JP4136220B2 - Method for producing insoluble tannin and method for adsorption of hexavalent chromium using this tannin - Google Patents
Method for producing insoluble tannin and method for adsorption of hexavalent chromium using this tannin Download PDFInfo
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【０００１】
【発明の属する技術分野】
本発明はウラン、トリウム、超ウラン元素等のアクチニド元素、又はカドミウム、鉛、クロム、水銀及び鉄を含む重金属元素、或いはコバルト、セシウム、ストロンチウム等の金属元素を吸着し得る不溶性タンニンの製造方法に関する。また本発明はこのタンニンを用いた六価クロムの吸着方法に関するものである。
【０００２】
【従来の技術】
核燃料を取扱う工程において排出される廃液中には、ウラン、トリウム等の核燃料元素が含まれている。従来、この核燃料元素を吸着するための吸着剤の製造方法として、本出願人は、アルカリ水溶液に縮合型タンニン粉末を溶解し、この溶液にアルデヒド水溶液を混合してゲル状組成物を生成し、このゲル状組成物を室温下で熟成、又は加熱して安定化する不溶性タンニンの製造方法を提案した（特開平５−６６２９１）。
また本出願人は、アンモニア水に加水分解型タンニン粉末を溶解し、この溶液にアルデヒド水溶液を混合して沈殿物を生成し、この沈殿物を加熱し、この加熱した沈殿物を硝酸のような鉱酸に浸漬した後、濾過する加水分解型不溶性タンニンの製造方法を提案した（特開平５−１７７１３５）。
上記２つの方法で得られる不溶性タンニンは、金属元素の吸着能力を有し、かつ廃液処理装置のカラムにおける通液性が極めて良好な特長がある。この吸着剤である不溶性タンニンはその含水率を制御すると、ゲルの網目構造が変化して、吸着させる金属元素のイオンの大きさに応じた適切な網目構造及びその分子空間を確保でき、金属元素の吸着容量及び吸着速度を変えることができる可能性がある。特に特開平５−１７７１３５号公報に示される不溶性タンニンは、鉱酸と接触することにより、タンニン表面が硬くなりカラムに入れたときにつぶれにくく金属元素の吸着率がより向上する利点があり、またゲルを酸性に保持することにより、不溶性タンニンにカビが発生するのを防止する効果も有する。
【０００３】
【発明が解決しようとする課題】
しかし、上記２つの方法で製造された不溶性タンニンは、その含水率の制御し得る範囲が実用上約７０％から約８５％までに限られていた。
また上記２つの方法において、ゲル状組成物を室温下で熟成、又は加熱して安定化することにより得られた不溶性タンニンは、カラム等に充填して使用するときにミキサー等の機械的手段で粒子状に解砕し、篩い分けにより所望の大きさの粒子を得ているが、粒子の粒径及び形状が一定でなく、微粒子の不溶性タンニンを必要とするときには特別に微細化しなければならなかった。
【０００４】
本発明の目的は、上記従来の吸着剤に比較してゲルの網目構造とその分子空間をより広く変化させて金属の吸着容量と吸着速度を変えることができる不溶性タンニンを製造する方法を提供することにある。
本発明の別の目的は、吸着剤として使用するに際して解砕する必要がなく、所望の粒径及び所望の含水率の不溶性タンニンを製造し得る方法を提供することにある。
【０００５】
【課題を解決するための手段】
請求項１に係る発明は、(a) アルカリ水溶液に縮合型タンニン粉末を溶解する工程と、(b) 工程(a)で得られた水溶液にアルデヒド水溶液を添加混合する工程と、(c) ポリエーテル型非イオン性界面活性剤を含む疎水性溶媒を加熱温度下で撹拌させながら前記工程(b)で得られた水溶液を添加して液滴の形態で前記疎水性溶媒中に分散させる工程と、(d) 前記液滴から水分を蒸発させて球状でかつゲル状不溶性タンニンを形成する工程とを含む不溶性タンニンの製造方法である。
なお、本明細書において「不溶性タンニン」とは、水、酸又はアルカリのいずれに対しても溶解しないタンニンをいう。
【０００６】
工程(a)及び工程(b)を経てタンニンの予備架橋が行われ、粘性の高い溶液が生成される。工程(c)で疎水性溶媒を撹拌させると、溶媒の液面は円錐状になり気体と液体との界面積が増大する。ここで疎水性溶媒中に分散している粘性の高い溶液は球状の液滴となってこの界面に沿って流動し、工程(d)で液滴から水分が蒸発することにより、液滴が粒子化して様々な網目構造とその分子空間からなるゲル状不溶性タンニンが形成される。疎水性溶媒の疎水性の程度や粘度、撹拌速度等の疎水性溶媒の流動条件等に応じてゲル状不溶性タンニンの粒径及び形状が制御される。また疎水性溶媒の温度、液滴からの水分蒸発時間等に応じてゲル状不溶性タンニンの網目構造及び分子空間を変えることにより不溶性タンニンの含水率が制御される。
得られた不溶性タンニンをウラン、トリウム、超ウラン元素、又はカドミウム、鉛、クロム、水銀、鉄、コバルト、セシウム、ストロンチウム等の金属元素を含有した溶液に接触させると、ゲル状不溶性タンニンは金属元素を極めて効率良く吸着する。これはゲルを構成するタンニンのもっているポリフェノール性水酸基が官能基となって、金属元素と水素イオン交換反応により吸着するためである。またゲルにすることによりその分子鎖の自由度が増大し、分子鎖の官能基が金属元素と配位し易い立体構造になるため、ゲル状不溶性タンニンは極めて優れた金属元素の吸着性能を示す。
【０００７】
請求項４に係る発明は、請求項１記載の方法によって不溶性タンニンを製造する工程、及び該工程で得られた含水率が７０〜９０％の球状のゲル状不溶性タンニンを六価クロムを含有する水溶液に添加して六価クロムを不溶性タンニンに吸着する工程とからなる六価クロムの吸着方法である。
含水率を７０〜９０％に調整したゲル状不溶性タンニンは六価クロムを効率よく吸着することができる。
【０００８】
【発明の実施の形態】
本発明の製造方法は、前述した工程(a)及び工程(b)からなるタンニンの予備架橋工程と、前述した工程(c)及び工程(d)からなる粘性の高い溶液の粒子化・構造形成工程からなる。
【０００９】
(1) タンニンの予備架橋工程
図１に示すように、この(1)タンニンの予備架橋工程では、先ず縮合型タンニン粉末をｐＨ８〜１０の室温のアルカリ水溶液に溶解する。ｐＨ８未満ではタンニン粉末が溶解しにくく、ｐＨ１０を超えると部分的に架橋した粘性の高い溶液が不安定でゲルになりにくくなるからである。タンニン粉末の混合割合はアルカリ水溶液に対してはタンニン粉末を１〜４０重量％の範囲で混合することが好ましく、３５重量％がより好ましい。１重量％未満ではタンニン粉末が架橋しにくく、４０重量％を超えると粘度が高くなり取扱いにくくなる。
本発明に用いられるタンニン粉末は縮合型タンニンである。例示すれば、ケブラコタンニン、ワットルタンニン、マングローブタンニン、スプルースタンニン、ガンビールタンニン、アカカテキン、カシワ樹皮タンニン等が挙げられる。この縮合型タンニン粉末を溶解するアルカリ水溶液としては、水酸化ナトリウム、水酸化カリウム、水酸化リチウム等のアルカリ金属水酸化物の水溶液、アンモニア水が挙げられる。
次いで、タンニン粉末が溶解した水溶液にアルデヒド水溶液を添加混合する。アルデヒド水溶液としては、例えばホルムアルデヒド水溶液、アセトアルデヒド水溶液、グルタールアルデヒド水溶液等が挙げられる。
【００１０】
最初にアルカリ水溶液に縮合型タンニン粉末を溶解し、その後にアルデヒド水溶液と混合することにより、縮合型タンニンは沈殿物とならずに、タンニンが部分的に架橋した粘性の高い溶液となる。従来の特開平５−６６２９１号公報に示された方法では、架橋反応が遅延して母液全体がヒドロゲル化するのに対して、本発明ではアルカリ金属イオンもしくはアンモニウムイオンの存在、母液のｐＨ値及び温度、部分架橋時間等によって、前記架橋反応の程度を幅広く制御することができ、アルデヒド水溶液との反応時間に相応して架橋反応が進行し、それぞれの条件に相応した溶液粘度を得ることができる。
【００１１】
(2) 粘性の高い溶液の粒子化・構造形成工程
次に、ポリエーテル型非イオン性界面活性剤を含む疎水性溶媒を用意する。この疎水性溶媒は上記アルデヒド水溶液を添加混合した水溶液と混和性のない溶媒であれば特に限定されない。本発明に好ましいポリエーテル型非イオン性界面活性剤としては、アルキルフェノール系非イオン性界面活性剤であるノニフェノール系（商品名：ノニポール）(Ｃ9Ｈ19)、オクチルフェノール系(Ｃ8Ｈ17)、ドデシルフェノール系(Ｃ12Ｈ25)等が挙げられる。また本発明に好ましい疎水性溶媒としては、デカリン、ポリブテン、ヘキサン、トルエン等が挙げられる。ポリエーテル型非イオン性界面活性剤は疎水性溶媒１００重量％に対して５〜１０重量％添加する。この界面活性剤の添加量が５重量％未満ではタンニン水溶液の液滴の安定性に乏しく、１０重量％を超えると吸着剤としてのゲル状不溶性タンニンの性能に不都合が生じる。更にポリエーテル型非イオン性界面活性剤を含む疎水性溶媒を室温〜１００℃、好ましくは５０〜９０℃に加熱する。室温未満では次に述べる液滴が蒸発しにくい。また１００℃を超えると沸騰が起こりゲルの構造形成が困難になる。上記温度に加熱した疎水性溶媒を撹拌しながら、アルデヒド水溶液を添加混合することにより予備架橋させた粘性の高い溶液を疎水性溶媒に添加する。撹拌により、この水溶液を疎水性溶媒中に懸濁させ分散させる。
【００１２】
疎水性溶媒の疎水性の程度や粘度、撹拌速度等の疎水性溶媒の流動条件、疎水性溶媒の温度等に応じてゲル状不溶性タンニンの粒径、形状及び網目構造が制御される。具体的には疎水性溶媒の疎水性の程度が高い程、ゲル状不溶性タンニンの粒径は小さくなり、反対に疎水性の程度が低くなり親水性を兼ね備えると、ゲル状不溶性タンニンの粒径は大きくなる。また疎水性溶媒の粘度が高い程、ゲル状不溶性タンニンの粒径は小さくなり、反対に粘度が低くなる程、ゲル状不溶性タンニンの粒径は大きくなる。更に撹拌速度が高い程、ゲル状不溶性タンニンの粒径は小さくなり、反対に撹拌速度が遅い程、ゲル状不溶性タンニンの粒径は大きくなる。本発明の方法によれば、約０．０１ｍｍ〜５ｍｍの範囲の粒径を有するゲル状不溶性タンニンを作製することができる。
また疎水性溶媒の温度、液滴からの水分蒸発時間等に応じてゲル状不溶性タンニンの網目構造及びその分子空間が変化し、不溶性タンニンの含水率が制御される。具体的には温度が高く、水分蒸発時間が長い程、ゲル状不溶性タンニンの含水率は低く、温度が低く、水分蒸発時間が短い程、ゲル状不溶性タンニンの含水率は高くなる。本発明の方法によれば、様々な網目構造と分子空間を有する約５〜９０％の範囲の含水率を有するゲル状不溶性タンニンを作製することができる。
【００１３】
(3) 後処理
疎水性溶媒中で粒子化したゲル状不溶性タンニンは、疎水性溶媒から取出した後、アセトン等の水溶性有機溶剤で洗浄して界面活性剤及び疎水性溶媒をゲル状不溶性タンニンから除去する。次いで蒸留水でゲル状不溶性タンニンを洗浄することにより、残留する水溶性有機溶剤を除去し、様々な網目構造と分子空間を有するゲル状不溶性タンニンが得られる。
【００１４】
【実施例】
次に本発明の実施例を比較例とともに図面に基づいて説明する。
＜実施例１〜１０＞
縮合型タンニンであるワットルタンニンの粉末２３ｇをｐＨ８．７の２５℃のＮａＯＨ水溶液６５ｍｌに添加して溶解させた。タンニンの粉末を加えるに従って溶液のｐＨは徐々に低下するため、ＮａＯＨ水溶液を随時添加して溶液のｐＨがアルカリ側になるように保持した。次いでホルムアルデヒドの３７重量％水溶液６ｍｌを添加した。この溶液を３つに分割し、３つの水溶液をそれぞれ５分間、３０分間及び６０分間放置した。時間が長くなるに従って、タンニンが部分的に架橋して溶液の粘度が上昇し、図１(1)に示すように、粘性の高い溶液１０が得られた。
【００１５】
一方、容積２０リットルの反応器１１にポリエーテル型非イオン性界面活性剤（商品名：ノニポール）を含む疎水性溶媒１２であるデカリン（沸点１８９℃）を貯えた。上記粘度の異なる３種類の粘性の高い溶液１０を注入器１３にそれぞれ採取し、この溶液１０を５０℃、６０℃、７０℃及び８０℃にそれぞれ加熱した４種類の疎水性溶媒１２中に添加し、２０００ｒｐｍの速度で表１に示す時間だけ撹拌し溶液１０を懸濁し分散させた。これにより溶液の液滴から水分が蒸発し、液滴が球状に粒子化して特定な網目構造と分子空間からなるゲル状不溶性タンニン１４が形成された。
このゲル状で粒子状の不溶性タンニン１４を反応器１１から取出した後、アセトンに続いて蒸留水で洗浄した。洗浄後の粒子形態及びその平均粒径を透過型電子顕微鏡により調べた。その結果を図２（ａ）及び（ｂ）に示す。またアセトンで洗浄した直後及び蒸留水で洗浄した直後の粒子の含水率を測定した。その結果を表１に示す。
【００１６】
＜比較例１＞
実施例１と同じ縮合型タンニンであるワットルタンニンの粉末に実施例１と同様にしてＮａＯＨ水溶液を添加して溶解させた。次いで実施例１と同様にこの溶液にホルムアルデヒド水溶液を添加した後、この溶液を８０℃で一昼夜加熱した。これによりゲル化が進行し、安定化したゲル状組成物が得られた。このゲル状組成物を蒸留水で洗浄した後、ミキサーで解砕し、篩い分けにより粒径の揃ったゲル状不溶性タンニンを得た。このゲル状不溶性タンニンの粒子形態及びその平均粒径を透過型電子顕微鏡により調べた。その結果を図３（ａ）及び（ｂ）に示す。また蒸留水で洗浄した直後の粒子の含水率を測定した。その結果を表１に示す。
【００１７】
＜比較例２＞
比較例１で得られた、篩い分けにより粒径の揃ったゲル状不溶性タンニンを０．１Ｎの希硝酸に入れ、３０分間撹拌した。この硝酸液を濾紙（東洋濾紙Ｎｏ．２）で濾過し、濾別したこのゲル状不溶性タンニンを蒸留水で洗浄した後、直ちに粒子の含水率を測定した。その結果を表１に示す。
【００１８】
【表１】
図２（ａ）及び（ｂ）に示すように、実施例９のゲル状不溶性タンニンはほぼ球形であって、その表面には数１０μｍの網目構造の細孔が観察された。一方、比較例１で得られたゲル状不溶性タンニンは、図３（ａ）及び（ｂ）に示すように、表面の凹凸の激しい塊の破砕物であって、その表面には大きな細孔は見られなかった。
実施例１〜１０のアセトンで洗浄した直後の粒子の含水率は、６６．１〜１．７９％であり、これらの粒子を更に蒸留水で洗浄すると、粒子の含水率は７７．６〜４０．１％に増大し、膨潤した。これに対して、比較例１及び比較例２の蒸留水で洗浄した直後の粒子の含水率は、約６６〜７７％の範囲にばらつき、平均値は７２％であった。このことから、実施例では比較例に見られない低い含水率のゲル状不溶性タンニンが得られることが確認された。また実施例ではアセトン中では粒子は収縮し、粒子は蒸留水と接触すると膨潤することが判った。
【００２０】
＜六価クロムの吸着試験例＞
(a) 疎水性溶媒であるデカリンの温度を８０℃（実施例８〜１０）にして、含水率が約４０〜５９％のゲル状不溶性タンニンを用意した。また同じく７０℃（実施例５〜７）にして、含水率が約４９〜６０％のゲル状不溶性タンニンを用意した。更に６０℃（実施例２〜４）にして、含水率が約５８〜７１％のゲル状不溶性タンニンを用意した。比較のため、比較例１及び比較例２の含水率が約６８〜８６％のゲル状不溶性タンニンを用意した。上記から、デカリンの温度が高い程、含水率は低く、デカリンの温度が低い程、含水率が高いことが判る。
【００２１】
実施例１〜１０及び比較例１、２のゲル状不溶性タンニンをそれぞれ０．２ｇ採取して、六価クロム（ＣｒＯ3）濃度が１０００ｐｐｍの溶液４０ｍｌに各別に添加し平衡に達した後、ゲル状不溶性タンニンを容器から取出し、残液のクロムの濃度を測定し、各不溶性タンニンに吸着したクロムの吸着容量を求めた。その結果を図４に示す。
図４から明らかなように、含水率が高くなる程、六価クロム吸着容量が高くなることが判った。特に比較例２の硝酸処理した含水率が７２％の不溶性タンニンでは、ゲル状不溶性タンニン１ｇ当り１９２〜２８７ｍｇの六価クロムの吸着容量を得たのに対して、実施例１の含水率が７７．６％の不溶性タンニンでは、比較例２の約１．９〜２．８倍に相当する５４０ｍｇの六価クロムの吸着容量を得た。また同じ高い含水率であっても、比較例１に比べて実施例１〜１０のゲル状不溶性タンニンの機械的強度は高かった。
【００２２】
(b) 疎水性溶媒であるデカリンの温度を６０℃にして、含水率が約７０％のゲル状不溶性タンニンを用意した（実施例１１）。また同じく５０℃にして、含水率が約８３％のゲル状不溶性タンニンを用意した（実施例１２）。
実施例１１と１２のゲル状不溶性タンニンをそれぞれ０．２ｇ採取して、六価クロム（ＣｒＯ3）濃度が１０００ｐｐｍの溶液８０ｍｌに各別に添加し、六価クロムの不溶性タンニンへの吸着速度を調べた。その結果を図５に示す。
【００２３】
図５から明らかなように、両実施例１１及び１２とも、添加した後、６０時間程度で吸着容量は飽和状態に達するが、含水率が約８３％と高い実施例１２の不溶性タンニンの方が、約７０％の実施例１１の不溶性タンニンよりも吸着速度が高く、比較的短時間で高い吸着容量が得られた。
【００２４】
【発明の効果】
以上述べたように、本発明の製造方法によれば、ゲル状不溶性タンニンの含水率を制御することができ、かつゲルの網目構造とその分子空間を変化させることができる。これにより吸着させる金属元素のイオンの大きさに応じた適切な網目構造とその分子空間を確保することができ、従来の吸着剤に比較して金属の吸着容量が極めて高い不溶性タンニンが得られ、また吸着剤として使用するに際して解砕する必要がなく、所望の粒径及び形状が得られる優れた効果を奏する。
【図面の簡単な説明】
【図１】本発明の製造方法を示す工程図。
【図２】（ａ） 実施例９のゲル状不溶性タンニンの５０倍の顕微鏡写真図。
（ｂ） 実施例９のゲル状不溶性タンニンの１０００倍の顕微鏡写真図。
【図３】（ａ） 比較例１のゲル状不溶性タンニンの５０倍の顕微鏡写真図。
（ｂ） 比較例１のゲル状不溶性タンニンの１０００倍の顕微鏡写真図。
【図４】実施例及び比較例の含水率に応じたゲル状不溶性タンニンのクロム吸着容量を示す図。
【図５】実施例１１と実施例１２の含水率に応じたゲル状不溶性タンニンのクロム吸着速度を示す図。
【符号の説明】
１０ 粘性の高い溶液
１１ 反応器
１２ 疎水性溶媒
１３ 注入器
１４ ゲル状不溶性タンニン[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing insoluble tannin capable of adsorbing actinide elements such as uranium, thorium and transuranium elements, heavy metal elements including cadmium, lead, chromium, mercury and iron, or metal elements such as cobalt, cesium and strontium. . The present invention also relates to a method for adsorbing hexavalent chromium using this tannin.
[0002]
[Prior art]
The waste liquid discharged in the process of handling nuclear fuel contains nuclear fuel elements such as uranium and thorium. Conventionally, as a method for producing an adsorbent for adsorbing this nuclear fuel element, the present applicant dissolved a condensed tannin powder in an alkaline aqueous solution, mixed an aldehyde aqueous solution with this solution to produce a gel composition, A method for producing insoluble tannin has been proposed in which this gel composition is aged at room temperature or stabilized by heating (JP-A-5-66291).
The present applicant also dissolves hydrolyzable tannin powder in aqueous ammonia, mixes this solution with an aldehyde aqueous solution to form a precipitate, heats the precipitate, and converts the heated precipitate into nitric acid. A method for producing hydrolyzable insoluble tannin that has been immersed in a mineral acid and then filtered is proposed (Japanese Patent Laid-Open No. 5-177135).
The insoluble tannin obtained by the above two methods has the ability to adsorb metal elements and has extremely good liquid permeability in the column of the waste liquid treatment apparatus. When the moisture content of the insoluble tannin, which is the adsorbent, is controlled, the network structure of the gel changes, and an appropriate network structure corresponding to the size of ions of the metal element to be adsorbed and its molecular space can be secured. There is a possibility that the adsorption capacity and the adsorption speed of the resin can be changed. In particular, the insoluble tannin disclosed in JP-A-5-177135 has an advantage that the tannin surface is hardened by being brought into contact with a mineral acid and is hard to be crushed when placed in a column, and the adsorption rate of the metal element is further improved. By keeping the gel acidic, it also has the effect of preventing mold from forming on the insoluble tannin.
[0003]
[Problems to be solved by the invention]
However, the insoluble tannin produced by the above two methods has practically limited the range in which the water content can be controlled from about 70% to about 85%.
Further, in the above two methods, the insoluble tannin obtained by aging or stabilizing the gel composition at room temperature is charged by mechanical means such as a mixer when used in a column or the like. Particles of the desired size are obtained by crushing into particles and sieving, but the particle size and shape of the particles are not constant and must be specially refined when insoluble tannin is required It was.
[0004]
An object of the present invention is to provide a method for producing insoluble tannin that can change the adsorption capacity and adsorption rate of metal by changing the gel network structure and its molecular space more widely than the above conventional adsorbents. There is.
Another object of the present invention is to provide a method capable of producing an insoluble tannin having a desired particle size and a desired water content without the need for crushing when used as an adsorbent.
[0005]
[Means for Solving the Problems]
The invention according to claim 1 includes: (a) a step of dissolving condensed tannin powder in an alkaline aqueous solution; (b) a step of adding and mixing an aldehyde aqueous solution to the aqueous solution obtained in step (a); Adding the aqueous solution obtained in the step (b) while stirring a hydrophobic solvent containing an ether type nonionic surfactant at a heating temperature, and dispersing the aqueous solution obtained in the form of droplets in the hydrophobic solvent; And (d) evaporating water from the droplets to form spherical and gel-like insoluble tannins.
In the present specification, “insoluble tannin” refers to tannin that does not dissolve in water, acid, or alkali.
[0006]
The tannin is pre-crosslinked through the steps (a) and (b) to produce a highly viscous solution. When the hydrophobic solvent is stirred in step (c), the liquid level of the solvent becomes conical and the interface area between the gas and the liquid increases. Here, the highly viscous solution dispersed in the hydrophobic solvent becomes spherical droplets and flows along this interface, and moisture is evaporated from the droplets in step (d). As a result, gel-like insoluble tannin composed of various network structures and their molecular spaces is formed. The particle size and shape of the gel-like insoluble tannin are controlled according to the flow conditions of the hydrophobic solvent such as the degree of hydrophobicity, the viscosity, and the stirring speed of the hydrophobic solvent. Further, the water content of insoluble tannin is controlled by changing the network structure and molecular space of the gel-like insoluble tannin according to the temperature of the hydrophobic solvent, the time for evaporating water from the droplets, and the like.
When the obtained insoluble tannin is brought into contact with a solution containing a metal element such as uranium, thorium, transuranium element, or cadmium, lead, chromium, mercury, iron, cobalt, cesium, strontium, etc., the gel-like insoluble tannin is a metal element. Is adsorbed extremely efficiently. This is because the polyphenolic hydroxyl group possessed by the tannin constituting the gel becomes a functional group and is adsorbed by a hydrogen ion exchange reaction with the metal element. In addition, gels increase the degree of freedom of the molecular chain and form a three-dimensional structure in which the functional group of the molecular chain is easily coordinated with the metal element. Therefore, the gel-like insoluble tannin exhibits extremely excellent metal element adsorption performance. .
[0007]
The invention according to claim 4 includes a step of producing insoluble tannin by the method of claim 1 , and a spherical gel-like insoluble tannin having a water content of 70 to 90% obtained in this step, containing hexavalent chromium. A method for adsorbing hexavalent chromium comprising a step of adding hexavalent chromium to insoluble tannin by adding to an aqueous solution.
Gel-like insoluble tannins having a water content adjusted to 70-90% can adsorb hexavalent chromium efficiently.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The production method of the present invention comprises a tannin pre-crosslinking step comprising the steps (a) and (b) described above, and a granulation / structure formation of a highly viscous solution comprising the steps (c) and (d) described above. It consists of a process.
[0009]
(1) Tannin Pre-Crosslinking Step As shown in FIG. 1, in this (1) tannin pre-crosslinking step, the condensed tannin powder is first dissolved in a room temperature alkaline aqueous solution of pH 8-10. If the pH is less than 8, the tannin powder is difficult to dissolve, and if the pH is more than 10, the partially crosslinked highly viscous solution is unstable and hardly becomes a gel. The mixing ratio of the tannin powder is preferably 1 to 40% by weight and more preferably 35% by weight with respect to the alkaline aqueous solution. If it is less than 1% by weight, the tannin powder is difficult to crosslink, and if it exceeds 40% by weight, the viscosity becomes high and handling becomes difficult.
The tannin powder used in the present invention is condensed tannin. Examples include quebraco tannin, wattle tannin, mangrove tannin, sprue tannin, gambir tannin, red catechin, oak bark tannin and the like. Examples of the alkaline aqueous solution for dissolving the condensed tannin powder include aqueous solutions of alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, and aqueous ammonia.
Next, an aldehyde aqueous solution is added to and mixed with the aqueous solution in which the tannin powder is dissolved. Examples of the aldehyde aqueous solution include formaldehyde aqueous solution, acetaldehyde aqueous solution, and glutaraldehyde aqueous solution.
[0010]
First, the condensed tannin powder is dissolved in an alkaline aqueous solution, and then mixed with an aldehyde aqueous solution, whereby the condensed tannin does not become a precipitate but becomes a highly viscous solution in which tannin is partially crosslinked. In the conventional method disclosed in Japanese Patent Application Laid-Open No. 5-66291, the cross-linking reaction is delayed and the entire mother liquor is hydrogelated. In the present invention, the presence of alkali metal ions or ammonium ions, the pH value of the mother liquor, and The degree of the cross-linking reaction can be widely controlled by temperature, partial cross-linking time, etc., and the cross-linking reaction proceeds according to the reaction time with the aldehyde aqueous solution, and a solution viscosity corresponding to each condition can be obtained. .
[0011]
(2) Particle formation / structure formation process of highly viscous solution Next, a hydrophobic solvent containing a polyether type nonionic surfactant is prepared. The hydrophobic solvent is not particularly limited as long as it is not miscible with the aqueous solution to which the aldehyde aqueous solution is added and mixed. Preferred polyether type nonionic surfactants for the present invention are noniphenol type (trade name: Nonipol) (C 9 H 19 ) and octylphenol type (C 8 H 17 ), which are alkylphenol nonionic surfactants. , Dodecylphenol (C 12 H 25 ) and the like. In addition, preferred hydrophobic solvents for the present invention include decalin, polybutene, hexane, toluene and the like. The polyether type nonionic surfactant is added in an amount of 5 to 10% by weight based on 100% by weight of the hydrophobic solvent. If the added amount of the surfactant is less than 5% by weight, the stability of the tannin aqueous solution droplets is poor, and if it exceeds 10% by weight, the performance of the gel-like insoluble tannin as an adsorbent is inconvenient. Further, a hydrophobic solvent containing a polyether type nonionic surfactant is heated to room temperature to 100 ° C, preferably 50 to 90 ° C. Below room temperature, the droplets described below are difficult to evaporate. If it exceeds 100 ° C., boiling occurs and it becomes difficult to form a gel structure. While stirring the hydrophobic solvent heated to the above temperature, a highly viscous solution preliminarily crosslinked by adding and mixing an aqueous aldehyde solution is added to the hydrophobic solvent. This aqueous solution is suspended and dispersed in a hydrophobic solvent by stirring.
[0012]
The particle size, shape, and network structure of the gel-like insoluble tannin are controlled according to the hydrophobicity of the hydrophobic solvent, the viscosity, the flow conditions of the hydrophobic solvent such as the stirring speed, the temperature of the hydrophobic solvent, and the like. Specifically, the higher the degree of hydrophobicity of the hydrophobic solvent, the smaller the particle size of the gel-like insoluble tannin, and conversely, when the degree of hydrophobicity is low and has hydrophilicity, the particle size of the gel-like insoluble tannin is growing. Further, the higher the viscosity of the hydrophobic solvent, the smaller the particle size of the gel-insoluble tannin, and conversely, the lower the viscosity, the larger the particle size of the gel-insoluble tannin. Furthermore, the higher the stirring speed, the smaller the particle size of the gel-insoluble tannin, and the lower the stirring speed, the larger the particle size of the gel-insoluble tannin. According to the method of the present invention, a gel-like insoluble tannin having a particle size in the range of about 0.01 mm to 5 mm can be produced.
Further, the network structure of the gel-like insoluble tannin and the molecular space thereof are changed according to the temperature of the hydrophobic solvent, the time for evaporating water from the droplets, etc., and the water content of the insoluble tannin is controlled. Specifically, the higher the temperature and the longer the water evaporation time, the lower the water content of the gel-insoluble tannin, and the lower the temperature and the shorter the water evaporation time, the higher the water content of the gel-insoluble tannin. According to the method of the present invention, a gel-like insoluble tannin having a water content in a range of about 5 to 90% having various network structures and molecular spaces can be produced.
[0013]
(3) The gel-like insoluble tannin formed into a particle in the post-treatment hydrophobic solvent is taken out from the hydrophobic solvent and washed with a water-soluble organic solvent such as acetone to remove the surfactant and the hydrophobic solvent from the gel-like insoluble tannin. Remove from. Next, by washing the gel-like insoluble tannin with distilled water, the remaining water-soluble organic solvent is removed, and gel-like insoluble tannin having various network structures and molecular spaces is obtained.
[0014]
【Example】
Next, examples of the present invention will be described based on the drawings together with comparative examples.
<Examples 1 to 10>
23 g of powder of wattle tannin, which is condensed tannin, was added to 65 ml of a 25 ° C. aqueous NaOH solution at pH 8.7 and dissolved. Since the pH of the solution gradually decreased as tannin powder was added, an aqueous NaOH solution was added as needed to maintain the pH of the solution at the alkali side. Then 6 ml of a 37% by weight aqueous solution of formaldehyde was added. This solution was divided into three, and the three aqueous solutions were allowed to stand for 5 minutes, 30 minutes and 60 minutes, respectively. As the time increased, the tannin partially cross-linked to increase the viscosity of the solution, and as shown in FIG. 1 (1), a highly
[0015]
On the other hand, decalin (boiling point 189 ° C.), which is a hydrophobic solvent 12 containing a polyether type nonionic surfactant (trade name: Nonipol), was stored in a reactor 11 having a volume of 20 liters. Three kinds of high-
The gel-like and particulate
[0016]
<Comparative Example 1>
In the same manner as in Example 1, an aqueous NaOH solution was added to a powder of Watru tannin, which is the same condensed tannin as in Example 1, and dissolved. Next, an aqueous formaldehyde solution was added to this solution in the same manner as in Example 1, and then this solution was heated at 80 ° C. overnight. As a result, gelation proceeded and a stabilized gel-like composition was obtained. This gel composition was washed with distilled water and then crushed with a mixer, and a gel-like insoluble tannin having a uniform particle size was obtained by sieving. The particle form of the gel-like insoluble tannin and the average particle size thereof were examined with a transmission electron microscope. The results are shown in FIGS. 3 (a) and 3 (b). Further, the water content of the particles immediately after washing with distilled water was measured. The results are shown in Table 1.
[0017]
<Comparative example 2>
The gel-like insoluble tannin having a uniform particle size obtained by sieving obtained in Comparative Example 1 was placed in 0.1N dilute nitric acid and stirred for 30 minutes. The nitric acid solution was filtered with a filter paper (Toyo Filter Paper No. 2), and the gel-like insoluble tannin separated by filtration was washed with distilled water, and the water content of the particles was immediately measured. The results are shown in Table 1.
[0018]
[Table 1]
As shown in FIGS. 2 (a) and 2 (b), the gel-like insoluble tannin of Example 9 was almost spherical, and pores having a network structure of several tens of μm were observed on the surface thereof. On the other hand, the gel-like insoluble tannin obtained in Comparative Example 1 is a crushed material of a massive lump as shown in FIGS. 3 (a) and 3 (b), and the surface has large pores. I couldn't see it.
The water content of the particles immediately after washing with acetone in Examples 1 to 10 is 66.1 to 1.79%. When these particles are further washed with distilled water, the water content of the particles is 77.6 to 40. Increased to 1% and swollen. On the other hand, the moisture content of the particles immediately after washing with distilled water of Comparative Example 1 and Comparative Example 2 varied in the range of about 66 to 77%, and the average value was 72%. From this, it was confirmed that gel-insoluble tannin having a low water content not found in the comparative example was obtained in the examples. In the examples, it was found that the particles shrink in acetone and the particles swell when contacted with distilled water.
[0020]
<Example of adsorption test of hexavalent chromium>
(a) The temperature of decalin which is a hydrophobic solvent was set to 80 ° C. (Examples 8 to 10), and gel-like insoluble tannin having a water content of about 40 to 59% was prepared. Similarly, a gel-like insoluble tannin having a water content of about 49 to 60% was prepared at 70 ° C. (Examples 5 to 7). Furthermore, it was 60 degreeC (Examples 2-4), and the gelatinous insoluble tannin whose water content is about 58-71% was prepared. For comparison, gel-insoluble tannin having a water content of about 68 to 86% in Comparative Examples 1 and 2 was prepared. From the above, it can be seen that the higher the decalin temperature, the lower the moisture content, and the lower the decalin temperature, the higher the moisture content.
[0021]
0.2 g of the gel-like insoluble tannins of Examples 1 to 10 and Comparative Examples 1 and 2 were sampled and added to 40 ml of a solution having a hexavalent chromium (CrO 3 ) concentration of 1000 ppm to reach equilibrium, and then the gel was reached. The insoluble tannin was taken out from the container, the concentration of chromium in the residual liquid was measured, and the adsorption capacity of chromium adsorbed on each insoluble tannin was determined. The result is shown in FIG.
As apparent from FIG. 4, it was found that the higher the water content, the higher the hexavalent chromium adsorption capacity. In particular, the insoluble tannin having a water content of 72% treated with nitric acid in Comparative Example 2 obtained an adsorption capacity of 192 to 287 mg of hexavalent chromium per 1 g of gel-like insoluble tannin, whereas the water content of Example 1 was 77. With .6% insoluble tannin, an adsorption capacity of 540 mg of hexavalent chromium corresponding to about 1.9 to 2.8 times that of Comparative Example 2 was obtained. Moreover, even if it was the same high water content, compared with the comparative example 1, the mechanical strength of the gel-like insoluble tannin of Examples 1-10 was high.
[0022]
(b) The temperature of decalin, which is a hydrophobic solvent, was set to 60 ° C., and gel-like insoluble tannin having a water content of about 70% was prepared (Example 11). Similarly, a gel-like insoluble tannin having a water content of about 83% was prepared at 50 ° C. (Example 12).
0.2 g of the gel-like insoluble tannin of each of Examples 11 and 12 was sampled and added separately to 80 ml of a solution having a hexavalent chromium (CrO 3 ) concentration of 1000 ppm, and the adsorption rate of hexavalent chromium to the insoluble tannin was examined. It was. The result is shown in FIG.
[0023]
As is apparent from FIG. 5, both of Examples 11 and 12 reach the saturated adsorption capacity after about 60 hours after the addition, but the insoluble tannin of Example 12 having a high water content of about 83% is more preferable. About 70% of the insoluble tannin of Example 11 was higher in adsorption rate, and a high adsorption capacity was obtained in a relatively short time.
[0024]
【The invention's effect】
As described above, according to the production method of the present invention, the water content of the gel-like insoluble tannin can be controlled, and the gel network structure and its molecular space can be changed. As a result, an appropriate network structure corresponding to the size of the ions of the metal element to be adsorbed and its molecular space can be secured, and insoluble tannins with extremely high metal adsorption capacity compared to conventional adsorbents can be obtained, Further, there is no need to crush when used as an adsorbent, and an excellent effect of obtaining a desired particle size and shape is obtained.
[Brief description of the drawings]
FIG. 1 is a process diagram showing a production method of the present invention.
2A is a 50 × micrograph of the gel-like insoluble tannin of Example 9. FIG.
(B) 1000-times micrograph of the gel-like insoluble tannin of Example 9.
FIG. 3 (a) is a 50 × micrograph of the gel-like insoluble tannin of Comparative Example 1.
(B) 1000 times as many photomicrographs of the gel-like insoluble tannin of Comparative Example 1.
FIG. 4 is a graph showing the chromium adsorption capacity of gel-like insoluble tannin according to the moisture content of Examples and Comparative Examples.
5 is a graph showing the chromium adsorption rate of gel-like insoluble tannin according to the water content of Example 11 and Example 12. FIG.
[Explanation of symbols]
10 Highly viscous solution 11
Claims (4)
(b) 工程(a)で得られた水溶液にアルデヒド水溶液を添加混合する工程と、
(c) ポリエーテル型非イオン性界面活性剤を含む疎水性溶媒を加熱温度下で撹拌させながら前記工程(b)で得られた水溶液を添加して液滴の形態で前記疎水性溶媒中に分散させる工程と、
(d) 前記液滴から水分を蒸発させて球状でかつゲル状不溶性タンニンを形成する工程と
を含む不溶性タンニンの製造方法。(a) dissolving the condensed tannin powder in an alkaline aqueous solution;
(b) adding and mixing an aqueous aldehyde solution to the aqueous solution obtained in step (a);
(c) While stirring the hydrophobic solvent containing the polyether type nonionic surfactant at a heating temperature, the aqueous solution obtained in the step (b) is added to the hydrophobic solvent in the form of droplets. A step of dispersing;
(d) A method for producing insoluble tannins, comprising the step of evaporating water from the droplets to form spherical and gel-like insoluble tannins.
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| JP2016047505A (en) * | 2014-08-28 | 2016-04-07 | 元基 井上 | Noble metal adsorbent using polyphenol derived from grape seeds as raw material |
| CN112427024A (en) * | 2020-09-29 | 2021-03-02 | 核工业北京化工冶金研究院 | Process for adsorbing uranium by using tannic acid precipitate |
| CN115215829B (en) * | 2022-08-12 | 2023-07-25 | 西南科技大学 | Preparation method of green plant tannin type nuclide detersive surfactant |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPH07344U (en) * | 1993-04-09 | 1995-01-06 | 充博 風間 | A health appliance that can be used for both body correction, manipulative treatment, and exercise |
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| JP2000308825A (en) | 2000-11-07 |
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