Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B15/00—Peroxides; Peroxyhydrates; Peroxyacids or salts thereof; Superoxides; Ozonides
  • C01B15/01—Hydrogen peroxide
  • C01B15/013—Separation; Purification; Concentration
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B15/00—Peroxides; Peroxyhydrates; Peroxyacids or salts thereof; Superoxides; Ozonides
  • C01B15/01—Hydrogen peroxide
  • C01B15/029—Preparation from hydrogen and oxygen

Definitions

• the present invention relates to a process for the production of concentrated aqueous solutions of hydrogen peroxide (H 2 0 2 ) suitable for industrial and commercial use.
• aqueous solutions of H 2 0 2 by means of a complex two-step process, is applied on an industrial scale.
• a solution of an anthraquinone such as ethyl-anthraquinone or tert-butyl-anthraquinone
• an organic medium immiscible with water is first hydrogenated and then oxidized with air to produce H 2 0 2 , which is subsequently extracted in aqueous phase.
• This process is expensive owing to the high investment costs necessary for the complex production unit involved and the necessity of separating and disposing of the byproducts generated during the oxidation phase and purifying and reintegrating the anthraquinone solution before being re-used.
• U.S. patent 5,194,242 describes a continuous process for the preparation of H2O2 in aqueous solution from H 2 and 0 2 , which, by means of a specific design of the reaction zone, comprises the use of H 2 and O in ra- tios within the explosivity range in the feeding to the reactor, but outside this range in the gaseous stream leaving the reactor.
• U.S. patent 5,641,467 describes a continuous process for the preparation of H 2 0 2 from H 2 and 0 2 which operates within the inflammability range of H 2 / ⁇ 2 mixtures under safety conditions, using a reaction apparatus suitable for producing a series of gas bubbles sufficiently small and sufficiently dispersed and separate from each other in the liquid reaction medium as to avoid any possible explosion in the reactor.
• U.S. patent 5,500,202 describes a continuous process for the preparation of aqueous solutions of H 2 0 2 from H 2 and 0 2 which operates in a trickle bed reactor using, in the feeding, a gaseous mixture of H 2 /0 2 /N 2 containing 4.6-6.2% by volume of H 2 and 57-62% by volume of 0 2 , so that the mixture leaving the reactor is outside the explosivity limits.
• U.S. patent 4,279,883 describes a continuous process for the preparation of aqueous solutions of H 2 0 2 from H 2 and 0 2 characterized by a particular pre-treatment of the solution and catalyst with H 2 and in which the mixture of gases at the outlet of the reactor is kept with the volume composition of 3% H 2 and 30% 0 2 , the remaining percentage being N 2 .
• European patent application EP 0,627,381 describes a process for the preparation of aqueous solutions of H 2 0 2 from H 2 and 0 2 characterized by the use of particular catalysts and carried out in the presence of gaseous mixtures kept outside the explosivity limits of H 2 in the presence of inert gases such as nitrogen so as to obtain a preferred H 2 /0 2 /N 2 composition equal to 3%/47%/50% respectively, by volume.
• U.S. patent 5,082,647 describes a process for the preparation of aqueous solutions of H 2 O 2 from H 2 and 0 2 characterized by the use of particular catalysts and carried out in a trickle bed reactor, feeding a gaseous mixture containing 3% of H 2 by volume in air.
• the solution re-circulated through the reactor contained 0.3% of H 2 0 2 .
• An object of the present invention therefore relates to a process for the production of concentrated solutions of hydrogen peroxide by means of direct synthesis, starting from H 2 and 0 2 , comprising the following steps: (a) feeding to a reactor containing a catalyst based on palladium and platinum, heterogeneous and maintained in dispersion in a liquid reaction medium: (i) a liquid stream consisting of an alcohol or a mixture of C 1 -C3 alcohols or a mixture of said alcohols with water containing at least 50% by weight of alcohol, also containing an acid promoter and a halogenated promoter, the alcohol and optionally all or part of the water contained in the stream being recycled from the subsequent phase d) ;
• the patent MI 2000 A001218 relates to a process for the continuous production of alcohol or hydro-alcohol solutions of hydrogen peroxide in a concentration ranging from 2 to 10% by weight.
• the process for the production of concentrated aqueous solutions of hydrogen peroxide substantially comprises steps (a) and (b) already described by Italian patent MI 2000 A001218, to which an optional feeding or additional feeding of water and a final distillation phase for the removal and recycling of the alcohol or a hydro-alcohol mixture and the recovery of a con- centrated aqueous solution of hydrogen peroxide, are added.
• the aqueous solution of H 2 0 2 contains the acid promoter and halogenated promoter contained in the starting alcohol or hydro-alcohol mixture and a residual content of alcohol generally less than or equal to 2% by weight and preferably less than or equal to 1% by weight.
• the reactor used can be any reactor suitable for operating in continuous and conducting the reaction in a tri- phasic system such as that described, obtaining an effective contact between the gaseous phase, liquid phase and the catalyst maintained in dispersion (so-called slurry system) .
• Reactors suitable for the purpose are, for example, stirred reactors, bubble reactors, gas-lift reactors with internal or external circulation, as described in the art .
• the reactor is kept under suitable temperature and pressure conditions.
• the temperature normally ranges from -10°C to 60°C, preferably from 0°C to 40°C.
• the pressure normally ranges from 1 to 300 bars, preferably from 40 to 150 bars.
• the residence time of the liquid medium in the reactor normally ranges from 0.05 to 5 hours, preferably from 0.10 to 2 hours.
• the catalyst which can be used for the purposes of the present invention is a heterogeneous catalyst containing palladium and platinum as active components.
• the palladium is normally present in a quantity ranging from 0.1 to 3% by weight and the platinum in a quantity ranging from 0.01 to 1% by weight, with an atomic ratio between platinum and palladium ranging from 1/500 to 100/100.
• the palladium is preferably present in a quantity ranging from 0.4 to 2% by weight and the platinum in a quantity ranging from 0.02 to 0.5% by weight, with an atomic ratio between platinum and palladium ranging from
• metals of group VIII or IB such as for example, ruthenium, rhodium, iridium and gold, can be present as active components or promoters, in a concentration generally not higher than that of the palladium.
• the catalyst can be prepared by dispersing the active components on an inert carrier by means of precipitation and/or impregnation starting from precursors consisting for example of solutions of their salts or soluble complexes, and then reduced to the metal state by means of thermal and/or chemical treatment with reducing substances such as hydrogen, sodium formiate, sodium citrate using preparative techniques well known in the art.
• the inert carrier may typically consist of silica, alumina, silica-alumina, zeolites, activated carbon, and other materials well known in the art.
• Activated carbon is preferred for the preparation of the catalysts useful for the invention.
• Activated carbons which can be used for the purposes of the invention are selected from those of a fossil or natural origin deriving from wood, lignite, peat or coconut and having a surface area greater than 300 m 2 /g and which can reach 1400 m 2 /g, in particular those having a surface area greater than 600 m 2 /g.
• Preferred activated carbons are those with a low ash content .
• Sulfonated activated carbons described in Italian patent application MI 98A01843 are also useful for the pur- pose.
• the activated carbon Before supporting or impregnating the metals, the activated carbon can be subjected to treatment such as washing with distilled water or treatment with acids, bases or diluted oxidizing agents, for example acetic acid, hydro- chloric acid, sodium carbonate and hydrogen peroxide.
• the catalyst is normally dispersed in the reaction medium at a concentration ranging from 0.1 to 10% by weight, preferably from 0.3 to 3% by weight.
• the liquid stream (i) consists of an alcohol or ix- ture of C1-C3 alcohols or a mixture of these alcohols with water with a prevalent alcoholic content.
• a mixture with a prevalent alcoholic content means a mixture containing more than 50% by weight of alcohol or mixture of alcohols.
• C1-C3 alcohols methanol is preferred for the purposes of the present invention.
• a mixture of methanol and water containing at least 70% by weight of methanol is preferred.
• the liquid stream also contains an acid promoter and a halogenated promoter.
• the acid promoter can be any substance capable of generating H + hydrogen ions in the liquid reaction medium and is generally selected from inorganic acids such as sulfu- ric, phosphoric, nitric acids or from organic acids such as sulfonic acids. Sulfuric acid and phosphoric acid are preferred.
• the concentration of the acid generally ranges from 20 to 1000 mg per kg of liquid medium and preferably from 50 to 500 mg per kg of liquid medium.
• the halogenated promoter can be any substance capable of generating halogen ions in the liquid reaction medium.
• Substances capable of generating bromide ions are preferred. These substances are generally selected from hydro- bromic acid and its salts soluble in the reaction medium, for example alkaline bromides, hydrobromic acid being pre- ferred.
• the concentration of halogenated promoter generally ranges from 0.1 to 50 mg per kg of liquid medium and preferably from 1 to 10 mg per kg of liquid medium.
• the gaseous stream (ii) at the inlet contains a con- centration of hydrogen of less than 4.5% by volume and a concentration of oxygen of less than 21% by volume, the complement to 100 being an inert gas, which is generally selected from nitrogen, helium, argon. Said gas is preferably nitrogen.
• the concentration of hydrogen preferably ranges from 2% to 4% by volume and the concentration of oxygen preferably ranges from 6% to 15% by volume.
• the oxygen can be supplied in said stream using as raw material, pure or substantially pure oxygen, enriched air, containing for example from 21 to 90% of oxygen or air, the composition of the stream then being brought to the desired values, defined above, by the addition of a suitable concentration of inert gas.
• the liquid stream (iii) at the outlet of the reactor normally has a concentration of hydrogen peroxide usually ranging from 2% to 10% by weight and preferably from 3% to 8% by weight. It also contains the acid promoter and halogenated promoter in quantities equal to those introduced together with the liquid stream fed, and water in a quantity equal to that introduced with the liquid stream fed, to which the water obtained as reaction by-product is added.
• the latter normally represents an additional concen- tration ranging from 0.5% to 2.5% by weight.
• the liquid stream (iii) is separated from the catalyst by means of filtration techniques well known in the art, for example by the use of filter plugs situated inside the reactor or in a specific re-circulation cycle of the reac- tion mixture, outside the reactor. In this latter case the tangential filtration technique can also be conveniently used.
• the gaseous stream (iv) at the outlet of the reactor essentially consisting of non-reacted hydrogen and oxygen and of the inert gas, generally contains a volume concentration of hydrogen equal to or lower than 2%, normally ranging from 0.5 to 1.5%, and a volume concentration of oxygen generally lower than 18%, normally ranging from 6% to 12%.
• the gaseous stream (iv) at the outlet of the reactor is recycled to the feeding to the reactor, after flushing from the system, the fraction necessary for eliminating the quantity of inert gas introduced in excess with the feed- ing, particularly when air is used as oxygen source.
• the gaseous stream (ii) fed to the reactor consists of the recycled fraction of the above stream (iv) , with the addition of a quantity of hydrogen and oxygen (as such or in the form of air or enriched air) essentially equal to that used up by the reaction and that flushed.
• the gaseous stream (iv) leaving the reactor is fed to one or more subsequent reactors operating analogously to the one previously described, after adding each time a quantity of hydrogen and oxygen (as such or in the form of air or enriched air) essentially equal to that used up by the reaction which takes place in the single reactors.
• the optional addition of water in (c) and subsequent feeding in (d) are preferably carried out after depressuri- zation to atmospheric pressure and washing with inert gas, for example nitrogen, to eliminate the reactive reaction gases.
• inert gas for example nitrogen
• the optional addition of water can be effected before any of the evaporators or columns form- ing the distillation chain. In this case, the addition of water can be carried out separately and contemporaneously in various points .
• the distillation system may comprise one or more evaporators and/or distillation columns, of the type well known in the art, for example drop film or thin film evaporators and plate or filled distillation columns.
• the distillation system When the distillation system comprises several evaporators or columns, it normally has a chain of evaporators or columns whose bases are connected in series, for recovery at the head of the single apparatuses of alcohol or hydro-alcohol solutions, which can be recycled to (a) - (i) , after being mixed or separately, whereas solutions of H 2 0 2 are obtained from the bottoms at an increasing concentra- tion until an aqueous solution of H 2 0 2 is removed from the tail of the last column, at the desired concentration.
• the optional stream in (vii) is preferably recovered by subjecting one or more of the hydro-alcohol fractions removed from the head(s), to distillation.
• the distillation system in (d) preferably operates at atmospheric or almost atmospheric pressure or under reduced pressure, ranging for example from atmospheric pressure to 50 mbars .
• the distillation system in (d) consists of several columns, the columns preferably operate at a vary- ing pressure, normally decreasing, within the above range. Operating under these conditions, the temperature at the bottom of the columns normally ranges from 50 to 75°C.
• a stream having a high alcohol titer is preferably removed from the head of the first column, and hydro-alcohol mixtures, having a concentration of alcohol varying within a wide range, for example between 90% and 20% by weight of alcohol, from the heads of the subsequent columns.
• hydro-alcohol mixtures having a concentration of alcohol varying within a wide range, for example between 90% and 20% by weight of alcohol, from the heads of the subsequent columns.
• Mixtures with a decreasing concentration of alcohol, within the above range are normally removed along the distillation column chain.
• mixtures are removed from the bottom of the first and subsequent columns, with an increasing concentration of hydrogen peroxide and with an increasing water/alcohol ratio in the mixture, until the complete elimination of the alcohol and production of the aqueous solution of hydrogen peroxide at the desired concentration.
• the temperature at the head of the columns normally ranges from 20 to 50°C.
• the optional addition of water in (c) has the objective of allowing the desired end-titer of H 2 O 2 to be reached and of maintaining the compositions in the column (s) well outside the instability limits of H 2 0 2 solu- tions in the presence of organic solvents, in order to avoid risks associated with the combination of high concentrations of H 2 0 2 and organic solvent, well known in the art.
• the addition of water also contributes to reducing the temperatures at the bottom of the column (s) to avoid decom- position of the hydrogen peroxide.
• distillation as a method for separating the alcohol content from the alcohol or hydro-alcohol mixture has, on the one hand, the problem of satisfying the necessity of maintaining a low temperature at the bottom of the column (s), and therefore the pressure, to avoid possible decomposition of the hydrogen peroxide, and on the other hand, the convenience of maintaining a sufficiently high temperature at the head, and therefore the pressure, to enable industrial water to be used as thermal exchange fluid for the condensa- tion of the streams at the head of the column.
• the use of a system with a single column has, in addition to the obvious advantage of simplicity, the necessity of adopting a cooled fluid as thermal exchange fluid to condense the stream at the head of the column, in order to maintain the boiler temperature at values ranging from 50 to 75°C.
• the use of a system with two or more columns allows the use of industrial water as thermal exchange fluid and at the same time enables the temperature at the bottoms to be maintained at values ranging from 50 to 75°C.
• aqueous solutions of hydrogen peroxide at a concentration ranging from 15 to 60% by weight, preferably varying from 20 to 50%, more preferably equal to 35% of hydrogen peroxide, under safety conditions and with a molar selectivity towards the formation of H 2 0 2 , referring to the hydrogen used up, generally higher than 65%.
• the suspension is kept at room temperature for 10 minutes and is then heated in a water bath for 10 minutes to 90°C.
• a solution containing 0.85 g of sodium formiate in 10 ml of water is then added and the stirring is continued at 90°C for 2 hours.
• a micropilot plant consisting of a Hastelloy C autoclave having a volume of 400 ml, equipped with a thermostat-regulation system, a magnetic drag stirring system, a regulation and control system of the pressure during the reaction, a feeding system of the mixture of solvent and promoters in which the reaction takes place, a filter for continuously removing the liquid phase containing the reaction products, a feeding and discharging system of the gaseous reagents and a series of regulation and control instruments .
• reaction trend is followed by continuously analyz-ing the hydrogen and oxygen in the feeding and at the outlet of the reactor.
• the concentration of H 2 0 2 which is formed is determined in the reactor liquid effluent by titration with potassium permanganate.
• the selectivity with respect to the converted hydrogen is calculated on the basis of the concentration of H 2 0 2 in the reaction effluent and on the basis of analysis of the H 2 leaving the reactor, once the stationary state has been reached in the reactor, the liquid and gaseous flow-rates being known.
• 1.2 g of catalyst prepared as described in example 2 and 150 g of methanol :water solution (97/3 by weight) containing 4 ppm of HBr and 200 ppm of H 2 SO are charged into the reactor.
• the autoclave is pressurized, without stirring, at 130 bars with a gaseous mixture consisting of 3.6% of H 2 , 13% of 0 2 and 83.4% of N by volume.
• the stirring is then started up to 800 revs/minute, the pressure is maintained with a continuous stream, 810 normal liters (Nl) , of the same gaseous mixture, and 300 g/hour of a methanol: ater solution having the composition defined above, is fed at the same time.
• the temperature inside the reactor is kept at 4°C.
• the liquid stream consisting of the feeding and reaction product is brought to atmospheric pressure and appro- priately flushed with nitrogen in order to eliminate the dissolved reaction gases.
• the test was carried out in continuous for 1100 hours of reaction obtaining the following results:
• the discharge from the reactor ranges from 325 to 330 g/h with an average weight composition of H 2 0 2 6.8-7.2%; H 2 0 3.8-4.1%, the rest being methanol.
• the mixture obtained in example 3 is sent to a system consisting of two distillation steps.
• the first step operating at 400 mbars, produces a hy- dro-alcohol solution of H 2 0 2 at 20% by weight at the tail, at 60°C, and methanol with a high titer (99.5%) at the head, at 42°C.
• H 2 0 is added to the product at the bottom of the first column, in a weight ratio of 1.5:1 with respect to the H 2 0 2 contained and the resulting mixture is sent to a second distillation step, which operates at 160 mbars, producing at the tail, at 61°C, an aqueous solution of H 2 0 2 having a titer of 35% by weight, and a hydro-alcohol solution containing 60% by weight of methanol, at the head, at 35°C.

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• Oxygen, Ozone, And Oxides In General (AREA)
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• 2000
  • 2000-08-11 IT IT2000MI001881A patent/IT1318679B1/it active
• 2001
  • 2001-08-03 AU AU2001289788A patent/AU2001289788A1/en not_active Abandoned
  • 2001-08-03 US US10/343,323 patent/US7048905B2/en not_active Expired - Fee Related
  • 2001-08-03 RU RU2003104014A patent/RU2237614C1/ru not_active IP Right Cessation
  • 2001-08-03 AT AT01969572T patent/ATE458697T1/de not_active IP Right Cessation
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  • 2001-08-03 WO PCT/EP2001/009039 patent/WO2002014217A1/en not_active Ceased
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  • 2001-08-03 EP EP01969572A patent/EP1307399B1/en not_active Expired - Lifetime
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