CN115261147A

CN115261147A - Method for catalytically synthesizing biodiesel by using carbon-based solid acid

Info

Publication number: CN115261147A
Application number: CN202210923032.3A
Authority: CN
Inventors: 汪群慧; 张秉昕; 唐卫奇; 王晓娜; 高明; 吴川福
Original assignee: University of Science and Technology Beijing USTB
Current assignee: University of Science and Technology Beijing USTB
Priority date: 2022-06-23
Filing date: 2022-08-02
Publication date: 2022-11-01

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

Method for catalytically synthesizing biodiesel by using carbon-based solid acid

Technical Field

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

Background

In order to cope with the large consumption of fossil fuels and the growing environmental problems, the development of more green and renewable energy sources has become a new need 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 be used in combination with diesel oil, and thus is considered as an excellent substitute for fossil fuels. Biodiesel is generally prepared from animal and vegetable oils by esterification or transesterification under acidic or alkaline conditions. However, in order to reduce the production cost, waste oils and fats having a high free fatty acid content are often selected as the raw material. Saponification occurs when it reacts directly with a basic catalyst, thus requiring the conversion of free fatty acids to methyl esters by pre-esterification under acidic catalysis.

In practical production, a homogeneous acid catalyst (such as concentrated sulfuric acid, hydrochloric acid and the like) which is cheap and easy to obtain and has a good catalytic effect is often adopted to catalyze the esterification reaction. However, they remain in methanol, which causes problems such as difficulty in separating and recovering the catalyst, serious corrosion of equipment, and environmental pollution of a large amount of waste liquid. In contrast, heterogeneous catalysts can effectively solve the above problems, reducing overall production costs. Among them, the carbon-based solid acid catalyst has the characteristics of low cost, large specific surface area, abundant surface functional groups, renewability and the like, and initiates the intensive research of numerous scholars. In order to fully utilize biomass energy and reduce the preparation cost of the catalyst, firstly, biochar obtained by pyrolyzing waste biomass is taken as a precursor, and then the biochar is sulfonated by concentrated sulfuric acid to prepare the acid catalyst.

However, in the process of producing biodiesel by solid acid catalysis, the phenomenon of catalyst failure becomes a difficult problem to be solved. This is because an excess of methanol is generally added at a time to accelerate the reaction in the esterification reaction. On the one hand, however, methanol is easily combined with sulfonic acid groups which are also polar, so that active groups which are not firmly loaded are largely leached out; on the other hand, excessive methanol and sulfonic acid groups also undergo esterification reaction at high temperature to form sulfonic ester on the surface of the catalyst, resulting in deactivation of the catalyst. In order to improve the recycling performance of the catalyst, researchers improve the catalytic activity of the catalyst by further modifying the catalyst. However, in order to solve this problem, it is necessary to develop a method for reducing the contact time of methanol with the catalyst.

Disclosure of Invention

The main purpose of the present application is to provide a method for synthesizing biodiesel by using carbon-based solid acid catalysis, wherein methanol vapor and/or ethanol vapor is used to replace traditional liquid methanol or ethanol, so as to improve the catalytic efficiency of the catalyst and prolong the service life of the catalyst.

In order to achieve the above purpose, the invention provides the following technical scheme:

a method for synthesizing biodiesel by using carbon-based solid acid catalysis 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 adoption of alcohol steam can lead the grease and the catalyst to contact with more alcohols in a short time, thus improving the activity; meanwhile, the method slows down the loss rate of the acid groups on the surface of the catalyst and prolongs the service life of the catalyst.

As a preferred embodiment, the method for catalytically synthesizing the biodiesel by using the carbon-based solid acid is used for preparing the waste oil, the waste animal fat and the industrial waste acidified oil.

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

In the method for catalytically synthesizing biodiesel by using the carbon-based solid acid, as a preferred embodiment, 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.

the adding method of the methanol steam and/or the ethanol steam comprises the following steps: filling methanol and/or ethanol into a single-neck flask, and plugging the bottle mouth by using a plug with a stainless steel pipe; heating the single-mouth flask, controlling the generated methanol steam and/or ethanol steam to be introduced into the waste grease at the speed of 0.5-1 mL/min, wherein the outlet of the stainless steel pipe needs to extend to the position below the liquid level of the waste grease, and the overflowed methanol steam and/or ethanol steam can be recovered and recycled.

As a preferred embodiment, the method for catalytically synthesizing the biodiesel by using the carbon-based solid acid has the esterification reaction temperature of 70-100 ℃ and the esterification reaction time of 2-15h.

As a preferable embodiment, the esterification reaction is completed when the acid value in the reaction solution is less than or equal to 2mg KOH/g.

As a preferred embodiment, the method for catalytically synthesizing biodiesel by using a 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 by using deionized water after sulfonation is finished, filtering until filtrate is neutral, and drying the filter cake to obtain the carbon-based solid acid catalyst.

The crop straw can be wheat straw, corn straw, soybean straw, etc., and can also be replaced by peanut shell, wood dust, bamboo or banana straw.

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

As a preferred embodiment, 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 a nitrogen atmosphere; the pyrolysis temperature is 200-600 ℃, and the pyrolysis time is 1-5h.

In the method for catalytically synthesizing biodiesel by using the carbon-based solid acid, as a preferred embodiment, 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.

As a preferred embodiment of the method for catalytically synthesizing biodiesel by using the carbon-based solid acid, in the step (2), the drying temperature is 80-180 ℃, and the drying time is 10-36h.

The beneficial effects of the invention are as follows: the method for synthesizing the biodiesel by using the carbon-based solid acid catalyst uses methanol vapor and/or ethanol vapor to replace the traditional liquid methanol to participate in the esterification reaction, thereby reducing the consumption of the methanol, effectively improving the catalytic performance of the catalyst and the conversion rate of the waste grease, and integrally reducing the production cost of the biodiesel.

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.

Detailed Description

In order to make the technical solutions in the embodiments of the present application better understood, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to examples, and it is obvious that the described embodiments are only some embodiments of the present application, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Example 1

The method for catalytically synthesizing the biodiesel by using the carbon-based solid acid comprises the following steps of:

crushing a certain amount of wheat straws, passing through a 40-mesh screen, and drying at 105 ℃ for 12 hours; the dried powder was transferred to a crucible and placed in a pyrolysis muffle furnace, set at a nitrogen flow rate of 80ml/min, and pyrolyzed at 350 ℃ for 1.5h. And mixing the product with a certain amount of deionized water, washing and filtering to remove ash. Collecting the filtered biochar, and drying at 105 ℃ for 12h.

Mixing 5g of dried biochar with 100g of concentrated sulfuric acid, heating at 150 ℃ for 4h, cooling to room temperature, adding deionized water for multiple times, washing, and filtering until the filtrate is neutral. Drying the obtained filtered solid at 105 ℃ for 10h to obtain the finished product of the carbon-based solid acid catalyst. The sulfonic acid density of the catalyst was determined to be 1.51mmol/g using titration.

30g of waste grease (waste cooking oil) is weighed and placed in a three-neck flask connected with a condensing device, and 3g of carbon-based solid acid catalyst is added. 160g of a mixed alcohol of methanol and ethanol (methanol to ethanol mass ratio of 9). Heating a single-neck flask in water bath at 85 ℃, introducing mixed alcohol steam of generated methanol steam and ethanol steam to the position below the liquid level of the waste oil through a stainless steel pipe, heating a three-neck flask at 76 ℃ for 4 hours to perform esterification reaction, and after the reaction is finished (the esterification reaction is finished when the acid value in reaction liquid is less than or equal to 2mg KOH/g), centrifuging the esterification product to separate the residual methanol, methyl oleate (biodiesel), water and catalyst. The conversion of fatty acids was found to be 99.32% by calculation.

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

The acid number was measured as follows: weighing about 1g of grease sample material and placing the grease sample material in a conical flask; transferring 50mL of ethanol into a conical flask filled with a grease sample to be detected, and fully mixing; and adding 0.5mL of phenolphthalein indicator, titrating with a KOH-ethanol standard solution, fully shaking in the titration process until the color changes, and keeping the color unchanged for 15s, thus obtaining the titration end point.

Acid value = (V × c × 56.1)/m

In the formula: v-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-mass of sample, g.

Example 2

crushing certain amount of bamboo, sieving with 40 mesh sieve, and drying at 105 deg.C for 12 hr; the dried powder was transferred to a crucible and placed in a pyrolysis muffle furnace for pyrolysis at 250 ℃ for 1.5h with a nitrogen flow rate of 100 ml/min. And mixing the product with a certain amount of deionized water, washing and filtering to remove ash. The filtered charcoal was collected and dried at 105 ℃ for 12h.

Mixing 5g of dried biochar with 100g of concentrated sulfuric acid, heating at 150 ℃ for 4h, cooling to room temperature, adding deionized water for multiple times, washing, and filtering until the filtrate is neutral. Drying the obtained filtered solid at 105 ℃ for 10h to obtain a finished product of the carbon-based solid acid catalyst. The sulfonic acid density of the catalyst was determined to be 1.25mmol/g using titration.

30g of waste grease (waste animal fat) is weighed and placed in a three-neck flask connected with a condensing device, and 3g of carbon-based solid acid catalyst is added. 160g of methanol was weighed into a single-neck flask and connected to a three-neck flask. Heating a single-neck flask in water bath at 74 ℃, introducing generated methanol steam below the liquid level of the waste oil through a stainless steel pipe, heating a three-neck flask at 76 ℃ for 4 hours to perform esterification reaction, and after the reaction is finished (the esterification reaction is finished when the acid value in a reaction liquid is less than or equal to 2mg KOH/g), centrifuging the esterification product to separate residual methanol, methyl oleate (biodiesel), water and a catalyst. The conversion of fatty acid was found to be 97.54% by calculation.

Example 3

crushing a certain amount of peanut shells, passing through a 40-mesh screen, and drying at 105 ℃ for 12h; the dried powder was transferred to a crucible and placed in a pyrolysis muffle furnace, set at a nitrogen flow rate of 80ml/min, and pyrolyzed at 350 ℃ for 1.5h. And mixing the product with a certain amount of deionized water, washing and filtering to remove ash. Collecting the filtered biochar, and drying at 105 ℃ for 12h.

5g of dried biochar was mixed with 100g of concentrated sulfuric acid and heated at 150 ℃ for 4 hours. Cooling to room temperature, adding deionized water for several times, washing, and filtering until the filtrate is neutral. Drying the obtained filtered solid at 105 ℃ for 10h to obtain a finished product of the carbon-based solid acid catalyst. The sulfonic acid density of the catalyst was determined to be 1.32mmol/g using titration.

30g of waste grease (waste cooking oil) is weighed and placed in a three-neck flask connected with a condensing device, and 3g of carbon-based solid acid catalyst is added. 160g of a mixed alcohol of methanol and ethanol (methanol to ethanol mass ratio of 9). Heating a single-neck flask in water bath at 85 ℃, introducing mixed alcohol steam of generated methanol steam and ethanol steam to the position below the liquid level of the waste oil through a stainless steel pipe, heating a three-neck flask at 76 ℃ for 4 hours to perform esterification reaction, and after the reaction is finished (the esterification reaction is finished when the acid value in reaction liquid is less than or equal to 2mg KOH/g), centrifuging the esterification product to separate the residual methanol, methyl oleate (biodiesel), water and catalyst. The conversion of fatty acid was found to be 97.14% by calculation.

Example 4

Example 4 differs from example 2 in that: the same procedure as in example 2 was repeated except that the alcohol used was ethanol, that is, the esterification reaction was carried out using ethanol vapor. The conversion of fatty acid was calculated to be 98.76% by measuring the change in acid value before and after the reaction.

Comparative example 1

The method for catalytically synthesizing biodiesel by using carbon-based solid acid described in comparative example 1 is different from the method described in example 1 in that: comparative example 1 the same procedure as in example 1 was repeated except that the alcohol used in the catalytic synthesis of biodiesel using a carbon-based solid acid was a mixed alcohol of liquid methanol and liquid ethanol, and the esterification reaction was carried out.

Comparative example 2

The method for catalytically synthesizing biodiesel by using the carbon-based solid acid described in the comparative example 2 is different from the method described in the example 4 in that:

in comparative example 2, the alcohol used for catalytically synthesizing the biodiesel by using the carbon-based solid acid is liquid ethanol for esterification reaction, and the rest of the operation is the same as that of example 4.

The research on the repeatability of the catalyst for synthesizing the biodiesel by using the carbon-based solid acid catalyst is shown in the table 1:

TABLE 1

Sample (I)	Sulfonic acid Density (mmol g) ^-1 )	Esterification ratio (%)
			First time of steam esterification	1.51	99.32
Steam esterification was repeated 4 times	0.92	97.48
			Steam esterification was repeated 8 times	0.35	83.36
Comparative example 1 liquid esterification first time	1.51	96.87
			Comparative example 1 liquid esterification was repeated 4 times	0.32	79.76
Comparative example 2 liquid esterification first time	1.51	95.84
			Comparative example 2 liquid esterification was repeated 4 times	0.29	77.65

Remarking:

the steam esterification in the table is the first sulfonic acid density, esterification rate of the carbon-based solid acid catalyst described in example 1.

The steam esterification was repeated 4 times in the table as: the catalytic synthesis of biodiesel was repeated 4 times, i.e. the carbon-based solid acid catalyst was used 4 times, according to the method described in example 1.

The steam esterification was repeated 8 times in the table as: according to the method described in example 1, the catalytic synthesis of biodiesel was repeated 8 times, i.e. the carbon-based solid acid catalyst was reused 8 times.

Comparative example 1 liquid esterification was repeated 4 times in the table as: the catalytic synthesis of biodiesel was repeated 4 times, i.e. the catalyst was reused 4 times, according to the method described in comparative example 1.

Comparative example 2 liquid esterification was repeated 4 times in the table as: the catalytic synthesis of biodiesel was repeated 4 times, i.e. the catalyst was reused 4 times, according to the method described in comparative example 2.

As can be seen from table 1: although the catalytic activities of the two are close to each other in the first esterification, the catalyst is obviously deactivated after being repeatedly used for 4 times in the liquid esterification, and the conversion rate of the fatty acid is less than 80 percent. In contrast, the mixed alcohol vapor esterification using methanol vapor and ethanol vapor was recycled 8 times, and the fatty acid conversion was still higher than 80%.

Table 1 shows the change in catalyst sulfonic acid density during two esterification recycles catalysts. After the liquid is esterified and recycled for 4 times, the density of the sulfonic acid is reduced to 0.32mmol g ^-1 (ii) a And the sulfonic acid density after repeating the steam esterification 4 times is 0.92mmol g ^-1 And shows good catalytic performance.

The carbon-based solid acid catalyst can play a catalytic role mainly because the surface is loaded with sulfonic acid groups, carboxylic acid and other weak acid groups, and sulfonic acid plays a main role. The density of sulfonic acid can be regarded as one of the indicators for measuring its catalytic activity.

The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and additions can be made without departing from the method of the present invention, and these modifications and additions should also be regarded as the protection scope of the present invention.

Claims

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

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;

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:

(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;

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.