以下にて透折した時は蔗糖分損失も少なく膜
抵抗の上昇もほとんどなく安定した運転ができ
た。しかるに比較例のNo.７に示すように脱塩液側
に酸を添加してPH調節を実施した場合は、蔗糖の
酸分解損失が大きく経済的に非常に不利である。
なお電気透析中における脱塩側から濃縮側への蔗
糖分漏出は0.1％（対蔗糖分）前後と僅少であつ
た。
実施例 ２
甘蔗糖工場のケーンシラツプ（BX65）を上水
にてBX45に希釈した糖液を実施例１と同様の条
件で、脱塩処理した。結果を表１に示す。
No.８、９は実施例で濃縮液側をPH調節した場
合、No.10はPH調節なしの比較例である。
実施例 ３
実施例１の結果に基づき、精糖工場の２番蜜に
て繰返し実験を行ない、イオン交換膜のライフテ
ストを実施した。
精糖工場の２番蜜を上水にてBX45に希釈し、
濃縮室液を塩酸にてPH1.5に調整した上で、徳山
曹達(株)製の電気透析装置TS−220型にて、3ms／
cmまで脱塩する実験を繰返し行ない、６サイクル
毎にCIP洗浄（アルカリ塩酸洗浄）を行なつた。
その結果、第１サイクル目の脱塩終了時の膜抵
抗は41.4Ωcm2で、50サイクル目のそれは41.2Ωcm2
更に100サイクル目は42.0Ωcm2と殆んど膜抵抗の
上昇（即ち膜汚染）は認められず、而も、電流効
率は何れも91％、88％及び88％と良好であつた。
又、高温下（50℃）で電気透析を行なつたため
に、イオン交換膜面の菌そうも発生せず、微生物
増殖は完全に回避できた。
The present invention relates to a method for desalting a sugar solution in an ion exchange membrane electrodialysis device. Conventionally, methods using ion exchange resins, ion exchange membranes, or a combination of the two have been proposed as methods for desalting sugar solutions. Among these methods, the sugar solution desalting method using an ion exchange membrane involves disposing a cation exchange membrane and an anion exchange membrane between negative and positive electrodes.
The process is carried out in an electrodialysis tank consisting of a desalination chamber and a concentration chamber. That is, by applying a DC voltage between the two electrodes while flowing a sugar solution into the demineralization chamber of such an ion exchange membrane electrodialysis tank and a solution containing an electrolyte, such as dilute saline solution, into the concentration chamber. The salts (ash) present in the sugar solution pass through the ion exchange membrane as ions and move to the concentrate side where they are desalted. Generally, in the sugar manufacturing industry, when a large amount of salts (ash) is present in the sugar solution, the growth of sugar crystals is inhibited during the sugar crystallization process, and the ash content causes sucrose to move to the molasses side, which reduces the sugar recovery rate. The ash content that has migrated into blackstrap molasses has adverse effects such as a bitter taste, which limits its edible use. Therefore, several methods for removing salt have been researched and proposed in order to eliminate these obstacles, but the reality is that no method has been found that is effective in terms of removal ability and economy. However, in recent years,
Desalination treatment using ion-exchange membrane electrodialysis has gained attention, and research into its application to the sugar industry has become active. However, when desalting a sugar solution using such an ion-exchange membrane electrodialysis device, the anion exchange membrane in particular is contaminated by ionized organic contaminants contained in the sugar solution, and the membrane resistance increases. , increases, and other phenomena. For this reason, conventional dialysis methods for sugar solutions had major drawbacks, such as an increase in cell voltage, an increase in dialysis energy, and the inability to continue stable operation, as well as a short period of use for ion exchange membranes. . As a countermeasure for these, common ion exchange resins,
A method has also been proposed in which the sugar solution is pretreated to remove impurities by ultrafiltration, activated carbon treatment, etc., and then electrodialyzed, but even with these pretreatments, the removal of contaminants is insufficient. In addition, there are many practical problems economically, such as equipment costs and reprocessing costs. Furthermore, the contaminated ion exchange membrane is cleaned with a chemical solution.
Although it is possible to regenerate the ion exchange membrane by reverse current treatment, it is actually extremely difficult to completely regenerate the ion exchange membrane. For example, Japanese Patent Publication No. 56-38119 describes a method for desalting molasses by ion-exchange membrane electrodialysis, in which molasses is treated in advance with a weakly basic anion exchange resin to effectively selectively remove contaminants. A purification method has been proposed. However, this method also has the problem of complicating the desalting process since it requires pretreatment such as a treatment step with a weakly basic anionic resin and a regeneration step. In view of the above-mentioned problems, the present inventors have conducted intensive research on a simple method for efficiently desalting sugar solution by avoiding as much as possible sugar loss during conversion and decomposition of sugar with acid in an ion-exchange membrane electrodialysis tank. . As a result, when desalting a sugar solution in an ion exchange membrane electrodialysis tank, by adding acid to the concentrated solution and preferably adjusting its pH to 4 or less, contamination of the anion exchange membrane can be prevented and efficient desalination can be achieved. The inventors discovered that salts can be used, and were able to provide the present invention. Although it is not fully clear how the effects of the present invention are exerted, it is possible to add
Existing hydrogen ions diffuse and permeate through the anion exchange membrane into the demineralization chamber, and this hydrogen ion permeation causes organic contamination on the anion exchange membrane surface or interface that is in contact with the demineralization solution (sugar solution). It is assumed that the adhesion of substances is prevented and suppressed, which in turn suppresses the increase in cell voltage. Therefore, in the present invention, acid is added to the concentrate side to adjust the concentrate pH to 4.
Below, it is particularly desirable to adjust it to 3 or less. As the acid used, inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid are generally preferred, and organic acids such as acetic acid, citric acid, and propionic acid can also be used. As the concentrated solution, an aqueous solution of an electrolyte such as sodium chloride or potassium chloride is generally used, but a diluted aqueous solution of an acid can also be used as is. The pH of such a concentrated solution may be adjusted to 4 or less by continuously or intermittently adding acid to the concentrated solution itself, or the pH may be adjusted to 4 or less outside the system while being supplied to the electrodialysis tank. good. In order to more reliably exhibit the effects of the present invention, it is preferable to maintain the pH of the concentrated solution at least 0.5 or more, preferably 2 or more lower than the PH of the desalted solution. Type, concentration, temperature of sugar solution to be desalted,
The optimum PH value of the concentrate changes depending on conditions such as PH, but the PH of the concentrate should generally be 4 or less, and the PH value of the concentrate should be 0.5 or more lower than the desalination solution PH value, preferably 2 or more lower. By doing so, it is possible to prevent an increase in cell voltage due to organic contamination of the anion exchange membrane, resulting in good results in continued stable operation of the dialysis cell. In the present invention, by adding an acid to the concentrated liquid and adjusting the pH of the concentrated liquid to 4 or less, the pH of the desalting chamber side liquid (sugar solution) also tends to be slightly lowered. As a result, the electrical conductivity of the sugar solution increases, which improves the desalination efficiency by electrodialysis. Japanese Patent Publication No. 56-39638 has already proposed a method of reducing the pH of molasses liquid in such a desalting chamber. However, in the method disclosed in Japanese Patent Publication No. 56-39638, an acid is present in the molasses liquid on the desalination side to lower the pH.
This is a method of adjusting the pH of the concentrated liquid to 0.5 to 3.5, and is essentially different from the method of the present invention in which the pH of the concentrated liquid is adjusted by making an acid exist on the side of the concentrated liquid. Generally, the sugar solution in the desalting chamber
The acid used for pH adjustment is neutralized with an alkaline agent after desalting and returned to its original pH value. Therefore, the amount of acid and alkali consumed for adjustment becomes a value that cannot be ignored from the viewpoint of processing costs. On the other hand, in the present invention, the concentrated liquid adjusted to a pH of 4 or less can be used repeatedly in the desalting process, so theoretically, the concentrated liquid can be transferred from the concentrated liquid side to the desalted sugar solution through the ion exchange membrane. Only the acid is consumed, and neutralization requires only an alkaline agent corresponding to the acid content. Therefore, the present invention makes it possible to reduce the amount of acid consumed to the minimum necessary, and correspondingly reduce the amount of neutralizing agent required to neutralize the sugar solution after desalting.
In the present invention, the amount of acid consumed in the desalting process varies depending on the type of sugar solution, desalination rate, and PH value, but is generally about 1/2 to 1/10 of that of the sugar solution side PH adjustment method. reduced. Furthermore, according to the present invention, the conversion and decomposition of the sugar solution is suppressed as much as possible by using the minimum necessary amount of acid in the concentrated solution, instead of adding acid directly to the sugar solution of the desalted solution. It has the advantage of being able to Normally, the hydrolysis of sugar solution with acid is called conversion, which results in the loss of sugar, but this conversion rate depends on the type of acid added and the amount of sugar solution.
Varies depending on PH, temperature, concentration, contact time, etc.
For example, the conversion power of inorganic acids such as hydrochloric acid and sulfuric acid is several ten times stronger than that of organic acids such as citric acid and acetic acid. Furthermore, by increasing the temperature of the sugar solution, as can be seen from Figure 1, even if the concentration of the sugar solution is increased,
It is possible to increase the conductivity of the liquid, which is very advantageous in terms of the efficiency of electrodialysis, but on the other hand,
When the pH of the sugar solution is low, the conversion rate of the sugar solution tends to increase rapidly as the temperature of the sugar solution increases.
It is practically difficult to employ high-temperature electrodialysis under low pH conditions in the sugar industry. As mentioned above, when the pH of the sugar solution decreases, the conversion rate increases and sugar loss occurs. For example, PH=5.1,
BX40, the pH of the molasses liquid at a temperature of 50°C was adjusted with hydrochloric acid, and the sugar decomposition conversion rate after 2 hours was PH = 4, 3, 2.
The pH of the sugar solution is 0.1%, 3.5%, and 3.0%, respectively.
It can be seen that lowering the amount of sugar significantly promotes sugar decomposition. As described above, from the viewpoint of sugar decomposition and conversion rate, it is desirable to maintain the pH value of the sugar solution as high as possible during dialysis, and this is particularly important in high-temperature dialysis. The present invention is very effective in preventing sugar conversion without essentially lowering the pH of the desalted solution. In addition, in the present invention, there is nothing to prevent the use of a method of adjusting the pH by adding acid to the desalted solution, that is, the sugar solution, and if there is no problem in terms of the sugar decomposition conversion rate, the amount of acid used, etc., it may be used as appropriate. Just use it. Furthermore, the present inventors have discovered that by increasing the temperature of the sugar solution during desalting, preferable desalting can be achieved while keeping the degree of dilution of the sugar solution suppressed. As shown in FIG. 1, maintaining the dialysis temperature of the sugar solution significantly increases the electrical conductivity of the sugar solution, and in particular, even when the sugar concentration is high, the electrical conductivity of the solution becomes high and desalination becomes easy. That is, in the past, desalination of sugar solution was generally carried out by dialysis at room temperature of 20 to 35°C, but in the present invention, since the conversion rate of sugar is very low, desalting is carried out at a high temperature of 45°C or higher. It is possible to supply the sugar solution to an ion-exchange membrane electrodialysis tank, and it is possible to improve desalination efficiency and prevent microorganism contamination (proliferation) in the dialysis tank. In addition, since it is possible to charge a highly concentrated sugar solution into the dialysis tank at high temperatures, the concentration energy (mainly steam energy in the evaporation process) in the subsequent process after desalting by electrodialysis is reduced, and the sugar solution is further reduced. Due to the reduction in the viscosity of the liquid and the reduction in the amount of liquid treated per unit solid content due to the high concentration liquid charged, the power of auxiliary machines such as pumps and stirrers is also greatly reduced, which is extremely advantageous from an industrial perspective. Therefore, the temperature of the sugar solution in the present invention can of course be at room temperature, but a higher temperature is more desirable, generally 45°C or higher, particularly 50°C or higher, preferably in the range of 50 to 70°C. The sugar solution used in the present invention is not particularly limited as long as it contains ash (salts), such as refined sugar,
It can be applied to sugar juice, molasses, washed molasses, blackstrap molasses in the sugar industry such as beet sugar and cane sugar, as well as starch sugar solutions from sweet starch. These sugar solutions are generally diluted with water and supplied to an ion exchange membrane electrodialysis tank at a predetermined concentration, but in the present invention, as described above, electrodialysis at high temperatures is possible, so for example
Can supply high concentration sugar solution with BX40-50. The ion exchange membrane electrodialysis tank of the present invention can be any so-called filter press type electrodialysis tank in which anion exchange membranes are arranged alternately between negative and positive electrodes via gaskets to form a desalination chamber and a concentration chamber. model can also be used. As for the cation exchange membrane and anion exchange membrane used in these, general commercially available products can be used without particular restriction. Moreover, any of the batch, partial circulation, and continuous electrodialysis methods can be applied, and the method may be appropriately selected depending on conditions such as throughput. Further, any method of applying current to the dialysis tank can be applied, such as a constant voltage method, a constant current method, or a desalination solution conductivity tracking method, but the conductivity tracking method is often preferred because it is economical. In addition, the operating current density varies depending on the type and properties of the sugar solution, but the current density i
(A/dm 2 ), sugar solution conductivity k (ms/cmat 25° C.), preferably i/k is in the range of 0.01 to 1. In the present invention, before supplying the sugar solution to the dialysis tank, in order to remove impurities coexisting in the sugar solution or decolorize the sugar solution, for example, pre-coated filtration, ultrafiltration, precision filtration, ion exchange resin, etc. process,
There are no particular restrictions on carrying out carbonate filling treatment, activated carbon treatment, etc. Similar to conventional methods, the sugar solution desalted according to the present invention is generally adjusted in properties and components by addition of an alkali, neutralization with an ion exchange resin, or concentration, depending on its use. As described above, according to the present invention, in an ion exchange membrane electrodialysis device, contamination of the ion exchange membrane can be prevented by a simple method of adding an acid to the concentrated liquid side and adjusting the pH of the liquid to 4 or less. Therefore, the sugar solution can be desalted while suppressing the increase in cell voltage and minimizing loss of sugar due to decomposition and conversion of sugar. Furthermore, according to the present invention, the desalination treatment by electrodialysis enables continuous long-term operation, and the ion exchange membrane has many advantages such as a long period of use. Reduction of processing energy such as steam, prevention of sucrose conversion,
Many economic effects can be expected, such as reducing the amount of acid used and preventing microbial growth. Examples will be specifically explained below. Example 1 Sugar Refining Industry's No. 2 honey (BX80) in tap water to BX45
The diluted sugar solution was used as the liquid to be desalted and desalted by electrodialysis. The electrodialysis device used was TS-220 manufactured by Tokuyama Soda Co., Ltd., and the cation exchange membrane was Neosepta CL −.
25T, 20 pairs of anion exchange membranes of Neocepta AFN with an effective current carrying area of 2 dm 2 were used. A batch desalting method was used for desalting, the amount of sugar solution charged per batch was 8, and the dialysis temperature was set at 50°C ± 2°C. A 0.2 N saline solution was used as the concentrated solution, and the pH value for each experimental condition shown in Table 1 was adjusted by adding hydrochloric acid. The concentration of added hydrochloric acid was appropriately within the range of 1 to 5 N depending on the set PH value. The current application method uses a current-conductivity tracking method that sets the current value according to the conductivity of the desalination solution, and in the entire desalination process, i/k =
0.15 (i = current density A/dm 2 , k = desalination liquid conductivity
ms/cm). The membrane surface flow velocity of the desalted solution and concentrated solution was 6 cm/sec, respectively. As shown in Table 1, Nos. 1, 2, 3, 4, 5, and 6 are examples in which the concentrated liquid was PH-adjusted, and No. 7 is a comparative example in which the desalted liquid side was PH-adjusted. As can be seen from the experimental results, the pH of the concentrate was adjusted by adding hydrochloric acid, and stable operation was possible with little loss of sucrose and almost no increase in membrane resistance, especially when the concentrate was filtered at a pH value of 4 or less. However, as shown in Comparative Example No. 7, when the pH is adjusted by adding an acid to the desalted solution, the loss of sucrose due to acid decomposition is large, which is very economically disadvantageous.
The leakage of sucrose from the desalination side to the concentration side during electrodialysis was as small as around 0.1% (based on sucrose). Example 2 A sugar solution obtained by diluting cane syrup (BX65) from a cane sugar factory to BX45 with tap water was desalted under the same conditions as in Example 1. The results are shown in Table 1. Nos. 8 and 9 are examples in which the pH of the concentrate side was adjusted, and No. 10 is a comparative example without pH adjustment. Example 3 Based on the results of Example 1, repeated experiments were conducted at the second sugar refinery, and a life test of the ion exchange membrane was conducted. The second honey from the sugar refinery is diluted with tap water to BX45.
After adjusting the concentration chamber solution to pH 1.5 with hydrochloric acid, it was heated for 3ms/
The experiment of desalting to cm was repeated, and CIP cleaning (alkaline hydrochloric acid cleaning) was performed every 6 cycles. As a result, the membrane resistance at the end of the first cycle of desalination was 41.4 Ωcm 2 and that at the 50th cycle was 41.2 Ωcm 2
Furthermore, at the 100th cycle, the resistance was 42.0 Ωcm 2 , with almost no increase in membrane resistance (ie, membrane contamination) observed, and the current efficiencies were all good at 91%, 88%, and 88%.
Furthermore, since electrodialysis was performed at high temperature (50°C), no bacterial growth occurred on the ion exchange membrane surface, and microbial growth was completely avoided.
【表】【table】
【表】【table】
【図面の簡単な説明】[Brief explanation of the drawing]
第１図は廃糖蜜の各温度における濃度と電導度
の関係を示す。
Figure 1 shows the relationship between the concentration and conductivity of blackstrap molasses at various temperatures.