The great interest in the oxidation reaction of benzene to phenol is linked to some disadvantages of the cumene process, such as environmental impact, production of an explosive intermediate and the fact that this is a multi-step process that involves a low yield of phenol and a high capital investment. Moreover the high acetone production as a co-product, which results in an oversupply in the market, is another drawback. Various studies concerning a new approach based on a one-step and acetone-free method for phenol production have been reviewed by Molinari and Poerio (2010). Particular attention was devoted to phenol production processes using various configurations of membrane reactors (MRs) and a photocatalytic membrane reactor (PMR). In particular, the biphasic MR allowed to achieving high selectivity values (97-98%). The various methods have been classified according to oxidant type such as N2O, O2, and H2O2. All of them indicated that direct oxidation of benzene to phenol is a difficult task and further efforts are needed to search and to replace the three step traditional process with a process of direct oxidation to convert benzene in phenol. Phenol production through the direct hydroxylation of benzene with hydrogen peroxide using a catalytic membrane reactor was studied y Molinari et al (2006). The reaction was carried out in a biphasic system separated by a membrane. This new system showed a high selectivity to phenol, minimizing its over-oxidation in over-oxygenated by-products. The effect of various reaction parameters such as the addition of hydrogen peroxide mode, amount of hydrogen peroxide, type of membrane, type of catalyst and organic acid was investigated. The results showed that iron(II) sulphate as the catalyst, 18 mmol of hydrogen peroxide pumped for 4 h in the aqueous phase as oxidant feeding, acetic acid and polypropylene hydrophobic porous support gave the best system performance in terms of produced phenol (17.42 mmol), selectivity to phenol (99.94%), benzene conversion to phenol (1.20%), and conversion of hydrogen peroxide to phenol (96.78%). Use of vanadium based catalysts and product recovery in benzene hydroxylation to phenol was studied in a two-phase membrane reactor by Molinari et al (2012). Benzene permeates, through the hydrophobic polypropylene membrane, in the aqueous phase containing the catalyst while phenol permeates back accumulating in the organic phase. The following fundamental aspects have been studied: dose of hydrogen peroxide, initial oxidation states of vanadium catalysts, duration of catalytic tests and lifetime of the membrane in terms of physical and chemical resistance. It was observed that feeding the oxidant by a micro pump, working in the "bulk tube" mode, phenol yield, final phenol concentration in the organic phase, phenol turnover number and system productivity increased, and no tar was formed. Initial oxidation state of vanadium catalysts influenced system performance: indeed improved results in terms of yield (35.2% vs. 25.1%), conversion of hydrogen peroxide to phenol (36.6% vs. 25.9%), productivity (0.97 g g(cat)-1 h-1 vs. 0.78 g g(cat)-1 h-1) were obtained by using vanadium(III) chloride compared to vanadium(IV) acetyl acetonate. Higher phenol extraction/recovery in the organic phase (61.1% vs. 46.3%) and then higher selectivity (97.5% vs. 92.8%) were obtained by increasing test duration from 270 to 510 min. A weak membrane resistance was observed after 246 h of consecutive catalytic runs on the same membrane piece, showing degradation of the membrane material (polypropylene) caused by the OH radical generated in the reacting mixture. The one-step hydroxylation of benzene to phenol with oxygen and hydrogen was studied by Shu et al (2009). It is a promising process, but there are severe challenges associated with the low phenol production. It was shown that the reaction can be greatly promoted by the simultaneous use of a dense palladium membrane as a catalyst and as a hydrogen distributor. This reaction concept with palladium membranes was tested under different reaction conditions, but it was found that the palladium membranes were almost inert for both the target reaction and the benzene combustion. The Authors summarized and compared their results with those reported in the literature investigating the effects of the membrane preparation method and the combustion of hydrogen and benzene. The hypotheses on the mechanism and feasibility of the membrane concept are also given. A simple, low-cost design of glass capillary microreactor for the catalytic oxidation of benzene to phenol at ambient conditions was studied by Basheer (2013). Polyvinylchloride-nanofiber-membrane-supported titania nanoparticles (TiO2-PVC) as catalyst was used by producing in situ hydroxyl radicals as oxidant.The reaction was monitored by gas chromatography-mass spectrometry (GC-MS). The reaction conditions were optimized and the performance of the microreactor was then compared with the conventional laboratory scale reaction which used hydrogen peroxide as oxidant. The microreactor gave a better yield of 14% for phenol compared to 0.14% in the conventional laboratory scale reaction. Reaction conditions such as reaction time, reaction pH, and applied potential were optimized. With optimized reaction conditions selectivity higher than 37% and conversion of benzene higher than 88% were obtained. The study of a new reactor design with separate membranes for distributed dosage of hydrogen and oxygen, respectively, into microstructured reaction channels for the direct conversion of benzene to phenol in the gas phase in a palladium membrane reactor has been investigated by Bortolotto and Dittmeyer (2010). The highest phenol selectivity so far obtained on a palladium-coated PdCu foil at 423 K was 9.6% with carbon dioxide being the dominant product. References Basheer C (2013) Nanofiber-Membrane-Supported TiO2 as a catalyst for oxidation of benzene to phenol. Journal of Chemistry Vol. 2013, Article ID 562305, 7 pages Bortolotto L, Dittmeyer R (2010) Direct hydroxylation of benzene to phenol in a novel microstructured membrane reactor with distributed dosing of hydrogen and oxygen. Separation and Purification Technology 73:51-58 Molinari R, Poerio T, Argurio P (2006) One-step production of phenol by selective oxidation of benzene in a biphasic system. Catalysis Today 118:52-56 Molinari R, Poerio T (2010) Remarks on studies for direct production of phenol in conventional and membrane reactors. Asia-Pacific Journal of Chemical Engineering 5:191-206 Molinari R, Argurio P, Poerio T (2012) Vanadium(III) and vanadium(IV) catalysts in a membrane reactor for benzene hydroxylation to phenol and study of membrane material resistance. Applied Catalysis A: General 437:131-138 Shu SL, Huang Y, Hu XJ, Fan YQ, Xu NP (2009) On the membrane reactor concept for one-step hydroxylation of benzene to phenol with oxygen and hydrogen. Journal of Physical Chemistry C 113:19618-19622
Phenol production by membrane reactor
MOLINARI, Raffaele
2013-01-01
Abstract
The great interest in the oxidation reaction of benzene to phenol is linked to some disadvantages of the cumene process, such as environmental impact, production of an explosive intermediate and the fact that this is a multi-step process that involves a low yield of phenol and a high capital investment. Moreover the high acetone production as a co-product, which results in an oversupply in the market, is another drawback. Various studies concerning a new approach based on a one-step and acetone-free method for phenol production have been reviewed by Molinari and Poerio (2010). Particular attention was devoted to phenol production processes using various configurations of membrane reactors (MRs) and a photocatalytic membrane reactor (PMR). In particular, the biphasic MR allowed to achieving high selectivity values (97-98%). The various methods have been classified according to oxidant type such as N2O, O2, and H2O2. All of them indicated that direct oxidation of benzene to phenol is a difficult task and further efforts are needed to search and to replace the three step traditional process with a process of direct oxidation to convert benzene in phenol. Phenol production through the direct hydroxylation of benzene with hydrogen peroxide using a catalytic membrane reactor was studied y Molinari et al (2006). The reaction was carried out in a biphasic system separated by a membrane. This new system showed a high selectivity to phenol, minimizing its over-oxidation in over-oxygenated by-products. The effect of various reaction parameters such as the addition of hydrogen peroxide mode, amount of hydrogen peroxide, type of membrane, type of catalyst and organic acid was investigated. The results showed that iron(II) sulphate as the catalyst, 18 mmol of hydrogen peroxide pumped for 4 h in the aqueous phase as oxidant feeding, acetic acid and polypropylene hydrophobic porous support gave the best system performance in terms of produced phenol (17.42 mmol), selectivity to phenol (99.94%), benzene conversion to phenol (1.20%), and conversion of hydrogen peroxide to phenol (96.78%). Use of vanadium based catalysts and product recovery in benzene hydroxylation to phenol was studied in a two-phase membrane reactor by Molinari et al (2012). Benzene permeates, through the hydrophobic polypropylene membrane, in the aqueous phase containing the catalyst while phenol permeates back accumulating in the organic phase. The following fundamental aspects have been studied: dose of hydrogen peroxide, initial oxidation states of vanadium catalysts, duration of catalytic tests and lifetime of the membrane in terms of physical and chemical resistance. It was observed that feeding the oxidant by a micro pump, working in the "bulk tube" mode, phenol yield, final phenol concentration in the organic phase, phenol turnover number and system productivity increased, and no tar was formed. Initial oxidation state of vanadium catalysts influenced system performance: indeed improved results in terms of yield (35.2% vs. 25.1%), conversion of hydrogen peroxide to phenol (36.6% vs. 25.9%), productivity (0.97 g g(cat)-1 h-1 vs. 0.78 g g(cat)-1 h-1) were obtained by using vanadium(III) chloride compared to vanadium(IV) acetyl acetonate. Higher phenol extraction/recovery in the organic phase (61.1% vs. 46.3%) and then higher selectivity (97.5% vs. 92.8%) were obtained by increasing test duration from 270 to 510 min. A weak membrane resistance was observed after 246 h of consecutive catalytic runs on the same membrane piece, showing degradation of the membrane material (polypropylene) caused by the OH radical generated in the reacting mixture. The one-step hydroxylation of benzene to phenol with oxygen and hydrogen was studied by Shu et al (2009). It is a promising process, but there are severe challenges associated with the low phenol production. It was shown that the reaction can be greatly promoted by the simultaneous use of a dense palladium membrane as a catalyst and as a hydrogen distributor. This reaction concept with palladium membranes was tested under different reaction conditions, but it was found that the palladium membranes were almost inert for both the target reaction and the benzene combustion. The Authors summarized and compared their results with those reported in the literature investigating the effects of the membrane preparation method and the combustion of hydrogen and benzene. The hypotheses on the mechanism and feasibility of the membrane concept are also given. A simple, low-cost design of glass capillary microreactor for the catalytic oxidation of benzene to phenol at ambient conditions was studied by Basheer (2013). Polyvinylchloride-nanofiber-membrane-supported titania nanoparticles (TiO2-PVC) as catalyst was used by producing in situ hydroxyl radicals as oxidant.The reaction was monitored by gas chromatography-mass spectrometry (GC-MS). The reaction conditions were optimized and the performance of the microreactor was then compared with the conventional laboratory scale reaction which used hydrogen peroxide as oxidant. The microreactor gave a better yield of 14% for phenol compared to 0.14% in the conventional laboratory scale reaction. Reaction conditions such as reaction time, reaction pH, and applied potential were optimized. With optimized reaction conditions selectivity higher than 37% and conversion of benzene higher than 88% were obtained. The study of a new reactor design with separate membranes for distributed dosage of hydrogen and oxygen, respectively, into microstructured reaction channels for the direct conversion of benzene to phenol in the gas phase in a palladium membrane reactor has been investigated by Bortolotto and Dittmeyer (2010). The highest phenol selectivity so far obtained on a palladium-coated PdCu foil at 423 K was 9.6% with carbon dioxide being the dominant product. References Basheer C (2013) Nanofiber-Membrane-Supported TiO2 as a catalyst for oxidation of benzene to phenol. Journal of Chemistry Vol. 2013, Article ID 562305, 7 pages Bortolotto L, Dittmeyer R (2010) Direct hydroxylation of benzene to phenol in a novel microstructured membrane reactor with distributed dosing of hydrogen and oxygen. Separation and Purification Technology 73:51-58 Molinari R, Poerio T, Argurio P (2006) One-step production of phenol by selective oxidation of benzene in a biphasic system. Catalysis Today 118:52-56 Molinari R, Poerio T (2010) Remarks on studies for direct production of phenol in conventional and membrane reactors. Asia-Pacific Journal of Chemical Engineering 5:191-206 Molinari R, Argurio P, Poerio T (2012) Vanadium(III) and vanadium(IV) catalysts in a membrane reactor for benzene hydroxylation to phenol and study of membrane material resistance. Applied Catalysis A: General 437:131-138 Shu SL, Huang Y, Hu XJ, Fan YQ, Xu NP (2009) On the membrane reactor concept for one-step hydroxylation of benzene to phenol with oxygen and hydrogen. Journal of Physical Chemistry C 113:19618-19622I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
