JP5106721B2 - Method for producing photocatalyst and method for treating hydrogen sulfide using the photocatalyst - Google Patents

Method for producing photocatalyst and method for treating hydrogen sulfide using the photocatalyst Download PDF

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JP5106721B2
JP5106721B2 JP2001112293A JP2001112293A JP5106721B2 JP 5106721 B2 JP5106721 B2 JP 5106721B2 JP 2001112293 A JP2001112293 A JP 2001112293A JP 2001112293 A JP2001112293 A JP 2001112293A JP 5106721 B2 JP5106721 B2 JP 5106721B2
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hydrogen
photocatalyst
sulfide
hydrogen sulfide
solution
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JP2002306966A (en
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和幸 田路
厚生 粕谷
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National Institute of Japan Science and Technology Agency
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/04—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of inorganic compounds, e.g. ammonia
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    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/39—Photocatalytic properties
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B17/00—Sulfur; Compounds thereof
    • C01B17/02—Preparation of sulfur; Purification
    • C01B17/04—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides
    • C01B17/05—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides by wet processes
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B17/00—Sulfur; Compounds thereof
    • C01B17/02—Preparation of sulfur; Purification
    • C01B17/06—Preparation of sulfur; Purification from non-gaseous sulfides or materials containing such sulfides, e.g. ores
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis

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Description

【０００１】
【発明の属する技術分野】
本発明は、水素や硫黄等の化学物質を生成する化学工業分野、脱硫工程などで発生した硫化水素等を処理する化学工業分野、及び悪臭物質や大気汚染物質を除去する環境保全分野などで利用可能な高活性光触媒の製造技術、並びにその利用技術に関する。
【０００２】
【従来の技術】
光触媒技術の応用は、環境汚染物質や悪臭成分・雑菌などの分解など、様々な化学反応を促進する特性を利用した実用化が始まっている。その例としては、病院の手術室などで利用される抗菌タイル、空気清浄機やエア・コンディショナーのフィルタ、高速道路等の照明灯のガラスなどが挙げられる。これら光触媒の酸化促進能力を利用した実用化の一方で、水などに光触媒を作用させて水素を得ることや、炭酸ガスに作用させて炭素を固定還元することを目的とした研究も行われている。また、光触媒の応用はこれにとどまらず、有害物質に光触媒を作用させて有用な化学物質を得ることも可能である。例えば、石油精製や金属精練の脱硫工程に応用することが考えられる。
【０００３】
図４は、現在、一般的に行われている原油の脱硫工程を示すもので、原油を蒸留する際に、重質ナフサを水素化精製して原油に含まれる硫黄分を全て硫化水素にして回収している。さらに、ここで発生した硫化水素は、図５に示すように、クラウス法と呼ばれるプロセスを経て、酸化して硫黄を回収している。このクラウス法は、硫化水素の３分の１を酸化して亜硫酸ガスとし、これと残りの硫化水素とを反応させて硫黄とするプロセスである。すなわち、化学式では以下のように表される。
【０００４】
【化１】
２Ｈ2Ｓ ＋ ３Ｏ2 → ２Ｈ2Ｏ ＋ ２ＳＯ2
４Ｈ2Ｓ ＋ ２ＳＯ2 → ４Ｈ2Ｏ＋ ６Ｓ
【０００５】
この硫黄回収工程は、亜硫酸ガスと硫化水素の触媒反応だけでなく、加熱や凝集を繰り返すため、膨大なエネルギーを要している。また、亜硫酸ガスの管理にコストがかかるなどの問題を有している。
【０００６】
一方、図４に示す原油の脱硫工程の重質ナフサの水素化精製に水素ガスが用いられるが、水素ガスは一般に図６及び図７に示すような方法で製造される。図６は、炭化水素ガス分解法と呼ばれる水素ガス製造方法を示す。この水素ガス製造方法では、パラフィンやエチレン、プロピレンを原料として、まずは硫黄化合物を除いた後、ニッケル触媒上で４００℃以上で水蒸気と反応させて水素、二酸化炭素、一酸化炭素を発生させ、ついで、水蒸気を加えて２００℃前後まで冷却し、一酸化鉄の触媒上を通して、一酸化炭素から二酸化炭素と水素を発生させた後、生成ガスを冷却し、ガーボトール法により二酸化炭素を除去して水素を得ている。
【０００７】
図７に示す水素ガス製造方法は、深冷水素精製法もしくは窒素洗浄法と呼ばれ、水素に富んだガスから水素を生成するもので、前述の炭化水素分解以外の工程から生成する粗ガスにも適用できる。この製造方法では、原料ガスを圧縮し、水酸化ナトリウムで洗浄して炭酸ガス、硫化水素などをまず除去する。次に、熱交換器で低温の精製水素ガスによって冷却し、メタン及びＣ４以上の炭化水素ガスを液化除去する。ついで、窒素洗浄塔において塔底から塔頂へ上昇させて塔頂から下降する液化窒素によって洗浄することによって、一酸化炭素及び窒素が液状で塔底から排出され、精製分離された水素が塔頂から取り出される。
【０００８】
これらの水素製造方法では、主に硫化水素などの硫黄化合物による触媒の被毒を避けるための精製工程を必要とし、また加熱や凝集を繰り返すために膨大なエネルギーを要している。
【０００９】
【発明が解決しようとする課題】
上述したように、従来の硫化水素処理方法や水素製造方法では、加熱や凝集を繰り返すために膨大なエネルギーを必要としている。したがって、簡便に硫化水素から硫黄と水素を取り出すことができれば、硫化水素の処理と水素の製造を同時に行うことができ、従来の硫化水素処理方法及び水素製造方法の問題を解決することができるとともに、取り出した水素を脱硫工程に使用することで、有用なケミカル・リサイクルを実現することができる。
【００１０】
本発明は、上記従来技術の問題点に対処してなされたもので、硫化水素から硫黄と水素を生成することができる高活性光触媒の製造方法を提供することを目的とする。
【００１１】
また、本発明は、高活性光触媒を用いて硫化水素から工業全般に有用な硫黄と水素を経済的な工程で効率よく回収することができる硫化水素処理方法を提供することを目的とする。
【００１２】
【課題を解決するための手段】
上述の目的を達成するため検討を行った結果、本発明者らは光触媒として知られる金属硫化物を酸化処理によって改質することが有効であることを見出した。金属硫化物としては、例えば亜鉛、カドミウム、水銀等の硫化物が挙げられるが、中でも硫化亜鉛が好適である。
【００１３】
金属硫化物の酸化処理方法としては、金属硫化物を液体中で酸化剤を用いて酸化する。酸化剤としては、過マンガン酸またはその塩（ＨＭｎＯ4 、ＭＭｎＯ4 ）を単独または二種以上混合して使用することができる。
【００１４】
このようにして金属硫化物を酸化して得られた光触媒は種々の反応促進に使用することができる。特に、硫化水素を含有する溶液に光触媒を添加することで、光触媒の酸化還元作用により硫化水素から硫黄と水素を回収することができる。
【００１５】
この光触媒による硫化水素処理方法は、次の（１）〜（３）の工程からなることが望ましい。すなわち、（１）中性またはアルカリ性の溶液に硫化水素を溶解する工程、（２）硫化水素の溶液に光触媒を添加し、紫外線等の光を照射して水素ガスを回収する工程、（３）水素ガス回収後の溶液から硫黄を回収し、硫黄回収後の溶液を硫化水素を溶解する溶液として（１）の工程に再循環する工程とで構成することができる。各工程の反応式は次式で表される。
【００１６】
【化２】
（１）Ｈ2Ｓ → Ｈ+ ＋ ＨＳ-
（２）２ＨＳ- → Ｈ2 ＋ Ｓ2 2-
（３）Ｓ2 2- → Ｓ2- ＋ Ｓ
【００１７】
光触媒である金属硫化物粒子は、酸化処理を行うことで金属硫化物の表面近傍と粒子内部とで硫黄原子、酸素原子、金属原子、酸化状態など何らかの濃度勾配が生じているものと考えられる。このため、光照射によって生じた自由電子と自由ホールは互いに離れる方向に移動し、自由電子と自由ホールの再結合が減少し、また酸化反応のサイトと還元反応のサイトが完全分離することから、酸化反応生成物と還元反応生成物との再結合を防ぐことができる。これによって、光照射によって生成した自由電子及び自由ホールが、目的とする酸化還元反応に有効に使われるので、本発明の方法によって酸化処理された金属硫化物粒子は高い光触媒活性を有する。
【００１８】
硫化亜鉛や硫化カドミウムのような金属硫化物粒子は、溶液中で用いると、それ自体の強い酸化力のために金属硫化物中の金属原子が金属酸イオンとなって溶解するという問題がある。したがって、本発明にかかる光触媒を使用する反応体系には硫化物イオンを共存させている。これにより、溶液中の硫化物イオンがポリ硫化物イオンに酸化されるため、金属硫化物中の金属原子が金属酸イオンとなって水溶液中に溶出することを防止でき、光触媒特性が劣化しない。なお、硫化物イオンを共存させる方法としては、中性またはアルカリ性の溶液中に硫化水素を溶かし込む方法や、硫化水素ナトリウム（ＮａＨＳ）や硫化ナトリウム（Ｎａ2Ｓ）のような硫化物イオンをもった塩を溶解する方法などが挙げられる。
【００１９】
【発明の実施の形態】
以下、本発明にかかる光触媒の製造方法及びその光触媒を用いた硫化水素の処理方法の実施の形態を説明する。本発明にかかる光触媒の製造方法の第１の実施の形態は、化合物半導体のうち金属硫化物、例えば亜鉛、カドミウムまたは水銀の硫化物を原料とし、これを酸化性雰囲気中で焼成するものである。
【００２０】
また、本発明にかかる光触媒の製造方法の第２の実施の形態は、前述の金属硫化物を溶液中で、過マンガン酸またはその塩の酸化剤により酸化処理するものである。
【００２１】
原料となる硫化亜鉛を生成する場合、亜鉛イオンを含む溶液と硫化水素の化学反応プロセスを用いるのが一般的であるが、このプロセスによって生じる硫化亜鉛は光触媒としての活性は乏しい。これに上記したいずれかの酸化処理を施すことで光触媒としての活性を著しく高めることができる。
【００２２】
図１は、本発明にかかる硫化水素の処理方法の一実施の形態を説明するための処理システムを概略的に示すもので、この処理システムは、硫化水素を溶解する硫化水素溶解槽１と、硫化水素を溶解した溶液から水素ガスを回収する光触媒反応槽３と、水素ガス回収後の溶液から硫黄を回収し、硫黄回収後の溶液を硫化水素溶解槽１へリサイクルする硫黄回収槽５とで構成されている。
【００２３】
上記構成において、硫化水素溶解槽１は中性またはアルカリ性の溶液を収容し、この中に硫化水素ガスが導入され、溶解される。中性またはアルカリ性の溶液は、硫化水素の溶解・解離と反応の場の提供を行うだけで、それ自体の変化は起こらない。ここでは水酸化ナトリウム水溶液を例に挙げて説明するが、硫化水素を溶解・解離させる液体であれば水溶液に限らない。すなわち、メタノール、エタノールなども利用可能である。
【００２４】
硫化水素溶解槽１内において、水酸化ナトリウム水溶液に硫化水素ガスが混入されると、次式に示すような中和反応が起こり、硫化水素ガスは水酸化ナトリウム水溶液に溶解し、硫化ナトリウム溶液となる。
【００２５】
【化３】
２ＮａＯＨ ＋ Ｈ2Ｓ → Ｎａ2Ｓ ＋ ２Ｈ2Ｏ
【００２６】
硫化ナトリウム溶液は光触媒反応槽３に送られ、ここで本発明にかかる光触媒が添加され、紫外線光源７から紫外線が照射されると、次式に示すように、水素ガスとポリ硫化物イオンが生成し、水素ガスが回収される。
【００２７】
【化４】
２Ｓ2- → Ｓ2 2- ＋ ２ｅ-
２Ｈ+ ＋ ２ｅ- → Ｈ2↑
【００２８】
この溶液系にて硫化水素の溶解と水素発生を続けると、ポリ硫化物イオンはその溶解度を越えてしまい、ついには不均化反応（自己酸化還元反応）を起こして、次式に示すように、硫黄と硫化物イオンに変化する。
【００２９】
【化５】
Ｓ2 2- → Ｓ2- ＋ Ｓ
【００３０】
硫黄回収槽５では、上記不均化反応を利用してポリ硫化物イオンを硫黄として回収する。硫黄を回収された溶液は水酸化ナトリウムに戻るため、硫化水素を溶解するための溶液として再利用される。
【００３１】
上記の説明からも明らかなように、本実施の形態においては、光触媒により硫化水素を分解することで、クラウス法と同様に硫黄を回収することができ、しかも脱硫工程で消費される水素を供給することができる。さらに、この硫化水素処理方法では、クラウス法のような加熱及び凝集など多くのエネルギーを必要とする操作を省くことができ、しかも硫化水素よりもさらに危険な亜硫酸ガスが関与しないという点で非常に優れている。
【００３２】
【実施例】
以下、本発明を実施例についてさらに詳細に説明する。まず、光触媒としての試料を３種類、以下のようにして作製した。
【００３３】
実施例１
高純度化学社製硫化亜鉛（純度９９．９９９％以上）１０．０ｇを、電気炉で１０００℃の設定温度で１時間焼成した。この際、酸化性雰囲気とするために酸素ガスを流量１０ｍｌ／分で流した。これを乳鉢で擦って微粒子状にした。
【００３４】
実施例２
高純度化学社製硫化亜鉛（純度９９．９９９％以上）１０．０ｇを、０．１Ｎの過マンガン酸カリウム溶液１００ｍｌ中に投入し、５分間超音波洗浄機にかけた。その後、硫化亜鉛をろ過し、純水で洗浄し、一般環境（約２５℃、６０ＲＨ％）にて乾燥させた。これを乳鉢で擦って微粒子状にした。
【００３５】
比較例
高純度化学社製硫化亜鉛（純度９９．９９９％以上）１０．０ｇを乳鉢で擦って微粒子状にした。
【００３６】
次に、上記試料について光触媒としての活性を調べるため、図２に示すような装置を用いて、光触媒による水素発生の実験を行った。この装置は、図２に示すように、石英ガラス製の光反応部分１１と、発生した水素ガスの定量を行う水素定量部分１３と、水素ガス発生によって装置内の圧力が上昇することを防ぐための溶液溜１５と、紫外線照射用の５００Ｗ水銀灯（図示省略）と、紫外線１７を集光するための集光レンズ１９と、紫外線１７を光触媒に照射するための反射鏡２１とで構成されている。操作は、初めに系全体を硫化ナトリウム水溶液で満たし、一定量の光触媒を光反応部分１１の底に沈殿させ、ガス抜き栓２３を閉じた後、５００Ｗ水銀灯を点灯し、水素定量部分１３で一定照射時間ごとに水素発生量を測定するものである。本実験では、光触媒の量は各試料とも５０ｍｇ、硫化ナトリウム水溶液は０．１モル／ｌ、１４０ｍｌ使用した。なお、参考例として、光触媒を投入しないで、紫外線照射のみの水素発生量も測定した。
【００３７】
実施例１、実施例２、比較例の各試料を光触媒にして上記実験を行った結果を表１及び図３に示す。なお、図３において、実線ａは実施例１を添加したときの水素発生量を、実線ｂは比較例を添加したときの水素発生量を、破線ｃは参考例の水素発生量を示す。
【００３８】
【表１】

Figure 0005106721
【００３９】
表１及び図３からも明らかなように、実施例１、２の光触媒は、比較例の光触媒に比べて触媒活性が格段に高いことを示している。また、光触媒なしの参考例は比較例と比べて水素発生量がほとんど変わらなかった。このことから、元の硫化亜鉛は光触媒活性に乏しいが、前述の酸化処理を施すことによって硫化亜鉛の性状が変化し、Ｈ+ とＳＨ- を酸化還元反応により水素とポリ硫化物イオンにする触媒としての活性が高まっていることが判る。
【００４０】
このような酸化処理によって高い触媒活性が得られる理由は、硫化亜鉛の硫黄原子の一部が酸素原子に置換され、その割合は粒子表面ほど高くなるという連続的な組成の変化のため、空間電荷が発生し、粒子の深さ方向に電界が発生しているためと考えられる。この電界により、自由電子と自由ホールが互いに離れる方向に移動するため、自由電子と自由ホールの再結合が低減し、また酸化反応の反応場所と還元反応の反応場所も離れることから、酸化反応生成物と還元反応生成物との再結合が抑制され、触媒活性が高くなると考えられる。
【００４１】
上記の説明からも明らかなように、硫化亜鉛のような金属硫化物に前述の酸化処理を施すことによって、高活性光触媒を得ることができる。そして、この高活性光触媒を硫化水素の処理に用いることで、環境有害物質である硫化水素を原料として、光源に必要なエネルギー以外のエネルギーを要することなく、かつ亜硫酸ガスのような有害物質を発生することなく、有用な硫黄と水素を製造することができる。また、光源として太陽光を利用すれば、さらに処理コストを低減することも可能である。さらに、この高活性光触媒を用いた硫化水素処理方法を原油などの脱硫工程に適用すれば、脱硫工程で生じた硫化水素を原料に水素を発生し、ここで生じた水素を再度脱硫工程に使用することができ、非常に経済的な脱硫プロセスを実現することができる。
【００４２】
【発明の効果】
上述したように、請求項１及び２の発明によれば、亜鉛、カドミウムまたは水銀の硫化物から選ばれる金属硫化物を液相中で酸化処理することにより、廉価で寿命の長い光触媒を得ることができ、この光触媒により硫化水素から硫黄と水素を効率よく回収することができるようになる。
【００４３】
また、請求項３及び４の発明によれば、硫化水素を光触媒を用いて処理することにより、環境有害物質である硫化水素を原料として、簡単な工程で、亜硫酸ガスのような有害物質を発生することなく、工業全般に有用な硫黄と水素を効率よく安価に生成することができる。さらに、この光触媒を用いた硫化水素の処理方法を原油などの脱硫工程に適用すれば、硫化水素の処理によって生じた水素を再度脱硫工程に使用することができ、極めて有用なケミカル・リサイクルが可能となる。
【図面の簡単な説明】
【図１】本発明の一実施の形態にかかる硫化水素の処理システムを概略的に示す図である。
【図２】本発明にかかる高活性光触媒の活性を調べるための実験装置を示す図である。
【図３】本発明にかかる高活性光触媒の活性を示す図である。
【図４】一般的な原油の脱硫工程を概略的に示す図である。
【図５】硫化水素の処理方法の従来技術（クラウス法）を例示する図である。
【図６】水素製造方法の従来技術（炭化水素ガス分解法）を例示する図である。
【図７】水素製造方法の従来技術（深冷水素精製法もしくは窒素洗浄法）を例示する図である。
【符号の説明】
１……硫化水素溶解槽、３……光触媒反応槽、５……硫黄回収槽、７……紫外線光源、１１……光反応部分、１３……水素定量部分、１５……溶液溜、１７……紫外線、１９……集光レンズ、２１……反射鏡、２３……ガス抜き栓[0001]
BACKGROUND OF THE INVENTION
The present invention is used in the chemical industry field for producing chemical substances such as hydrogen and sulfur, the chemical industry field for treating hydrogen sulfide generated in the desulfurization process, and the environmental conservation field for removing malodorous substances and air pollutants. The present invention relates to a technique for producing a highly active photocatalyst that can be used, and a technique for using the same.
[0002]
[Prior art]
The application of photocatalytic technology has begun to be put into practical use by utilizing characteristics that promote various chemical reactions, such as decomposition of environmental pollutants, malodorous components and bacteria. Examples include antibacterial tiles used in hospital operating rooms, filters for air purifiers and air conditioners, and glass for lighting on highways. While these photocatalysts have been put into practical use using the ability to promote oxidation, research aimed at obtaining hydrogen by acting a photocatalyst on water, etc., and fixing carbon by acting on carbon dioxide gas has also been conducted. Yes. The application of the photocatalyst is not limited to this, and it is also possible to obtain a useful chemical substance by causing the photocatalyst to act on a harmful substance. For example, it can be considered that it is applied to a desulfurization process of petroleum refining or metal smelting.
[0003]
Fig. 4 shows the process of desulfurization of crude oil, which is generally performed at present. When distilling crude oil, hydrorefining heavy naphtha to convert all sulfur contained in the crude oil to hydrogen sulfide. Collected. Further, as shown in FIG. 5, the hydrogen sulfide generated here is oxidized to recover sulfur through a process called Claus method. This Claus method is a process in which one third of hydrogen sulfide is oxidized to sulfurous acid gas, and this is reacted with the remaining hydrogen sulfide to form sulfur. That is, the chemical formula is expressed as follows.
[0004]
[Chemical 1]
2H 2 S + 3O 2 → 2H 2 O + 2SO 2
4H 2 S + 2SO 2 → 4H 2 O + 6S
[0005]
This sulfur recovery process requires enormous energy because it repeats not only the catalytic reaction of sulfurous acid gas and hydrogen sulfide but also heating and aggregation. In addition, there is a problem such as costly management of sulfurous acid gas.
[0006]
On the other hand, hydrogen gas is used in the hydrorefining of heavy naphtha in the crude oil desulfurization process shown in FIG. 4, and hydrogen gas is generally produced by the method shown in FIGS. FIG. 6 shows a hydrogen gas production method called a hydrocarbon gas decomposition method. In this hydrogen gas production method, paraffin, ethylene, and propylene are used as raw materials. First, sulfur compounds are removed, and then reacted with water vapor at 400 ° C. or higher on a nickel catalyst to generate hydrogen, carbon dioxide, and carbon monoxide. Then, steam is added to cool to around 200 ° C., carbon dioxide and hydrogen are generated from carbon monoxide through an iron monoxide catalyst, the product gas is cooled, carbon dioxide is removed by the garbotol method, and hydrogen is removed. Have gained.
[0007]
The hydrogen gas production method shown in FIG. 7 is called a cryogenic hydrogen refining method or a nitrogen cleaning method, which produces hydrogen from a gas rich in hydrogen. Is also applicable. In this manufacturing method, the raw material gas is compressed and washed with sodium hydroxide to first remove carbon dioxide, hydrogen sulfide, and the like. Next, it cools with the low temperature refinement | purification hydrogen gas with a heat exchanger, and liquefies and removes methane and C4 or more hydrocarbon gas. Next, in the nitrogen scrubber tower, the carbon monoxide and nitrogen are discharged from the tower bottom in a liquid state by being raised from the tower bottom to the tower top and washed with liquefied nitrogen descending from the tower top, and the purified and separated hydrogen is removed from the tower top. Taken from.
[0008]
These hydrogen production methods require a purification step to avoid poisoning of the catalyst mainly by sulfur compounds such as hydrogen sulfide, and enormous amounts of energy are required to repeat heating and aggregation.
[0009]
[Problems to be solved by the invention]
As described above, the conventional hydrogen sulfide treatment method and hydrogen production method require enormous energy in order to repeat heating and aggregation. Therefore, if sulfur and hydrogen can be easily extracted from hydrogen sulfide, the treatment of hydrogen sulfide and the production of hydrogen can be performed simultaneously, and the problems of the conventional hydrogen sulfide treatment method and the hydrogen production method can be solved. By using the extracted hydrogen in the desulfurization process, useful chemical recycling can be realized.
[0010]
The present invention has been made in response to the above-mentioned problems of the prior art, and an object thereof is to provide a method for producing a highly active photocatalyst capable of generating sulfur and hydrogen from hydrogen sulfide.
[0011]
Another object of the present invention is to provide a method for treating hydrogen sulfide that can efficiently recover sulfur and hydrogen useful for the whole industry from hydrogen sulfide in an economical process using a highly active photocatalyst.
[0012]
[Means for Solving the Problems]
As a result of studies to achieve the above-mentioned object, the present inventors have found that it is effective to modify a metal sulfide known as a photocatalyst by oxidation treatment. Examples of the metal sulfide include sulfides such as zinc, cadmium, and mercury. Among them, zinc sulfide is preferable.
[0013]
As the oxidation treatment method of a metal sulfide, a metallic sulfide acid by using an oxidizing agent in a liquid. As the oxidizing agent, permanganic acid or a salt thereof (HMnO 4 , MMnO 4 ) can be used alone or in combination of two or more.
[0014]
In this way, the photocatalyst obtained by oxidizing the metal sulfide can be used in various reactions promoted. In particular, by adding a solution to the photocatalyst containing hydrogen sulfide, the oxidation-reduction action of the photocatalyst can be recovered sulfur and hydrogen from the hydrogen sulfide.
[0015]
Hydrogen sulfide processing method by the photocatalyst of this may be formed of the following steps (1) to (3). That is, (1) dissolving the neutral or alkaline solution of hydrogen sulfide, (2) recovering the hydrogen gas into a solution of hydrogen sulfide by adding a photocatalyst is irradiated with light such as ultraviolet rays, (3 ) Sulfur is recovered from the solution after the hydrogen gas recovery, and the solution after the sulfur recovery is recirculated to the step (1) as a solution for dissolving hydrogen sulfide. The reaction formula of each process is represented by the following formula.
[0016]
[Chemical 2]
(1) H 2 S → H + + HS −
(2) 2HS - → H 2 + S 2 2-
(3) S 2 2- → S 2- + S
[0017]
It is considered that the metal sulfide particles that are photocatalysts are subjected to oxidation treatment to cause some concentration gradients such as sulfur atoms, oxygen atoms, metal atoms, and oxidation states between the surface of the metal sulfide and inside the particles. For this reason, the free electrons and free holes generated by light irradiation move away from each other, the recombination of free electrons and free holes is reduced, and the oxidation reaction site and the reduction reaction site are completely separated. Recombination between the oxidation reaction product and the reduction reaction product can be prevented. As a result, free electrons and free holes generated by light irradiation are effectively used for the target redox reaction, so that the metal sulfide particles oxidized by the method of the present invention have high photocatalytic activity.
[0018]
When metal sulfide particles such as zinc sulfide and cadmium sulfide are used in a solution, there is a problem that metal atoms in the metal sulfide are dissolved as metal acid ions due to their strong oxidizing power. Therefore, the reaction system that uses a photocatalyst that written to the present invention is allowed to coexist sulfide ions. As a result, sulfide ions in the solution are oxidized to polysulfide ions, so that metal atoms in the metal sulfide can be prevented from being eluted into the aqueous solution as metal acid ions, and the photocatalytic properties are not deteriorated. In addition, as a method for allowing sulfide ions to coexist, a method in which hydrogen sulfide is dissolved in a neutral or alkaline solution, or a sulfide ion such as sodium hydrogen sulfide (NaHS) or sodium sulfide (Na 2 S) is used. And a method of dissolving the salt.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the processing method of the hydrogen sulfide using the manufacturing method and its photocatalytic photocatalyst that written to the present invention. The first embodiment of a method for manufacturing a photocatalyst that written in the present invention, a metal sulfide of the compound semiconductor, for example, zinc, sulfide cadmium or mercury as a raw material, firing them in an oxidizing atmosphere Is.
[0020]
The second embodiment of the manufacturing method of a photocatalyst that written in the present invention, in a solution of the foregoing metal sulfides, is intended to oxidation treatment with an oxidizing agent of permanganic acid or a salt thereof.
[0021]
When producing zinc sulfide as a raw material, it is common to use a chemical reaction process of a solution containing zinc ions and hydrogen sulfide, but the zinc sulfide produced by this process is poor in activity as a photocatalyst. The activity as a photocatalyst can be remarkably enhanced by subjecting this to any of the oxidation treatments described above.
[0022]
FIG. 1 schematically shows a treatment system for explaining an embodiment of a method for treating hydrogen sulfide according to the present invention. This treatment system comprises a hydrogen sulfide dissolution tank 1 for dissolving hydrogen sulfide, A photocatalytic reaction tank 3 that recovers hydrogen gas from a solution in which hydrogen sulfide is dissolved, and a sulfur recovery tank 5 that recovers sulfur from the solution after hydrogen gas recovery and recycles the solution after sulfur recovery to the hydrogen sulfide dissolution tank 1. It is configured.
[0023]
In the above configuration, the hydrogen sulfide dissolution tank 1 contains a neutral or alkaline solution, into which hydrogen sulfide gas is introduced and dissolved. Neutral or alkaline solutions only provide dissolution / dissociation and dissociation of hydrogen sulfide and provide a reaction field, and do not change themselves. Here, an aqueous sodium hydroxide solution will be described as an example. That is, methanol, ethanol, etc. can also be used.
[0024]
In the hydrogen sulfide dissolution tank 1, when hydrogen sulfide gas is mixed into the sodium hydroxide aqueous solution, a neutralization reaction as shown in the following formula occurs, and the hydrogen sulfide gas is dissolved in the sodium hydroxide aqueous solution, Become.
[0025]
[Chemical 3]
2NaOH + H 2 S → Na 2 S + 2H 2 O
[0026]
Sodium sulfide solution is sent to the photocatalytic reaction vessel 3, wherein the photocatalyst that written to the present invention is added, the ultraviolet rays are irradiated from the ultraviolet light source 7, as shown in the following equation, hydrogen gas and polysulphides Ions are generated and hydrogen gas is recovered.
[0027]
[Formula 4]
2S 2- → S 2 2- + 2e -
2H + + 2e - → H 2 ↑
[0028]
If dissolution of hydrogen sulfide and generation of hydrogen continue in this solution system, polysulfide ions will exceed their solubility and eventually cause a disproportionation reaction (auto-redox reaction), as shown in the following equation: , Changes to sulfur and sulfide ions.
[0029]
[Chemical formula 5]
S 2 2- → S 2- + S
[0030]
In the sulfur recovery tank 5, polysulfide ions are recovered as sulfur using the above disproportionation reaction. Since the solution from which sulfur is recovered returns to sodium hydroxide, it is reused as a solution for dissolving hydrogen sulfide.
[0031]
As is apparent from the above description, in this embodiment, to decompose the hydrogen sulfide by the photocatalytic can be recovered sulfur like the Claus process, yet the hydrogen consumed in the desulfurization step Can be supplied. Furthermore, in this hydrogen sulfide treatment method, operations that require a lot of energy such as heating and coagulation as in the Claus method can be omitted, and in addition, sulfur dioxide gas, which is more dangerous than hydrogen sulfide, is not involved. Are better.
[0032]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. First, three types of samples as photocatalysts were prepared as follows.
[0033]
Example 1
10.0 g of zinc sulfide (purity 99.999% or more) manufactured by Kojundo Chemical Co., Ltd. was baked for 1 hour at a set temperature of 1000 ° C. in an electric furnace. At this time, oxygen gas was flowed at a flow rate of 10 ml / min in order to obtain an oxidizing atmosphere. This was rubbed with a mortar to form fine particles.
[0034]
Example 2
10.0 g of zinc sulfide (purity: 99.999% or more) manufactured by Kojundo Chemical Co., Ltd. was put into 100 ml of a 0.1 N potassium permanganate solution and subjected to an ultrasonic cleaner for 5 minutes. Then, zinc sulfide was filtered, washed with pure water, and dried in a general environment (about 25 ° C., 60 RH%). This was rubbed with a mortar to form fine particles.
[0035]
Comparative Example 10.0 g of zinc sulfide (purity 99.999% or higher) manufactured by Kojun Chemical Co., Ltd. was rubbed with a mortar to form fine particles.
[0036]
Next, in order to investigate the activity of the above sample as a photocatalyst, an experiment of hydrogen generation by the photocatalyst was performed using an apparatus as shown in FIG. As shown in FIG. 2, this apparatus prevents the pressure in the apparatus from rising due to the generation of hydrogen gas, the photoreaction part 11 made of quartz glass, the hydrogen determination part 13 for quantifying the generated hydrogen gas, and the hydrogen gas generation. , A 500 W mercury lamp (not shown) for ultraviolet irradiation, a condensing lens 19 for condensing the ultraviolet light 17, and a reflecting mirror 21 for irradiating the photocatalyst with the ultraviolet light 17. . In the operation, the entire system is first filled with an aqueous sodium sulfide solution, a certain amount of photocatalyst is precipitated at the bottom of the photoreactive portion 11, the gas vent 23 is closed, a 500 W mercury lamp is turned on, and the hydrogen quantifying portion 13 is constant. The amount of hydrogen generation is measured for each irradiation time. In this experiment, the amount of the photocatalyst was 50 mg for each sample, and the sodium sulfide aqueous solution was 0.1 mol / l, 140 ml. As a reference example, the amount of hydrogen generated only by ultraviolet irradiation was also measured without introducing a photocatalyst.
[0037]
Table 1 and FIG. 3 show the results of the above experiment using the samples of Example 1, Example 2, and Comparative Example as photocatalysts. In FIG. 3, the solid line a indicates the hydrogen generation amount when Example 1 is added, the solid line b indicates the hydrogen generation amount when the comparative example is added, and the broken line c indicates the hydrogen generation amount of the reference example.
[0038]
[Table 1]
Figure 0005106721
[0039]
As is clear from Table 1 and FIG. 3, the photocatalysts of Examples 1 and 2 have much higher catalytic activity than the photocatalyst of the comparative example. Further, in the reference example without the photocatalyst, the hydrogen generation amount was hardly changed as compared with the comparative example. For this reason, the original zinc sulfide is poor in photocatalytic activity, but the properties of zinc sulfide are changed by the above-described oxidation treatment, and H + and SH - are converted into hydrogen and polysulfide ions by oxidation-reduction reaction. It can be seen that the activity is increasing.
[0040]
The reason why a high catalytic activity is obtained by such an oxidation treatment is that space charges are caused by a continuous compositional change in which a part of the sulfur atoms of zinc sulfide is replaced by oxygen atoms, and the proportion thereof becomes higher as the particle surface. This is probably because an electric field is generated in the depth direction of the particles. This electric field causes the free electrons and free holes to move away from each other, reducing the recombination of free electrons and free holes, and also separating the reaction site for the oxidation reaction and the reaction site for the reduction reaction. It is considered that the recombination between the product and the reduction reaction product is suppressed, and the catalytic activity is increased.
[0041]
As is clear from the above description, a highly active photocatalyst can be obtained by subjecting a metal sulfide such as zinc sulfide to the oxidation treatment described above. By using this highly active photocatalyst for the treatment of hydrogen sulfide, hydrogen sulfide, which is an environmentally hazardous substance, is used as a raw material, and no harmful energy such as sulfurous acid gas is generated without requiring energy other than that required for the light source. Without having to do so, useful sulfur and hydrogen can be produced. Further, if sunlight is used as the light source, the processing cost can be further reduced. Furthermore, if this hydrogen sulfide treatment method using a highly active photocatalyst is applied to a desulfurization process such as crude oil, hydrogen is generated from the hydrogen sulfide generated in the desulfurization process, and the hydrogen generated here is used again in the desulfurization process. And a very economical desulfurization process can be realized.
[0042]
【Effect of the invention】
As described above, according to the invention of claim 1 and 2, zinc, by oxidizing the metal sulfide selected from sulfide cadmium or mercury in the liquid phase, to obtain a long photocatalyst life inexpensive This photocatalyst makes it possible to efficiently recover sulfur and hydrogen from hydrogen sulfide.
[0043]
In addition, according to the inventions of claims 3 and 4 , by processing hydrogen sulfide using a photocatalyst, harmful substances such as sulfurous acid gas are generated in a simple process using hydrogen sulfide, which is an environmentally hazardous substance, as a raw material. Therefore, it is possible to efficiently and inexpensively produce sulfur and hydrogen useful for the entire industry. In addition, if this hydrogen sulfide treatment method using photocatalyst is applied to desulfurization processes such as crude oil, the hydrogen generated by the treatment of hydrogen sulfide can be used again in the desulfurization process, enabling extremely useful chemical recycling. It becomes.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a hydrogen sulfide treatment system according to an embodiment of the present invention.
FIG. 2 is a diagram showing an experimental apparatus for examining the activity of a highly active photocatalyst according to the present invention.
FIG. 3 is a diagram showing the activity of a highly active photocatalyst according to the present invention.
FIG. 4 is a diagram schematically showing a general crude oil desulfurization process.
FIG. 5 is a diagram illustrating a conventional technique (Klaus method) of a method for treating hydrogen sulfide.
FIG. 6 is a diagram illustrating a conventional technique (hydrocarbon gas decomposition method) of a hydrogen production method.
FIG. 7 is a diagram illustrating a conventional technique for hydrogen production (deep cold hydrogen refining method or nitrogen cleaning method).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Hydrogen sulfide dissolution tank, 3 ... Photocatalytic reaction tank, 5 ... Sulfur recovery tank, 7 ... Ultraviolet light source, 11 ... Photoreaction part, 13 ... Hydrogen determination part, 15 ... Solution reservoir, 17 ... ... UV, 19 ... Condenser lens, 21 ... Reflector, 23 ... Degassing tap

Claims (4)

亜鉛、カドミウムまたは水銀の硫化物から選ばれる金属硫化物を過マンガン酸またはその塩により酸化処理してなることを特徴とする光触媒の製造方法。  A method for producing a photocatalyst comprising oxidizing a metal sulfide selected from zinc, cadmium or mercury sulfide with permanganic acid or a salt thereof. 金属硫化物が硫化亜鉛であることを特徴とする請求項１記載の光触媒の製造方法。The process according to claim 1 Symbol placement of the photocatalyst, wherein the metal sulphide is zinc sulphide. 硫化水素を含有する溶液中に、請求項１又は２に記載の方法により製造された光触媒を添加して水素と硫黄を回収することを特徴とする光触媒を用いた硫化水素の処理方法。A method for treating hydrogen sulfide using a photocatalyst, wherein the photocatalyst produced by the method according to claim 1 or 2 is added to a solution containing hydrogen sulfide to recover hydrogen and sulfur. 中性またはアルカリ性の溶液に硫化水素を溶解する第１の工程と、該硫化水素溶解後の溶液に請求項１又は２に記載の方法により製造された光触媒を添加し、光を照射して水素ガスを回収する第２の工程と、該水素ガス回収後の溶液から硫黄を回収する第３の工程とを備え、前記第３の工程における硫黄回収後の溶液を前記第１の工程の溶液として再利用することを特徴とする硫化水素の処理方法。A first step of dissolving hydrogen sulfide in a neutral or alkaline solution, and adding the photocatalyst produced by the method of claim 1 or 2 to the solution after dissolving the hydrogen sulfide, and irradiating light to generate hydrogen A second step of recovering the gas and a third step of recovering sulfur from the solution after the recovery of the hydrogen gas, and the solution after the recovery of sulfur in the third step is used as the solution of the first step A method for treating hydrogen sulfide, which is reused.
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