Patent ID: 6432376
Filing Date: 2002-08-13
Classification: B01J,C01B

Abstract:
A process for the production of hydrogen peroxide by the non-hazardous direct oxidation of hydrogen by oxygen, without the formation of an explosive H2 and O2 gas mixture, using a novel tubular hydrophobic composite Pd-membrane catalyst, represented by a formula:HPM(c)/SOMF(b)/MxPd1âˆ’x(a)/IPM wherein, IPM is an inorganic porous membrane, permeable to all gases and vapors, in a form of tube having a thickness of at least 0.5 mm and internal diameter of at least 0.6 cm; MxPd1âˆ’x is a metal alloy, permeable only to hydrogen gas, deposited on the inner side of IPM: Pd is a palladium metal; M is a metal other than palladium, or a mixture of two or more metals; x is a mole fraction of the metal M in the metal alloy (MxPd1âˆ’x) in the range from about 0.03 to about 0.6; (a) is the weight of the metal alloy per unit area of IPM in the range from about 5.0 g.mâˆ’2 to about 500 g.mâˆ’2; SOMF is a surface oxidized thin metal film comprising palladium which is permeable only to hydrogen, deposited on the metal alloy (MxPd1âˆ’x); (b) is the thickness of SOMF in the range from about 0.05 &mgr;m to about 5.0 &mgr;m; HPM is a hydrophobic polymer membrane permeable to hydrogen and oxygen gases and also to vapors of water and hydrogen peroxide but not to liquid water or aqueous solution; and (c) is the weight of the HPM per unit area of SOMF in the range from about 0.2 g.mâˆ’2 to about 40 g.mâˆ’2; said process being conducted in a membrane reactor comprising two zones: a gas zone and a liquid medium zone, separated from each other by the membrane catalyst; the said process comprisingi) pretreating in situ the tubular hydrophobic composite Pd-membrane catalyst from its hydrophobic polymer membrane (HPM) side with a gaseous oxidizing agent selected from the group consisting of oxygen, nitrous oxide, H2O2 vapors and mixtures thereof, at a temperature below about 200Â° C. for a period at least about 0.5 h; ii) contacting simultaneously 1) a hydrogen gas, at a pressure above 1.0 atm, from the gas zone of the membrane reactor with the tubular composite membrane catalyst from its IPM (inorganic porous membrane) side and 2) an aqueous reaction medium which is an aqueous solution comprising a mineral acid, while bubbling continuously an oxygen containing gas at a gas hourly space velocity in the range from about 10 hâˆ’1 to about 10,000 hâˆ’1 at a pressure above 1.0 atm, with the tubular composite membrane catalyst from its HPM (hydrophobic polymer membrane) side, in two separate compartments separated by the tubular composite membrane catalyst, which is permeable only to hydrogen, such that the pressure drop across the tubular composite membrane catalyst is less than 5.0 atm, in the membrane reactor comprising single or optionally multiple membrane catalyst tubes, operating the membrane reactor as a batch reactor with respect to the aqueous reaction medium with an external recirculation of the aqueous reaction medium in the membrane reactor for a period more than about 1.0 h or optionally operating the membrane reactor as a continuous flow reactor with respect to the aqueous reaction medium at a liquid hourly space velocity in the range from about 0.01 hâˆ’1 to about 100 hâˆ’1, optionally with external recirculation of the aqueous reaction medium, at a temperature below about 75Â° C., such that the hydrogen permeated through the composite Pd-membrane catalyst reacts with the dissolved oxygen from the aqueous reaction medium on the surface of palladium oxide at the interface between SOMF and HPM of the composite Pd-membrane catalyst to produce hydrogen peroxide, which is absorbed in the aqueous reaction medium, producing and aqueous hydrogen peroxide solution.