CN115261147A - A kind of method that utilizes carbon-based solid acid to catalyze synthesis of biodiesel - Google Patents

Abstract

The invention discloses a method for catalytically synthesizing biodiesel by using carbon-based solid acid, which comprises the following steps: adding a carbon-based solid acid catalyst into the waste oil, introducing methanol steam and/or ethanol steam into the waste oil, condensing and refluxing to perform esterification reaction, and separating to obtain the biodiesel after the reaction is finished. The invention has the beneficial effects that: according to the method for synthesizing the biodiesel by using the carbon-based solid acid as the catalyst, methanol steam and/or ethanol steam are/is used for replacing the traditional liquid methanol to participate in the esterification reaction, so that the consumption of the methanol is reduced, the catalytic performance of the catalyst and the conversion rate of waste oil are effectively improved, and the production cost of the biodiesel is integrally reduced; the method for catalytically synthesizing the biodiesel by using the carbon-based solid acid synthesizes the carbon-based solid acid catalyst by using the waste biomass as the raw material, reduces the cost of the catalyst, and enhances the recyclability and the reusability of the catalyst.

Description

A kind of method utilizing carbon-based solid acid to catalyze biodiesel synthesis

technical field

The invention belongs to the technical field of waste recycling, and in particular relates to a method for catalytically synthesizing biodiesel with carbon-based solid acid.

Background technique

In response to the massive consumption of fossil fuels and growing environmental concerns, developing more green and renewable energy has become a new demand for development. Among them, biodiesel has many advantages such as high flash point, low sulfur content, high cetane number and good transportation safety, and can also be mixed with diesel oil, so it is regarded as an excellent substitute for fossil fuels. Biodiesel is generally produced from animal and vegetable oils through esterification or transesterification under acidic or alkaline conditions. However, in order to reduce production costs, waste oils with higher free fatty acid content are often selected as raw materials. When it directly reacts with a basic catalyst, it will produce saponification, so the free fatty acid needs to be converted into methyl ester by pre-esterification under acid catalysis.

In actual production, a homogeneous acid catalyst (such as concentrated sulfuric acid, hydrochloric acid, etc.) is often used to catalyze the esterification reaction. However, they will remain in methanol, causing problems such as difficulty in catalyst separation and recovery, serious equipment corrosion, and environmental pollution of a large amount of waste liquid. In contrast, heterogeneous catalysts can effectively solve the above problems and reduce the overall production cost. Among them, carbon-based solid acid catalysts have the characteristics of low cost, large specific surface area, rich surface functional groups, and reproducibility, which have triggered in-depth research by many scholars. In order to make full use of biomass energy and reduce the cost of catalyst preparation, it is considered to first use biochar after pyrolysis of waste biomass as a precursor, and then sulfonate it with concentrated sulfuric acid to prepare an acid catalyst.

However, in the process of solid acid catalysis to catalyze the actual production of biodiesel, the phenomenon of catalyst failure has become a problem that needs to be solved. This is because it is generally necessary to add excess methanol at one time in the esterification reaction to speed up the reaction. But on the one hand, methanol is easy to combine with the same polar sulfonic acid groups, resulting in a large amount of leaching of active groups that are not firmly loaded; on the other hand, excess methanol and sulfonic acid groups will also undergo esterification reaction at high temperature , forming sulfonate on the surface of the catalyst, resulting in deactivation of the catalyst. In order to improve the reusability of catalysts, some researchers have further modified the catalysts to enhance their catalytic activity. But to fundamentally solve this problem, it is necessary to develop a method to reduce the contact time of methanol with the catalyst.

Contents of the invention

The main purpose of this application is to provide a method of using methanol vapor and/or ethanol vapor to replace traditional liquid methanol or ethanol, improve the catalytic efficiency of the catalyst, and prolong the service life of the catalyst. The method of using carbon-based solid acid to catalyze the synthesis of biodiesel.

In order to achieve the above object, the present invention provides the following technical solutions:

A method utilizing carbon-based solid acid to catalyze biodiesel synthesis, comprising the following steps:

Adding a carbon-based solid acid catalyst to the waste oil, while passing methanol vapor and/or ethanol vapor into the waste oil, condensing and refluxing for esterification, and separating the biodiesel after the reaction is completed.

The use of alcohol vapor can make the grease and the catalyst contact with more alcohols in a short time to improve the activity; at the same time, this method slows down the loss rate of the acidic groups on the surface of the catalyst and prolongs the life of the catalyst.

As a preferred embodiment of the above-mentioned method for synthesizing biodiesel with carbon-based solid acid catalysis, the waste oil is catering waste oil, waste animal fat, and industrial waste acidified oil.

In the method for synthesizing biodiesel with carbon-based solid acid catalyst, as a preferred embodiment, the weight ratio of the waste oil to the carbon-based solid acid catalyst is 100:6-12.

The method for synthesizing biodiesel using carbon-based solid acid catalysis, as a preferred embodiment, the molar ratio of methanol vapor and/or ethanol vapor to waste oil is 5:1-15:1;

When it is the mixed alcohol vapor of methanol vapor and ethanol vapor, the mass ratio of methanol vapor and ethanol vapor is 99:1-9:1.

The method of adding methanol vapor and/or ethanol vapor is as follows: put methanol and/or ethanol into a single-necked flask, and use a stopper with a stainless steel tube to block the bottle mouth; heat the single-necked flask to control the generated methanol vapor and/or ethanol The steam is passed into the waste oil at a rate of 0.5-1mL/min, and the outlet of the stainless steel tube needs to extend below the liquid level of the waste oil, so that the overflowed methanol vapor and/or ethanol vapor can be recovered and reused.

As a preferred embodiment of the above-mentioned method for synthesizing biodiesel with carbon-based solid acid catalysis, the temperature of the esterification reaction is 70-100° C., and the time of the esterification reaction is 2-15 hours.

As a preferred embodiment of the above-mentioned method for synthesizing biodiesel with carbon-based solid acid catalysis, the esterification reaction is completed when the acid value in the reaction solution is ≤ 2 mg·KOH/g.

Above-mentioned a kind of method that utilizes carbon-based solid acid to catalyze the synthesis of biodiesel, as a kind of preferred embodiment, the preparation method of described carbon-based solid acid catalyst is:

(1) Crushing and drying the crop straw, pyrolyzing the dried crop straw powder in an inert atmosphere, after the pyrolysis is completed, washing with deionized water to remove ash, filtering, and drying the filter cake;

(2) Mix the filter cake with concentrated sulfuric acid for sulfonation treatment. After the sulfonation is completed, wash with deionized water, filter until the filtrate is neutral, and dry the filter cake to obtain a carbon-based solid acid catalyst.

The crop stalks can be wheat stalks, corn stalks, soybean stalks, etc., and can also be replaced by peanut shells, sawdust, bamboo or banana stalks.

The carbon-based solid acid catalyst of the present invention can be used repeatedly, and if the catalyst fails, sulfonation can be carried out again, and the sulfonation method is the same as above.

The above-mentioned method for synthesizing biodiesel using carbon-based solid acid catalysis, as a preferred embodiment, in step (1), the drying temperature of the crop stalks is 80°C-180°C, and the drying time is 6-36h ; The inert atmosphere is a nitrogen atmosphere; the pyrolysis temperature is 200-600°C, and the pyrolysis time is 1-5h.

The above-mentioned method for utilizing carbon-based solid acid to catalyze biodiesel synthesis, as a preferred embodiment, in step (2), the weight ratio of filter cake to concentrated sulfuric acid is 1:20-1:150;

The sulfonation treatment is: heating at a temperature of 60-200° C. for 0.5-10 hours.

The method for synthesizing biodiesel by using carbon-based solid acid catalysis as a preferred embodiment, in step (2), the drying temperature is 80°C-180°C, and the drying time is 10-36h .

The beneficial effects of the present invention are: the method of utilizing carbon-based solid acid to catalyze biodiesel synthesis in the present invention uses methanol vapor and/or ethanol vapor instead of traditional liquid methanol to participate in the esterification reaction, which reduces the consumption of methanol and effectively improves the The catalytic performance of the catalyst and the conversion rate of waste oil reduce the production cost of biodiesel as a whole.

The method for synthesizing biodiesel with carbon-based solid acid catalysis in the present invention uses waste biomass as a raw material to synthesize a carbon-based solid acid catalyst, while reducing the cost of the catalyst and enhancing the recyclability and reusability of the catalyst.

Detailed ways

In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiment of the application will be clearly and completely described below in conjunction with a case. Obviously, the described embodiment is only a part of the embodiment of the application. rather than all examples. Based on the embodiments in this application, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the scope of protection of this application.

Example 1

The method for utilizing carbon-based solid acid catalysis to synthesize biodiesel described in embodiment 1 may further comprise the steps:

A certain amount of wheat straw was crushed and passed through a 40-mesh sieve, and dried at 105°C for 12 hours; the dried powder was transferred to a crucible, and placed in a pyrolysis muffle furnace with a nitrogen flow rate of 80ml/min. Pyrolysis at ℃ for 1.5h. The product is mixed with a certain amount of deionized water, washed and filtered to remove ash. The filtered biochar was collected and dried at 105 °C for 12 h.

Mix 5g of dried biochar with 100g of concentrated sulfuric acid and heat at 150°C for 4h. After cooling to room temperature, add deionized washing and filter until the filtrate is neutral. The obtained filtered solid was dried at 105° C. for 10 h to obtain a finished carbon-based solid acid catalyst. The sulfonic acid density of the catalyst was determined by titration to be 1.51 mmol/g.

Weigh 30g of waste oil (restaurant waste oil) into a three-necked flask connected to a condensing device, and add 3g of carbon-based solid acid catalyst. Weigh 160 g of mixed alcohol of methanol and ethanol (the mass ratio of methanol to ethanol is 9:1) and place it in a single-necked flask, and connect it to the three-necked flask. Heat the one-necked flask in a water bath at 85°C, pass the generated mixed alcohol vapor of methanol vapor and ethanol vapor through a stainless steel tube under the liquid surface of the waste oil, and heat the three-necked flask at 76°C for 4 hours to carry out esterification reaction. After the end (the esterification reaction is completed when the acid value in the reaction solution is ≤ 2mg·KOH/g), the esterification product is centrifuged to separate the remaining methanol, methyl oleate (biodiesel), water and catalyst. The conversion rate of fatty acid was calculated to be 99.32%.

Fatty acid conversion rate = (acid value of waste oil - biodiesel acid value) / acid value of waste oil × 100%

The test method of the acid value is: weigh about 1g of the oil sample material and place it in the conical flask; transfer 50mL of ethanol to the conical flask containing the oil sample to be tested, and mix thoroughly; add 0.5mL of phenolphthalein indicator, and use KOH-ethanol standard solution was titrated, and the titration process was shaken sufficiently until the color changed and remained unchanged for 15 seconds, which was the end point of the titration.

Acid value=(V×c×56.1)/m

In the formula: V—the volume of KOH-ethanol standard solution consumed by titration, mL;

c—concentration of KOH-ethanol standard solution, mol/L;

56.1——Molar mass of KOH, g/mol;

m - the mass of the sample, g.

Example 2

The method for utilizing charcoal-based solid acid catalysis to synthesize biodiesel described in embodiment 2 may further comprise the steps:

Take a certain amount of bamboo and crush it through a 40-mesh sieve, and dry it at 105°C for 12 hours; transfer the dried powder to a crucible, and put it into a pyrolysis muffle furnace, set the nitrogen flow rate to 100ml/min, and dry it at 250°C Under pyrolysis for 1.5h. The product is mixed with a certain amount of deionized water, washed and filtered to remove ash. The filtered biochar was collected and dried at 105 °C for 12 h.

Mix 5g of dried biochar with 100g of concentrated sulfuric acid, heat at 150°C for 4h, cool to room temperature, add deionized washes several times, and filter until the filtrate is neutral. The obtained filtered solid was dried at 105° C. for 10 h to obtain a finished carbon-based solid acid catalyst. The sulfonic acid density of the catalyst was determined by titration to be 1.25 mmol/g.

Weigh 30 g of waste oil (waste animal fat) and place it in a three-neck flask connected to a condensing device, and add 3 g of a carbon-based solid acid catalyst. Weigh 160g of methanol and place it in a one-necked flask, and connect it with a three-necked flask. The one-necked flask was heated in a water bath at 74°C, the generated methanol vapor was passed through a stainless steel tube under the liquid surface of the waste oil, and the three-necked flask was heated at 76°C for 4h to carry out the esterification reaction. The esterification reaction is completed when the acid value is less than or equal to 2mg·KOH/g), and the esterification product is centrifuged to separate the remaining methanol, methyl oleate (biodiesel), water and catalyst. The conversion rate of fatty acid was calculated to be 97.54%.

Example 3

The method for utilizing carbon-based solid acid catalysis to synthesize biodiesel described in embodiment 3 may further comprise the steps:

Take a certain amount of peanut shells and crush them through a 40-mesh sieve, and dry them at 105°C for 12 hours; transfer the dried powder to a crucible, and put it into a pyrolysis muffle furnace, set the nitrogen flow rate to 80ml/min, Pyrolysis at ℃ for 1.5h. The product is mixed with a certain amount of deionized water, washed and filtered to remove ash. The filtered biochar was collected and dried at 105 °C for 12 h.

Mix 5 g of dried biochar with 100 g of concentrated sulfuric acid and heat at 150 °C for 4 h. After cooling to room temperature, add deionized washing several times, and filter until the filtrate is neutral. The obtained filtered solid was dried at 105° C. for 10 h to obtain a finished carbon-based solid acid catalyst. The sulfonic acid density of the catalyst was determined by titration to be 1.32 mmol/g.

Weigh 30g of waste oil (restaurant waste oil) into a three-necked flask connected to a condensing device, and add 3g of carbon-based solid acid catalyst. Weigh 160 g of mixed alcohol of methanol and ethanol (the mass ratio of methanol to ethanol is 9:1) and place it in a single-necked flask, and connect it to the three-necked flask. Heat the one-necked flask in a water bath at 85°C, pass the generated mixed alcohol vapor of methanol vapor and ethanol vapor through a stainless steel tube under the liquid surface of the waste oil, and heat the three-necked flask at 76°C for 4 hours to carry out esterification reaction. After the end (the esterification reaction is completed when the acid value in the reaction solution is ≤ 2mg·KOH/g), the esterification product is centrifuged to separate the remaining methanol, methyl oleate (biodiesel), water and catalyst. The conversion rate of fatty acid was calculated to be 97.14%.

Example 4

The difference between Example 4 and Example 2 is that the alcohol used is ethanol, that is, the esterification reaction is carried out with ethanol vapor, and the rest of the operations are the same as in Example 2. The conversion rate of fatty acid was calculated as 98.76% by measuring the change of acid value before and after the reaction.

Comparative example 1

The difference between the method of utilizing carbon-based solid acid to catalyze the synthesis of biodiesel described in Comparative Example 1 and the method described in Example 1 is that the alcohols used in the synthesis of biodiesel by utilizing carbon-based solid acid to catalyze the synthesis of biodiesel described in Comparative Example 1 are liquid methanol and The mixed alcohol of liquid ethanol carries out esterification reaction, all the other operations are identical with embodiment 1.

Comparative example 2

The difference between the method described in Comparative Example 2 and the method described in Example 4 utilizing carbon-based solid acid to catalyze the synthesis of biodiesel is:

The alcohol used in the synthesis of biodiesel by carbon-based solid acid as described in Comparative Example 2 is liquid ethanol for esterification, and the rest of the operations are the same as in Example 4.

The present invention utilizes the research on the reproducibility of carbon-based solid acid catalysis to synthesize biodiesel catalyst, and the research results are as shown in table 1:

Table 1

sample Sulfonic acid density (mmol g^-1) Esterification rate (%) steam esterification for the first time 1.51 99.32 Steam esterification repeated 4 times 0.92 97.48 Steam esterification repeated 8 times 0.35 83.36 Comparative example 1 liquid esterification for the first time 1.51 96.87 Comparative example 1 liquid esterification was repeated 4 times 0.32 79.76 Comparative example 2 liquid esterification for the first time 1.51 95.84 Comparative example 2 liquid esterification was repeated 4 times 0.29 77.65

Remark:

In the table, steam esterification is the sulfonic acid density and esterification rate of the carbon-based solid acid catalyst described in Example 1 for the first time.

In the table, steam esterification was repeated 4 times: according to the method described in Example 1, biodiesel was catalyzed and synthesized 4 times, that is, the carbon-based solid acid catalyst was reused 4 times.

In the table, steam esterification was repeated 8 times: according to the method described in Example 1, biodiesel was catalyzed and synthesized 8 times, that is, the carbon-based solid acid catalyst was reused 8 times.

In the table, the liquid esterification of Comparative Example 1 was repeated 4 times: according to the method described in Comparative Example 1, the catalytic biodiesel was synthesized 4 times, that is, the catalyst was reused 4 times.

In the table, the liquid esterification of Comparative Example 2 was repeated 4 times: according to the method described in Comparative Example 2, the catalytic biodiesel was synthesized 4 times, that is, the catalyst was reused 4 times.

It can be seen from Table 1 that although the catalytic activities of the two catalysts were close to each other during the first esterification, the catalyst was obviously deactivated after repeated use for 4 times in liquid esterification, and the conversion rate of fatty acid was less than 80%. In contrast, the mixed alcohol vapor esterification using methanol vapor and ethanol vapor was reused 8 times, and the fatty acid conversion was still higher than 80%.

Table 1 shows the change of catalyst sulfonic acid density during the process of two esterification recycling catalysts. The density of sulfonic acid decreased to 0.32mmol g ^-1 after the liquid esterification was repeated 4 times; while the density of sulfonic acid was 0.92mmolg ^-1 after the vapor esterification was repeated 4 times, showing good catalytic performance.

The carbon-based solid acid catalyst can play a catalytic role mainly because the surface supports weak acid groups such as sulfonic acid groups and carboxylic acids, and sulfonic acid plays the main role. The density of sulfonic acid can be regarded as one of the indicators to measure its catalytic activity.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the method of the present invention, some improvements and supplements can also be made, and these improvements and supplements should also be considered Be the protection scope of the present invention.

Claims (10)

1. A method for catalytically synthesizing biodiesel by using carbon-based solid acid is characterized by comprising the following steps:

adding a carbon-based solid acid catalyst into the waste oil, introducing methanol steam and/or ethanol steam into the waste oil, condensing and refluxing to perform esterification reaction, and separating to obtain the biodiesel after the reaction is finished.

2. The method for catalytically synthesizing biodiesel by using carbon-based solid acid according to claim 1, wherein the waste oil is waste cooking oil, waste animal fat and industrial waste acidified oil.

3. The method for catalytically synthesizing biodiesel by using the carbon-based solid acid as claimed in claim 1, wherein the weight ratio of the waste oil to the carbon-based solid acid catalyst is 100:6-12.

4. The method for catalytically synthesizing biodiesel by using carbon-based solid acid according to claim 1, wherein the molar ratio of the methanol steam and/or the ethanol steam to the waste oil is 5:1-15:1;

when the mixed alcohol vapor is methanol vapor and ethanol vapor, the mass ratio of the methanol vapor to the ethanol vapor is 99:1-9:1.

5. the method for catalytically synthesizing biodiesel by using the carbon-based solid acid as claimed in claim 1, wherein the esterification reaction temperature is 70-100 ℃ and the esterification reaction time is 2-15h.

6. The method for catalytically synthesizing biodiesel by using carbon-based solid acid according to claim 1, wherein the esterification reaction is completed when the acid value in the reaction solution is less than or equal to 2 mg-KOH/g.

7. The method for catalytically synthesizing biodiesel by using the carbon-based solid acid as claimed in claim 1, wherein the preparation method of the carbon-based solid acid catalyst comprises the following steps:

(1) Crushing crop straws, drying, pyrolyzing the dried crop straw powder in an inert atmosphere, washing with deionized water to remove ash after pyrolysis is finished, filtering, and drying a filter cake;

(2) And mixing the filter cake with concentrated sulfuric acid for sulfonation treatment, washing with deionized water after sulfonation is finished, filtering until the filtrate is neutral, and drying the filter cake to obtain the carbon-based solid acid catalyst.

8. The method for catalytically synthesizing biodiesel by using carbon-based solid acid according to claim 7, wherein in the step (1), the drying temperature of the crop straws is 80-180 ℃, and the drying time is 6-36h; the inert atmosphere is nitrogen atmosphere; the pyrolysis temperature is 200-600 ℃, and the pyrolysis time is 1-5h.

9. The method for catalytically synthesizing biodiesel by using carbon-based solid acid according to claim 7, wherein in the step (2), the weight ratio of the filter cake to the concentrated sulfuric acid is 1:20-1:150;

the sulfonation treatment comprises the following steps: heating at 60-200 deg.C for 0.5-10h.

10. The method for catalytically synthesizing biodiesel by using carbon-based solid acid according to claim 7, wherein in the step (2), the drying temperature is 80-180 ℃, and the drying time is 10-36h.