A preparation method of m-methylbenzyl alcohol

Abstract

The present invention belongs to the field of chemical catalysis technology, and discloses a method for preparing m-methylbenzyl alcohol. The present invention provides a route and corresponding catalyst for directly producing m-methylbenzyl alcohol from low-carbon alcohol aldehydes through hydrogen transfer or dehydrogenation-coupling-aromatization reaction. The selectivity of m-methylbenzyl alcohol is as high as 47.7%, and the selectivity of m-methylbenzaldehyde is 4.6%. m-methylbenzaldehyde can be converted into m-methylbenzyl alcohol by simple hydrogenation. Mild reaction conditions avoid the generation of excessive oxidation products. The reaction route produces hydrogen as a by-product, which is a clean energy source. The route also generates high-carbon chain alcohols, which are easy to separate by distillation and can be used as fuels or oil additives. In addition, the route also generates o- and p-methylbenzyl alcohols and methylbenzaldehyde, which can be used in the fields of spices, medicine, cosmetics, pesticides, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical catalysis and relates to a method for preparing m-methylbenzyl alcohol. Background Art

[0002] o-, m-, and p-methylbenzyl alcohol are important fine chemicals used in pharmaceutical synthesis and as solvents. m- and p-methylbenzyl alcohol, with their distinctive aroma, are used in flavorings and fragrances. p-methylbenzyl alcohol is also used to make plasticizers and pesticides.

[0003] Industrially, methylbenzyl alcohol is primarily produced by the oxidation of xylene. Chinese patent CN 1333200 A discloses a method for catalytic air oxidation of xylene to produce methylbenzaldehyde, methylbenzyl alcohol, and methylbenzoic acid. This method uses a metalloporphyrin or its solid support as a catalyst, either alone or with a metal salt as a co-catalyst, to achieve xylene oxidation at a temperature of 50-160°C, a pressure of 4-10 atm, and a reaction time of 8-12 hours. Chinese patent CN 105237344B discloses a method for the co-production of methylbenzoic acid, methylbenzyl alcohol, and methylbenzaldehyde. This method oxidizes xylene in stages, separates the products of the second oxidation, and separates and purifies them to produce methylbenzoic acid, methylbenzyl alcohol, and methylbenzaldehyde. These methods have relatively harsh reaction conditions, making the reaction process difficult to control, and methylbenzyl alcohol is prone to further oxidation to produce byproducts such as methylbenzoic acid. Furthermore, the xylene raw material is heavily dependent on petroleum resources. Therefore, the development of new synthetic routes for methylbenzyl alcohol using renewable resources is of great research significance. The research routes and catalyst systems for catalytically converting low-carbon molecules (such as biomass ethanol) into high-value chemicals have attracted the attention of many scientific researchers.

[0004] Currently, patents have reported routes for preparing o- and p-methylbenzyl alcohol from ethanol (CN109111344B; US10960386 B2), and routes for synthesizing benzyl alcohol and ethylbenzyl alcohol using ethanol and methanol / propanol as raw materials (CN109111343 B; US11338275 B2). Other literature reports have also reported the synthesis of o- and p-methylbenzaldehyde and methylbenzyl alcohol from ethanol and acetaldehyde [ChemSusChem 2016, 9, 736; ACS Catal. 2016, 6, 7278]. However, the methylbenzyl alcohols currently reported from lower-carbon aldols all produce o- and p-products, and the synthesis of m-methylbenzyl alcohol and m-methylbenzaldehyde has not yet been reported. Summary of the Invention

[0005] The present invention aims to develop a new route for preparing m-methylbenzyl alcohol via a coupling-aromatization reaction using ethanol / acetaldehyde and alkenal / enol as raw materials, and to provide the catalyst required for this catalytic conversion. The most significant feature of this route is the one-step production of the target product, m-methylbenzyl alcohol, using a single bed of catalyst.

[0006] This invention innovatively proposes a production route for m-methylbenzyl alcohol, achieving a selectivity of up to 47.7%. The byproduct, higher alcohols, can be used as fuels or oil additives. This route also produces o- and p-methylbenzyl alcohol and o-, m-, and p-methylbenzaldehyde, which can be used in flavorings, medicine, cosmetics, and other fields. This route offers the advantage of easy product separation, avoiding the formation of excessive oxidation products, and has promising industrial application prospects. The innovations of this patent include both innovative reaction pathways and catalyst systems.

[0007] The technical solution of the present invention:

[0008] A method for preparing m-methylbenzyl alcohol, the scheme is as follows:

[0009] Option 1: The mixture of raw materials is passed into a reactor loaded with a catalyst to produce m-methylbenzyl alcohol in one step.

[0010] The raw material mixture is a mixed liquid of ethanol and alkenal, which are respectively brought into the gas path through two carrier gas bubbling processes for premixing, and then enter the reactor for catalysis.

[0011] Preferably, the molar ratio of ethanol to alkenal is 0.5 to 10.

[0012] The catalyst is hydroxyphosphate or hydroxyphosphate modified by transition metal.

[0013] The reaction formula is as follows:

[0014]

[0015] Option 2: The mixed liquid of raw materials is passed into a reactor loaded with a catalyst to produce m-methylbenzyl alcohol in one step.

[0016] The raw material mixture is a mixed liquid of ethanol and enol, which are respectively brought into the gas path through two carrier gas bubbling processes for premixing, and then enter the reactor for catalysis.

[0017] Preferably, the molar ratio of ethanol to enol is 0.5 to 10.

[0018] The catalyst is a transition metal-modified hydroxyphosphate.

[0019] The reaction formula is as follows:

[0020]

[0021] Option 3: The mixed liquid of raw materials is passed into a reactor loaded with a catalyst to produce m-methylbenzyl alcohol in one step through a coupling-aromatization reaction.

[0022] The raw material mixture is a mixed liquid of acetaldehyde and alkenal, which are respectively brought into the gas path through two carrier gas bubblings for premixing, and then enter the reactor for catalysis.

[0023] The molar ratio of acetaldehyde to alkenal is preferably 0.5 to 10.

[0024] The catalyst is hydroxyphosphate or hydroxyphosphate modified by transition metal.

[0025] The reaction formula is as follows:

[0026]

[0027] Option 4: The mixed liquid of raw materials is passed into a reactor loaded with a catalyst to produce m-methylbenzyl alcohol in one step through a coupling-aromatization reaction.

[0028] The raw material mixture is a mixed solution of acetaldehyde and enol. Acetaldehyde and enol are respectively introduced into the gas path through two carrier gas bubbling processes for pre-mixing, and then enter the reactor for catalysis.

[0029] The molar ratio of acetaldehyde to enol is preferably 0.5 to 10.

[0030] The catalyst is hydroxyphosphate or hydroxyphosphate modified by transition metal.

[0031] The reaction formula is as follows:

[0032]

[0033] The reactor is preferably a fixed bed reactor.

[0034] The preferred reaction temperature is 200-400°C.

[0035] The partial pressure of ethanol and acetaldehyde in the above raw materials is preferably in the range of 0.1 to 15 kPa, and the partial pressure of enal and enol is preferably in the range of 0.1 to 10 kPa. An inert gas (such as nitrogen or argon) is used as a carrier gas to maintain the total pressure of the reaction system at 1 atm.

[0036] Optionally, the alkenal is selected from at least one of acrolein, 2-methylacrolein, 2-pentenal, 2-ethylacrolein, hexenal, 2-methyl-2-pentenal, and 2,4-hexadienal.

[0037] Optionally, the enol is selected from at least one of propenol, 2-hexen-1-ol, 3-buten-2-ol, methylallyl alcohol, and 3-methyl-2-buten-1-ol.

[0038] The catalyst is a hydroxyphosphate or a transition metal modified hydroxyphosphate catalyst, and contains the following components in weight percentage.

[0039] (1) The general chemical formula of hydroxyphosphate is A x B y C z D m E n (OH)2(PO4)6, wherein x+y+z+m+n=9-10, 9-10≥x,y,z,m,n≥0. A, B, C, D, and E are the same or different and are selected from one or a combination of two or more of Mg, Ca, Sr, and Ba; and the hydroxyphosphate is a mechanical mixture of one or more of the two.

[0040] (2) The transition metal in the transition metal-modified hydroxyphosphate catalyst is selected from one or a combination of two or more of Co, Ni, Cu, Ir, Zn, Y, Ag, and Pt. Furthermore, the transition metal element is one or more of Co, Ni, Cu, Zn, and Ag.

[0041] Using transition metal nitrate, chloride, levulinate, sulfate or acetate as a precursor, the concentration of the transition metal salt solution is 0.05g / mL to 5g / mL, and the modification amount is 0.1 to 10wt% of the weight of the hydroxyphosphate;

[0042] The catalyst is tableted and sieved to a specified particle size for filling.

[0043] The transition metal-modified hydroxyphosphate catalyst is reduced at 300-600°C for 0.5-6h before the reaction in a hydrogen atmosphere, wherein the concentration of the hydrogen atmosphere is one of 5-20vol% H2 / N2, 5-20vol% H2 / He, and 5-20vol% H2 / Ar.

[0044] The beneficial effects of the present invention are as follows: Compared with the prior art, the present invention provides a pathway and corresponding catalyst for directly producing m-methylbenzyl alcohol from low-carbon alcohols and aldehydes via a hydrogen transfer (or dehydrogenation)-coupling-aromatization reaction. The selectivity for m-methylbenzyl alcohol is as high as 47.7%, while the selectivity for m-methylbenzaldehyde is 4.6%. m-methylbenzaldehyde can be converted to m-methylbenzyl alcohol by simple hydrogenation. Mild reaction conditions avoid the formation of excessive oxidation products. This reaction route produces hydrogen as a byproduct, which is a clean energy source. This route also produces high-carbon chain alcohols that are easily separated by distillation and can be used as fuels or oil additives. In addition, this route also produces o- and p-methylbenzyl alcohols and methylbenzaldehyde, which can be used in fragrances, medicines, cosmetics, pesticides, and other fields. DETAILED DESCRIPTION

[0045] The specific implementation of the present invention is further described below in conjunction with the technical solution.

[0046] Hydroxyphosphate is represented by HAP-M, wherein: HAP represents hydroxy metal phosphate, M refers to metal, and is one or more of Mg, Ca, Sr, Ba, etc.

[0047] Transition metal modified hydroxyphosphate is represented by xMetal-HAP-M, wherein: Metal represents the loaded transition metal, which is one or more transition metals such as Co, Ni, Cu, Zn, Ag, etc., and x is the percentage of the Metal modification amount in the total weight of the catalyst × 100.

[0048] Example 1

[0049] Preparation process of HAP-Ca catalyst:

[0050] (1) Prepare Ca(NO3)2·xH2O and (NH4)2HPO4 into 0.5 mol / L and 0.3 mol / L aqueous solutions;

[0051] (2) At 25°C, the two salt solutions were mixed in a volume ratio of 1:1, the pH of the mixture was adjusted to 10 with aqueous ammonia, and the mixture was stirred with a magnetic stirrer for 2 h;

[0052] (3) the mixture obtained after stirring in step (2) was reacted in a rotary oven or hydrothermal device at 80°C for 24 hours;

[0053] (4) The precipitate obtained in step (3) was filtered and dried at 100° C. The obtained precursor was calcined at 600° C. in air atmosphere for 2 h to obtain HAP-Ca catalyst, corresponding to number 1 in Table 1;

[0054] (5) Different HAP-Ms can be prepared by controlling the type of metal (one or more of Mg, Ca, Sr, and Ba) in the nitrate solution. The preparation method is the same as the above steps.

[0055] The preparation conditions and processes of other catalysts were the same as those in Example 1. The corresponding relationship between sample numbers and preparation conditions is shown in Table 1.

[0056] Table 1 Correspondence between sample numbers and preparation conditions of Example 1

[0057]

[0058] Example 2

[0059] Preparation process of transition metal modified HAP-Ca catalyst:

[0060] (1) Take HAP-Ca and dry it in an air flow oven at 100°C for 2 h to remove the physically adsorbed water on the surface;

[0061] (2) preparing a transition metal salt solution of a certain mass concentration at 25° C., impregnating an equal volume of the HAP-Ca obtained by drying in step (1) and allowing to stand for 2 h;

[0062] (3) drying the mixture obtained in step (2) in an air atmosphere at 100° C. to obtain a catalyst precursor;

[0063] (4) The catalyst precursor obtained in step (3) was oxidized in air at 600°C for 2 h, and then reduced in a hydrogen atmosphere (10 vol% H2 / N2) at 600°C for 2 h to obtain a transition metal-modified HAP-Ca catalyst, which was recorded as xMetal-HAP-Ca catalyst.

[0064] (5) The type and amount of metal modification can be controlled by controlling the type, concentration and number of immersions of the metal salt solution. The preparation method is the same as the above steps.

[0065] The preparation conditions and processes of other catalysts were the same as those in Example 2. The corresponding relationship between sample numbers and preparation conditions is shown in Table 2.

[0066] Table 2 Correspondence between sample numbers and preparation conditions of Example 2

[0067]

[0068] Example 3

[0069] The reaction is carried out in a fixed-bed reactor using a mixture of ethanol and enal as raw materials and hydroxyphosphate as a catalyst. Ethanol and enal are introduced into the gas path through two separate carrier gas bubbling lines for premixing before entering the reactor for catalysis.

[0070] The reaction conditions were as follows: a fixed bed reactor with an inner diameter of 8 mm was filled with the catalyst, atmospheric pressure was applied, and the reaction temperature was 300° C. After the reaction stabilized, the reaction materials and products were analyzed using online chromatography.

[0071] Preferably, the molar ratio of ethanol to alkenal is 0.5 to 10.

[0072] The catalytic activity of hydroxyphosphates for the conversion of ethanol and alkenal is shown in Table 3.

[0073] Table 3 Catalytic activity of Example 3

[0074]

[0075] Example 4

[0076] The reaction is carried out in a fixed-bed reactor using a mixture of ethanol and enol as the raw material and a transition metal-modified hydroxyphosphate (xMetal-HAP-M) as the catalyst. Ethanol and enol are introduced into the gas line via two separate carrier gas bubbling lines for premixing before entering the reactor for catalysis.

[0077] The reaction conditions were as follows: a fixed bed reactor with an inner diameter of 8 mm was filled with the catalyst, atmospheric pressure was applied, and the reaction temperature was 300° C. After the reaction stabilized, the reaction materials and products were analyzed using online chromatography.

[0078] The molar ratio of ethanol to enol is 4.

[0079] The catalytic activity of xMetal-HAP-M for the conversion of ethanol and enol is shown in Table 4.

[0080] Table 4 Catalytic activity of Example 4

[0081]

[0082]

[0083] Example 5

[0084] The reaction is carried out in a fixed-bed reactor using a mixture of acetaldehyde and alkenal as raw materials and hydroxyphosphate as a catalyst. Acetaldehyde and alkenal are introduced into the gas path through two separate carrier gas bubbling channels for pre-mixing before entering the reactor for catalysis.

[0085] The reaction conditions were as follows: a fixed-bed reactor with an inner diameter of 8 mm was loaded with the catalyst and the reaction was carried out under normal pressure. After the reaction stabilized, the reaction materials and products were analyzed by online chromatography.

[0086] The molar ratio of acetaldehyde to alkenal is 4.

[0087] The catalytic activity of hydroxyphosphates in the conversion of acetaldehyde and alkenal is shown in Table 5.

[0088] Table 5 Catalytic activity of Example 5

[0089]

[0090] Example 6

[0091] The reaction is carried out in a fixed-bed reactor using a mixture of acetaldehyde and enol as the raw material and a transition metal-modified hydroxyphosphate (xMetal-HAP-M) as the catalyst. Acetaldehyde and enol are introduced into the gas path using two separate carrier gas bubbling lines for premixing before entering the reactor for catalysis.

[0092] The reaction conditions were as follows: a fixed bed reactor with an inner diameter of 8 mm was filled with the catalyst, atmospheric pressure was applied, and the reaction temperature was 300° C. After the reaction stabilized, the reaction materials and products were analyzed using online chromatography.

[0093] The molar ratio of acetaldehyde to enol is 4.

[0094] The catalytic activity of xMetal-HAP-M for the conversion of acetaldehyde and enol is shown in Table 6.

[0095] Table 6 Catalytic activity of Example 6

[0096]

[0097] Comparative Example 1

[0098] Product distribution when ethanol and alkenal are fed separately over HAP-Ca catalyst.

[0099] Catalytic reaction tests were conducted in a fixed-bed reactor using ethanol and enal as reactants. The reaction conditions were as follows: the catalyst was loaded into an 8 mm inner diameter fixed-bed reactor, atmospheric pressure, and a reaction temperature of 300°C. After the reaction stabilized, the raw materials and products were analyzed using online chromatography. The product distributions for different reactants are shown in Table 7.

[0100] Table 7 Product selectivity corresponding to different reaction raw materials in Comparative Example 1

[0101]

[0102] Comparative Example 2

[0103] 2.0Product distribution when ethanol and aldehyde are fed separately over Zn-HAP-Ca catalyst.

[0104] Catalytic reaction tests were conducted in a fixed-bed reactor using ethanol and enal as reactants. The reaction conditions were as follows: the catalyst was loaded into an 8 mm inner diameter fixed-bed reactor, atmospheric pressure, and a reaction temperature of 300°C. After the reaction stabilized, the raw materials and products were analyzed using online chromatography. The product distributions for different reactants are shown in Table 7.

[0105] Table 8 Product selectivity corresponding to different reaction raw materials in Comparative Example 2

[0106]

Claims

1. A method for preparing m-methylbenzyl alcohol, characterized in that: Here are the steps: The mixture of raw materials is passed into a reactor loaded with a catalyst to produce m-methylbenzyl alcohol in one step; The raw material mixture is a mixed solution of ethanol and alkenal, which are respectively brought into the gas path through two carrier gas bubbles for pre-mixing, and then enter the reactor for catalysis; The molar ratio of ethanol to alkenal is 0.5 to 10; The catalyst is hydroxyphosphate or transition metal-modified hydroxyphosphate; The reaction formula is as follows: The alkenal is selected from at least one of acrolein, 2-methylacrolein, 2-pentenal, 2-ethylacrolein, hexenal, 2-methyl-2-pentenal, and 2,4-hexadienal; The partial pressure of ethanol in the raw material is 0.1-15 kPa, the partial pressure of olefinic aldehyde is 0.1-10 kPa, and an inert gas is used as a carrier gas to maintain the total pressure of the reaction system at 1 atm.

2. The method according to claim 1, characterized in that Here are the steps: The raw material mixture is replaced by a mixture of ethanol and enol, which are respectively introduced into the gas path through two carrier gas bubbles for pre-mixing, and then enter the reactor for catalysis; The molar ratio of ethanol to enol is 0.5 to 10; The catalyst is a transition metal-modified hydroxyphosphate; The reaction formula is as follows: The enol is selected from at least one of propenol, 2-hexen-1-ol, 3-buten-2-ol, methylallyl alcohol, and 3-methyl-2-buten-1-ol; The partial pressure of ethanol in the raw material is 0.1-15 kPa, the partial pressure of enol is 0.1-10 kPa, and an inert gas is used as a carrier gas to maintain the total pressure of the reaction system at 1 atm.

3. The method according to claim 1, characterized in that Here are the steps: The raw material mixture is replaced by a mixture of acetaldehyde and alkenal, which are respectively brought into the gas path through two carrier gas bubbles for pre-mixing, and then enter the reactor for catalysis; The molar ratio of acetaldehyde to alkenal is 0.5 to 10; The catalyst is hydroxyphosphate or transition metal-modified hydroxyphosphate; The reaction formula is as follows: The alkenal is selected from at least one of acrolein, 2-methylacrolein, 2-pentenal, 2-ethylacrolein, hexenal, 2-methyl-2-pentenal, and 2,4-hexadienal; The partial pressure of acetaldehyde in the raw materials is 0.1-15 kPa, the partial pressure of olefinic aldehyde is 0.1-10 kPa, and an inert gas is used as a carrier gas to maintain the total pressure of the reaction system at 1 atm.

4. The method according to claim 1, wherein Here are the steps: The raw material mixture is replaced with a mixture of acetaldehyde and enol; acetaldehyde and enol are respectively introduced into the gas path through two carrier gas bubbles to be pre-mixed, and then enter the reactor for catalysis; The molar ratio of acetaldehyde to enol is 0.5 to 10; The catalyst is hydroxyphosphate or transition metal-modified hydroxyphosphate; The reaction formula is as follows: The enol is selected from at least one of propenol, 2-hexen-1-ol, 3-buten-2-ol, methylallyl alcohol, and 3-methyl-2-buten-1-ol; The partial pressure of acetaldehyde in the raw materials is 0.1-15 kPa, the partial pressure of enol is 0.1-10 kPa, and an inert gas is used as a carrier gas to maintain the total pressure of the reaction system at 1 atm.

5. The method according to any one of claims 1 to 4, characterized in that: The reaction temperature in the reactor is 200-400°C.

6. The method according to any one of claims 1 to 4, characterized in that: The catalyst is a hydroxyphosphate catalyst or a transition metal-modified hydroxyphosphate catalyst; The general chemical formula of the hydroxyphosphate catalyst is A x B y C z D m E n (OH)2(PO4)6, wherein x+y+z+m+n=9-10, 9-10≥x, y, z, m, n≥0; wherein A, B, C, D and E are the same or different and are selected from one or a combination of two or more of Mg, Ca, Sr and Ba; the hydroxyphosphate catalyst is a mechanical mixture of one or more of the two; The transition metal in the transition metal-modified hydroxyphosphate catalyst is selected from one or a combination of two or more of Co, Ni, Cu, Ir, Zn, Y, Ag, and Pt; a nitrate, chloride, acetylation, sulfate, or acetate of the transition metal is used as a precursor; the concentration of the transition metal salt solution is 0.05 g / mL to 5 g / mL; and the modification amount is 0.1 to 10 wt% of the weight of the hydroxyphosphate.

7. The method according to claim 6, characterized in that The transition metal-modified hydroxyphosphate catalyst is reduced at 300-600°C for 0.5-6h before the reaction in a hydrogen atmosphere, wherein the concentration of the hydrogen atmosphere is one of 5-20vol% H2 / N2, 5-20vol% H2 / He, and 5-20vol% H2 / Ar.

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