Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C41/00—Preparation of ethers; Preparation of compounds having groups, groups or groups
  • C07C41/48—Preparation of compounds having groups
  • C07C41/50—Preparation of compounds having groups by reactions producing groups
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
  • C07C45/27—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation
  • C07C45/32—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen
  • C07C45/37—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of >C—O—functional groups to >C=O groups
  • C07C45/38—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of >C—O—functional groups to >C=O groups being a primary hydroxyl group

Definitions

• the present invention relates to a process for the synthesis of dialkoxyalkanes by selective oxidation of light alcohols.
• dialkoxyalkanes of the process of the invention correspond to the following general formula: ## STR1 ## in which R and R 'are either H or a radical CH 3 - (CH 2 ) n ⁇ , n being between 0 and 2 and such that the total number of carbon atoms of the radicals R and R 'is ⁇ 3.
• These compounds are obtained by oxidation of light alcohols, that is to say linear alcohols containing from 1 to 4 carbon atoms. They are primary alcohols such as methanol, ethanol, 1-propanol, 1-butanol or secondary alcohols such as 2-propanol (or isopropanol) or 2-butanol.
• aldehydes formaldehyde from methanol
• acids or esters They are generally used to form aldehydes (formaldehyde from methanol) or acids or esters. It is moreover known that the oxidation of methanol in the presence of various catalysts leads at low temperature to the production of a poorly selective mixture of various oxidized compounds, such as in particular formaldehyde, methyl formate or methylal (dimethoxymethane). .
• the same scheme can be transposed to ethanol and other light alcohols.
• the partial oxidation processes of the light alcohols make it possible to synthesize dialkoxyalkanes according to the following overall reaction corresponding to the primary alcohols: 6 RCH 2 OH + O 2 * 2 RCH 2 ORCHOCH 2 R + 4H 2 O which is the result of two successive stages: 2 RCH 2 OH + O 2 "* 2 RCHO + 2H 2 O 2 RCHO + 4 RCH 2 OH - * 2 RCH 2 ORCHOCH 2 R + 2H 2 O Des Similar mechanisms are used in the oxidation reactions of secondary light alcohols such as 2-propanol and 2-butanol.
• the initial oxidation of the secondary alcohol leads to a ketone of formula CH 3 -CO-CH 3 with isopropanol and CH 3 -CO-C 2 H 5 with 2-butanol.
• the following reaction step of the ketone with the light alcohol leads to the dialkoxyalkanes of the respective formulas (CH 3 ) 2 CH-O-C (CH 3 ) 2 -O-CH (CH 3 ) 2 and (C 2 H 5 ) (CH 3 ) CH-OC (CH 3 ) (C 2 H 5 ) -O-CH (CH 3 ) (C 2 H 5 ).
• the overall reaction for the oxidation to 2,2-diisopropoxypropane dialkoxyalkane of isopropanol is as follows.
• the parasitic reactions can be caused by the nature of the catalysts used for the oxidation.
• the applicant company has surprisingly discovered that the catalysts described for the catalysis of the partial oxidation reaction of light alcohols which are homogeneous or solid multiphase materials insoluble in the reaction medium may have certain "basic" undesirable sites which are presumably at the origin of the formation of the by-products by mechanisms of reaction sometimes unpredictable.
• the object of the present invention is to overcome these disadvantages by implementing the method by adding within the reaction gas medium a compound capable of being fixed at least temporarily on these sites and, by inhibiting them during the process, to avoid for a large part the formation of by-products.
• the present invention relates to the synthesis of dialkoxyalkanes having the following general formula: RR 'CH-O-CRR' -O-CHRR ', in which R and R' are either H or a CH 3 - (CH 2 ) n radical ⁇ , n being between 0 and 2 and such that the total number of carbon atoms of the radicals R and R 'is ⁇ to 3 by partial selective oxidation of a light alcohol comprising from 1 to 4 carbon atoms, characterized in that it is implemented in the presence of oxygen and a solid oxidation catalyst in a reaction medium comprising a gaseous phase containing an acidic compound.
• the term "acid compound” means a compound which, in addition to what will be specified below, after, will present in solution in water a pKa lower than 6.3.
• CO2 is not an acid within the meaning of the present invention.
• the light alcohols used are either primary alcohols such as methanol, ethanol, 1-propanol, isopropanol, n-butanol, 1-butanol, or secondary alcohols such as 2-propanol (or isopropanol). ) or 2-butanol.
• the oxidation is carried out by gas phase contact using oxygen or a gas containing molecular oxygen (for example air).
• the oxidation is carried out in the presence of a solid catalyst based on at least one metal selected from Mo, V, W, Re, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Te, Sb, Bi, Pt, Pd, Ru, Rh.
• a solid catalyst based on at least one metal selected from Mo, V, W, Re, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Te, Sb, Bi, Pt, Pd, Ru, Rh.
• the catalysts selected for this reaction are acidic solids.
• the acidity of solids can be measured in many ways and Hammett's method is just one of them. It has been observed by the applicant that these naturally acidic catalysts can also have rather basic sites.
• we will mention the publications of Aline Auroux where are described different methods for measuring acidity scales of solids such as: A. Auroux and A. Gervasini, "J. Microcalorimetric Study of the Acidity and Basicity of Metal Oxide Surfaces" Phys. Chem., (1990) 94, 6371-79 and L. Damjanovic and A.
• the process is carried out in the presence in the gaseous phase of the reaction medium of an acid compound added and which has an affinity with the basic undesirable sites carried by the catalyst.
• This compound will be selected from hard and soft acids as defined in the so-called Pearson classification illustrated in the following articles RG Pearson, J. Am. Chem. Soc., 85, 3533 (1963); RG Pearson, Science, 151 (1966) 172; RG Pearson, Chemistry in England, March 1967, 103; RG Pearson, J. Chemical Education, Vol45 # 9 (1968) 581 and Vol 45 N 0 IO (1968) 643; RG Parr and RG Pearson, J. Am. Chem.
• This acidic compound will be chosen in particular from SO 3, SO 2, NO 2, etc. It would not be outside the scope of the invention, if a mixture of these compounds is used, it is indeed possible to use a mixture of compounds combining different acidities. in order to inhibit the various basic sites present on the catalyst. Indeed, according to Pearson's theory, it seems that hard acids prefer to associate with hard bases and soft acids with moles.
• the content of acidic compounds will depend on the nature of the catalyst chosen for the reaction. It will generally be between 1 and 3000 ppm of the gas phase.
• the catalysts used in the process of the invention are catalysts already known for the oxidation of alcohols and also for the partial oxidation of said alcohols to dialkoxyalkanes. They have already been the subject of various publications. There may be mentioned the use of a rhenium-antimony-based catalyst (SbRe2 ⁇ ) for the manufacture of methylal by oxidation of methanol described in US Pat. No. 6,403,841. Furthermore, J. Sambeth, L. Gambaro and H.
• the Applicant has also filed a patent application WO2007 / 034264 describing the use in this type of process of partial oxidation of methanol of a catalyst consisting of a mixed oxide based on molybdenum and vanadium associated where appropriate with other metallic elements.
• the preferred catalyst had the formula M012 V 3 Wi -2 CU1.2 Sbo.5 O x where x is a numerical value determined by the degree of oxidation of the other elements.
• these catalysts consist of metal oxides, generally mixed oxides of metals.
• the preferred catalysts in the process of the invention are those based on molybdenum and iron. Mention may be made, for example, of mixed oxides of formulas: M012BiFe3.7C04.7Ni2.6Ko.09Sb1Si7.9Ox, MOi 2 BiFe 3 . 7 Co 4 .7Ni 2 ⁇ K 0 .09Ti 0 .5S 1 IgO x or MoO 3 -Fe 2 (MoO 4 ) 3 •
• the reaction will generally be carried out at a temperature of between 10 and 400 ° C. and at a pressure of between 50 and 1000 kPa and a rate of introduction of the charge mixture such as the hourly volume velocity (VVH), that is to say ie the flow rate of the reaction mixture relative to the volume of catalyst used will be in particular between 2000 and 100,000 h -1 .
• VVH hourly volume velocity
• the oxidation is preferably carried out by contact in the vapor phase at a temperature of in particular between 100 and 350 ° C., and more preferably between 200 and 300 ° C.
• the pressure will preferably be between 100 and 500 kPa.
• the space velocity of introduction of the reaction mixture will preferably be between 11 000 and 44 000 h -1 .
• the reaction according to the invention can also be carried out in the liquid phase.
• a catalyst at a temperature ranging from 150 ° C. to 500 ° C., preferably between 250 ° C. and 350 ° C., and a pressure greater than 5 bar and preferably comprised between between 20 and 80 bars.
• various process technologies can be used, namely fixed bed process, fluidized bed process or circulating fluidized bed process. In the first two processes, in a fixed bed or in a fluidized bed, the regeneration of the catalyst can be separated from the reaction.
• the temperature and pressure at which the regeneration is effected need not be the same as those at which the reaction is carried out.
• the addition of the Pearson acid compound is not carried out during the regeneration.
• it can be carried out continuously in situ, at the same time as the reaction, given the presence of a small amount of molecular oxygen or an oxygen-containing gas. molecular in the reactor.
• the regeneration is similar to an inhibition of the deactivation and is done at the temperature and pressure of the reaction. Because of these particular conditions where the regeneration takes place continuously, the injection of the gaseous acid compound is found to be simultaneous.
• the catalyst circulates in two capacities, a reactor and a regenerator.
• the injection of the gaseous acid compound is preferably carried out at the reactor.
• Zone 0 flammable flammable mixtures.
• Zone 3 is the one where the concentration in alcohol is weak and that in oxygen more or less important but always below the threshold of inflammability, whereas, in the left part, Zones 1 and 2 correspond to a low oxygen content (above the flammability threshold).
• Lines 3, 4 and 5 correspond to the stoichiometries of the The main oxidation reactions of alcohol, methanol in this case, an ethanol rearrangement can easily be achieved using the appropriate flammability diagram.
• Line 3 corresponds to the combustion of methanol (CH 3 OH + 3/2 O 2 * CO 2 + 2H 2 O), line 4 to the formaldehyde oxidation (CH 3 OH + 1 ⁇ O 2 -> CH 2 O + H 2 O), line 5 to the synthesis of methylal (3 CH 3 OH + ⁇ O 2 -> CH 3 OCH 2 OCH 3 + H 2 O) and finally the line 6 to air is to say the straight line joining the top methanol to the mixture N 2 (Inert) / O 2 80/20.
• Zone 1 corresponds to mixtures in which an oxygen content is used which is lower than that of air (use of diluted air). It is located entirely above line 6.
• Zone 2 corresponds to mixtures in which an oxygen content higher than that of air is used. It is entirely below line 6.
• Zones 1 and 2 In the Id zone, we have more of oxygen as stoichiometry for the synthesis of methylal, one can thus expect conversions and high yields. It is possible in each of Zones 1 and 2 to distinguish zones: Id, Ig and l 'and 2d, 2g, 2'.
• zones 1 the reaction can be carried out with air as oxidant
• Zone 3 is the area bounded by the lower flammability limit.
• Zones Id, Ig and 2g are delimited by the maximum oxygen content (MOC). Below this oxygen content, it is guaranteed to be outside the limits of flammability. It is therefore preferred to work in this area for safety reasons.
• MOC maximum oxygen content
• Zones l, ld and Ig, and 2g, 2d and 2 ' are delimited by the stoichiometric line of the reaction methanol -> methylal (6 CH 3 OH / O 2 ). On the right of this line, there is enough oxygen to have a total conversion of methanol to 100% selectivity to methylal; on the left, there is not enough oxygen and the conversion will only be partial. It is therefore preferred to work in zones I, II and 2 '.
• Zones Id, Ia and Ig in which it is possible to work with high levels of both alcohols (30 to 40 or even 50 or 60% by volume) and oxygen, of the order of 15% while working with air as an oxygen source by avoiding the use of a large source of inert gas.
• O 2 the maximum content of O 2 depends on the alcohol and it rises.
• This ternary diagram can be transposed on one hand with the same constituents to other conditions of temperature and pressure and on the other hand to other alcohols with reference to the publications and in particular that of Zebetakis which also illustrates the diagram of ethanol.
• page 67 of this publication is a table from which one can deduce the maximum levels of oxygen according to the alcohol used.
• the invention therefore also relates to the use of the process as defined above for the synthesis of diethoxyethane by oxidation of ethanol.
• the evaluation of the catalyst is carried out in a fixed bed reactor.
• the flow of helium and oxygen is regulated by mass flow meters.
• the gas flow passes through an evaporator / saturator containing the methanol.
• the evaporator is either at room temperature or heated by heating strips.
• the temperature of the saturator is adjusted to control the partial pressure of methanol.
• the temperature of the gas mixture is controlled by a thermocouple at the top of the saturator.
• the gaseous mixture is then sent to the reactor which is placed in an oven.
• the reaction temperature is measured using a thermocouple that is in the catalytic bed.
• gaseous effluents are analyzed by in-line gas phase chromatography using a microGC equipped with 2 columns (Molecular sieve and Plot U).
• the catalyst is ground and the 250 micron particle size fraction is mixed with a double amount of silicon carbide of the same particle size and placed in the glass reactors.
• MicrogC calibration was performed with reference gas mixtures, and calibration for condensables (dimethoxymethane, methanol, methyl formate) was performed using a saturator evaporator.
• the catalyst is prepared as in Example 1 of patent application WO2007 / 034264.
• the catalyst has the formula M012 V 3 Wi -2 CU1.2 Sbo.5 O x where x is a numerical value determined by the degree of oxidation of the other elements.
• 150 mg of this catalyst are mixed with 300 mg of silicon carbide and are loaded into the reactor.
• the catalyst is activated under a gaseous flow composed of a mixture of helium and oxygen (48 Nm 1 min -1 / 12 Nm 1 min -1 ) at 340 ° C. for 15 hours and 30 minutes.
• the catalyst temperature is lowered to 280 0 C and the data are recorded.
• the efficiency of the catalyst is recorded.
• the catalyst temperature is decreased at the following temperature: 280 0 C, 270 0 C, 260 ° C and 250 0 C where the data are recorded.
• the flow rates of oxygen and helium are respectively 4.7 and 46.3 NmI. min -1 and the concentration of methanol is set at 7.5%.
• MoVWSbCu 260 33 .1 90, 9 1, 4 5 8 1, 5 0, 4 0, 0 100
• the evaluation of the catalysts is carried out in a fixed bed reactor.
• the flow of helium and oxygen is regulated by mass flow meters.
• the gas flow passes through an evaporator / saturator containing the methanol.
• the evaporator is either at room temperature or heated by heating strips.
• the temperature of the saturator is adjusted to control the partial pressure of methanol.
• the temperature of the gas mixture is controlled by a thermocouple at the top of the saturator.
• the gaseous mixture is then sent to the reactor which is placed in an oven.
• the reaction temperature is measured using a thermocouple which is in the catalytic bed.
• the gaseous effluents are analyzed by in-line gas phase chromatography using a microGC equipped with 2 columns (Molecular sieve and Plot U).
• the catalysts are ground and the 250 micron particle size fraction is mixed with a double amount of silicon carbide of the same particle size and placed in the glass reactors.
• MicrogC calibration was performed with reference gas mixtures, and calibration for condensables (dimethoxymethane, methanol, methyl formate) was performed using a saturator evaporator.
• Example 5 Reaction of oxidation of methanol. (according to the invention)
• the catalyst is first activated under a stream of Helium / Oxygen (48 Nml / min - 12 Nml / min) at 340 ° C. for 15 hours and 30 minutes. Then, the temperature is reduced to 250 0 C and data acquisition begins. After stabilization, the performances of the catalyst are recorded. Then the catalyst temperature is increased by trays and at each level (260, 271 and 281 0 C) data are taken.
• Helium / Oxygen 48 Nml / min - 12 Nml / min
• the flow rates of oxygen and helium are respectively 6.7 and 26.4 Nml / min and the concentration of methanol is adjusted to 37%. (conditions: Methanol / 02 / inert: 37/13/50) for a VVH of 22000 ml.h-l.g-1.
• the concentration of SO2 is 1000 ppm vol relative to the total flow.
• Example 7 Operating Conditions for the Selective Oxidation of Ethanol
• the catalyst is tested in a fixed bed reactor.
• the flow rates of the helium and oxygen gases are regulated by a mass flow controller.
• the gas mixture passes through an evaporator / saturator filled with ethanol.
• the evaporator may be at room temperature or heated by a heating cord.
• the saturator temperature is adjusted and controlled to obtain the desired ethanol partial pressure.
• the temperature is measured using a thermocouple at the output of the saturator.
• the reaction mixture feeds the reactor which is placed in an oven.
• the temperature of the reaction is measured by a thermocouple placed in the catalytic bed.
• the gaseous effluents are analyzed online by a micro-GC equipped with three columns (molecular sieve, Plot U and OV-I).
• a flow of helium and oxygen passes through the evaporator / saturator adjusted to the appropriate temperatures to obtain the desired composition of ethanol / oxygen / helium.
• the catalyst is mixed with the quadruple amount of silicon carbide in the glass reactor.
• Calibration of the micro-GC is performed with reference gas mixtures and the condensables are calibrated using the evaporator / saturator.
• Example 8 150 mg of the MFM3-MS catalyst (supplied by MAPCO) are mixed with 600 mg of silicon carbide and charged to the reactor.
• the catalyst is activated at a temperature of 340 ° C. under a helium / oxygen mixture (48 Nm 1 min-1/12
• the temperature of the catalyst is increased to the next temperature

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