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Photocatalytic production of a stoichiometric mixture of hydrogen and oxygen from an aqueous carbonate solution
N31
Caprolactam IS a commerciaiiy rmportant product whose productron, 1 36 brllron lb n 1992, ranks 46th among all chemicals produced in the Unrted States It IS used n the manufacture of synthetic fibers (especraiiy nylon 6) and in many other appilcatrons The production of caproiactam involves several steps, the final step being the Beckmann rearrangement of cyclohexanone oxrme to caprolactam The tradrtronai commercial process for this step uses storchiometnc quantities of sulfuric acid, resuitng In the formation of large amounts of ammonium suifate byproduct (1 2 to 5 tons per ton of caproiactam product, depending on the particular version of the process) Hence, this process IS coming under severe environmental scrutiny, and a new process based on a solid acid catalyst would be highly desirable However, the marn problem wrth the Beckmann rearrangement in the gas phase over sold catalysts has been catalyst deactrvatron resulting from pore clogging by coke deposition If this problem could be solved, this reaction would become a more attractive, environmentally superior alternative to the current technoiogy Two recent papers discuss the progress towards this goal T Curtin, J B McMonagie and B K Hodnett (Catai Lett, 17 (1993) 145) studied a range of alumrnas modrfied by sodrum, phosphate, sulfate, chionde, and bona for the Beckmann rearrangement of cyclohexanone oxrme to caprolactam at 300450°C These investigators found a strong posttrve correlation between the selectivity to caproiactam and the surface concentration of srte.$of intermediate acid strength Among ail the catalysts tested, the highest selactrvrty, about 75%, was obtained wrth a 20 wt -% bona/alumna catalyst
applied catalysis B: environmental
Zeolrtes have also been tested for caprolactam production but have not been used commercially J S Reddy, R Rawshankar, S Srvasanker and P Ratnasamy (Catai Lett , 17 (1663) 139) tested various MEL zedltes and molecular sieves (which have the framework structure of ZSM-11) including s~l~cairte-2,TS-2, ZSM-11, and Al-TS-2, as well as fumed srlrca The expenmen& were performed at atmosphenc pressure In a vertical down-flow tubular silica reactor containing 1 g of catalyst of l-2 mm particle size The feed was 6 wt -% cyciohexanone oxrme in benzene TS-2 gave a selectivity to caprolactam of about 60% at 166% conversion, and tt was the most resrstant to deactrvation throughout the expenmental temperature range (276-340°C)
Photocatalytic Production of a Stoichiometric Mixture of Hydrogen and Oxygen from an Aqueous Carbonate Solutlon
Photocataiytrc decomposrtron of water into hydrogen and oxygen IS one of the ultimate solutions to energy and global environmental problems The major targets in research on this subject might be, a complete decomposrtion of water into hydrogen and oxygen, and secondly to use the visible part of the solar spectrum Up to now, most of the studies on photocataiysrs have been drrected toward the decomposnron of organic compounds But the recent work of Domen et al (J Catai ,120 (1666) 337) on potassium nrobates wrth layered structure has demonstrated, for the first trme, the detectable perfect decomposrtron of water Also, qurte recently, Sayama and Arakawa of the National Instrtute of Matenai and Chemrcai Research in Tsukuba, Japan, have reVoiume3No
4-24MaylW4
ported that the additron of carbonate species makes rt possible to decompose water untohydrogen and oxygen even wrth TIO* and ZrOn (Shokubar (Catalyst) 35 (1663) 142-145,356356) In the case of TIOn, Pt or RuO? IS normally loaded to actrvate the surface reaction of water with photoexcrted holes and electrons However, these catalysts also enhance the recombination reaction of produced hydrogen with oxygen resulting In the photoregeneration of mainly hydrogen wdhout detectable production of oxygen They have found that the addrtion of sodium carbonate to a Pt-Ti02 suspension, at a concentration close to saturation (2 2 mol/dm3, pH=lO 6) drastically increases the production rate of hydrogen and oxygen in a ratio of 2 1 (Chem Lett , (1662) 253, J Chem Sot, Chem Commun, (1662) 156) What IS Interesting tnZrOgis that without metal or metal oxide loading It can photocatalytically decompose water into a stoichiometnc mtxture of hydrogen and oxygen In this case, the highest efficiency IS obtained in an aqueous solution of 0 63 mol/dm3 NaHC03 at pH =6 4 The surprisingly large effect of carbonate addrtion is explained mainly by the suppression of the photoadsorption of oxygen on the photosensrtive oxide caused by carbonate formatron on the surface MASATAKE HARUTA
Recycling of Rubber Products
Vol 26, 1664 of ES&T features reports of two new technologies which have been developedto tackle recycling of rubber products, especially automobile tyres Of the 235 million tyres dumped annually applied catalysis 8: envlronmental
in the United States only 17% are recycled or burned for energy The rest end up in landfills Studies by Japanese researchers indicate that cured rubbers may be decomposed in supercntical water to potentially recyclable hydrocarbons Toshrnan Tennoh (Nishikawa Rubber Co, Hrroshima) and his colleagues claim that rubber treated at temperatures above 466°C in the presence of 1 M NaOH will decompose within 15 min into mainly c2 carbon aliphatic and olefin hydrocarbons The sulfur IS converted to Ha, which in turn reacts with ZnO in the rubber to form ZnS Meanwhile, EC02, Inc (Hawthorne, FL), has received approval to operate a tyre pyrolysis reactor The company shredstyres “crumb rubber”, separating out the steel and the cotton from the tyre The crumb rubber IS sold for other uses or converted via pyrolysls into fuel oil and carbon black Methane IS collected from the pyrotysa and used to fuel the reactor
Solvent Users Face tiefty 8111:EC Sotvent Emluione Directhre
The final draft of the EC directtve on solvent emissions IS due for decision in 1663 The chemical industry has achieved some success in reducing rts number of prescriptive rules However, there IS still major concern over the cost of implementatron, estimated at Ecu 2 bn (62 4 bn)/y, wnh several years at Ecu 3 bn/y The directrve applies to processes not covered by the Integrated Pollution Prevention and Control Directive but which use 2 tonnes& of solvent Those using over 3775 tonnes/y of VOCs will have to obtain permits to operate under IPPC legislation At the other end of the scale, the EC is considering a VOC directive covering usage under 2 tonnes/y and domestic solvent use The Volume 3 No 4 -24May1664
Caprolactam IS a commerciaiiy rmportant product whose productron, 1 36 brllron lb n 1992, ranks 46th among all chemicals produced in the Unrted States It IS used n the manufacture of synthetic fibers (especraiiy nylon 6) and in many other appilcatrons The production of caproiactam involves several steps, the final step being the Beckmann rearrangement of cyclohexanone oxrme to caprolactam The tradrtronai commercial process for this step uses storchiometnc quantities of sulfuric acid, resuitng In the formation of large amounts of ammonium suifate byproduct (1 2 to 5 tons per ton of caproiactam product, depending on the particular version of the process) Hence, this process IS coming under severe environmental scrutiny, and a new process based on a solid acid catalyst would be highly desirable However, the marn problem wrth the Beckmann rearrangement in the gas phase over sold catalysts has been catalyst deactrvatron resulting from pore clogging by coke deposition If this problem could be solved, this reaction would become a more attractive, environmentally superior alternative to the current technoiogy Two recent papers discuss the progress towards this goal T Curtin, J B McMonagie and B K Hodnett (Catai Lett, 17 (1993) 145) studied a range of alumrnas modrfied by sodrum, phosphate, sulfate, chionde, and bona for the Beckmann rearrangement of cyclohexanone oxrme to caprolactam at 300450°C These investigators found a strong posttrve correlation between the selectivity to caproiactam and the surface concentration of srte.$of intermediate acid strength Among ail the catalysts tested, the highest selactrvrty, about 75%, was obtained wrth a 20 wt -% bona/alumna catalyst
applied catalysis B: environmental
Zeolrtes have also been tested for caprolactam production but have not been used commercially J S Reddy, R Rawshankar, S Srvasanker and P Ratnasamy (Catai Lett , 17 (1663) 139) tested various MEL zedltes and molecular sieves (which have the framework structure of ZSM-11) including s~l~cairte-2,TS-2, ZSM-11, and Al-TS-2, as well as fumed srlrca The expenmen& were performed at atmosphenc pressure In a vertical down-flow tubular silica reactor containing 1 g of catalyst of l-2 mm particle size The feed was 6 wt -% cyciohexanone oxrme in benzene TS-2 gave a selectivity to caprolactam of about 60% at 166% conversion, and tt was the most resrstant to deactrvation throughout the expenmental temperature range (276-340°C)
Photocatalytic Production of a Stoichiometric Mixture of Hydrogen and Oxygen from an Aqueous Carbonate Solutlon
Photocataiytrc decomposrtron of water into hydrogen and oxygen IS one of the ultimate solutions to energy and global environmental problems The major targets in research on this subject might be, a complete decomposrtion of water into hydrogen and oxygen, and secondly to use the visible part of the solar spectrum Up to now, most of the studies on photocataiysrs have been drrected toward the decomposnron of organic compounds But the recent work of Domen et al (J Catai ,120 (1666) 337) on potassium nrobates wrth layered structure has demonstrated, for the first trme, the detectable perfect decomposrtron of water Also, qurte recently, Sayama and Arakawa of the National Instrtute of Matenai and Chemrcai Research in Tsukuba, Japan, have reVoiume3No
4-24MaylW4
ported that the additron of carbonate species makes rt possible to decompose water untohydrogen and oxygen even wrth TIO* and ZrOn (Shokubar (Catalyst) 35 (1663) 142-145,356356) In the case of TIOn, Pt or RuO? IS normally loaded to actrvate the surface reaction of water with photoexcrted holes and electrons However, these catalysts also enhance the recombination reaction of produced hydrogen with oxygen resulting In the photoregeneration of mainly hydrogen wdhout detectable production of oxygen They have found that the addrtion of sodium carbonate to a Pt-Ti02 suspension, at a concentration close to saturation (2 2 mol/dm3, pH=lO 6) drastically increases the production rate of hydrogen and oxygen in a ratio of 2 1 (Chem Lett , (1662) 253, J Chem Sot, Chem Commun, (1662) 156) What IS Interesting tnZrOgis that without metal or metal oxide loading It can photocatalytically decompose water into a stoichiometnc mtxture of hydrogen and oxygen In this case, the highest efficiency IS obtained in an aqueous solution of 0 63 mol/dm3 NaHC03 at pH =6 4 The surprisingly large effect of carbonate addrtion is explained mainly by the suppression of the photoadsorption of oxygen on the photosensrtive oxide caused by carbonate formatron on the surface MASATAKE HARUTA
Recycling of Rubber Products
Vol 26, 1664 of ES&T features reports of two new technologies which have been developedto tackle recycling of rubber products, especially automobile tyres Of the 235 million tyres dumped annually applied catalysis 8: envlronmental
in the United States only 17% are recycled or burned for energy The rest end up in landfills Studies by Japanese researchers indicate that cured rubbers may be decomposed in supercntical water to potentially recyclable hydrocarbons Toshrnan Tennoh (Nishikawa Rubber Co, Hrroshima) and his colleagues claim that rubber treated at temperatures above 466°C in the presence of 1 M NaOH will decompose within 15 min into mainly c2 carbon aliphatic and olefin hydrocarbons The sulfur IS converted to Ha, which in turn reacts with ZnO in the rubber to form ZnS Meanwhile, EC02, Inc (Hawthorne, FL), has received approval to operate a tyre pyrolysis reactor The company shredstyres “crumb rubber”, separating out the steel and the cotton from the tyre The crumb rubber IS sold for other uses or converted via pyrolysls into fuel oil and carbon black Methane IS collected from the pyrotysa and used to fuel the reactor
Solvent Users Face tiefty 8111:EC Sotvent Emluione Directhre
The final draft of the EC directtve on solvent emissions IS due for decision in 1663 The chemical industry has achieved some success in reducing rts number of prescriptive rules However, there IS still major concern over the cost of implementatron, estimated at Ecu 2 bn (62 4 bn)/y, wnh several years at Ecu 3 bn/y The directrve applies to processes not covered by the Integrated Pollution Prevention and Control Directive but which use 2 tonnes& of solvent Those using over 3775 tonnes/y of VOCs will have to obtain permits to operate under IPPC legislation At the other end of the scale, the EC is considering a VOC directive covering usage under 2 tonnes/y and domestic solvent use The Volume 3 No 4 -24May1664