JP4160350B2 - Silica and method for producing silica - Google Patents

Description

【００２３】
本発明のシリカの最大の特徴は、上記のＱ⁴ピークのケミカルシフトをδ（ｐｐｍ）とした場合に、δが下記式（Ｉ）を満足する点にある。
−０．０７０５×（Ｄ_max）−１１０．３６＞δ ・・・（Ｉ）
この事実は、Ｓｉに対して２個の−ＯＳｉで表される結合角にひずみが少ないことを意味する。
【００２４】
上記のＱ⁴ピークの値δは、通常は上記式（Ｉ）の左辺に基づいて計算した値よりも大きくなる。よって、本発明のシリカは、従来のシリカに比べて、Ｑ⁴ピークのケミカルシフトがより小さな値を有することになる。これは、本発明のシリカにおいて、ケミカルシフトが高磁場に存在するということに他ならず、上記の結合角がより均質であり、ひずみが少ないことを意味する。本発明において、シリカのＱ⁴ピークのケミカルシフトδは、好ましくは、前記式（Ｉ）の左辺に基づき算出される値（−０．０７０５×（Ｄ_max）−１１０．３６）よりも、通常０．０５％以上、中でも０．１％以上、特に０．１５％以上小さい値であることが好ましい。
【００２５】
また、上記のＱ⁴ピークのケミカルシフトの値δは、通常のシリカでは−１０６．００〜−１１３．００ｐｐｍの範囲に観察されるが、本発明のシリカではより小さな値となり、具体的には、−１１１．００〜−１１２．００ｐｐｍの範囲に存在することが好ましい。これも、本発明のシリカでは、上記の結合角がより均質であり、歪みが少ないことを意味している。なお、Ｑ⁴ピークが上述の様な幅を持つ理由は、通常、観察しているＳｉに対して２個の−ＯＳｉで表される結合角が種々の値を持つことによる。
【００２６】
本発明のシリカが有する、優れた耐熱性や耐水性と、上記の様な構造的ひずみの関係については、必ずしも明らかではないが、次の様に推定される。すなわち、シリカは大きさの異なる球状粒子の集合体で構成されているが、上記の様な構造的にひずみの少ない状態においては、球状粒子全体のミクロ構造的な高度の均質性が維持されるので、その結果、優れた耐熱性や耐水性が発現されるものと考えられる。なお、Ｑ³以下のピークは、Ｓｉ−Ｏのネット構造の広がりに制限があるため、シリカの構造的なひずみが現れにくい。
【００２７】
更に、本発明のシリカは、固体Ｓｉ−ＮＭＲ測定によるＱ⁴／Ｑ³の値が、通常１．３以上、好ましくは１．５以上である。ここで、Ｑ⁴／Ｑ³の値とは、上述したシリカの繰り返し単位の中で、−ＯＳｉが３個結合したＳｉ（Ｑ³）に対する−ＯＳｉが４個結合したＳｉ（Ｑ⁴）のモル比を意味する。なお、上限値は特に制限されないが、通常は１０以下である。一般にこの値が高い程、シリカの熱安定性が高いことが知られており、ここから本発明のシリカは、熱安定性に極めて優れていることが判る。対して、結晶性のミセルテンプレートシリカは、Ｑ⁴／Ｑ³の値が１．３を下回ることが多く、熱安定性、特に水熱安定性が低い。
【００２８】
なお、Ｑ⁴ピークのケミカルシフト及びＱ⁴／Ｑ³の値は、実施例の説明において後述する方法を用いて固体Ｓｉ−ＮＭＲ測定を行ない、その結果に基づいて算出することができる。また、測定データの解析（ピーク位置の決定）は、例えば、ガウス関数を使用した波形分離解析等により、各ピークを分割して抽出する方法で行なう。
【００２９】
本発明のシリカは、細孔容積及び比表面積が通常の値よりも大きい範囲にあることを、特徴の一つとする。具体的には、細孔容積の値は、通常０．６ｍｌ／ｇ以上、好ましくは０．７ｍｌ／ｇ以上であり、通常１．６ｍｌ／ｇ以下である。また、比表面積の値は、通常２００ｍ²／ｇ以上、好ましくは３００ｍ²／ｇ以上、更に好ましくは４００ｍ²／ｇ以上、特に好ましくは５００ｍ²／ｇ以上であり、通常１０００ｍ²／ｇ以下、好ましくは９５０ｍ²／ｇ以下、更に好ましくは９００ｍ²／ｇ以下である。これらの細孔容積及び比表面積の値は、窒素ガス吸脱着によるＢＥＴ法で測定される。
【００３０】
更に、本発明のシリカは、上記の最頻直径（Ｄ_max）の値の±２０％の範囲にある細孔の総容積が、全細孔の総容積の通常５０％以上、好ましくは６０％以上、更に好ましくは７０％以上である。このことは、本発明のシリカゲルが有する細孔の直径が、最頻直径（Ｄ_max）付近の細孔で揃っていることを意味する。なお、上記の最頻直径（Ｄ_max）の値を中心として±２０％の範囲にある細孔の総容積は、上限は特に制限されないが、通常は全細孔容積の通常９０％以下である。
【００３１】
かかる特徴に関連して、本発明のシリカは、上記のＢＪＨ法により算出された最頻直径（Ｄ_max）における微分細孔容積ΔＶ／Δ（ｌｏｇｄ）が、通常２ｍｌ／ｇ以上、好ましくは３ｍｌ／ｇ以上、更に好ましくは５ｍｌ／ｇ以上であり、通常２０ｍｌ／ｇ以下、好ましくは１２ｍｌ／ｇ以下である（なお、上式において、ｄは細孔直径（ｎｍ）であり、Ｖは窒素ガス吸着容積である）。微分細孔容積ΔＶ／Δ（ｌｏｇｄ）が前記範囲に含まれるものは、最頻直径（Ｄ_max）の付近に揃っている細孔の絶対量が極めて多いものと言える。
【００３２】
本発明のシリカの更なる特徴は、シリカ中に存在することでその物性に影響を与えることが知られている、アルカリ金属，アルカリ土類金属，周期表の３Ａ族，４Ａ族及び５Ａ族並びに遷移金属からなる群に属する金属元素（不純物元素）の合計の含有率が、非常に低く、極めて高純度なことである。具体的には、金属不純物の合計の含有率が、通常１００ｐｐｍ以下、好ましくは５０ｐｐｍ以下、更に好ましくは１０ｐｐｍ以下、特に好ましくは１ｐｐｍ以下である。特に、シリカゲルの物性に与える影響が大きい、アルカリ金属及びアルカリ土類金属からなる群に属する元素の総含有率が、通常１００ｐｐｍ以下、中でも５０ｐｐｍ以下、更には１０ｐｐｍ以下、特に１ｐｐｍ以下であることが好ましい。このように不純物の影響が少ないことが、本発明のシリカが高い耐熱性や耐水性などの優れた性質を発現できる大きな要因の一つである。
【００３３】
（２）本発明のシリカの製法
本発明のシリカは、従来のゾル−ゲル法とは異なり、シリコンアルコキシドを加水分解する（加水分解工程）と共に得られたシリカヒドロゾルを縮合してシリカヒドロゲルを形成する加水分解・縮合工程と、当該加水分解・縮合工程に引き続きシリカヒドロゲルを熟成することなく水熱処理する物性調節工程とを包含する方法で製造される。
【００３４】
本発明のシリカの原料として使用されるシリコンアルコキシドとしては、トリメトキシシラン、テトラメトキシシラン、トリエトキシシラン、テトラエトキシシラン、テトラプロポキシシラン、テトラブトキシシラン等の炭素数１〜４の低級アルキル基を有するトリまたはテトラアルコキシシラン或いはそれらのオリゴマーが挙げられるが、好ましくはテトラメトキシシラン、テトラエトキシシラン及びそれらのオリゴマーである。以上のシリコンアルコキシドは蒸留により容易に精製し得るので、高純度のシリカの原料として好適である。シリコンアルコキシド中のアルカリ金属又はアルカリ土類金属に属する金属元素（金属不純物）の総含有量は、通常１００ｐｐｍ以下、中でも５０ｐｐｍ以下、更には３０ｐｐｍ以下、特に１０ｐｐｍ以下が好ましく、最も好ましくは１ｐｐｍ以下である。これらのいわば金属不純物の含有率は、一般的なシリカ中の不純物含有率の測定法と同じ方法で測定できる。
【００３５】
本発明では、先ず、加水分解・縮合工程において、触媒の不存在下にシリコンアルコキシドを加水分解すると共に得られたシリカヒドロゾルを縮合してシリカヒドロゲルを形成する。
【００３６】
シリコンアルコキシドの加水分解は、シリコンアルコキシド１モルに対して、通常２モル以上、好ましくは３モル以上、特に好ましくは４モル以上、通常２０モル以下、好ましくは１０モル以下、特に好ましくは８モル以下の水を用いて行なう。シリコンアルコキシドの加水分解により、目的異元素をドープしたシリカのシリカヒドロゾルとアルコールとが生成し、生成したシリカヒドロゾルは逐次縮合してシリカヒドロゲルとなる。加水分解時の温度は、通常室温以上、好ましくは３０℃以上、中でも好ましくは４０℃以上、更に好ましくは５０℃以上、通常１００℃以下、好ましくは９０℃以下、中でも好ましくは８０℃以下、更に好ましくは７０℃以下である。この加水分解反応は、加圧下で液相を維持することで、より高い温度で行なうことも可能である。
【００３７】
また、加水分解時には必要に応じて、水と相溶性のあるアルコール類等の溶媒の存在下で行なっても良い。具体的には、炭素数１〜３の低級アルコール類、ジメチルホルムアミド、ジメチルスルホキシド、アセトン、テトラヒドロフラン、メチルセロルブ、エチルセロルブ、メチルエチルケトン、その他の水と任意に混合できる有機溶媒を任意に用いることができるが、中でも強い酸性や塩基性を示さないものが、均一なシリカヒドロゲルを生成できる理由から好ましい。
【００３８】
これらの溶媒を使用しない場合、本発明のシリカの製造のためには、特に加水分解の際の攪拌速度が重要である。すなわち、シリコンアルコキシドと加水分解用の水は初期には分液しているため、攪拌によりエマルジョン化し、反応を促進させる。
【００３９】
この際、攪拌を充分に行うことが重要となる。例えば回転軸に攪拌翼を備えた攪拌装置を用いた場合、その攪拌速度（回転軸の回転数）としては、攪拌翼の形状・枚数・液との接触面積等にもよるが、通常は３０ｒｐｍ以上、好ましくは５０ｒｐｍ以上である。
【００４０】
またこの攪拌速度は、一般的に速すぎると槽内で生じた飛沫が各種のガスラインを閉塞させたり、また反応器内壁に付着して熱伝導を悪化させ、物性制御に重要な温度管理に影響を及ぼす場合がある。更に、この内壁の付着物が剥離し、製品に混入して品質を悪化させる場合もある。この様な理由から、攪拌速度は２０００ｒｐｍ以下、中でも１０００ｒｐｍ以下であることが好ましい。
【００４１】
本発明に於いて、分液している二液相（水相、及びシリコンアルコキシド相）の攪拌方法は、反応を促進させる方法であれば任意の攪拌方法を用いることが出来る。中でも、この二相をより混合させるような装置としては、例えば以下の▲１▼、▲２▼が挙げられる。
【００４２】
▲１▼：回転軸が液面に対し垂直又は僅かに角度を持って挿入され、上下に液の流動が生じる攪拌翼を有する装置。
▲２▼：回転軸方向を二液相の界面と略平行に設け、二相相間に攪拌を生じさせる攪拌翼を有する攪拌装置。
【００４３】
上述した▲１▼、▲２▼の様な装置を用いた際の攪拌翼回転速度は、攪拌翼の周速度（攪拌翼先端速度）で、０．０５〜１０ｍ／ｓ、中でも０．１〜５ｍ／ｓ、さらには０．１〜３ｍ／ｓであることが好ましい。
攪拌翼形状や攪拌翼長さ等は任意であり、攪拌翼としては例えばプロペラ型、平羽根型、角度付平羽根型、ピッチ付平羽根型、平羽根ディスクタービン型、湾曲羽根型、ファウドラー型、ブルマージン型、アンカー型、リボン型等が挙げられる。
【００４４】
翼の幅、枚数、傾斜角等は反応器の形状、大きさ、目的とする攪拌動力に応じて適宜選定すればよい。たとえば反応器の槽内径（回転軸方向に対して垂直面を形成する液相面の最長径）に対する翼幅（回転軸方向の翼の長さ）の比率（ｂ／Ｄ）は０．０５〜０．２、傾斜角（θ）９０゜±１０゜、翼枚数３〜１０枚の攪拌装置が好適な例として挙げられる。
中でも上述の回転軸を反応容器内の液面よりも上に設け、この回転軸から伸ばした軸の先端部分に攪拌翼を設ける構造が、攪拌効率及び設備メンテナンスの観点から好適に使用される。
【００４５】
上記の攪拌速度条件を満足しない場合には、本発明のシリカを得るのが困難になる。なお、加水分解によりアルコールが生成して液が均一液となり、発熱が収まった後には、均一なヒドロゲルを形成させるために攪拌を停止することが好ましい。
【００４６】
結晶性を示すシリカは、水中熱安定性に乏しくなる傾向にあり、シリカ中に細孔を形成するのに用いられる界面活性剤等のテンプレートの存在下でシリコンアルコキシドを加水分解すると、シリカは容易に結晶構造を含むものとなる。従って、本発明においては、界面活性剤等のテンプレートの非存在下で、すなわち、これらがテンプレートとしての機能を発揮するほどの量は存在しない条件下で加水分解するのが好ましい。
【００４７】
加水分解の反応時間は、反応液組成（シリコンアルコキシドの種類や、水とのモル比）並びに反応温度に依存し、ゲル化するまでの時間が異なるので、一概には規定されない。なお、反応系に触媒として、酸、アルカリ、塩類などを添加することで加水分解を促進させることができる。しかしながら、かかる添加物の使用は、後述するように、生成したヒドロゲルの熟成を引き起こすことになるので、本発明のシリカの製造においてはあまり好ましくない。
上記のシリコンアルコキシドの加水分解反応では、シリコンアルコキシドが加水分解してシリケートが生成するが、引き続いて該シリケートの縮合反応が起こり、反応液の粘度が上昇し、最終的にゲル化してシリカヒドロゲルとなる。
【００４８】
次いで、本発明では、物性調整工程として、上記の加水分解により生成したシリカのヒドロゲルの硬さが上昇しないように、実質的に熟成することなく、直ちに水熱処理を行なう。シリコンアルコキシドを加水分解すると、軟弱なシリカのヒドロゲルが生成するが、このヒドロゲルを安定した熟成、あるいは乾燥させ、更にこれに水熱処理を施す方法では、最終的に細孔特性の制御された、本発明で規定する物性範囲のシリカを製造することは困難である。
【００４９】
上記にある、加水分解により生成したシリカのヒドロゲルを、実質的に熟成することなく、直ちに水熱処理を行なうということは、シリカのヒドロゲルが生成した直後の軟弱な状態が維持されたままで、次の、水熱処理に供するようにするということを意味する。
【００５０】
具体的には、シリカヒドロゲルが生成した時点から、一般的には１０時間以内に水熱処理することが好ましく、中でも８時間以内、更には６時間以内、特に４時間以内にシリカヒドロゲルを水熱処理することが好ましい。
また工業用プラント等に於いては、大量に生成したシリカヒドロゲルを一旦サイロ等に貯蔵し、その後水熱処理を行う場合が考えられる。この様な場合、シリカヒドロゲルは、シリカヒドロゲルが生成してから水熱処理に供されるまでの時間、いわゆる放置時間が、上述の範囲を超える場合が考えられる。この様な場合には、熟成が実質的に生じないように、サイロ内での静置中に、例えばシリカヒドロゲル中の液体成分が乾燥しないようにすればよい。
【００５１】
具体的には例えば、サイロ内を密閉したり、湿度を調節すればよい。また、水やその他の溶媒にシリカヒドロゲルを浸した状態で、シリカヒドロゲルを静置してもよい。
静置の際の温度はできるだけ低くすることが好ましく、例えば５０℃以下、中でも３５℃以下、特に３０℃以下で静置することが好ましい。また熟成が実質的に生じないようにする別の方法としては、シリカヒドロゲル中のシリカ濃度が低くなるように、予め原料組成を制御してシリカヒドロゲルを調製する方法が挙げられる。
【００５２】
シリカヒドロゲルを実質的に熟成せずに水熱処理することにより奏する効果と、この効果が得られる理由を考察すると、以下のことが考えられる。
つまり、シリカヒドロゲルを熟成させると、−Ｓｉ−Ｏ−Ｓｉ−結合によるマクロ的網目構造が、シリカヒドロゲル全体に形成されると考えられる。この網目構造がシリカヒドロゲル全体に有ることで、水熱処理の際、この網目構造が障害となり、メソポーラスの形成が困難となることが考えられる。よって本発明では、シリカヒドロゲルを熟成することなく、水熱処理を行うことが重要である。
なお、シリカヒドロゲル中のシリカ濃度が低くなるように、予め原料組成を制御して得られたシリカヒドロゲルは、静置中に生ずるシリカヒドロゲルにおける架橋の進行を抑制できる。その為、シリカヒドロゲルが熟成しないと考える。
【００５３】
シリコンアルコキシドの加水分解反応系に酸、アルカリ、塩類等を添加すること、または該加水分解反応の温度を厳しくし過ぎることなどは、ヒドロゲルの熟成を進行させるため好ましくない。また、加水分解後の後処理における水洗、乾燥、放置などにおいて、必要以上に温度や時間をかけるべきではない。
【００５４】
ヒドロゲルの熟成状態を具体的に確認する手段としては、後述の実施例に示すような方法で測定したヒドロゲルの硬度を参考にすることができる。即ち、破壊応力が、通常６ＭＰａ以下、好ましくは３ＭＰa以下、更に好ましくは２ＭＰａ以下の柔らかい状態のヒドロゲルを水熱処理することで、本発明で規定する物性範囲のシリカを得ることができる。
【００５５】
この水熱処理の条件としては、水の状態が液体、気体のいずれでもよく、溶媒や他の気体によって希釈されていてもよいが、好ましくは液体の水をシリカのヒドロゲルに加えてスラリー状として行なう。使用する水の量は、シリカのヒドロゲルに対して、通常０．１重量倍以上、好ましくは０．５重量倍以上、特に好ましくは１重量倍以上、また、通常１０重量倍以下、好ましくは５重量倍以下、特に好ましくは３重量倍以下である。水熱処理の温度は、通常４０℃以上、好ましくは５０以上、また、通常２５０℃以下、好ましくは２００℃以下である。また、水熱処理の時間は、通常０．１時間以上、好ましくは１時間以上、また、通常１００時間以下、好ましくは１０時間以下である。
【００５６】
なお、水熱処理に使用される水には低級アルコール類、メタノール、エタノール、プロパノールや、ジメチルホルムアミド（ＤＭＦ）やジメチルスルホキシド（ＤＭＳＯ）、その他の有機溶媒などが含まれてもよい。また、メンブランリアクターなどを作る目的で、シリカを膜状あるいは層状に粒子、基板、あるいは管などの基体上に形成させた材料の場合にも、この水熱処理方法は適用される。なお、加水分解反応の反応器を用い、続けて温度条件変更により水熱処理を行なうことも可能であるが、加水分解反応とその後の水熱処理では最適条件が通常は異なっているため、この方法で本発明のシリカを得ることは一般的には難しい。
【００５７】
以上の水熱処理条件において温度を高くすると、得られるシリカの細孔径、細孔容積が大きくなる傾向がある。水熱処理温度としては、１００〜２００℃の範囲であることが好ましい。また、処理時間とともに、得られるシリカの比表面積は、一度極大に達した後、緩やかに減少する傾向がある。以上の傾向を踏まえて、所望の物性値に応じて条件を適宜選択する必要があるが、水熱処理は、シリカの物性を変化させる目的なので、通常、前記の加水分解の反応条件より高温条件とすることが好ましい。
【００５８】
水熱処理の温度、時間を上記範囲外に設定すると本発明のシリカを得ることが困難となる。例えば、水熱処理の温度が高すぎると、シリカの細孔径、細孔容積が大きくなりすぎ、また、細孔分布も広がる。逆に、水熱処理の温度が低過ぎると、生成するシリカは、架橋度が低く、熱安定性に乏しくなり、細孔分布にピークが発現しなくなったり、前述した固体Ｓｉ−ＮＭＲにおけるＱ⁴／Ｑ³値が極端に小さくなったりする。
【００５９】
なお、水熱処理をアンモニア水中で行なうと、純水中で行なう場合よりも低温で同様の効果が得られる。また、アンモニア水中で水熱処理すると、純水中で処理する場合と比較して、最終的に得られるシリカゲルは一般に疎水性となるが、通常３０℃以上、好ましくは４０℃以上、また、通常２５０℃以下、好ましくは２００℃以下という比較的高温で水熱処理すると、特に疎水性が高くなる。ここでのアンモニア水のアンモニア濃度としては、好ましくは０．００１％以上、特に好ましくは０．００５％以上、または、好ましくは１０％以下、特に好ましくは５％以下である。
【００６０】
水熱処理されたシリカヒドロゲルは、通常４０℃以上、好ましくは６０℃以上、また、通常２００℃以下、好ましくは１２０℃以下で乾燥する。乾燥方法は特に限定されるものではなく、バッチ式でも連続式でもよく、且つ、常圧でも減圧下でも乾燥することができる。必要に応じ、原料のシリコンアルコキシドに由来する炭素分が含まれている場合には、通常４００〜６００℃で焼成除去することができる。また、表面状態をコントロールするため、最高９００℃の温度で焼成することもある。更に、必要に応じて粉砕、分級することで、最終的に目的としていた本発明のシリカを得る。
【００６１】
（３）本発明のシリカの用途
本発明のシリカは、従来からのシリカの用途の他、いかなる用途においても利用することができる。このうち従来の用途としては、以下のようなものが挙げられる。
【００６２】
例えば、産業用設備で製品の製造及び処理に用いられる用途分野においては、各種触媒及び触媒担体（酸塩基触媒、光触媒、貴金属触媒等）、廃水・廃油処理剤、臭気処理剤、ガス分離剤、工業用乾燥剤、バイオリアクター、バイオセパレーター、メンブランリアクター等の用途が挙げられる。建材用途では、調湿剤、防音・吸音材、耐火物、断熱材等の用途が挙げられる。また、空調分野の用途では、デシカント空調機用調湿剤、ヒートポンプ用蓄熱剤等が挙げられる。塗料・インク用途分野においては、艶消し剤、粘度調整剤、色度調整剤、沈降防止剤、消泡剤、インク裏抜け防止剤、スタンピングホイル用、壁紙用等の用途が挙げられる。樹脂用添加剤用途分野においては、フィルム用アンチブロッキング剤（ポリオレフィンフィルム等）、プレートアウト防止剤、シリコーン樹脂用補強剤、ゴム用補強剤（タイヤ用・一般ゴム用等）、流動性改良材、パウダー状樹脂の固結防止剤、印刷適性改良剤、合成皮革やコーティングフィルム用の艶消し剤、接着剤・粘着テープ用充填剤、透光性調整剤、防眩性調整剤、多孔性ポリマーシート用フィラー等の用途が挙げられる。また、製紙用途分野においては、感熱紙用フィラー（カス付着防止剤等）、インクジェット紙画像向上用フィラー（インク吸収剤等）、ジアゾ感光紙用フィラー（感光濃度向上剤等）、トレーシングペーパー用筆記性改良剤、コート紙用フィラー（筆記性、インク吸収性、アンチブロッキング性改良剤等）、静電記録用フィラー等の用途が挙げられる。食品用途分野においては、ビール用濾過助剤、醤油・清酒・ワイン等発酵製品のおり下げ剤、各種発酵飲料の安定化剤（混濁因子タンパクや酵母の除去等）、食品添加剤、粉末食品の固結防止剤等の用途が挙げられる。医農薬分野においては、薬品等の打錠助剤、粉砕助剤、分散・医薬用担体（分散・徐放・デリバリー性改善等）、農薬用担体（油状農薬キャリア・水和分散性改善、徐放・デリバリー性改善等）、医薬用添加剤（固結防止剤・粉粒性改良剤等）・農薬用添加剤（固結防止剤・沈降防止剤等）等が挙げられる。分離材料分野では、クロマトグラフィー用充填剤、分離剤、フラーレン分離剤、吸着剤（タンパク質・色素・臭等）、脱湿剤等の用途が挙げられる。農業用分野では、飼料用添加剤、肥料用添加剤が挙げられる。さらにその他の用途として、生活関連分野では、調湿剤、乾燥剤、化粧品添加剤、抗菌剤、消臭・脱臭・芳香剤、洗剤用添加剤（界面活性剤粉末化等）、研磨剤（歯磨き用等）、粉末消火剤（粉粒性改良剤・固結防止剤等）、消泡剤、バッテリーセパレーター等が挙げられる。
【００６３】
特に、本発明のシリカは、同等の細孔径を持つ従来のシリカと比較して細孔容積及び比表面積が大きいため、高い吸着・吸収容量を有し、精密な細孔制御も可能である。従って、上述した各種用途の中でも、特に優れた耐熱性や耐水熱性が要求されるとともに、制御された細孔特性や、長期にわたって物性変化の少ないことが要求される分野において、好適に用いることができる。
【００６４】
また、本発明のシリカは、５０μｍ以下の粒径が要求され、精密に制御された細孔特性と安定した物性が要求される分野においても、好適に使用される。一般的に、シリカを平均粒径５０μｍ以下にすると、単位重量当たりの外表面積が増加し、且つ粒界にも各種物質を吸着・吸収することが出来るようになるため、吸着・吸収性能が更に高くなる。すなわち、本発明のシリカの粒径を小さくすることによって、本発明のシリカが既に持つ高細孔容積、高比表面積、シャープな細孔分布、高純度で物性変化が少ない等の各種の特徴を発展させ、更に吸着・吸収性に優れたシリカとすることが出来る。
【００６５】
本発明のシリカをこうした分野に使用する場合、平均粒径はその分野で要求される値に応じて調整すればよいが、通常５０μｍ以下、好ましくは３０μｍ以下、特に好ましくは５μｍ以下として使用される。下限としては特に制限は無いが、好ましくは０．１μｍ以上である。このように粒径の小さなシリカの用途としては、各種吸着剤、樹脂用充填剤、インクジェット紙用インク吸収剤、フィルム用アンチブロッキング剤、飲料用濾過助剤、各種触媒担体など様々なものがある。例えば、平均粒径５μｍ以下の本発明のシリカはインク吸収速度が速く、吸油性能が高いためインクジェット紙用吸収剤として有用である。
【００６６】
一方、本発明のシリカは、平均粒径を大きくしても好ましい。平均粒径を大きくすることによって、本発明のシリカは、上述した高比表面積、高細孔容積、細孔分布がシャープ、高純度で物性変化が少ない等の特徴と、大きな粒子特有の特徴とを併せ持つことになり、その双方を要求される分野において極めて有用となる。例えば、平均粒径が大きなシリカは、光の散乱が小さくなり、光学用途のガラス体として用いることが可能になる。
【００６７】
具体的には、本発明のシリカは、５００μｍ以上の粒径が要求され、精密に制御された細孔特性と安定した物性が要求される分野においても、好適に使用される。本発明のシリカをこうした分野に使用する場合、平均粒径はその分野で要求される値に応じて調整すればよいが、通常５００μｍ以上、好ましくは５ｍｍ以上として使用される。また、上限としては特に制限は無いが、好ましくは５ｃｍ以下である。例えば、平均粒径５００μｍ以上の本発明のシリカは、制御されたナノ細孔を有するため、この細孔を利用して光学的に有用な色素、金属、光触媒、フォトクロミック化合物、その他の光機能性材料を細孔径に応じた一定の大きさで担持することが出来、機能性光学材料として有用である。一般に、平均粒径の大きい粒子を、粗大な割れを生じることなくして製造することは難しいが、本発明のシリカは均質な構造を持ち、水熱処理等の体積変化を伴う処理によっても粗大な割れが生じることが少なく、制御された細孔特性を有し、かつ比較的平均粒径の大きな製品を得ることが可能である。
【００６８】
【実施例】
以下、本発明を実施例により、更に詳細に説明するが、本発明はその要旨を超えない限り、以下の実施例に制約されるものではない。
【００６９】
［Ａ］シリカのヒドロゲルの硬度測定
５Ｌセパラブルフラスコ中でシリコンアルコキシドと６モル倍の水を反応させ、反応液の温度が反応により生成するアルコールの沸点に達した後に、反応液をフラスコより抜き取り、抜き出した反応液を５０ｃｃのガラス製スクリュー管に一定量（液深で２０ｍｍ程度）移し、密栓して実質的に一定温度にコントロールされた水浴に保持し、熟成時間の経過と共に破壊強度をデジタルフォースゲージ（株式会社エイ・アンド・ディー社製、型式：ＡＤ−４９３５）にて測定した。該測定器にはプローブ（ステンレス製直径５ｍｍの丸棒）が装着されており、ヒドロゲル中にゆっくりと押し込まれることにより、容器中に保持されたヒドロゲルを圧縮破壊する。ヒドロゲルが圧縮されて破壊される迄の間に示される最大の応力値をもって破壊応力とした。
【００７０】
測定結果を図１に示す。なお、図１は、シリカのヒドロゲルの熟成時間の常用対数を横軸に、破壊応力を縦軸にプロットしたグラフである。図１より、熟成時間の経過とともに破壊応力が大きくなること、熟成速度が温度に依存していることが判る。
［Ｂ］実施例・比較例群Ｉ
【００７１】
（１）シリカの分析方法
１−１）細孔容積、比表面積、微分細孔容積：
カンタクローム社製ＡＳ−１にてＢＥＴ窒素吸着等温線を測定し、細孔容積、比表面積を求めた。具体的には細孔容積は相対圧Ｐ／Ｐ₀＝０．９８のときの値を採用し、比表面積はＰ／Ｐ₀＝０．１，０．２，０．３の３点の窒素吸着量よりＢＥＴ多点法を用いて算出した。また、ＢＪＨ法で細孔分布曲線及び最頻直径（Ｄ_max）における微分細孔容積を求めた。測定する相対圧の各点の間隔は０．０２５とした。
【００７２】
１−２）粉末Ｘ線回折
理学電機社製ＲＡＤ-ＲＢ装置を用い、ＣｕＫαを線源として測定を行った。発散スリット１／２ｄｅｇ、散乱スリット１／２ｄｅｇ、受光スリット０．１５ｍｍとした。
【００７３】
１−３）金属不純物の含有量
試料２．５ｇにフッ酸を加えて加熱し、乾涸させたのち、水を加えて５０ｍｌとした。この水溶液を用いてＩＣＰ発光分析を行った。なお、ナトリウム及びカリウムはフレーム炎光法で分析した。
【００７４】
１−４）固体Ｓｉ−ＮＭＲ測定
Ｂｒｕｋｅｒ社製固体ＮＭＲ装置（「ＭＳＬ３００」）を使用するとともに、共鳴周波数５９．２ＭＨｚ（７．０５テスラ）、７ｍｍのサンプルチューブを使用し、ＣＰ／ＭＡＳ（Cross Polarization / Magic Angle Spinning）プローブの条件で測定した。具体的な測定条件を下の表１に示す。
【００７５】
【表１】

【００７６】
測定データの解析（Ｑ⁴，Ｑ³ピーク位置の決定）は、ピーク分割によって各ピークを抽出する方法で行なう。具体的には、ガウス関数を使用した波形分離解析を行なう。この解析には、サーモガラテック（Thermogalatic）社製の波形処理ソフト「ＧＲＡＭＳ３８６」を使用することが出来る。この様にピーク分割により求めたＱ⁴，Ｑ³の各ピーク面積を用い、その比（Ｑ⁴／Ｑ³）を求めた。
【００７７】
１−５）シリカの水中熱安定性試験
試料に純水を加えて４０重量％のスラリーを調製した。容積６０ｍｌのステンレススチール製のミクロボンベに、上記で調製したスラリー約４０ｍｌを入れて密封し、２８０±１℃のオイルバス中に３日間浸漬した。ミクロボンベからスラリーの一部を抜出し、５Ａ濾紙で濾過した。濾滓は１００℃で５時間真空乾燥した後、残った試料の比表面積を測定した。
【００７８】
（２） シリカの製造、評価
実施例I−１〜I−３：
ガラス製で、上部に大気開放の水冷コンデンサが取り付けてある５Ｌセパラブルフラスコ（ジャケット付き）に、純水１０００ｇを仕込んだ。攪拌翼先端速度が２．５ｍ／ｓになるような攪拌速度で撹拌しながら、これにテトラメトキシシラン１４００ｇを３分間かけて仕込んだ。水／テトラメトキシシランのモル比は約６である。セパラブルフラスコのジャケットには５０℃の温水を通水した。引き続き撹拌を継続し、内容物が沸点に到達した時点で、撹拌を停止した。引き続き約０．５時間、ジャケットに５０℃の温水を通水して生成したゾルをゲル化させた。その後、速やかにゲルを取り出し、目開き６００ミクロンのナイロン製網を通してゲルを粉砕し、粉体状のウェットゲル（シリカヒドロゲル）を得た。このヒドロゲル４５０ｇと純水４５０ｇを１Ｌのガラス製オートクレーブに仕込み、実施例I−１については１３０℃×３Ｈｒ、実施例I−２については１５０℃×３Ｈｒ、実施例I−３については２００℃×３Ｈｒの条件で、それぞれ水熱処理を実施した。所定時間水熱処理した後、Ｎｏ．５Ａ濾紙で濾過し、得られたシリカを水洗することなく１００℃で恒量となるまで減圧乾燥して、それぞれ実施例I−１〜I−３のシリカとした。
【００７９】
実施例I−４：
上記実施例I−１〜I−３と同じ条件にてヒドロゲルを製造した。得られたヒドロゲル４５０ｇと０．５６％アンモニア水４５０ｇを１Ｌオートクレーブに仕込み、６０℃×３Ｈｒの条件で水熱処理を実施した。所定時間水熱処理した後、Ｎｏ．５Ａ濾紙で濾過し、得られたシリカを水洗することなく１００℃で恒量となるまで減圧乾燥して、実施例I−４のシリカとした。
【００８０】
実施例I−５：
６リッターのＳＵＳ３１６製オートクレーブを用い、１６０℃×３Ｈｒの条件で水熱処理した以外は、実施例Ｉ−１と同様にしてシリカを得た。得られたシリカの平均粒径は、３３１μｍであった。
このシリカを、ホソカワミクロン社製１００ＡＦＧ型粉砕機を使用し、ジェットミル粉砕を２６分間行ったところ、シリカの平均粒径は５．３μｍとなった。この際の粉砕・分級等に関する条件は以下の通りである。
粉砕圧空量 ：０．７２ ｍ³／ｍｉｎ
空気圧力 ：０．５９ ＭＰａ
ノズル径＊本数：φ１．９ ｍｍ ＊ ３本
分級機形式 ：５０ ＡＴＰ
回転速度 ：１７８００ ｒｐｍ
集塵布 ：バグフィルター
処理能力 ：０．９７ ｋｇ／ｈ
【００８１】
実施例I−６：
目開き６００ミクロン（μｍ）のナイロン製網を、目開き５ｍｍのナイロン製網に変えた以外は、実施例Ｉ−２と同様に行った。得られたシリカの平均粒子径は２．８ｍｍ（＝２８００μｍ）であった。
【００８２】
得られた実施例I−１〜I−６のシリカの諸物性を表２及び表４に示す（但し、実施例Ｉ−６についてはＱ⁴ピークのケミカルシフトの実測値がないので表２にのみ示す）。何れのシリカも粉末Ｘ線回折図には結晶性のピークは出現しておらず、また、周期的構造による低角度側（２θ≦５ｄｅｇ）のピークも認められない。なお、実施例I−１〜I−６のシリカの不純物金属含有率は、実施例I−１〜I−６何れのシリカについても、ナトリウム０．２ｐｐｍ、カリウム０．１ｐｐｍ、カルシウム０．２ｐｐｍであり、その他の金属は検出されなかった。
【００８３】
また、図２に、実施例I−１〜I−５及び後述する比較例I−１〜I−６のシリカについて、最頻細孔径（Ｄ_max）とＱ⁴ピークのケミカルシフトの値（δ）との相関を表わすグラフを示す。図２に明らかなように、実施例I−１〜I−５の何れのシリカについても、固体Ｓｉ−ＮＭＲのＱ⁴ピークのケミカルシフトの値（図２のグラフ中、系列１としてプロットされた値）は、上記式（Ｉ）の左辺（−０．０７０５×（Ｄ_max）−１１０．３６）より計算される値（図２のグラフ中、黒線分で表わされる値）と比べて、より小なる領域にあった。
【００８４】
なお、実施例I−５にて得られた、平均粒径５．３μｍのシリカは、上述した物性値から明らかな通り、粒径が小さいにもかかわらずシャープな細孔径分布と高い細孔容積を有するので、吸湿性能に優れ、各種の材に調湿機能を有することが明らかである。そしてこのシリカは、例えば表面の平滑性を保ち、かつアンチブロッキング性を求められるような各種フィルムのフィラーとして、好適に使用することが出来る。
【００８５】
また実施例I−６にて得られた、平均粒径が５００μｍを超える大粒径シリカは、例えば触媒担体や吸着材用として塔内に充填して使用した際に、圧力損失を大幅に低減できるので、非常に好ましい。さらに、実施例I−６で得られたシリカは、不純物が少なく純度が高いので、経年劣化も抑えられ、触媒担体等としての寿命の伸長が可能である。またこのシリカは、高純度でシャープな細孔分布を有しているので、目的の化合物のみを高選択的に吸着除去する能力がある上に、食品や医薬の分野でも好適に使用することが出来る。
【００８６】
比較例I−１〜I−６として、以下のシリカを用意した。
比較例I−１：
富士シリシア化学（株）製の触媒担体用シリカ ＣＡＲＩＡＣＴ Ｇ−３ を用いた。
比較例I−２：
富士シリシア化学（株）製の触媒担体用シリカ ＣＡＲＩＡＣＴ Ｇ−６ を用いた。
比較例I−３：
富士シリシア化学（株）製の触媒担体用シリカ ＣＡＲＩＡＣＴ Ｇ−１０（Lot No. 703091）を用いた。
比較例I−４：
富士シリシア化学（株）製の触媒担体用シリカ ＣＡＲＩＡＣＴ Ｇ−１０（Lot No. C-OO09014）を用いた。
比較例I−５：
富士シリシア化学（株）製の触媒担体用シリカ ＣＡＲＩＡＣＴ Ｑ−１５を用いた。
比較例I−６：
水澤化学工業（株）製 Ｍｉｚｕｋａｓｏｒｂ Ｃ−１ を用いた。
【００８７】
以上の比較例I−１〜I−６のシリカの諸物性を、下記の表３及び４に示す。比較例I−１〜I−６のシリカの全てにつき、粉末Ｘ線回折図には結晶性のピークは出現しておらず、また、周期的構造による低角度側のピークも認められない。さらに、不純物金属含有率を測定したところ、各々下記表に示す通りとなり、比較例I−２〜I−６のシリカは実施例I−１〜I−６のシリカより不純物金属の含有量が多かった。また、図２に明らかなように、比較例I−１〜I−６のシリカの全てについて、固体Ｓｉ−ＮＭＲのＱ⁴ピークのケミカルシフトの値（図２のグラフ中、系列２としてプロットされた値）は、上記式（Ｉ）の左辺より計算される値（図２のグラフ中、黒線分で示される値）と比べて、より大なる領域にあることから、その構造は実施例I−１〜I−５のシリカと比べてひずみが多く、物性変化しやすいものと思われる。
【００８８】
また、実施例I−１〜I−６、比較例I−１〜I−６のシリカを試料として、上述の条件で水中熱安定性試験を行ない、比表面積を測定した結果を表２及び表３に示す。実施例I−１〜I−６のシリカは、比較例I−１〜I−６のシリカに比べて、比表面積の減少が少なく、水熱安定性に優れていた。
【００８９】
【表２】

【００９０】
【表３】

【００９１】
【表４】

【００９２】
［Ｃ］実施例・比較例群II：
（１）シリカの分析方法：
実施例・比較例群Iと同様の条件で行なった。さらに、以下のようにシリカの耐熱性試験を行なった。
シリカの耐熱性試験：
試料５ｇを石英ビーカーに入れ、電気炉中、空気雰囲気下にて２００℃／時間で１０００℃まで昇温させて１時間保持した後、直ちにビーカーを室温に取り出し、放冷した。この試料につきＢＥＴ法で比表面積を測定した。
【００９３】
（２）シリカの製造及び評価：
実施例II−１：
上部に大気開放の水冷コンデンサが具備された５Ｌセパラブルフラスコ（ジャケット付き）に、純水１０００ｇを仕込んだ。攪拌翼先端速度２．５ｍ／ｓで撹拌しながら、これにテトラメトキシシラン１４００ｇを１分間かけて仕込んだ。水／テトラメトキシシランのモル比は約６である。セパラブルフラスコのジャケットには５０℃の温水を通水した。引き続き撹拌を継続し、内容物の温度は６０〜７０℃に保持して暴走しない様にした。引き続き、約０．５時間、ジャケットに５０℃の温水を通水して生成したゾルをゲル化させた。得られたゲルの硬度は１．５ＭＰａであった。
【００９４】
その後、速やかにゲルを取り出し、目開き６００ミクロンのナイロン製網を通してゲルを粉砕し、粉体状のウェットゲル（シリカヒドロゲル）を得た。このヒドロゲル４５０ｇと純水４５０ｇを１Ｌのガラス製オートクレーブに仕込み、１３０℃で３時間の条件で水熱処理を行なった。その後、Ｎｏ．５Ａ濾紙で濾過し、濾滓を水洗することなく１００℃で恒量となるまで減圧乾燥した。得られたシリカの金属不純物濃度の測定結果は、ナトリウム０．２ｐｐｍ、カリウム０．１ｐｐｍ、カルシウム０．２ｐｐｍで、マグネシウム、アルミニウム、チタン及びジルコニウムは検出されなかった。その他の諸物性を表５に示す。
【００９５】
実施例II−２：
実施例II−１において、テトラメトキシシランの仕込み時間を３分に変更した以外は、実施例II−１と同様にしてシリカを得た。物性測定の結果を表５に示す。
【００９６】
比較例II−１：
実施例II−１において、テトラメトキシシランの仕込み時間を３０分に変更した以外は、実施例II−１と同様にしてシリカを得た。物性測定の結果を表５に示す。
【００９７】
比較例II−２及びII−３
本発明のシリカと通常の市販シリカとの比較のため、通常のシリカとして、富士シリシア化学（株）製の触媒担体用シリカ「ＣＡＲＩＡＣＴ Ｇシリーズ」の「Ｇ−３」及び「Ｇ−６」（破砕状）を使用し、それぞれ、比較例II−２及びII−３とした。また、因に、市販シリカ（「Ｇ−６」）の金属不純物濃度の測定結果は、ナトリウム１７０ｐｐｍ、マグネシウム３１ｐｐｍ、アルミニウム１５ｐｐｍ、カリウム２３ｐｐｍ、カルシウム１６０ｐｐｍ、チタン２６０ｐｐｍ、ジルコニウム４４ｐｐｍであった。その他の諸物性を表５に示す。
【００９８】
【表５】

【００９９】
【発明の効果】
本発明の新規なシリカは、従来からのシリカと比較して、最頻直径（Ｄ_max）が小さいことから、吸着や吸収の性能に優れ、また、極めて生産性に優れ、更に、その構造に歪みが少ないことから、耐熱性や耐水性などにも優れている。
【図面の簡単な説明】
【図１】 シリカのヒドロゲルを、３５℃、４５℃及び５５℃の各温度で熟成させた場合の各熟成時間とその際のヒドロゲルの破壊応力の関係を示す図である。
【図２】 本発明の実施例及び比較例のシリカについて、最頻細孔径（Ｄ_max）とＱ⁴ピークのケミカルシフトの値（δ）との相関を表わすグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel silica excellent in heat resistance, water resistance, etc., and particularly suitable as a catalyst carrier or adsorbent.
[0002]
[Prior art]
Silica has been widely used as a desiccant for a long time, but recently its use has expanded to catalyst carriers, separating agents, adsorbents, etc., and the demands on the performance of silica vary according to the spread of such applications. It has become. The performance of silica is determined by physical properties such as the surface area, pore diameter, pore volume, and pore size distribution of silica, but these physical properties are greatly influenced by the production conditions of silica.
[0003]
Here, “silica” refers to both anhydrous silicic acid and hydrous silicic acid. Examples of silicic acid anhydride include quartz, tridymite, cristobalite, corsite, stishovite, and quartz glass. In addition to the so-called amorphous “silica gel” obtained by gelling and drying the silica hydrosol, the hydrous silicic acid is formed using colloidal silica, silicate oligomer, and organic matter as a template, for example, manufactured by Mobil Corporation. : Silica of a type such as MCM-41 (so-called micelle template type silica). Examples of the raw material for “silica gel” include water glass and alkoxysilanes.
[0004]
As a method for producing silica gel, most commonly, a method in which an alkali silicate such as sodium silicate is hydrolyzed with a mineral acid, and the resulting silica hydrosol is gelled and dried is used. In order to improve performance, many proposals have been made for details of this manufacturing method.
[0005]
For example, in Patent Document 1, a silica hydrosol produced by the reaction between an alkali silicate aqueous solution and a mineral acid is gelled, treated with an acid solution having a pH of 2.5 or less, washed with water, and then in an aqueous solution having a buffering action. There has been proposed a method for producing silica gel having a narrow pore distribution by adjusting the pH to 4 to 9 and performing hydrothermal treatment. Patent Document 2 proposes a method in which silica hydrogel is dried by batch fluidized drying and then hydrothermally treated.
[0006]
According to these production methods, the performance of the obtained silica gel is surely changed, and a silica gel having a sharper pore distribution can be produced. However, since the pore volume, specific surface area and average pore diameter of the obtained silica gel are not sufficiently changed, and heat resistance and water resistance are not sufficient, it is not a method for obtaining silica gel having a desired physical property range. It is enough.
[0007]
Moreover, the silica obtained by using the alkali silicate salt as a raw material by the former method (the method described in Patent Document 1) usually contains impurities such as sodium, calcium, magnesium, titanium, aluminum, and zirconium derived from the raw material. Amount included. The presence of impurities in silica has a great influence on the performance of silica even if the total content is as small as several hundred ppm. For example, 1) the presence of these impurities promotes crystallization of silica gel at high temperatures, and 2) the presence of these impurities promotes the hydrothermal reaction of silica gel in the presence of water, resulting in pore size and pore size. 3) These impurities lower the sintering temperature, and heating silica gel containing these impurities promotes a reduction in specific surface area, resulting in an increase in volume, a decrease in specific surface area, and an increase in pore distribution. And the like. Such an effect is particularly strong in impurities including elements belonging to alkali metals and alkaline earth metals. Furthermore, when titanium or aluminum is present as an impurity on the surface of the silica gel or in the siloxane bond, the acidic point increases, and when used as a catalyst carrier or adsorbent, the silica gel itself may exhibit an undesirable catalytic action.
[0008]
On the other hand, as a method for producing high-purity silica gel with very few impurities, those skilled in the art can purify gels obtained by neutralizing alkali silicate salts and hydrolyze silicon alkoxides to those skilled in the art. It is known as a well-known technique. Particularly, in the latter method, since silicon alkoxide as a raw material can be purified by distillation or the like, high-purity silica gel can be obtained relatively easily.
[0009]
The method using an alkoxide as a raw material was basically obtained by hydrolyzing silicon alkoxide in the presence of a catalyst and condensing the obtained silica hydrosol to form a silica hydrogel, and a hydrolysis / condensation step obtained. And a physical property adjusting step of hydrothermally treating the silica hydrogel.
[0010]
In the hydrolysis / condensation step, an acid (sulfuric acid, hydrochloric acid or nitric acid) is usually used as a catalyst. In addition, an aging step is provided before the above physical property adjustment step (hydrothermal treatment), and it is said that physical properties such as improvement in silica gel strength can be improved by such aging step. Such a method is called a sol-gel method and is known to those skilled in the art.
However, silica gel obtained from silicon alkoxide by a sol-gel method generally has a small average pore diameter and a wide pore distribution. Moreover, even if this silica gel is subjected to hydrothermal treatment, there has been almost no report of remarkable improvement in performance.
[0011]
On the other hand, in Non-Patent Document 1, after forming a supramolecular structure consisting of a hydrogen bond between an electrically neutral gemini surfactant and a silica precursor, heat resistance is removed by removing the gemini surfactant. The production of mesoporous molecular sieves with (1000 ° C.) and water resistance (over 100 hours at 100 ° C.) is described. This is a kind of so-called micellar template silica that forms pores using an organic template, and can produce silica with a very sharp pore distribution compared to the above-mentioned conventional techniques. it can. However, this production method has a problem that the water resistance of the obtained silica is not sufficient, the production process is complicated, and the productivity is poor.
[Patent Document 1]
JP 62-1113713 A [Patent Document 2]
JP-A-9-30809 [Non-Patent Document 1]
Kim et al., "Ultrastable Mesostructured Silica Vesicles Science", 282, 1302 (1998)
[0012]
[Problems to be solved by the invention]
By the way, the macroscopic structure of silica is well known, and it is known that spherical particles of silica colloids have a close continuous three-dimensional structure in close contact with each other. However, the microscopic structure is still sufficiently elucidated. It has not been. Therefore, it has been desired to analyze the micro structure of such silica and find a novel silica that satisfies the above-mentioned various physical properties in a well-balanced manner from silica having a micro structure that is not conventionally known.
[0013]
The present invention has been made in view of the above-described problems. That is, the object of the present invention is a silica having a novel micro structure that has not been known so far, and not only has a large pore volume and specific surface area, but also has a narrow pore distribution and suppresses the amount of unnecessary metal impurities. Another object of the present invention is to provide silica having excellent physical properties such as heat resistance and water resistance, that is, having various desirable attributes in a well-balanced manner.
[0014]
[Means for Solving the Problems]
Therefore, as a result of intensive studies to solve the above problems, the present inventors have omitted the aging step after the step of hydrolyzing and condensing the silicon alkoxide, and subsequently performing the physical property adjustment step, whereby solid Si— Silica having a specific structure characterized by NMR is obtained, and this is excellent in terms of heat resistance, hydrothermal resistance, etc., and the knowledge that precise pore control is possible is completed, and the present invention is completed. It came to.
[0015]
That is, the gist of the present invention is that when the mode diameter of pores (D _max ) is silica of 20 nm or less, and the chemical shift of the Q ⁴ peak in solid Si-NMR is δ (ppm), δ Is represented by the following formula (I)
−0.0705 × (D _max ) −11.36> δ (I)
Is satisfied , the pore volume is 0.6 to 1.6 ml / g, and the specific surface area is 200 to 1000 m ² / g .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
(1) Features of the silica of the present invention The silica of the present invention is hydrous silicic acid, and is represented by the SiO ₂ .nH ₂ O characteristic formula. In the present invention, the effect is particularly remarkable in “silica gel” or micelle template type silica among silica.
[0017]
The silica of the present invention is characterized in that the mode diameter (D _max ) of the pores is smaller than usual. The mode diameter (D _max ) is a characteristic that affects the adsorption and absorption of gases and liquids. The smaller the mode diameter (D _max ), the higher the adsorption and absorption performance. Therefore, the mode diameter (D _max ) among various properties is an important physical property particularly for silica used as a catalyst support or an adsorbent. Specifically, the preferred mode diameter (D _max ) of the silica of the present invention is usually 20 nm or less, preferably 17 nm or less, more preferably 15 nm or less. Although a minimum in particular is not restrict | limited, Usually, it is 2 nm or more.
[0018]
The mode diameter (D _max ) is calculated from the isothermal desorption curve measured by the BET method by nitrogen gas adsorption / desorption, from EP Barrett, LG Joyner, PH Haklenda, J. Amer. Chem. Soc., Vol. 73, 373 ( 1951) is plotted to obtain a pore distribution curve calculated by the BJH method. Here, the pore distribution curve refers to the differential pore volume, that is, the differential nitrogen gas adsorption amount (ΔV / Δ (logd)) with respect to the pore diameter d (nm). The above V represents the nitrogen gas adsorption volume.
[0019]
In addition to the characteristics of the pore structure described above, it is preferable that the silica of the present invention is amorphous, that is, no crystalline structure is observed in view of its three-dimensional structure. This means that when the silica of the present invention is analyzed by X-ray diffraction, a crystalline peak is not substantially observed. In the present specification, non-amorphous silica refers to a silica having at least one crystal structure peak at a position exceeding 6 angstroms (Å Units d-spacing) in the X-ray diffraction pattern. Amorphous silica is extremely excellent in productivity as compared with crystalline silica.
[0020]
In addition, the silica of the present invention is characterized in that its structure is less distorted. The structural distortion of silica gel can be represented by the value of the chemical shift of the Q ⁴ peak in the solid-state Si-NMR measurement. Hereinafter, the relationship between the structural distortion of silica and the chemical shift value of the Q ⁴ peak will be described in detail.
[0021]
The silica of the present invention is represented by the above-described formula, but structurally, O is bonded to each vertex of the Si tetrahedron, and Si is further bonded to these Os to expand in a net shape. Have In some repeating units of Si—O—Si—O—, some of O is substituted with other members (for example, —OH, —OCH _3, etc.). As shown in the following formula (A), there are Si (Q ⁴ ) having ⁴ —OSi, Si (Q ³ ) having 3 —OSi as shown in the following formula (B), etc. In (A) and (B), the above tetrahedral structure is ignored, and the Si—O net structure is represented in a plane). In the solid Si-NMR measurement, the peaks based on the respective Si are called Q ⁴ peak, Q ³ peak,.
[0022]
[Chemical 1]

[0023]
The greatest feature of the silica of the present invention is that δ satisfies the following formula (I) when the chemical shift of the Q ⁴ peak is δ (ppm).
−0.0705 × (D _max ) −11.36> δ (I)
This fact means that there is little distortion in the bond angle represented by two -OSi with respect to Si.
[0024]
The Q ⁴ peak value δ is usually larger than the value calculated based on the left side of the formula (I). Therefore, the silica of the present invention has a smaller value of the chemical shift of the Q ⁴ peak as compared with the conventional silica. This means that in the silica of the present invention, the chemical shift is present in a high magnetic field, and the above bond angle is more uniform and less strained. In the present invention, the chemical shift δ of the Q ⁴ peak of silica is preferably usually more than the value (−0.0705 × (D _max ) −11.36) calculated based on the left side of the formula (I). It is preferably 0.05% or more, particularly 0.1% or more, and particularly preferably 0.15% or more.
[0025]
Further, the chemical shift value δ of the above-mentioned Q ⁴ peak is observed in the range of −106.00 to −113.00 ppm with normal silica, but becomes a smaller value with the silica of the present invention, specifically, , -111.00 to -112.00 ppm. This also means that in the silica of the present invention, the above bond angle is more uniform and distortion is less. The reason why the Q ⁴ peak has such a width is that the bond angle represented by two —OSi usually has various values with respect to the observed Si.
[0026]
The relationship between the excellent heat resistance and water resistance of the silica of the present invention and the structural strain as described above is not necessarily clear, but is estimated as follows. In other words, silica is composed of aggregates of spherical particles of different sizes, but in a state where there is little structural distortion as described above, the high degree of microstructural homogeneity of the entire spherical particles is maintained. As a result, it is considered that excellent heat resistance and water resistance are exhibited. In addition, since the peak of Q ³ or less is limited in the spread of the Si—O net structure, the structural strain of silica hardly appears.
[0027]
Furthermore, the silica of the present invention has a Q ⁴ / Q ³ value of 1.3 or more, preferably 1.5 or more, as determined by solid-state Si-NMR measurement. Here, the value of Q ⁴ / Q ³ is the mole of Si (Q ⁴ ) in which four —OSi are bonded to Si (Q ³ ) in which three —OSi are bonded in the silica repeating unit described above. Means ratio. The upper limit is not particularly limited, but is usually 10 or less. In general, it is known that the higher this value, the higher the thermal stability of the silica. From this, it can be seen that the silica of the present invention is extremely excellent in thermal stability. On the other hand, crystalline micelle template silica often has a Q ⁴ / Q ³ value of less than 1.3 and has low thermal stability, particularly hydrothermal stability.
[0028]
The value of chemical shift and Q ⁴ / Q ³ of Q ⁴ peak, performs solid Si-NMR measurement using the method described later in the description of embodiments, can be calculated based on the result. Further, analysis of measurement data (determination of peak position) is performed by a method of dividing and extracting each peak by, for example, waveform separation analysis using a Gaussian function.
[0029]
One feature of the silica of the present invention is that the pore volume and the specific surface area are in a range larger than usual values. Specifically, the value of the pore volume is usually 0.6 ml / g or more, preferably 0.7 ml / g or more, and usually 1.6 ml / g or less. The value of the specific surface area is usually 200 m ² / g or more, preferably 300 m ² / g or more, more preferably 400 m ² / g or more, particularly preferably 500 m ² / g or more, usually 1000 m ² / g or less, Preferably it is 950 m < ² > / g or less, More preferably, it is 900 m < ² > / g or less. These pore volume and specific surface area values are measured by the BET method by nitrogen gas adsorption / desorption.
[0030]
Further, in the silica of the present invention, the total volume of pores in the range of ± 20% of the value of the mode diameter (D _max ) is usually 50% or more, preferably 60% of the total volume of all pores. More preferably, it is 70% or more. This means that the diameters of the pores of the silica gel of the present invention are uniform in the pores near the mode diameter (D _max ). The upper limit of the total volume of the pores in the range of ± 20% centering on the value of the most frequent diameter (D _max ) is not particularly limited, but is usually 90% or less of the total pore volume. .
[0031]
In relation to such characteristics, the silica of the present invention has a differential pore volume ΔV / Δ (logd) at a mode diameter (D _max ) calculated by the BJH method of usually 2 ml / g or more, preferably 3 ml. / G or more, more preferably 5 ml / g or more, usually 20 ml / g or less, preferably 12 ml / g or less (where, d is the pore diameter (nm), and V is nitrogen gas) Adsorption volume). When the differential pore volume ΔV / Δ (logd) is included in the above range, it can be said that the absolute amount of pores arranged in the vicinity of the most frequent diameter (D _max ) is extremely large.
[0032]
Further features of the silica of the present invention are known to affect its physical properties by being present in the silica, alkali metals, alkaline earth metals, groups 3A, 4A and 5A of the periodic table and The total content of metal elements (impurity elements) belonging to the group consisting of transition metals is very low and extremely high in purity. Specifically, the total content of metal impurities is usually 100 ppm or less, preferably 50 ppm or less, more preferably 10 ppm or less, and particularly preferably 1 ppm or less. In particular, the total content of elements belonging to the group consisting of alkali metals and alkaline earth metals, which have a great influence on the physical properties of silica gel, is usually 100 ppm or less, especially 50 ppm or less, more preferably 10 ppm or less, especially 1 ppm or less. preferable. Such a small influence of impurities is one of the major factors that enable the silica of the present invention to exhibit excellent properties such as high heat resistance and water resistance.
[0033]
(2) Production method of silica of the present invention Unlike the conventional sol-gel method, the silica of the present invention hydrolyzes silicon alkoxide (hydrolysis step) and condenses the obtained silica hydrosol to produce silica hydrogel. It is produced by a method including a hydrolysis / condensation step to be formed and a physical property adjusting step of hydrothermally treating the silica hydrogel without aging following the hydrolysis / condensation step.
[0034]
The silicon alkoxide used as a raw material for the silica of the present invention includes a lower alkyl group having 1 to 4 carbon atoms such as trimethoxysilane, tetramethoxysilane, triethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane and the like. Examples thereof include tri- or tetraalkoxysilane or oligomers thereof, and tetramethoxysilane, tetraethoxysilane and oligomers thereof are preferable. Since the above silicon alkoxide can be easily purified by distillation, it is suitable as a raw material for high-purity silica. The total content of metal elements (metal impurities) belonging to the alkali metal or alkaline earth metal in the silicon alkoxide is usually 100 ppm or less, preferably 50 ppm or less, more preferably 30 ppm or less, particularly preferably 10 ppm or less, most preferably 1 ppm or less. is there. These so-called metal impurity contents can be measured by the same method as the method for measuring the impurity content in general silica.
[0035]
In the present invention, first, in the hydrolysis / condensation step, the silicon alkoxide is hydrolyzed in the absence of a catalyst and the silica hydrosol obtained is condensed to form a silica hydrogel.
[0036]
The hydrolysis of the silicon alkoxide is usually 2 mol or more, preferably 3 mol or more, particularly preferably 4 mol or more, usually 20 mol or less, preferably 10 mol or less, particularly preferably 8 mol or less with respect to 1 mol of silicon alkoxide. Of water. Hydrolysis of the silicon alkoxide produces a silica hydrosol of silica doped with a different element of interest and an alcohol, and the produced silica hydrosol is successively condensed into a silica hydrogel. The temperature during hydrolysis is usually room temperature or higher, preferably 30 ° C. or higher, particularly preferably 40 ° C. or higher, more preferably 50 ° C. or higher, usually 100 ° C. or lower, preferably 90 ° C. or lower, especially preferably 80 ° C. or lower, Preferably it is 70 degrees C or less. This hydrolysis reaction can be performed at a higher temperature by maintaining the liquid phase under pressure.
[0037]
Further, the hydrolysis may be performed in the presence of a solvent such as alcohol having compatibility with water, if necessary. Specifically, lower alcohols having 1 to 3 carbon atoms, dimethylformamide, dimethyl sulfoxide, acetone, tetrahydrofuran, methyl cellolbu, ethyl cellolb, methyl ethyl ketone, and other organic solvents that can be arbitrarily mixed with water can be arbitrarily used. Among them, those that do not exhibit strong acidity or basicity are preferable because a uniform silica hydrogel can be produced.
[0038]
When these solvents are not used, the stirring speed at the time of hydrolysis is particularly important for the production of the silica of the present invention. That is, since silicon alkoxide and water for hydrolysis are separated at the initial stage, they are emulsified by stirring to promote the reaction.
[0039]
At this time, it is important to sufficiently stir. For example, when a stirrer equipped with a stirring blade on the rotating shaft is used, the stirring speed (the number of rotations of the rotating shaft) depends on the shape, the number of the stirring blades, the contact area with the liquid, etc., but is usually 30 rpm. Above, preferably 50 rpm or more.
[0040]
In general, if the stirring speed is too high, droplets generated in the tank block various gas lines, or adhere to the inner wall of the reactor to deteriorate the heat conduction, which is important for temperature control for controlling physical properties. May have an effect. Furthermore, the deposits on the inner wall may be peeled off and mixed into the product to deteriorate the quality. For these reasons, the stirring speed is preferably 2000 rpm or less, and more preferably 1000 rpm or less.
[0041]
In the present invention, any stirring method can be used as the stirring method for the two liquid phases (aqueous phase and silicon alkoxide phase) which are separated, as long as the method promotes the reaction. Among them, examples of an apparatus for further mixing the two phases include the following (1) and (2).
[0042]
{Circle around (1)} A device having an agitating blade in which a rotating shaft is inserted perpendicularly or slightly at an angle with respect to the liquid surface and the liquid flows up and down.
{Circle around (2)} A stirrer having a stirring blade provided with a rotation axis direction substantially parallel to the interface between the two liquid phases and causing stirring between the two phase phases.
[0043]
The rotating speed of the stirring blade when using the apparatus as described in (1) and (2) above is 0.05 to 10 m / s in terms of the peripheral speed of the stirring blade (speed at the tip of the stirring blade). It is preferably 5 m / s, more preferably 0.1 to 3 m / s.
The shape of the stirring blade and the length of the stirring blade are arbitrary. Examples of the stirring blade include a propeller type, a flat blade type, a flat blade type with an angle, a flat blade type with a pitch, a flat blade disk turbine type, a curved blade type, and a fiddler type. , Bull margin type, anchor type, ribbon type and the like.
[0044]
The width, number of blades, inclination angle, etc. of the blades may be appropriately selected according to the shape and size of the reactor and the target stirring power. For example, the ratio (b / D) of the blade width (blade length in the rotation axis direction) to the tank inner diameter (the longest diameter of the liquid phase surface forming a plane perpendicular to the rotation axis direction) of the reactor is 0.05 to A suitable example is 0.2, an inclination angle (θ) of 90 ° ± 10 °, and a stirring device of 3 to 10 blades.
In particular, a structure in which the above-described rotation shaft is provided above the liquid level in the reaction vessel and a stirring blade is provided at the tip of the shaft extending from the rotation shaft is preferably used from the viewpoint of stirring efficiency and equipment maintenance.
[0045]
When the above stirring speed condition is not satisfied, it is difficult to obtain the silica of the present invention. In addition, after alcohol produces | generates by hydrolysis and a liquid turns into a uniform liquid and heat_generation | fever stops, it is preferable to stop stirring in order to form a uniform hydrogel.
[0046]
Silica that exhibits crystallinity tends to have poor thermal stability in water, and when silicon alkoxide is hydrolyzed in the presence of a template such as a surfactant used to form pores in silica, silica is easily Includes a crystal structure. Therefore, in the present invention, it is preferable to hydrolyze in the absence of a template such as a surfactant, that is, in a condition where there is no such an amount that it functions as a template.
[0047]
The reaction time for hydrolysis depends on the composition of the reaction solution (type of silicon alkoxide and molar ratio with water) and the reaction temperature, and since the time until gelation differs, it is not generally specified. In addition, hydrolysis can be accelerated | stimulated by adding an acid, an alkali, salts, etc. to a reaction system as a catalyst. However, the use of such additives is less preferred in the production of the silica of the present invention, as it will cause aging of the resulting hydrogel, as described below.
In the above silicon alkoxide hydrolysis reaction, the silicon alkoxide is hydrolyzed to produce a silicate. Subsequently, a condensation reaction of the silicate occurs, the viscosity of the reaction solution rises, and finally gelates to form a silica hydrogel. Become.
[0048]
Next, in the present invention, as a physical property adjusting step, hydrothermal treatment is immediately performed without substantial aging so that the hardness of the hydrogel of silica generated by the above hydrolysis does not increase. Hydrolysis of silicon alkoxide produces a soft silica hydrogel, but this hydrogel can be stably aged or dried, and then subjected to hydrothermal treatment. It is difficult to produce silica having a physical property range specified in the invention.
[0049]
The hydrothermal treatment of the silica hydrogel formed by hydrolysis, as described above, is performed immediately without substantially aging. This means that the soft state immediately after the formation of the silica hydrogel is maintained and the following conditions are maintained. It means to be subjected to hydrothermal treatment.
[0050]
Specifically, it is preferable that the hydrothermal treatment is generally performed within 10 hours from the time when the silica hydrogel is formed, and the hydrothermal treatment is preferably performed within 8 hours, more preferably within 6 hours, particularly within 4 hours. It is preferable.
In an industrial plant or the like, a case where a large amount of silica hydrogel is temporarily stored in a silo or the like and then hydrothermally treated is considered. In such a case, the silica hydrogel is considered to have a case where the time from when the silica hydrogel is formed to when it is subjected to hydrothermal treatment, the so-called standing time, exceeds the above range. In such a case, for example, the liquid component in the silica hydrogel may be prevented from drying during standing in the silo so that aging does not substantially occur.
[0051]
Specifically, for example, the inside of the silo may be sealed or the humidity may be adjusted. Alternatively, the silica hydrogel may be allowed to stand in a state where the silica hydrogel is immersed in water or another solvent.
The temperature at the time of standing is preferably as low as possible, for example, 50 ° C. or less, particularly 35 ° C. or less, particularly preferably 30 ° C. or less. Further, as another method for preventing aging substantially from occurring, a method of preparing a silica hydrogel by controlling the raw material composition in advance such that the silica concentration in the silica hydrogel is lowered can be mentioned.
[0052]
Considering the effect obtained by hydrothermal treatment without substantially aging the silica hydrogel and the reason why this effect is obtained, the following can be considered.
That is, when the silica hydrogel is aged, it is considered that a macroscopic network structure due to —Si—O—Si— bonds is formed in the entire silica hydrogel. It is considered that this network structure is present in the entire silica hydrogel, so that this network structure becomes an obstacle during hydrothermal treatment, and it becomes difficult to form mesoporous materials. Therefore, in the present invention, it is important to perform hydrothermal treatment without aging the silica hydrogel.
In addition, the silica hydrogel obtained by previously controlling the raw material composition so that the silica concentration in the silica hydrogel is low can suppress the progress of crosslinking in the silica hydrogel that occurs during standing. Therefore, it is considered that the silica hydrogel does not age.
[0053]
It is not preferable to add acid, alkali, salt, or the like to the silicon alkoxide hydrolysis reaction system, or to make the temperature of the hydrolysis reaction too strict, since the aging of the hydrogel proceeds. Also, temperature and time should not be taken more than necessary in washing, drying, leaving, etc. in post-treatment after hydrolysis.
[0054]
As a means for specifically confirming the aging state of the hydrogel, the hardness of the hydrogel measured by a method as shown in the examples described later can be referred to. That is, silica having a physical property range defined in the present invention can be obtained by hydrothermally treating a soft hydrogel having a fracture stress of usually 6 MPa or less, preferably 3 MPa or less, more preferably 2 MPa or less.
[0055]
As conditions for this hydrothermal treatment, the state of water may be either liquid or gas, and it may be diluted with a solvent or other gas. Preferably, liquid water is added to silica hydrogel to form a slurry. . The amount of water used is usually at least 0.1 times by weight, preferably at least 0.5 times by weight, particularly preferably at least 1 times by weight, and usually at most 10 times by weight, preferably 5 times by weight relative to the silica hydrogel. The weight is not more than 3 times, particularly preferably not more than 3 times by weight. The temperature of the hydrothermal treatment is usually 40 ° C. or higher, preferably 50 or higher, and usually 250 ° C. or lower, preferably 200 ° C. or lower. The hydrothermal treatment time is usually 0.1 hour or longer, preferably 1 hour or longer, and usually 100 hours or shorter, preferably 10 hours or shorter.
[0056]
The water used for the hydrothermal treatment may include lower alcohols, methanol, ethanol, propanol, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and other organic solvents. The hydrothermal treatment method is also applied to a material in which silica is formed on a substrate such as a particle, a substrate, or a tube in the form of a film or a layer for the purpose of making a membrane reactor or the like. It is also possible to perform hydrothermal treatment by changing the temperature conditions using a hydrolysis reaction reactor, but the optimum conditions are usually different between the hydrolysis reaction and the subsequent hydrothermal treatment. It is generally difficult to obtain the silica of the present invention.
[0057]
When the temperature is increased under the above hydrothermal treatment conditions, the pore diameter and pore volume of the resulting silica tend to increase. The hydrothermal treatment temperature is preferably in the range of 100 to 200 ° C. Further, with the treatment time, the specific surface area of the obtained silica tends to gradually decrease after reaching a maximum once. Based on the above tendency, it is necessary to appropriately select the conditions according to the desired physical property values, but since hydrothermal treatment is the purpose of changing the physical properties of silica, it is usually at a higher temperature than the hydrolysis reaction conditions described above. It is preferable to do.
[0058]
If the hydrothermal treatment temperature and time are set outside the above ranges, it will be difficult to obtain the silica of the present invention. For example, if the hydrothermal treatment temperature is too high, the pore diameter and pore volume of silica become too large, and the pore distribution is also widened. On the other hand, if the hydrothermal treatment temperature is too low, the resulting silica has a low degree of crosslinking, poor thermal stability, no peaks in the pore distribution, or Q ⁴ / Q ³ value may become extremely small.
[0059]
When the hydrothermal treatment is performed in ammonia water, the same effect can be obtained at a lower temperature than in pure water. In addition, when hydrothermal treatment is performed in ammonia water, the silica gel finally obtained is generally hydrophobic as compared with the case of treatment in pure water, but is usually 30 ° C. or higher, preferably 40 ° C. or higher, and usually 250 Hydrophobic treatment at a relatively high temperature of not higher than ° C., preferably not higher than 200 ° C., particularly increases hydrophobicity. The ammonia concentration here is preferably 0.001% or more, particularly preferably 0.005% or more, or preferably 10% or less, particularly preferably 5% or less.
[0060]
The hydrothermally treated silica hydrogel is usually dried at 40 ° C. or higher, preferably 60 ° C. or higher, and usually 200 ° C. or lower, preferably 120 ° C. or lower. The drying method is not particularly limited, and it may be a batch type or a continuous type, and can be dried under normal pressure or reduced pressure. If necessary, when a carbon component derived from the raw material silicon alkoxide is contained, it can be usually removed by baking at 400 to 600 ° C. Moreover, in order to control a surface state, it may bake at the temperature of a maximum of 900 degreeC. Furthermore, the final silica of the present invention is obtained by pulverizing and classifying as necessary.
[0061]
(3) Use of silica of the present invention The silica of the present invention can be used in any application other than the conventional use of silica. Among these, conventional applications include the following.
[0062]
For example, in application fields used for manufacturing and processing products in industrial facilities, various catalysts and catalyst carriers (acid-base catalysts, photocatalysts, noble metal catalysts, etc.), wastewater / waste oil treatment agents, odor treatment agents, gas separation agents, Applications include industrial desiccants, bioreactors, bioseparators, membrane reactors and the like. Examples of building materials include humidity control agents, soundproofing / absorbing materials, refractories, and heat insulating materials. Moreover, in applications in the air conditioning field, desiccant air conditioners, heat pump heat storage agents, and the like. In the paint / ink application field, matting agents, viscosity adjusting agents, chromaticity adjusting agents, anti-settling agents, antifoaming agents, ink back-through preventing agents, stamping foils, and wallpapering applications may be mentioned. In the field of resin additives, anti-blocking agents for films (polyolefin films, etc.), plate-out inhibitors, silicone resin reinforcing agents, rubber reinforcing agents (for tires, general rubbers, etc.), fluidity improvers, Anti-caking agent for powdered resin, printability improver, matting agent for synthetic leather and coating film, filler for adhesive / adhesive tape, translucency adjuster, antiglare adjuster, porous polymer sheet Uses for fillers and the like. In the papermaking field, thermal paper fillers (such as residue adhesion inhibitors), ink jet paper image enhancement fillers (ink absorbers, etc.), diazo photosensitive paper fillers (sensitivity density improvers, etc.), and tracing paper Uses such as a writing property improving agent, a filler for coated paper (writing property, ink absorbability, anti-blocking property improving agent, etc.), a filler for electrostatic recording and the like can be mentioned. In food applications, beer filter aids, soy sauce, sake, wine and other fermented product lowering agents, various fermented beverage stabilizers (such as turbidity factor protein and yeast removal), food additives, and powdered foods Uses such as anti-caking agents are mentioned. In the medical and agrochemical field, tableting aids for pharmaceuticals, grinding aids, dispersion / pharmaceutical carriers (dispersion, sustained release, improved delivery, etc.), agrochemical carriers (oily agrochemical carrier, improved hydration dispersibility, sustained release) -Delivery improvement etc.), Additives for medicine (anti-caking agent / powdering improver, etc.), additives for agricultural chemicals (anti-caking agent, anti-settling agent, etc.), etc. In the field of separation materials, there are applications such as chromatographic fillers, separation agents, fullerene separation agents, adsorbents (proteins, dyes, odors, etc.), and dehumidifiers. In the agricultural field, feed additives and fertilizer additives can be mentioned. As other applications, in life-related fields, humidity control agent, desiccant, cosmetic additive, antibacterial agent, deodorant / deodorant / fragrance, detergent additive (surfactant powder, etc.), abrasive (toothpaste) Etc.), powder fire extinguishing agents (powdering property improver, anti-caking agent, etc.), antifoaming agents, battery separators and the like.
[0063]
In particular, the silica of the present invention has a large pore volume and specific surface area as compared with conventional silica having the same pore diameter, and thus has a high adsorption / absorption capacity and enables precise pore control. Therefore, among the various uses described above, it is preferably used in fields where particularly excellent heat resistance and hydrothermal resistance are required, as well as controlled pore characteristics and a change in physical properties over a long period. it can.
[0064]
Further, the silica of the present invention is suitably used also in a field where a particle size of 50 μm or less is required, and precisely controlled pore characteristics and stable physical properties are required. In general, when silica has an average particle size of 50 μm or less, the outer surface area per unit weight increases, and various substances can be adsorbed / absorbed at the grain boundary. Get higher. That is, by reducing the particle size of the silica of the present invention, various characteristics such as the high pore volume, high specific surface area, sharp pore distribution, high purity and little physical property change that the silica of the present invention already has are provided. It is possible to develop silica that is further excellent in adsorption and absorption.
[0065]
When the silica of the present invention is used in such a field, the average particle diameter may be adjusted according to the value required in the field, but is usually 50 μm or less, preferably 30 μm or less, particularly preferably 5 μm or less. . Although there is no restriction | limiting in particular as a minimum, Preferably it is 0.1 micrometer or more. The use of silica having such a small particle size includes various adsorbents, resin fillers, ink absorbents for ink jet paper, antiblocking agents for films, filter aids for beverages, various catalyst carriers, and the like. . For example, the silica of the present invention having an average particle size of 5 μm or less is useful as an absorbent for inkjet paper because of its high ink absorption rate and high oil absorption performance.
[0066]
On the other hand, the silica of the present invention is preferable even if the average particle size is increased. By increasing the average particle size, the silica of the present invention has the above-mentioned characteristics such as high specific surface area, high pore volume, sharp pore distribution, high purity and little change in physical properties, and characteristics unique to large particles. It is extremely useful in fields where both are required. For example, silica having a large average particle size reduces light scattering and can be used as a glass body for optical applications.
[0067]
Specifically, the silica of the present invention is preferably used also in the field where a particle size of 500 μm or more is required, and precisely controlled pore characteristics and stable physical properties are required. When the silica of the present invention is used in such a field, the average particle diameter may be adjusted according to a value required in the field, but is usually 500 μm or more, preferably 5 mm or more. Moreover, although there is no restriction | limiting in particular as an upper limit, Preferably it is 5 cm or less. For example, since the silica of the present invention having an average particle size of 500 μm or more has controlled nanopores, optically useful dyes, metals, photocatalysts, photochromic compounds, and other optical functionalities utilizing the pores. The material can be supported at a certain size according to the pore diameter, and is useful as a functional optical material. In general, it is difficult to produce particles having a large average particle size without causing coarse cracks, but the silica of the present invention has a homogeneous structure and coarse cracks even by treatments involving volume changes such as hydrothermal treatment. It is possible to obtain a product having controlled pore characteristics and a relatively large average particle size.
[0068]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited to a following example, unless the summary is exceeded.
[0069]
[A] Hardness measurement of silica hydrogel In a 5 L separable flask, silicon alkoxide was reacted with 6 moles of water, and after the temperature of the reaction solution reached the boiling point of the alcohol produced by the reaction, the reaction solution was extracted from the flask. The transferred reaction solution is transferred to a 50 cc glass screw tube (approximately 20 mm in depth), kept tightly in a water bath controlled at a substantially constant temperature, and the breaking strength is digitalized over time. It was measured with a force gauge (manufactured by A & D Co., Ltd., model: AD-4935). A probe (stainless steel round bar with a diameter of 5 mm) is attached to the measuring instrument, and the hydrogel held in the container is compressed and broken by being slowly pushed into the hydrogel. The maximum stress value shown until the hydrogel was compressed and destroyed was taken as the breaking stress.
[0070]
The measurement results are shown in FIG. FIG. 1 is a graph in which the common logarithm of the aging time of the silica hydrogel is plotted on the horizontal axis and the fracture stress is plotted on the vertical axis. From FIG. 1, it can be seen that the fracture stress increases with the aging time, and that the aging rate depends on the temperature.
[B] Example / Comparative Group I
[0071]
(1) Analysis method of silica 1-1) Pore volume, specific surface area, differential pore volume:
The BET nitrogen adsorption isotherm was measured with AS-1 manufactured by Cantachrome, and the pore volume and specific surface area were determined. Specifically, the pore volume adopts a value when the relative pressure P / P ₀ = 0.98, and the specific surface area is nitrogen at three points of P / P ₀ = 0.1, 0.2, 0.3. It calculated using the BET multipoint method from the adsorption amount. Further, the pore distribution curve and the differential pore volume at the mode diameter (D _max ) were determined by the BJH method. The interval between each point of the relative pressure to be measured was 0.025.
[0072]
1-2) Powder X-ray diffraction Using a RAD-RB apparatus manufactured by Rigaku Corporation, measurement was performed using CuKα as a radiation source. The divergence slit was ½ deg, the scattering slit was ½ deg, and the light receiving slit was 0.15 mm.
[0073]
1-3) Content of metal impurities Fluoric acid was added to 2.5 g of the sample and heated to dryness, and then water was added to 50 ml. ICP emission analysis was performed using this aqueous solution. Sodium and potassium were analyzed by flame flame light method.
[0074]
1-4) Solid-state Si-NMR Measurement Using a Bruker solid-state NMR apparatus (“MSL300”), a resonance frequency of 59.2 MHz (7.05 Tesla), and a 7 mm sample tube, CP / MAS (Cross Measurement was performed under the conditions of a Polarization / Magic Angle Spinning probe. Specific measurement conditions are shown in Table 1 below.
[0075]
[Table 1]

[0076]
Analysis of measurement data (determination of Q ⁴ and Q ³ peak positions) is performed by a method of extracting each peak by peak division. Specifically, waveform separation analysis using a Gaussian function is performed. For this analysis, waveform processing software “GRAMS386” manufactured by Thermogalatic can be used. Thus, the ratio (Q ⁴ / Q ³ ) was obtained using the peak areas of Q ⁴ and Q ³ obtained by peak division.
[0077]
1-5) Silica underwater thermal stability test sample was added pure water to prepare a 40 wt% slurry. About 40 ml of the slurry prepared above was sealed in a stainless steel microbomb having a volume of 60 ml, and immersed in an oil bath at 280 ± 1 ° C. for 3 days. A part of the slurry was extracted from the microbomb and filtered through 5A filter paper. The filter cake was vacuum-dried at 100 ° C. for 5 hours, and then the specific surface area of the remaining sample was measured.
[0078]
(2) Production of silica, evaluation examples I-1 to I-3:
1000 g of pure water was charged into a 5 L separable flask (with a jacket) made of glass and fitted with a water-cooled condenser open to the atmosphere at the top. While stirring at a stirring speed such that the tip speed of the stirring blade was 2.5 m / s, 1400 g of tetramethoxysilane was charged over 3 minutes. The water / tetramethoxysilane molar ratio is about 6. Warm water at 50 ° C. was passed through the jacket of the separable flask. Stirring was continued, and the stirring was stopped when the contents reached the boiling point. Subsequently, hot water of 50 ° C. was passed through the jacket for about 0.5 hour to gel the sol produced. Thereafter, the gel was quickly taken out and pulverized through a nylon net having an opening of 600 microns to obtain a powdery wet gel (silica hydrogel). 450 g of this hydrogel and 450 g of pure water were charged into a 1 L glass autoclave, 130 ° C. × 3 Hr for Example I-1, 150 ° C. × 3 Hr for Example I-2, and 200 ° C. for Example I-3. Hydrothermal treatment was performed under the condition of 3Hr. After hydrothermal treatment for a predetermined time, no. It filtered with 5A filter paper, and it dried under reduced pressure until it became constant weight at 100 degreeC without washing with water, and it was set as the silica of Example I-1 to I-3, respectively.
[0079]
Example I-4:
Hydrogels were produced under the same conditions as in Examples I-1 to I-3. 450 g of the obtained hydrogel and 450 g of 0.56% aqueous ammonia were charged into a 1 L autoclave and hydrothermally treated under the conditions of 60 ° C. × 3 Hr. After hydrothermal treatment for a predetermined time, no. It filtered with 5A filter paper, and it dried under reduced pressure until it became constant weight at 100 degreeC, without washing with water, and was set as the silica of Example I-4.
[0080]
Example I-5:
Silica was obtained in the same manner as in Example I-1, except that a 6 liter SUS316 autoclave was used and hydrothermal treatment was performed at 160 ° C. × 3 Hr. The average particle diameter of the obtained silica was 331 μm.
This silica was subjected to jet mill pulverization for 26 minutes using a 100AFG type pulverizer manufactured by Hosokawa Micron Corporation. The average particle diameter of the silica was 5.3 μm. The conditions regarding pulverization, classification, etc. at this time are as follows.
Crushing air pressure: 0.72 m ³ / min
Air pressure: 0.59 MPa
Nozzle diameter * Number: φ1.9 mm * Three-class classifier type: 50 ATP
Rotation speed: 17800 rpm
Dust collection cloth: Bag filter processing capacity: 0.97 kg / h
[0081]
Example I-6:
The same procedure as in Example I-2 was performed, except that the nylon mesh having an aperture of 600 microns (μm) was changed to a nylon mesh having an aperture of 5 mm. The average particle diameter of the obtained silica was 2.8 mm (= 2800 μm).
[0082]
Various physical properties of the silicas of the obtained Examples I-1 to I-6 are shown in Table 2 and Table 4 (however, there is no measured value of the chemical shift of the Q ⁴ peak in Example I-6, so Table 2 Only). In any of the silicas, no crystalline peak appears in the powder X-ray diffraction pattern, and no peak on the low angle side (2θ ≦ 5 deg) due to the periodic structure is observed. In addition, the impurity metal content rate of the silica of Examples I-1 to I-6 is 0.2 ppm for sodium, 0.1 ppm for potassium, and 0.2 ppm for calcium for any silica of Examples I-1 to I-6. There were no other metals detected.
[0083]
FIG. 2 also shows the most frequent pore diameter (D _max ) and Q ⁴ peak chemical shift values (δ) for the silicas of Examples I-1 to I-5 and Comparative Examples I-1 to I-6 described later. The graph showing the correlation with () is shown. As is apparent from FIG. 2, the values of chemical shifts of the solid Si-NMR Q ⁴ peak (plotted as series 1 in the graph of FIG. 2) for any silica of Examples I-1 to I-5. (Value) is compared with the value calculated from the left side of the above formula (I) (−0.0705 × (D _max ) −11.36) (value represented by the black line segment in the graph of FIG. 2), It was in a smaller area.
[0084]
In addition, the silica having an average particle size of 5.3 μm obtained in Example I-5 has a sharp pore size distribution and a high pore volume despite the small particle size, as is apparent from the above-mentioned physical property values. Therefore, it is clear that the moisture absorption performance is excellent, and various materials have a humidity control function. And this silica can be used suitably as a filler of various films which maintain the smoothness of a surface, for example, and require antiblocking properties.
[0085]
Further, the large particle diameter silica having an average particle diameter of more than 500 μm obtained in Example I-6 greatly reduces pressure loss when used in a column for catalyst carrier or adsorbent, for example. This is very preferable because it can be done. Furthermore, since the silica obtained in Example I-6 has few impurities and high purity, deterioration over time can be suppressed, and the life of the catalyst carrier and the like can be extended. Further, since this silica has a high purity and sharp pore distribution, it has the ability to adsorb and remove only the target compound with high selectivity, and can be suitably used in the field of food and medicine. I can do it.
[0086]
The following silicas were prepared as Comparative Examples I-1 to I-6.
Comparative Example I-1:
Silica CARIACT G-3 for catalyst carrier manufactured by Fuji Silysia Chemical Ltd. was used.
Comparative Example I-2:
Silica CARIACT G-6 for catalyst carrier manufactured by Fuji Silysia Chemical Ltd. was used.
Comparative Example I-3:
Silica CARIACT G-10 (Lot No. 703091) for catalyst carrier manufactured by Fuji Silysia Chemical Co., Ltd. was used.
Comparative Example I-4:
Silica CARIACT G-10 (Lot No. C-OO09014) for catalyst support manufactured by Fuji Silysia Chemical Co., Ltd. was used.
Comparative Example I-5:
Silica CARIACT Q-15 for catalyst carrier manufactured by Fuji Silysia Chemical Co., Ltd. was used.
Comparative Example I-6:
Mizukasorb C-1 manufactured by Mizusawa Chemical Co., Ltd. was used.
[0087]
The various physical properties of the silica of Comparative Examples I-1 to I-6 are shown in Tables 3 and 4 below. For all of the silicas of Comparative Examples I-1 to I-6, no crystalline peak appears in the powder X-ray diffraction pattern, and no low-angle peak due to the periodic structure is observed. Further, when the impurity metal content was measured, it was as shown in the following table, and the silica of Comparative Examples I-2 to I-6 had a higher impurity metal content than the silica of Examples I-1 to I-6. It was. In addition, as is clear from FIG. 2, the values of chemical shifts of the solid Si-NMR Q ⁴ peak (all plotted as series 2 in the graph of FIG. 2) for all of the silicas of Comparative Examples I-1 to I-6. 2) is in a larger area than the value calculated from the left side of the above formula (I) (value indicated by the black line in the graph of FIG. 2). It seems that there are many distortions compared with the silicas of I-1 to I-5, and the physical properties are likely to change.
[0088]
Moreover, the thermal surface stability test was performed on the conditions mentioned above using the silicas of Examples I-1 to I-6 and Comparative Examples I-1 to I-6 as samples, and the results of measuring the specific surface area are shown in Tables 2 and 3 shows. The silicas of Examples I-1 to I-6 had less reduction in specific surface area and were excellent in hydrothermal stability compared to the silicas of Comparative Examples I-1 to I-6.
[0089]
[Table 2]

[0090]
[Table 3]

[0091]
[Table 4]

[0092]
[C] Examples and Comparative Examples II:
(1) Analysis method of silica:
The test was carried out under the same conditions as in Example / Comparative Example Group I. Furthermore, the heat resistance test of silica was performed as follows.
Silica heat resistance test:
5 g of the sample was put in a quartz beaker, heated to 1000 ° C. at 200 ° C./hour in an air furnace and held for 1 hour, and then the beaker was immediately taken to room temperature and allowed to cool. The specific surface area of this sample was measured by the BET method.
[0093]
(2) Production and evaluation of silica:
Example II-1:
To a 5 L separable flask (with a jacket) equipped with a water-cooled condenser open to the atmosphere at the top, 1000 g of pure water was charged. While stirring at a stirring blade tip speed of 2.5 m / s, 1400 g of tetramethoxysilane was charged over 1 minute. The water / tetramethoxysilane molar ratio is about 6. Warm water at 50 ° C. was passed through the jacket of the separable flask. Stirring was continued, and the temperature of the contents was kept at 60 to 70 ° C. to prevent runaway. Subsequently, the sol produced by passing hot water of 50 ° C. through the jacket for about 0.5 hour was gelled. The hardness of the obtained gel was 1.5 MPa.
[0094]
Thereafter, the gel was quickly taken out and pulverized through a nylon net having an opening of 600 microns to obtain a powdery wet gel (silica hydrogel). 450 g of this hydrogel and 450 g of pure water were charged into a 1 L glass autoclave and hydrothermally treated at 130 ° C. for 3 hours. Then, no. It filtered with 5A filter paper, and it dried under reduced pressure until it became constant weight at 100 degreeC, without washing with water. Measurement results of metal impurity concentration of the obtained silica were 0.2 ppm sodium, 0.1 ppm potassium, 0.2 ppm calcium, and magnesium, aluminum, titanium, and zirconium were not detected. Table 5 shows other physical properties.
[0095]
Example II-2:
In Example II-1, silica was obtained in the same manner as in Example II-1, except that the charging time of tetramethoxysilane was changed to 3 minutes. The results of physical property measurement are shown in Table 5.
[0096]
Comparative Example II-1:
In Example II-1, silica was obtained in the same manner as in Example II-1, except that the charging time of tetramethoxysilane was changed to 30 minutes. The results of physical property measurement are shown in Table 5.
[0097]
Comparative Examples II-2 and II-3
For comparison between the silica of the present invention and ordinary commercially available silica, “G-3” and “G-6” (G-6) of “CARIACT G series” silica for catalyst support manufactured by Fuji Silysia Chemical Co., Ltd. Crushed) were used as Comparative Examples II-2 and II-3, respectively. In addition, the measurement results of the metal impurity concentration of commercially available silica (“G-6”) were sodium 170 ppm, magnesium 31 ppm, aluminum 15 ppm, potassium 23 ppm, calcium 160 ppm, titanium 260 ppm, and zirconium 44 ppm. Table 5 shows other physical properties.
[0098]
[Table 5]

[0099]
【The invention's effect】
The novel silica of the present invention has a mode diameter (D _max ) smaller than that of conventional silica, so that it has excellent adsorption and absorption performance, extremely excellent productivity, and further has a structure thereof. Since there is little distortion, it is excellent in heat resistance and water resistance.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a graph showing the relationship between each aging time when a hydrogel of silica is aged at 35 ° C., 45 ° C., and 55 ° C. and the fracture stress of the hydrogel at that time.
FIG. 2 is a graph showing the correlation between the most frequent pore diameter (D _max ) and the Q ⁴ peak chemical shift value (δ) for the silica of the examples of the present invention and comparative examples.

Claims (16)

Silica having a mode diameter (D _max ) of pores of 20 nm or less,
The chemical shift δ (ppm) of the Q ⁴ peak in solid Si-NMR satisfies the following formula (I) :
The pore volume is 0.6-1.6 ml / g,
A silica having a specific surface area of 200 to 1000 m < ² > / g .
−0.0705 × (D _max ) −11.36> δ (I) The silica according to claim 1, wherein the chemical shift δ of the Q ⁴ peak is in the range of −111.00 to −112.00 ppm . The silica according to claim 1 or 2 , wherein the pore volume is 0.7 to 1.6 ml / g . The silica according to claim 1 , wherein the specific surface area is 300 to 900 m ² / g. 5. The total volume of pores having a diameter within a range of D _max ± 20% is 50% or more of the total volume of all pores, according to claim 1 , silica. The silica according to claim 5 , wherein the total volume of pores having a diameter within D _max ± 20% is 60% or more of the total volume of all the pores. The silica according to any one of claims 1 to 6 , wherein the total content of metal impurities is 100 ppm or less. The total content of the element belonging to the group consisting of alkali metals and alkaline earth metals, characterized in that at 100ppm or less, the silica according to any one of claims 1 to 7. Silica according to any one of claims 1 to 8 , characterized in that the differential pore volume at the mode diameter ( _Dmax ) is 2 to 20 ml / g. 10. The silica according to claim 1 , wherein the value of Q ⁴ / Q ³ peak in solid-state Si-NMR measurement is 1.3 or more. The silica according to any one of claims 1 to 10 , wherein an average particle size is 50 µm or less. The silica according to any one of claims 1 to 10 , wherein the average particle size is 500 µm or more. It manufactures through the process of hydrolyzing a silicon alkoxide, The silica as described in any one of Claims 1-12 characterized by the above-mentioned. Hydrolysis and condensation step of hydrolyzing silicon alkoxide and condensing silica hydrosol obtained to form silica hydrogel;
The silica according to claim 13 , wherein the silica hydrogel is produced by a method including a physical property adjusting step of hydrothermally treating a silica hydrogel in a state where the fracture stress is 6 MPa or less following the hydrolysis / condensation step. The silica according to claim 14 , wherein the hydrolysis / condensation step is performed in the absence of a catalyst. The silica according to claim 14 or 15 , wherein the hydrolysis is performed using 20 mol or less of water with respect to 1 mol of silicon alkoxide .

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