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  • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
  • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
  • C07C51/23—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of oxygen-containing groups to carboxyl groups
  • C07C51/235—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of oxygen-containing groups to carboxyl groups of —CHO groups or primary alcohol groups
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/08—Heat treatment
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/16—Reducing
  • B01J37/18—Reducing with gases containing free hydrogen
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/42—Separation; Purification; Stabilisation; Use of additives
  • C07C51/48—Separation; Purification; Stabilisation; Use of additives by liquid-liquid treatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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  • B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
  • B01J2229/10—After treatment, characterised by the effect to be obtained
  • B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself
  • B01J2229/186—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself not in framework positions
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  • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/56—Platinum group metals
  • B01J23/58—Platinum group metals with alkali- or alkaline earth metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/56—Platinum group metals
  • B01J23/63—Platinum group metals with rare earths or actinides
• • 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
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/56—Platinum group metals
  • B01J23/64—Platinum group metals with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
  • B01J23/648—Vanadium, niobium or tantalum or polonium
  • B01J23/6484—Niobium
• • 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
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/064—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof containing iron group metals, noble metals or copper
  • B01J29/068—Noble metals

Definitions

• the present invention relates to a process for obtaining lactic acid by selective oxidation of 1,2-propanediol.
• the present invention teaches an oxidative process in yields greater than 70% for the production of lactic acid from 1,2-propanediol in alkaline medium at low temperature and atmospheric or autogenous pressure employing a noble metal catalyst supported on metal oxide.
• Lactic acid is considered as one of the important inputs for the petrochemical industry, because besides being used to obtain biodegradable materials, it is synthesized from renewable sources, such as corn glucose, molasses and cheese whey.
• Lactic acid can also be obtained by chemical transformation from sources other than starch, but equally renewable.
• some proposals employ glycerine in a process where the reaction occurs in alkaline medium, in homogeneous phase and under hydrothermal conditions.
• lactic acid yields reach about 90%
• reactions occur at very high temperatures (300 ° C) and quite high pressures.
• EP 2100871 teaches the use as raw material of organic compounds with three carbon atoms, consisting of a primary alcohol or an aldehyde containing a hydroxyl group in the alpha position relative to the primary alcohol hydroxyl or aldehyde carbonyl.
• the catalytic process is based on a hydrogenolysis reaction thus occurring in the presence of hydrogen and requiring temperatures of the order of 90 ° C to 170 ° C. ° C. Even more hydrogen is generated during the process and it is vital to avoid reacting with oxygen in the air.
• the document makes clear the need for reactor atmosphere control and additional steps for nitrogen purge are indicated, making process control more complex.
• the formation of by-products such as acetic acid and higher aliphatic acids is reported.
• Patent document CN 101225041 (L. Haichao, S. Yihong, L. Hongjia, CN 01225041 A, Jul. 23, 2008) teaches a process where it is possible to obtain lactic acid, but has very low yields under the conditions specified therein. ranging from 9.7% to 32% and reaching a maximum of 81% glycerine conversion.
• Yields of lactic acid are always in the range of 5% to
• the present invention by contrast, teaches a selective catalytic process with yields greater than 70% for the production of lactic acid.
• the invention relates to the manufacture of high yield lactic acid by selective oxidation of 1,2-propanediol.
• the reaction takes place in the presence of oxygen and an activated catalyst comprising a noble metal supported on metal oxide.
• Oxidation of the primary carbon containing an OH group is selective at temperatures below 100 ° C, atmospheric or autogenous pressure and in alkaline medium. Under these conditions yields of around 70% of lactic acid are obtained using equipment already installed and commonly used in industrial chemical plants with lower energy expenditure than those practiced in state of the art processes.
• the catalyst is easily recovered by filtration at the end of the process.
• the process presented in the present application makes it possible to obtain lactic acid in yields of 70% or higher through the use of heterogeneous catalysts which provide high selectivity and also high yields for lactic acid using only oxygen from air and 1,2-propanediol. as reagents at temperatures below 100 ° C and under atmospheric pressure.
• the lactic acid manufacturing process involves the use of a gas stream selected from air, pure oxygen, or a mixture thereof which is bubbled into a reactor containing an aqueous 1,2-propanediol solution at atmospheric pressure and in alkaline medium.
• This reactor further contains the previously activated solid catalyst for converting the reactants to lactic acid, preferably.
• This process may be conducted in a semi-continuous, continuous, semi-semi-continuous regime or a combination of both gas and liquid phase.
• 1,2-propanediol is converted to lactic acid through the oxidation reaction of the primary carbon. Oxidation also occurs in the secondary carbon forming acetol. At higher temperatures, acetol reacts with oxygen from the gaseous stream resulting in the formation of pyruvic acid. Thus, the main byproducts of obtaining lactic acid by this process are acetol and pyruvic acid.
• the process of the present invention comprises the following steps: 1 a ) Catalyst activation: reduction of the catalyst at 350 ° C by 2 hours under H 2 flow.
• Reactor feed reactor loading, equipped with reflux system, 1,2-propanediol solution and pre-reduced catalyst.
• the catalyst is prepared by wet, dry or deposition-precipitation impregnation with metal precursor solution selected from hydroxides, nitrates, chlorides, sulphates, acetates and acetylacetonates or other decomposing compound to the corresponding metal oxide after calcination.
• metal precursor solution selected from hydroxides, nitrates, chlorides, sulphates, acetates and acetylacetonates or other decomposing compound to the corresponding metal oxide after calcination.
• the noble metal content in the catalyst ranges from 0.01% to 10%, preferably from 0.1% to 5% w / w.
• the support must have a specific surface high enough to guarantee good metal dispersion in the range between 50 m 2 g 1 and 1000 mV-
• the support is selected from range-AI 2 0 3 , Ti0 2 , Si0 2 and Zr0 2 , nb 2 0 5, EC0 2, MgO, ZSM-5, MCM-22, MCM-41, preferably Al 2 0 3, Ti0 2, and SI0 2 ZrC1 ⁇ 2.
• the noble metal is selected from Pt, Pd, Ru, Rh and Ir, preferably Pt and Pd.
• an oxidation catalyst comprising one of the noble metals or a combination thereof supported on a pure metal oxide, a mixture of metal oxides or zeolitic aluminosilicates is employed.
• the catalyst impregnation is performed from a solution of hexachloroplatinic acid (H 2 PtCl 6 ).
• the catalyst may also be obtained via dry impregnation.
• a compound selected from Platinum is H 2 Pt (OH) 6 , Pt (NO 3 ) 4 , Pt (NH 3 ) 4 (NO 3 ) 2 , Pt (NH 3 ) 4 (OH) 2 , PtCl 4 , Pt (NH 4 ) 2 CI 4 , Pt (NH 4 ) 2 CI 6 , Pt (C 5 H 7 0 2 ) 2 or any other compound that decomposes to form Pt0 2 .
• a commercial Pt / Al 2 O 3 catalyst with 5% w / w previously reduced Pt is used.
• Catalyst reduction is conducted ex situ at temperatures between 200 ° C and 500 ° C or in situ within the temperature range between 30 ° C and 100 ° C.
• the catalyst is added to the stirred propanediol solution.
• the reduction can still be performed sequentially, ex situ and in situ within the same temperature ranges as described.
• the oxidation reaction of 1,2-propanediol is carried out in a reactor using either pure 1,2-propanediol or aqueous solution as a reactant, and catalyst in amounts meeting the catalyst / 1,2-propanediol ratio in the range of 1/4 w / w 1/20 w / w, keeping the pH of the reaction fixed at a selected value in the range of 7 to 14.0, preferably between 8.0 and 12.0, by the controlled addition of an alkaline solution, selected from alkaline and alkaline earth metal hydroxide and carbonate solutions, preferably NaOH or KOH, with a concentration in the range 0.1 M to 2 M, preferably in the range 0.5 M to 1.5 M at a selected temperature in the range between 30 ° C and 100 ° C, autogenous pressure between 1 bar and 5 bar, under agitation in the range between 200 rpm and 2000 rpm.
• an alkaline solution selected from alkaline and alkaline earth metal hydroxide and carbonate solutions, preferably
• air, pure oxygen or oxygen enriched air mixture obtained via membranes or other suitable technology.
• catalyst performance assays were performed on an apparatus containing a glass reactor, a mechanical stirrer, a alkaline solution addition system by means of a metering pump associated with a pH meter.
• the alkaline solution selected was 1 M NaOH.
• a 0.2 M aqueous 1,2- propanediol solution was used, a synthetic air flow (20% 0 2 in N 2 v / v) between 10 mLmin "1 elOO mLmin " 1 and a pH of 7.0 to 14.0 and kept constant by the addition of alkaline solution.
• the reaction temperature ranged from 30 ° C to 80 ° C and the reaction pressure from 1 bar to 5 bar.
• the platinum on alumina catalyst containing 5% w / w Pt was prepared by wet impregnation using a commercial alumina as a support and the hexachloroplatinic acid precursor salt.
• the first stage of preparation consisted of calcination of the support which was performed in a muffle furnace from room temperature to 500 ° C following a heating rate of 10 ° Cmin -1 maintained at 500 ° C for 4 hours. Subsequently, the acid was solubilized. hexachloroplatin in water This solution was added to the support (already calcined) and this suspension was stirred for 1 hour at room temperature After this step, the material was vacuum dried at 80 ° C. Finally, the solid obtained remained in an oven at 100 ° C for 12 hours and was then calcined at 500 ° C for 4 hours with a heating rate of 10 ° C / min and synthetic air stream with a flow rate of 60 ml min "1.
• Example 2 The 5% w / w Pt platinum on alumina catalyst prepared as described in Example 1 above was activated ex situ, ie it was heated from room temperature to 350 ° C following a heating rate of 10 ° Cmin "1 , maintained. for 2 hours at 350 ° C and using a pure hydrogen stream at a flow rate of 50 ml min "1.
• the 5% w / w Pt platinum-alumina catalyst prepared as described in Example 1 and activated ex-situ as described in Example 2 was weighed, transferred to a 500 mL glass reactor containing 200 mL of distilled water and re-activated. this time in situ by heating the reactor to 90 ° C and using a flow of 50 ml min "1 of pure hydrogen introduced into the suspension for a connected bubbler to the reactor. the suspension was stirred at 600 rpm and this condition was maintained for 1 hour Evaporation of water was prevented by employing a reflux condenser with water current in the coil.
• the 5% w / w Pt platinum-alumina catalyst prepared and activated according to Examples 1 to 3 was employed in the oxidation reaction of 1,2-propanediol.
• a 0.2 M aqueous 1,2-propanediol solution was added to the reactor containing 1 g of catalyst under stirring at 700 rpm.
• a glass electrode for pH measurement of the reaction medium was connected to the reactor.
• a burette was coupled containing a 1 M NaOH solution allowing its drip by manual activation.
• the pH in the reactor was adjusted to 8.0 by adding sufficient NaOH solution and maintained throughout the reaction period.
• a flow of 30 mLmin "1 of air was admitted by the bubbler.
• the reaction temperature was maintained at 40 ° C. After 5 hours of reaction under these conditions, total conversion of 1,2-propanediol is obtained and the following selectivity distribution between acid lactic acid, pyruvic acid and acetol: 65%, 23% and 12% respectively.
• the 5% w / w Pt platinum-alumina catalyst prepared and activated according to Examples 1 to 3 was employed in the oxidation reaction of 1,2-propanediol.
• a 0.2 M aqueous 1,2-propanediol solution was added to the reactor containing 1 g of catalyst under stirring at 700 rpm.
• a glass electrode for pH measurement of the reaction medium was connected to the reactor.
• a burette was coupled containing a 1 M NaOH solution allowing its drip by manual activation.
• the pH in the reactor was adjusted to 10.0 by adding sufficient NaOH solution and maintained throughout the reaction period.
• a flow of 30 mLmin "1 of air was admitted by the bubbler.
• the reaction temperature was maintained at 40 ° C. After 6 hours of reaction under these conditions, total conversion of 1,2-propanediol is obtained and the following distribution of selectivities. between lactic acid, pyruvic acid and acetol: 70%, 19% and 11% respectively.
• the 5% w / w Pt platinum-alumina catalyst prepared and activated according to Examples 1 to 3 was employed in the oxidation reaction of 1,2-propanediol.
• a 0.2 M aqueous 1,2-propanediol solution was added to the reactor containing 1 g of catalyst under stirring at 700 rpm.
• a glass electrode for pH measurement of the reaction medium was connected to the reactor.
• a burette was coupled containing a 1 M NaOH solution allowing its drip by manual activation.
• the pH in the reactor was adjusted to 8.0 by adding sufficient NaOH solution and maintained throughout the reaction period.
• a flow of 30 mLmin "1 of air was admitted by the bubbler.
• the reaction temperature was maintained at 60 ° C. After 6 hours of reaction under these conditions, total conversion of 1,2-propanediol is obtained and the following distribution of selectivities. between acid lactic acid, pyruvic acid and acetol: 61%, 27% and 12% respectively.

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