Modified Raney cobalt catalyst as well as preparation method and application thereof

Abstract

The invention discloses a modified Raney cobalt catalyst as well as a preparation method and application thereof. The catalyst comprises the following metal elements in percentage by mass: 60-90% of Co, 1-10% of Zn, 0.5-5% of Mn, 0.1-5% of Mg and 5-30% of Al, preferably, the Co accounts for 75-85%, the Zn accounts for 2-6%, the Mn accounts for 1-3%, the Mg accounts for 1-2%, and the Al accounts for 10-20%. According to the method, citral is used as a raw material, modified Raney cobalt is used as a catalyst, and citral is selectively hydrogenated into citronellol and geraniol by using an intermittent hydrogenation method. Meanwhile, compared with a noble metal catalyst, the cost of the catalyst is remarkably reduced.

Description

Technical Field

[0001] The invention relates to the field of preparation of geraniol and citronellol, and in particular to a modified Raney cobalt catalyst and a preparation method thereof, and a method for preparing citronellol and simultaneously co-producing geraniol by using the modified Raney cobalt catalyst to selectively hydrogenate citral. Background Art

[0002] Citronellol is an important flavor raw material with a sweet floral scent similar to that of roses. It is often used in rose and citrus fragrances and can be used as a raw material for making dihydrocitronellol and hydroxydihydrocitronellal. Citronellol can also be used in edible flavors, such as soft drinks, baked goods, candies, jelly puddings, etc. It is one of the bulk flavor raw materials.

[0003] Geraniol (chemical name is trans-3,7-dimethyl-octadien-1-ol) is a precious fragrance. Together with citronellol and 2-phenylethanol, it belongs to the so-called rose alcohol. It is the main component of rose oil and an important aromatic chemical for making rose fragrance. Unlike nerol, geraniol has a more rounded and fruity fragrance.

[0004] The current mainstream method of chemical synthesis is to directly and selectively reduce citral to obtain the above-mentioned flavor substances. The citral molecule contains isolated C=C double bonds, C=O bonds, and C=C double bonds conjugated with carbonyl groups that can be hydrogenated. The products that may be generated after hydrogenation are relatively complex. Depending on the catalyst and reaction conditions, the hydrogenation reaction may occur in different locations, resulting in different products.

[0005]

[0006] Patent document US4029709 introduces a method for obtaining citronellol by selective hydrogenation of citral or citronellal. The method selects a Raney nickel catalyst modified with chromium as a reaction catalyst, and selects one or several saturated lower alcohols as reaction solvents. The direct selectivity mentioned in this method is as high as 92%. The catalyst used in this method does not involve precious metal elements, and the catalyst cost is relatively low. However, the disadvantages of this method are: 1. The reaction selectivity is relatively low, there are still many by-products, and the later separation is difficult; 2. The use of chromium elements leads to the risk of environmental pollution in the later catalyst treatment; 3. The raw material citral can undergo esterification reaction with the solvent lower alcohol, which further causes a reduction in the target yield of the reaction.

[0007] Patent documents US7005554 and CN1281564C introduce a continuous selective hydrogenation catalyst and a facility capable of intercepting catalyst particles for recycling. The catalyst described therein can preferentially hydrogenate carbon-oxygen double bonds, and its active components include ruthenium. The advantages of this invention are that the continuous process is easy to operate, has a high time-space yield, and also solves the problem of difficulty in replacing the catalyst in the continuous process. However, the catalyst uses the precious metal ruthenium, which is expensive. This makes it difficult to control production costs. The article does not describe in detail the details of the preparation and recovery of the catalyst, but it can be foreseen that the preparation of the catalyst and the recovery of the ruthenium metal are two quite complex and delicate operating processes.

[0008] Patent document CN1247182A introduces a method for preparing citronellol by gas phase catalytic hydrogenation using a cobalt active catalyst supported on alumina. The advantages of this invention are that it can be operated continuously, reacts at normal pressure, and has low equipment investment. The problems of this method are that the conversion rate and selectivity are low (up to 93%), and the boiling points of the raw material citral and the product citronellol are similar, making it difficult to separate and obtain citronellol by distillation.

[0009] Patent document CN102295531B relates to a method for obtaining citronellol by directly reducing citral using an intermittent hydrogenation method. The reaction system uses citral as a raw material, and an M2-type metal skeleton alloy solid as a catalyst. The reaction system also includes an aqueous solution of an amine substance and a non-polar solvent. The citral is selectively reduced to a crude citronellol product by hydrogen using an intermittent hydrogenation method, and a refined citronellol product is obtained by vacuum distillation. The target selectivity of this process is relatively high, and the reaction selectivity is more than 96%. However, this process still has the following two problems: (1) The reaction system is relatively complex, and the actual reaction process involves an aqueous phase, an oil phase, a solid phase (catalyst) and a gas phase (hydrogen). There are many factors affecting the reaction process, and it is not easy to operate in the actual industrial process; (2) The amines added to the reaction system have a potential adverse effect on the quality of the product because the amines have a relatively unacceptable odor.

[0010] The above document describes several catalysts and production methods with higher selectivity, but still does not thoroughly solve the problems of high cost and low operability. In addition, since the series products of citral hydrogenation all have similar structures and molecular weights, it is challenging to obtain a single pure substance by distillation separation, so it is required to have higher selectivity in the reaction process. The technical problem to be solved by the present invention is to overcome the defects of the above-mentioned prior art, and to provide a method and catalyst for the simultaneous co-production of citronellol and geraniol with high efficiency, low cost and ease of realization. Summary of the invention

[0011] The purpose of the present invention is to develop an improved preparation technology to address the problems of high cost and low operability of the prior art, as well as the technical difficulty of difficulty in subsequent separation due to poor selectivity. The technology uses a modified Raney cobalt catalyst to selectively hydrogenate the starting compound citral to prepare citronellol and co-produce geraniol, which has good industrial prospects.

[0012] In order to achieve the above invention object, the technical solution of the present invention is as follows:

[0013] According to the present invention, a method for preparing citronellol and simultaneously producing geraniol is provided, the method comprising: subjecting a starting compound citral to a selective hydrogenation reaction under the catalytic action of a heterogeneous catalyst to prepare citronellol and geraniol.

[0014] A modified Raney cobalt catalyst, wherein the mass percentage of metal elements in the catalyst is: Co is 60-90%, Zn is 1-10%, Mn is 0.5-5%, Mg is 0.1-5%, and Al is 5-30%; preferably, Co is 75-85%, Zn is 2-6%, Mn is 1-3%, Mg is 1-2%, and Al is 10-20%.

[0015] The preparation method of the present invention comprises the following steps: five metals, Co, Zn, Mn, Mg and Al, are sequentially melted, cooled and crushed into alloy particles, and then the aluminum element in the alloy particles is partially washed away with a strong alkaline aqueous solution, and finally the aluminate remaining in the skeletal solid pores is repeatedly washed with water (e.g. tap water) to finally obtain an activated modified Raney cobalt catalyst with a rich pore structure.

[0016] It should be noted that the addition of the metal promoter Mg significantly improves the activity of the catalyst, that is, the metal promoter Mg in a low oxidation state accepts the lone pair of electrons provided by the oxygen in the carbonyl group, polarizes the carbonyl group, and makes it easy for the H dissociated from the adjacent nickel to carry out nucleophilic attack on the C in the carbonyl group, thereby completing the hydrogenation reaction faster.

[0017] Generally, the melting temperature is 1600-2000°C.

[0018] There is no particular limitation on the strong alkali aqueous solution used, and it may be, for example, a 5-30 wt % sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, or the like.

[0019] The pulverization is, for example, pulverizing the melt of the four metals into a particle size of 10-500 meshes, especially 50-200 meshes.

[0020] The use of a strong alkaline aqueous solution to wash away the aluminum element in the alloy particles can be performed, for example, by boiling the crushed alloy particles in a strong alkaline aqueous solution for 0.5-10 hours, preferably 1-5 hours. The amount of the strong alkaline aqueous solution used can be 1.5-5 times the mass of the alloy particles.

[0021] The invention also relates to the use of the modified Raney cobalt catalyst as a catalyst for selectively hydrogenating citral to prepare citronellol and geraniol.

[0022] In the present invention, the content of geranaldehyde in the starting compound citral is not less than 90%, preferably not less than 95%, and more preferably not less than 99%.

[0023] It is more advantageous to add water to the reaction system in an amount of 0.1 to 1 wt % (based on the mass of the substrate) to further enhance the catalyst activity.

[0024] Furthermore, in the above catalyst system, the amount of the catalyst added is 0.5-5% of the mass of the substrate citral, preferably 1-3%, and more preferably 0.5-2%.

[0025] The reaction temperature range of hydrogenated citral is 50-100°C, the hydrogen pressure range is 0.1-10MPa, and the reaction time is 5-10h.

[0026] In the above method, the reaction conversion rate is not less than 90%, the citronellol selectivity is 60-95%, and the geraniol selectivity is 5-40%.

[0027] The significant progress of the present invention is that: a heterogeneous catalyst is used to obtain citronellol and geraniol in a one-step reaction, which can achieve high activity and high selectivity, and the cost is significantly reduced compared with precious metal catalysts. DETAILED DESCRIPTION

[0028] The following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention.

[0029] Metal analysis methods:

[0030] ICP (Inductively Coupled Plasma Emission Spectrometer): used for metal element detection, focal length 0.38m, medium step grating line 52.6 lines / mm, 21° prism, charge injection (CID) detector, 512×512 detection unit, wavelength range 175nm~1050nm, high frequency generator, high frequency power 2.0KW, working coil 3 turns, frequency 27.12MHZ, glass concentric atomizer, cyclonic spray chamber, built-in 4-channel peristaltic pump. The analysis conditions are as follows: high frequency power: 1.15KW, plasma gas flow: 15L / min, auxiliary gas flow: 0.5L / min, peristaltic pump speed: 100rpm, observation height: 15mm, atomization gas pressure: 0.22MPa, integration time: long wave > 275nm 15S, short wave < 275nm 25S.

[0031] Analytical methods:

[0032] Gas chromatograph: Agilent 7890, chromatographic column wax (conversion rate, selectivity determination), inlet temperature: 300 ° C; split ratio 50:1; carrier gas flow rate: 52.8 ml / min; heating program: maintain at 150 ° C for 10 min, increase to 260 ° C at a rate of 10 ° C / min, maintain for 5 min, detector temperature: 280 ° C.

[0033] Example 1

[0034] The metals Co, Zn, Mn, Mg, and Al are respectively fused at a high temperature (1650°C) in a ratio of 80%, 5%, 1.5%, 2%, and 11.5%. The alloy is cooled to room temperature and then crushed. The alloy particles with a size of more than 400 mesh and less than 50 mesh are screened for further processing. 250g of 10% sodium hydroxide solution is prepared, and 100g of alloy particles are slowly added after boiling. Continue boiling for 10 hours and cool. Pour out the gray upper turbid liquid, add clean water and wash repeatedly at room temperature for 5 times. After standing, the liquid layer is clear and transparent, and the pH value is less than 8.5. A self-made modified skeleton cobalt catalyst is prepared, in which the mass percentage of metal elements is: Co is 82%, Zn is 5%, Mn is 1.8%, Mg is 2.5%, and the rest is aluminum.

[0035] In a 500ml hydrogenation reaction autoclave, 1g of modified Raney cobalt catalyst and 100g of citral (geranial content 99%, the remaining 1% is neral) were added successively. 0.5g of water was added, the autoclave was sealed, and nitrogen and hydrogen were used for replacement 3 times respectively. Heating and stirring were started. When the temperature rose to 80°C, hydrogen was charged to 5.0MPa and maintained for 10h until the reaction was completed. The reaction results were analyzed by GC, and the results are shown in Table 1.

[0036] Example 2

[0037] The metals Co, Zn, Mn, Mg, and Al are fused at high temperature (1780°C) in proportions of 55%, 5%, 1.5%, 0.5%, and 38%, respectively. The alloy is cooled to room temperature and then crushed. The alloy particles with a size of more than 300 mesh and less than 50 mesh are screened for further processing. 500g of 5% sodium hydroxide solution is prepared, and 100g of alloy particles are slowly added after boiling. Continue boiling for 5 hours and cool. Pour out the gray upper turbid liquid, add clean water and wash repeatedly at room temperature for 5 times. After standing, the liquid layer is clear and transparent, and the pH value is less than 8.5. A self-made modified skeleton cobalt catalyst is prepared, in which the mass percentage of metal elements is: Co is 61%, Zn is 9%, Mn is 3%, Mg is 1%, and the rest is aluminum.

[0038] In a 500ml hydrogenation reaction autoclave, 3g of modified Raney cobalt catalyst and 100g of citral (geranial content 92%, the remaining 7% is neral) were added successively. 0.7g of water was added, the autoclave was sealed, nitrogen and hydrogen were replaced 3 times each, heating and stirring were started, and hydrogen was charged to 8MPa when the temperature rose to 90°C, and maintained for 8h until the reaction was completed. The reaction results were analyzed by GC, and the results are shown in Table 1.

[0039] Example 3

[0040] The metals Co, Zn, Mn, Mg, and Al are fused at high temperature (1830°C) in proportions of 65%, 2.5%, 3.5%, 0.05%, and 28.95%, respectively. The alloy is cooled to room temperature and then crushed. The alloy particles with a size of more than 200 mesh and less than 50 mesh are screened for further processing. 400g of 15% sodium hydroxide solution is prepared, and 100g of alloy particles are slowly added after boiling. Continue boiling for 8 hours and cool. Pour out the gray upper turbid liquid, add clean water and wash repeatedly at room temperature for 5 times. After standing, the liquid layer is clear and transparent, and the pH value is less than 8.5. A homemade modified skeleton cobalt catalyst is prepared, in which the mass percentage of metal elements is: Co is 70%, Zn is 3%, Mn is 4.6%, Mg is 0.1%, and the rest is aluminum.

[0041] In a 500ml hydrogenation reaction autoclave, 4g of modified Raney cobalt catalyst and 100g of citral (95% geranial content, the remaining 5% is neral) were added successively. 0.9g of water was added, the autoclave was sealed, and nitrogen and hydrogen were used for replacement 3 times respectively. Heating and stirring were started. When the temperature rose to 100°C, hydrogen was charged to 10MPa and maintained for 6h until the reaction was completed. The reaction results were analyzed by GC, and the results are shown in Table 1.

[0042] Example 4

[0043] The metals Co, Zn, Mn, Mg, and Al are fused at high temperature (1900°C) in proportions of 80%, 0.5%, 0.2%, 2%, and 17.3%, respectively. The alloy is cooled to room temperature and then crushed. The alloy particles with a size of more than 100 mesh and less than 50 mesh are screened for further processing. 300g of 20% sodium hydroxide solution is prepared, and 100g of alloy particles are slowly added after boiling. Continue boiling for 3 hours and cool. Pour out the gray upper turbid liquid, add clean water and wash repeatedly at room temperature for 5 times. After standing, the liquid layer is clear and transparent, and the pH value is less than 8.5. A homemade modified skeleton cobalt catalyst is prepared, in which the mass percentage of metal elements is: Co is 90%, Zn is 1%, Mn is 0.5%, Mg is 3.5%, and the rest is aluminum.

[0044] In a 500ml hydrogenation reaction autoclave, 2g of modified Raney cobalt catalyst, 100g of citral (geranial content 97%, the remaining 3% is neral), 1g of water, and the autoclave was sealed. Nitrogen and hydrogen were used for replacement 3 times each, and heating and stirring were started. When the temperature rose to 65°C, hydrogen was charged to 2MPa and maintained for 5h until the reaction was completed. The reaction results were analyzed by GC, and the results are shown in Table 1.

[0045] Example 5

[0046] The metals Co, Zn, Mn, Mg, and Al are fused at high temperature (2000°C) in the proportions of 70%, 5%, 3.5%, 4%, and 17.5%, respectively. The alloy is cooled to room temperature and then crushed. The alloy particles with a size of more than 500 mesh and less than 50 mesh are screened for further processing. 150g of 30% sodium hydroxide solution is prepared, and 100g of alloy particles are slowly added after boiling. Continue boiling for 0.5 hours and cool. Pour out the gray upper turbid liquid, add clean water and wash repeatedly at room temperature for 5 times. After standing, the liquid layer is clear and transparent, and the pH value is less than 8.5. A self-made modified skeleton cobalt catalyst is prepared, in which the mass percentage of metal elements is: Co is 75%, Zn is 7%, Mn is 5%, Mg is 5%, and the rest is aluminum.

[0047] In a 500ml hydrogenation reaction autoclave, 5g of modified Raney cobalt catalyst, 100g of citral (geranial content 98.5%, the remaining 1.5% is neral), 0.1g of water were added, the autoclave was sealed, nitrogen and hydrogen were replaced 3 times each, heating and stirring were started, and hydrogen was charged to 0.1MPa when the temperature rose to 50°C, and maintained for 7h until the reaction was completed. The reaction results were analyzed by GC, and the results are shown in Table 1.

[0048] Comparative Example

[0049] The metals Co, Zn, Mn, and Al are fused at high temperature (1650°C) in the proportions of 80%, 4%, 1.5%, and 14.5%, respectively. The alloy is cooled to room temperature and then crushed. The alloy particles with a size of more than 400 mesh and less than 50 mesh are screened for further processing. 250g of 10% sodium hydroxide solution is prepared, and 100g of alloy particles are slowly added after boiling. Continue boiling for 10 hours and cool. Pour out the gray upper turbid liquid, add clean water and wash repeatedly at room temperature for 5 times. After standing, the liquid layer is clear and transparent, and the pH value is less than 8.5. A homemade modified skeleton cobalt catalyst is prepared, in which the mass percentage of metal elements is: Co is 82%, Zn is 5%, Mn is 1.8%, and the rest is aluminum.

[0050] In a 500ml hydrogenation reaction autoclave, 1g of modified Raney cobalt catalyst and 100g of citral (99% geranial content, the remaining 1% is neral) were added successively. The autoclave was sealed, and nitrogen and hydrogen were used for replacement 3 times respectively. Heating and stirring were started. When the temperature rose to 80°C, hydrogen was charged to 5.0MPa and maintained for 10h until the reaction was completed. The reaction results were analyzed by GC, and the results are shown in Table 1.

[0051] Table 1 Example reaction performance data

[0052]

[0053]

Claims

1. A modified Raney cobalt catalyst, characterized in that: The mass percentage of metal elements in the catalyst is: Co is 60-90%, Zn is 1-10%, Mn is 0.5-5%, Mg is 0.1-5%, and Al is 5-30%; preferably, Co is 75-85%, Zn is 2-6%, Mn is 1-3%, Mg is 1-2%, and Al is 10-20%.

2. The method for preparing a modified Raney cobalt catalyst according to claim 1, wherein The method comprises the following steps: melting, cooling and crushing five metals, namely Co, Zn, Mn, Mg and Al, in sequence to obtain alloy particles, then washing away the aluminum element in the alloy particles with a strong alkaline aqueous solution, and finally washing the aluminate remaining in the skeletal solid pores with water for multiple times to finally obtain an activated modified Raney cobalt catalyst with a rich pore structure.

3. The preparation method according to claim 2, characterized in that: The fusion temperature is 1600-2000°C; and / or, crushed to a particle size of 10-500 mesh, preferably 50-200 mesh.

4. The preparation method according to claim 2 or 3, characterized in that: The strong alkali aqueous solution used is a 5-30wt% sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution, and the amount of the strong alkali aqueous solution used is 1.5-5 times the mass of the alloy particles.

5. The preparation method according to any one of claims 2 to 4, characterized in that: Washing away the aluminum element in the alloy particles with the strong alkali aqueous solution is carried out by boiling the alloy particles in the strong alkali aqueous solution for 0.5 to 10 hours, preferably 1 to 5 hours.

6. Use of the modified Raney cobalt catalyst according to claim 1 or the modified Raney cobalt catalyst prepared by the method according to any one of claims 2 to 5 as a catalyst for selectively hydrogenating citral to prepare citronellol and geraniol.

7. The use according to claim 6, characterized in that The catalyst addition amount is 0.1-5% of the mass of the substrate citral, preferably 0.5-2%.

8. The use according to claim 6 or 7, characterized in that Citral is used as a raw material, and in the presence of the modified Raney cobalt catalyst described in claim 1, citral is selectively reduced to citronellol and geraniol by intermittent hydrogenation; preferably, the geraniol content in the citral is not less than 90wt%, preferably not less than 95wt%, and more preferably not less than 99wt%.

9. The use according to any one of claims 6 to 8, characterized in that Water is added to the reaction system in an amount of 0.1 to 1 wt % based on the amount of citral used.

10. The use according to any one of claims 6 to 9, characterized in that: The reaction temperature ranges from 50 to 100°C, the hydrogen pressure ranges from 0.1 to 10 MPa, and the reaction time ranges from 5 to 10 hours.

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