A cooling reaction method for enhancing ethanol coupling

Abstract

The present invention discloses a cooling reaction method for enhancing ethanol coupling, which relates to the technical field of higher alcohol synthesis. In the present invention, alcohol molecules are induced to dehydrogenate through a heating reaction stage first, so that a large number of alcohol molecules are dehydrogenated and converted into aldehyde intermediates that are easy to undergo C-C coupling. Then, the reaction temperature is lowered to inhibit the C-C bond breaking side reaction and maintain the activation of aldehyde intermediate molecules and the C-C bond coupling condensation, thereby promoting the growth of the carbon chain of higher alcohols. Since the occurrence of side reactions is inhibited during the reaction process, the selectivity of higher alcohols is effectively improved, and the further growth of the carbon chain of higher alcohols is promoted. The present invention uses a cooling reaction method to enhance the synthesis of higher alcohols by ethanol coupling, which can promote the selective synthesis of higher alcohols with more than 6 carbon atoms, and takes into account the balance of ethanol conversion, the growth of the carbon chain of higher alcohols, the yield of higher alcohols, and selectivity.

Description

Technical Field

[0001] The invention relates to the technical field of high-carbon alcohol synthesis, and more specifically to a temperature-lowering reaction method for enhancing ethanol coupling. Background Art

[0002] Ethanol extracted from biomass sugar is considered to be the most economical and viable fuel additive, but ethanol has low cetane number, low energy density, high hygroscopicity and high autoignition temperature, which hinders its widespread use in diesel engines. 4+ High-carbon alcohols (alcohols with 4 or more carbon atoms, such as butanol) show higher cetane numbers, higher energy density, lower hygroscopicity and autoignition temperature, and can be mixed with diesel in higher proportions than ethanol, and are considered to be good additives for diesel. 8+ Alcohols can be directly used to produce heterogeneous hydrocarbons with the required carbon chain length and aviation fuel properties. They can also be used in plasticizers, food, medical and other fields. They have extremely high economic value and market potential.

[0003] Guerbet self-coupling can be used to directly synthesize high-carbon alcohols from aqueous bioethanol. In the Guerbet coupling of low-carbon alcohols, there are three main steps: (1) ethanol is first dehydrogenated to acetaldehyde; (2) a water molecule is lost through aldol condensation to generate unsaturated aldehydes; (3) further hydrogenation is performed to generate high-carbon alcohols. The reaction process generally requires the temperature to be raised to above 250°C. The first and third steps of the reaction require the participation of metal active centers, while the second step requires the addition of an alkaline catalyst. Among the various catalysts currently used in ethanol coupling reactions, homogeneous catalysts (such as ruthenium, iridium and other catalysts) have high selectivity, but are difficult to separate after the reaction; bifunctional catalysts at acidic and basic sites (such as hydrotalcite, hydroxyapatite and other catalysts) require reaction temperatures above 300°C and usually produce excessive side reactions, resulting in a low yield of high-carbon alcohols; transition metals (such as Ru, Rh, Pd, Au, etc.) combined with homogeneous bases can effectively accelerate the coupling reaction rate, but the cost is high. In addition, the main products of current ethanol coupling are still mainly butanol C4 alcohols, and C 4+ High carbon alcohols such as n-hexanol, 2-ethylbutanol, and C 8+ The high-carbon alcohols still face the problems of low selectivity and low yield. Therefore, it is urgent to study a method for enhancing ethanol coupling, improve the conversion rate of ethanol, promote the carbon chain growth of high-carbon alcohols, and improve the selectivity of the reaction and the yield of high-carbon alcohols.

[0004] The prior art discloses a method for converting ethanol, which utilizes high-energy electrons in the plasma generated by discharge to collide with ethanol gas molecules, thereby generating various hydrocarbon free radicals with hydroxyl groups, and the hydrocarbon free radicals are coupled with each other to generate corresponding high-carbon alcohols and polyols, which improves the conversion rate of ethanol to a certain extent, but the high-carbon alcohols obtained are still C 4+ Alcohol is the main component, and the selectivity is low, not exceeding 10%. Summary of the invention

[0005] In order to overcome the defects and shortcomings of the existing ethanol coupling reaction, such as the difficulty in growing the carbon chain of high-carbon alcohols and the low selectivity of high-carbon alcohols, the present invention provides a cooling reaction method for enhancing ethanol coupling, which reduces the temperature step by step, controls the reaction temperature at the same time, manipulates elementary reaction processes such as dehydrogenation and condensation, promotes the growth of the carbon chain of high-carbon alcohols, and improves the selectivity of high-carbon alcohols.

[0006] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0007] A cooling reaction method for enhancing ethanol coupling, using a catalyst and a homogeneous base in an aqueous phase to catalytically couple ethanol to a higher carbon alcohol, wherein the ethanol coupling process is carried out by a cooling reaction method, and the cooling reaction method comprises the following steps:

[0008] The reaction is first subjected to a temperature increase reaction, the reaction time being 2 to 12 hours, and then subjected to an n-step temperature reduction reaction, the reaction time of each step temperature reduction reaction being 2 to 12 hours; wherein n is a natural number, and n≥1;

[0009] The temperature of the temperature-raising reaction is raised to 180-280° C. and then kept warm;

[0010] The n-th order temperature reduction reaction reduces the temperature to 100-190° C. and then keeps the temperature;

[0011] The heating rate of the temperature-raising reaction is 2 to 10°C / min;

[0012] The cooling rate of the n-th order cooling reaction is 2-20°C / min;

[0013] The temperature of the temperature-raising reaction is greater than the temperature of the n-th-order temperature-lowering reaction.

[0014] It should be noted that:

[0015] The present invention comprehensively considers the suitable conditions of elementary reaction steps such as dehydrogenation and aldol condensation of high-carbon alcohols, and proposes a cooling reaction method for enhancing ethanol coupling. The cooling reaction method controls the progress of elementary reactions such as dehydrogenation and condensation through step-by-step cooling reactions to promote the carbon chain growth of high-carbon alcohols and improve the selectivity of high-carbon alcohols.

[0016] In the temperature-raising reaction stage, a large number of ethanol molecules are dehydrogenated and converted into aldehyde intermediates, and then the temperature is gradually lowered to perform an n-stage cooling reaction. During the n-stage cooling reaction, the reaction temperature is lowered to meet the requirements of suppressing the side reaction of CC bond breaking, while providing sufficient energy to ensure that the aldehyde intermediates in the system undergo CC coupling condensation and promote the growth of the carbon chain of high-carbon alcohols. At the same time, the cooling reaction method is used to suppress the occurrence of side reactions in the n-stage cooling reaction stage, thereby improving the selectivity of high-carbon alcohols.

[0017] Generally, in the reaction of ethanol coupling to synthesize high-carbon alcohols, the temperature needs to be raised to above 250°C. At the same time, the catalyst itself has a certain activity, which will cause the CC bond of the ethanol skeleton to break to generate gas byproducts, thereby reducing the yield of high-carbon alcohols, that is, the problem of the carbon number distribution of high-carbon alcohols being limited by the cascade distribution occurs. The present invention adopts a cooling reaction method, firstly inducing the dehydrogenation of alcohol molecules at a higher temperature, so that a large number of alcohol molecules are dehydrogenated and converted into aldehyde intermediates that are easy to CC couple, and then lowering the temperature. At a lower reaction temperature, the side reaction generated by the breakage of the CC bond is suppressed, and the growth of the carbon chain and the C 6+ Selectivity of higher carbon alcohols and yield of higher carbon alcohols.

[0018] Specifically, the temperature difference between the insulation temperature in the temperature-raising reaction and the insulation temperature in the n-th order temperature-lowering reaction is ≥5°C, more specifically 10-40°C.

[0019] Specifically, the catalyst is a nickel-based catalyst, and the homogeneous base is NaOH or KOH; the nickel-based catalyst is a carbon-coated nickel catalyst, which is synthesized by a sol-gel carbonization method, and the nickel source is selected from nickel nitrate, nickel chloride or nickel acetate, preferably nickel nitrate; the carrier in the nickel-based catalyst is a carbon carrier, and the carbon source of the carbon carrier is a polypropylene meltblown cloth.

[0020] Specifically, the reaction time of the temperature increase reaction and the reaction time of each stage of the temperature decrease reaction are both 2 to 10 hours.

[0021] Optionally, the total reaction time of the temperature raising reaction and the temperature lowering reaction is 12 h.

[0022] Specifically, the above-mentioned ethanol coupling process is carried out in an intermittent reactor reactor with an initial pressure of 0. Under the synergistic catalysis of a nickel-based catalyst and a homogeneous base, ethanol is selectively catalytically coupled in an aqueous phase to obtain high-carbon alcohols by a cooling reaction method. After the reaction is completed, the liquid product is centrifuged and separated into layers, and the upper organic phase and the lower aqueous phase are taken separately, and qualitative and quantitative detection and analysis are carried out by gas chromatography. At the same time, the gas generated during the reaction is collected and detected and analyzed by FID-TCD gas analysis spectrum.

[0023] Specifically, the temperature of the temperature-raising reaction is raised to 180-200° C. and then kept warm.

[0024] By controlling the temperature range of the temperature-raising reaction, the dehydrogenation and CC bond breaking of the ethanol molecules can be further promoted, the conversion rate of ethanol can be improved, and more aldehyde intermediates can be generated in the system, which is beneficial to the subsequent condensation of the aldehyde intermediates and the yield of high-carbon alcohols can be improved.

[0025] Specifically, the n-stage temperature reduction reaction reduces the temperature to 160-190° C. and then keeps the temperature.

[0026] Adjustment of the insulation temperature range of the n-order cooling reaction can further cooperate with the temperature increase reaction, and more aldehyde intermediates generated during the temperature increase reaction can be coupled and condensed, thereby increasing the yield of high-carbon alcohols. At the same time, temperature adjustment of the n-order cooling reaction is also conducive to further improvement of the selectivity of high-carbon alcohols, effectively promoting the further growth of the carbon chain of high-carbon alcohols.

[0027] Specifically, the n is 1-4.

[0028] The cooling reaction order n of the cooling reaction method described in the present invention will affect the yield and selectivity of high-carbon alcohols. With the increase of n, the yield and selectivity of high-carbon alcohols are improved, but as n increases, the degree of improvement is weak. Therefore, controlling the value of n is beneficial to improving the yield and selectivity of high-carbon alcohols while reducing energy consumption and reducing the number of cooling times.

[0029] Preferably, the reaction time of the temperature-raising reaction is 2 to 6 hours.

[0030] More preferably, the reaction time of the temperature-raising reaction is 2 to 4 hours.

[0031] Preferably, the reaction time of each stage of the temperature reduction reaction is 2 to 10 hours.

[0032] By controlling the reaction time of the temperature increase reaction and the n-th order temperature decrease reaction, the selectivity of the higher carbon alcohols can be further improved, so that the selectivity of the higher carbon alcohols reaches more than 60%.

[0033] Preferably, the reaction time of the temperature-raising reaction is ≤ the reaction time of each stage of the temperature-lowering reaction.

[0034] When the reaction time of the temperature rising reaction is ≤ the reaction time of each order of temperature falling reaction, a higher yield and selectivity of higher carbon alcohols can be obtained. For example, the temperature rising reaction is also heated to 200°C for insulation, and the first-order temperature falling reaction is also cooled to 160°C for insulation. The reaction time of the temperature rising reaction is 8h, and the reaction time of the first-order temperature falling reaction is 4h. The yield and selectivity of higher carbon alcohols are lower than those of the reaction time of the temperature rising reaction is 4h and the reaction time of the first-order temperature falling reaction is 8h.

[0035] More preferably, the temperature change mode of the temperature-raising reaction and the n-th order temperature-lowering reaction is one of the following A, B, C, D, and E:

[0036] A: The temperature rises to 180°C, and then the temperature drops to 160°C in the first-order cooling reaction.

[0037] B: The temperature rises to 200°C, and the first-order temperature drop reaction is carried out to 160°C;

[0038] C: The temperature rises to 180°C, and the second-order cooling reaction is carried out. The first-order cooling reaction is cooled to 170°C, and the second-order cooling reaction is cooled to 160°C;

[0039] D: The temperature is raised to 200°C for the temperature rise reaction, and the temperature is lowered to 180°C for the first temperature fall reaction, and to 160°C for the second temperature fall reaction;

[0040] E: The temperature is raised to 200°C for the temperature-raising reaction, and a fourth-order temperature-lowering reaction is performed. The first-order temperature-lowering reaction is cooled to 190°C, the second-order temperature-lowering reaction is cooled to 180°C, the third-order temperature-lowering reaction is cooled to 170°C, and the fourth-order temperature-lowering reaction is cooled to 160°C.

[0041] Specifically, the cooling rate of the n-th order cooling reaction is 5-10°C / min; the heating rate of the heating reaction is 5-10°C / min.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The invention provides a cooling reaction method for enhancing ethanol coupling, which firstly promotes dehydrogenation and C-C bond breaking through a high-temperature reaction stage, so that a large number of alcohol molecules are dehydrogenated and converted into aldehyde intermediates, and then the reaction temperature is lowered to weaken the side reaction generated by the C-C bond breaking, and sufficient energy is maintained in the system to promote the C-C bond coupling condensation of the aldehyde intermediate, thereby increasing the growth length of the high-carbon alcohol carbon chain. At the same time, since the occurrence of side reactions is suppressed during the reaction process, the selectivity of the high-carbon alcohol is effectively improved, and the further growth of the high-carbon alcohol carbon chain is promoted.

[0044] The present invention adopts a cooling reaction method to enhance ethanol coupling. After the reaction is completed, the ethanol conversion rate is not less than 50%, the yield of high-carbon alcohols is as high as 45.6%, and C 6+ The selectivity of alcohol is as high as 65.9%, taking into account the balance of ethanol conversion rate, high-carbon alcohol carbon chain growth, high-carbon alcohol yield and selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the reaction temperature of the cooling reaction method in Example 1. DETAILED DESCRIPTION

[0046] In a specific embodiment, the nickel-based catalyst in the ethanol-water phase coupling process is a carbon-coated nickel catalyst (Ni@MB); the calcination temperature of the carbon-coated nickel catalyst is 500° C., the molar ratio of nickel to carbon carrier is 1 / 26, and the preparation method is as follows:

[0047] S1. Wetting the polypropylene meltblown cloth (MB) with anhydrous ethanol;

[0048] S2. adding nickel nitrate hexahydrate to anhydrous ethanol to obtain a nickel ethanol solution;

[0049] S3. Add the nickel ethanol solution obtained in step S2 to the MB soaked in ethanol obtained in step S1, stir thoroughly and then dry, and carbonize at 500° C. in an inert atmosphere to obtain a carbon-coated nickel catalyst (Ni@MB) synthesized based on meltblown cloth.

[0050] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0051] Example 1

[0052] A cooling reaction method for enhancing ethanol coupling comprises the following steps:

[0053] Ni@MB catalyst and base catalyst NaOH were added to a 50ml steel high-pressure slurry bed reactor to synergistically catalyze the coupling of ethanol and water to synthesize high-carbon alcohols; wherein the mass ratio of catalyst: NaOH: ethanol: water was 0.06:0.17:1:1, and the initial pressure was 0MPa;

[0054] The ethanol-water phase coupling is carried out by a cooling reaction method, which specifically comprises the following steps:

[0055] The temperature was first increased at a rate of 5°C / min, from room temperature to 180°C and then kept warm for a total of 6 hours. A first-order cooling reaction was then performed at a cooling rate of 5°C / min, from the temperature being reduced to 160°C and then kept warm for a total of 6 hours. After sufficient reaction, the temperature was lowered to room temperature to terminate the reaction.

[0056] Embodiments 2 to 9

[0057] A cooling reaction method for enhancing ethanol coupling, the steps are the same as those in Example 1, and the differences are shown in Table 1.

[0058] Table 1. Reaction parameters of the cooling reaction method of Examples 1 to 9

[0059]

[0060]

[0061] Note: The above 180-160 means that the temperature of the heating reaction is raised to 180℃ and then kept warm, and the first-stage cooling reaction is cooled to 160℃ and then kept warm, and so on.

[0062] Comparative Example 1

[0063] An isothermal reaction method for ethanol coupling, the steps are the same as those in Example 1, except that this comparative example adopts a single-stage isothermal reaction method, the temperature is 160° C., and the reaction time is 12 hours.

[0064] Comparative Example 2

[0065] An isothermal reaction method for ethanol coupling, the steps are the same as those in Example 1, except that this comparative example adopts a single-stage isothermal reaction method, the temperature is 180° C., and the reaction time is 12 h.

[0066] Comparative Example 3

[0067] An isothermal reaction method for ethanol coupling, the steps are the same as those in Example 1, except that this comparative example adopts a single-stage isothermal reaction method, the temperature is 200° C., and the reaction time is 12 hours.

[0068] Results

[0069] The gases produced by the reactions of the above-mentioned embodiments and comparative examples were collected and detected and analyzed by FID-TCD gas analysis spectrum (Agilent 8860GC System). At the same time, the liquid products of the above-mentioned embodiments and comparative examples were centrifuged and layered, and the upper organic phase and the lower aqueous phase were taken after standing, and detected and analyzed by gas chromatography (Shimadzu GC-2010Pro); the results are shown in Table 2.

[0070] Table 2. Analysis of reaction results of various embodiments and comparative examples

[0071]

[0072] From the results in Table 2, it can be seen that for the Ni@MB catalyst with nickel as the active center metal and polypropylene melt-blown layer (MB) as the carbon carrier, a higher yield of high-carbon alcohols and C 2+ can be obtained after process optimization of the cooling reaction method compared with the single-stage constant temperature reaction. 6+ Alcohol selectivity.

[0073] During the cooling reaction, a gradient test was conducted by adjusting the holding time and the number of reaction temperature stages. In Examples 3 and 4, n was the same, but the holding time was different. It can be seen that a shorter holding time from room temperature to 200°C and then a longer holding time at 160°C was helpful to obtain a higher yield of higher alcohols and C 6+Alcohol selectivity; in Examples 3, 8, and 9, the total insulation time is the same, but n is different. It can be seen that as n increases, the yield of high-carbon alcohols and C 6+ The selectivity of alcohol increases, but the increase is not significant. Taking all factors into consideration, when n=2, it is more suitable for ethanol-water coupling.

[0074] Comparative Examples 1 to 4 are single-stage isothermal reactions. Combining Comparative Examples 1 to 4, it can be seen that as the reaction temperature increases, the conversion rate of ethanol increases, but the yield of higher carbon alcohols and C 6+ The selectivity of alcohol decreases with the increase of reaction temperature, while the selectivity of gaseous byproducts increases. It can be seen that for the single-stage constant temperature ethanol water phase coupling reaction, the increase in reaction temperature does not bring a higher yield of higher alcohols. On the contrary, due to the increase in temperature, the metal nickel has a stronger cracking ability, producing excessive C1 byproducts (such as CO, CO2, CH4), thereby reducing the selectivity for higher alcohols. Obviously, even if the reaction temperature is within the insulation temperature range of the cooling reaction method of the present invention, under the same reaction time, without the cooling reaction of the present invention, it is impossible to improve the yield of higher alcohols and C1 while ensuring the ethanol conversion rate. 6+ Alcohol selectivity. Compared with the traditional single-stage isothermal reaction, the cooling reaction method of the present invention comprehensively considers the coordinated regulation of different elementary reactions, and ensures that ethanol can achieve rapid dehydrogenation while suppressing the occurrence of side reactions, effectively promoting the further carbon chain growth of high-carbon alcohols.

[0075] Figure 1 Schematic diagram of the reaction temperature of the cooling reaction method of Example 1. It can be clearly seen from the figure that the cooling reaction method of Example 1 undergoes a process of first heating to 200°C and keeping warm, then cooling to 160°C and keeping warm, and the reaction time of each stage is 6h.

[0076] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A cooling reaction method for enhancing ethanol coupling, using a catalyst and a homogeneous base in an aqueous phase to catalyze the coupling of ethanol to C 4+ A higher alcohol, characterized in that The ethanol coupling process is carried out by a cooling reaction method, which comprises the following steps: First, a temperature rise reaction is carried out, and the reaction time is 2 to 12 hours, and then a temperature reduction reaction is carried out step by step, and the reaction time of each temperature reduction reaction is 2 to 12 hours; wherein n is a natural number, and n is 1 to 4; the catalyst is a carbon-coated nickel catalyst; and the homogeneous base is NaOH or KOH; The temperature of the temperature-raising reaction is raised to 180-280° C. and then kept warm; The n-th order temperature reduction reaction reduces the temperature to 100-190° C. and then keeps the temperature; The heating rate of the temperature-raising reaction is 2-10°C / min; The cooling rate of the n-th order cooling reaction is 2-20°C / min; The temperature of the temperature-raising reaction is greater than the temperature of the n-th-order temperature-lowering reaction.

2. The cooling reaction method according to claim 1, characterized in that: The temperature of the temperature-raising reaction is raised to 180-200° C. and then kept warm.

3. The cooling reaction method according to claim 1, characterized in that: The n-th order temperature reduction reaction reduces the temperature to 160-190° C. and then keeps the temperature.

4. The cooling reaction method according to claim 1, characterized in that: The reaction time of the temperature-raising reaction is 2 to 6 hours.

5. The cooling reaction method according to claim 4, characterized in that: The reaction time of the temperature-raising reaction is 2 to 4 hours.

6. The cooling reaction method according to claim 5, characterized in that: The reaction time of each step of the cooling reaction is 2 to 10 hours.

7. The cooling reaction method according to claim 1, characterized in that: The reaction time of the temperature increase reaction is ≤ the reaction time of each stage of temperature decrease reaction.

8. The cooling reaction method according to claim 7, characterized in that: The temperature change mode of the temperature-raising reaction and the n-th order temperature-lowering reaction is one of the following A, B, C, D, and E: A: The temperature rises to 180°C, and then the temperature drops to 160°C in the first-order cooling reaction. B: The temperature rises to 200°C, and the first-order temperature drop reaction is carried out to 160°C; C: The temperature rises to 180°C, and the second-order cooling reaction is carried out. The first-order cooling reaction is cooled to 170°C, and the second-order cooling reaction is cooled to 160°C; D: The temperature is raised to 200°C for the temperature rise reaction, and the temperature is lowered to 180°C for the first temperature fall reaction, and to 160°C for the second temperature fall reaction; E: The temperature is raised to 200°C for the temperature-raising reaction, and a fourth-order temperature-lowering reaction is performed. The first-order temperature-lowering reaction is cooled to 190°C, the second-order temperature-lowering reaction is cooled to 180°C, the third-order temperature-lowering reaction is cooled to 170°C, and the fourth-order temperature-lowering reaction is cooled to 160°C.

9. The cooling reaction method according to claim 1, characterized in that: The cooling rate of the n-th order cooling reaction is 5-10°C / min.

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