CN113881508A

CN113881508A - Method for producing biodiesel by continuous ester exchange

Info

Publication number: CN113881508A
Application number: CN202111339156.9A
Authority: CN
Inventors: 叶活动; 罗丹明
Original assignee: LONGYAN ZHUOYUE NEW ENERGY DEVELOPMENT CO LTD
Current assignee: LONGYAN ZHUOYUE NEW ENERGY DEVELOPMENT CO LTD
Priority date: 2021-11-12
Filing date: 2021-11-12
Publication date: 2022-01-04

Abstract

The invention discloses a method for producing biodiesel by continuous ester exchange, which comprises the following steps: waste oil, methanol and a catalyst are mixed according to the following ratio of (38-48): (4.0-4.5): 1, uniformly mixing the mixture in a static mixer, feeding the mixture into a No. 1 reaction kettle, stirring and heating the mixture to perform ester exchange reaction at the temperature of 67-71 ℃; after reaction, the material flows out of the bottom of the kettle and enters a No. 1 precipitation kettle, the material flows in a U shape under the action of a central partition plate in the kettle, glycerin is precipitated at the bottom of the kettle and is discharged, and the material flows out of the upper side of the kettle and enters a No. 2 reaction kettle; stirring and heating to 67-71 ℃ to continue the ester exchange reaction, and allowing the reacted materials to flow out of the bottom of the kettle and enter a No. 1 buffer kettle; pumping to a flash evaporator, evaporating most of excessive methanol under vacuum, leading out from the top to enter a cooler, automatically flowing the cooled methanol to a No. 3 buffer kettle for recycling, automatically flowing other materials to a No. 2 precipitation kettle, discharging glycerol from the bottom of the kettle, discharging the biodiesel from the upper side of the kettle to enter a No. 2 buffer kettle, and pumping to a crude biodiesel dealcoholization procedure. The invention has the advantages of low investment, high operation efficiency, low cost and high conversion rate.

Description

Method for producing biodiesel by continuous ester exchange

Technical Field

The invention relates to the technical field of biodiesel production methods, in particular to a method for producing biodiesel by continuous ester exchange.

Background

Raw oil used for producing biodiesel by the ester exchange method mainly comprises grease or waste grease after free fatty acid is removed, and waste grease is mainly used in China. The waste oil mainly comprises free fatty acid and triglyceride, wherein the waste oil contains a small amount of impurities such as water, oil sludge and the like, and most of the impurities such as water, oil sludge and the like in the waste oil can be removed by a method such as heating, precipitation, separation and the like. The methanol reacts with free fatty acid in the waste oil to generate biodiesel and water, and the waste oil after the water is removed reacts with excessive methanol to generate biodiesel and glycerin. That is, the ester interchange reaction uses waste oils and fats from which free fatty acids have been removed, and the acid value of the waste oils and fats is required to be less than 1 mgKOH/g. The method for producing biodiesel by ester exchange mainly comprises a reaction kettle method, a reaction tower method and a biological enzyme method. The reaction kettle method is intermittent production, and has the defects of unstable product quality, low production efficiency, low automatic control level, high labor intensity and the like; the reaction tower method uses medium-high temperature and medium-high pressure processes, and has the defects of large equipment investment, high energy consumption, high operation requirement, polymerization and decomposition of partial waste oil and fat due to the medium-high temperature process, low production conversion rate and the like; the biological enzyme method has the defects of long reaction time, high enzyme price, easy poisoning and inactivation of enzyme, high production cost, difficult achievement of the acid value of a product to national standard and the like.

Disclosure of Invention

The invention aims to provide a method for producing biodiesel by continuous ester exchange, which has the advantages of low investment, convenient and efficient operation, low product cost, good quality and high conversion rate of ester exchange reaction.

To achieve the above object, the method for producing biodiesel by continuous transesterification according to the present invention comprises the following steps:

metering the waste oil and fat with the free fatty acid removed and the acid value of less than 1mgKOH/g by using a flow meter, metering methanol and a catalyst by using a metering pump, and mixing the waste oil and fat, the methanol and the catalyst according to the mass ratio of (38-48): (4.0-4.5): the material 1 is uniformly mixed by a static mixer 1 and then enters a No. 1 reaction kettle 2, the kettle is stirred and heated by introducing steam into a heating coil, so that the material is subjected to ester exchange reaction at the temperature of 67-71 ℃;

(II) the material after the reaction in the reaction kettle No. 12 flows out of the kettle bottom and enters the precipitation kettle No. 13, the material flows in a U shape under the action of a central clapboard in the kettle, the glycerin generated by the reaction is insoluble in the biodiesel, and the glycerin is precipitated at the kettle bottom and discharged because the density of the glycerin is higher than that of the biodiesel, and the material flows out of the side surface of the upper part of the kettle and enters the reaction kettle No. 2 4;

(III) because the ester exchange reaction is a reversible reaction process, after glycerin generated by the ester exchange reaction is discharged from the No. 1 precipitation kettle 3, the original ester exchange reversible reaction balance is broken, the subsequent reaction is facilitated to be continuously carried out in the direction of generating the biodiesel and the glycerin, and the conversion rate of the ester exchange reaction is improved; the materials are stirred after entering a No. 2 reaction kettle 4 and are heated by introducing steam into a heating coil, so that the temperature of the materials is kept at 67-71 ℃, the transesterification reaction is continuously carried out on methanol in the materials and a small amount of residual triglyceride in the waste oil, and the reacted materials flow out from the bottom of the No. 2 reaction kettle 4 and enter a No. 1 buffer kettle 6 provided with a liquid level meter;

fourthly, the materials in the No. 1 buffer kettle 6 are conveyed to a flash evaporator 9 with a plurality of layers of sieve plates arranged therein by a pump 11, under the condition that a vacuum pump 13 forms vacuum, most of excessive methanol in the materials is evaporated due to the reduction of boiling point and is led out from the top of the flash evaporator 9 to enter a cooler 10 for cooling, and the cooled methanol automatically flows into the No. 3 buffer kettle 8 for recycling;

fifthly, the material after most of methanol is separated by flash evaporation automatically flows to a No. 2 sedimentation kettle 5 with a clapboard in the center, because part of methanol is dissolved in glycerin generated after ester exchange reaction, the density difference between glycerin and biodiesel is reduced, the separation time of glycerin and biodiesel is longer, after most of methanol is removed by flash evaporation, the density difference between glycerin and biodiesel is improved, the separation of glycerin and biodiesel in the No. 2 sedimentation kettle 5 is accelerated, glycerin is discharged from the bottom of the No. 2 sedimentation kettle 5, and the biodiesel containing part of methanol and a very small amount of glycerin is discharged from the side surface of the upper part of the No. 2 sedimentation kettle 5 and enters a No. 2 buffer kettle 7 with a liquid level meter;

and (VI) the materials in the buffer kettle 7 No. 2 are conveyed to the crude biodiesel dealcoholization procedure by the pump 12, most of the glycerol is discharged from the precipitation kettle 5 No. 2, so that the glycerol content in the materials is reduced, and the possibility of reverse reaction between residual glycerol in the materials and the biodiesel can be reduced or avoided in the subsequent continuous dealcoholization process of the materials, so that the transesterification conversion rate is integrally improved.

The method for producing the biodiesel by continuous ester exchange has the following technical characteristics and beneficial effects:

(1) due to continuous feeding and discharging, the automatic control level of the process is improved, the production safety is guaranteed, the stability of the product quality is improved, the equipment utilization rate and the production efficiency are high, and the labor intensity is low.

(2) The glycerin is discharged from the No. 1 precipitation kettle 3, so that the ester exchange reaction is promoted to be carried out in the direction of generating the biodiesel and the glycerin; after most of methanol is removed by flash evaporation, the density difference between the glycerol and the biodiesel is improved, and the glycerol and the biodiesel can be quickly separated in a No. 2 precipitation kettle 5; after the glycerol is discharged again from the No. 2 precipitation kettle 5, the glycerol content in the material is further reduced, and the possibility of reverse reaction of the material in the subsequent dealcoholization process can be reduced or avoided, so that the conversion rate of the ester exchange reaction is integrally improved.

(3) Compared with a batch method reaction kettle, the method has the advantages of high production efficiency, realization of automatic process control, stable product quality, high equipment utilization rate and the like; compared with medium-high temperature and medium-high pressure methods, the method has the advantages of less equipment investment, low energy consumption, good quality, high conversion rate and the like; compared with the biological enzyme method, the method has the characteristics of short reaction time, good quality, low cost and the like.

(4) Is suitable for industrial large-scale automatic production, and the annual output can reach 10 ten thousand ton scale.

Drawings

FIG. 1 is a schematic view of the structure of a production apparatus for the method for producing biodiesel by continuous transesterification according to the present invention.

Reference numerals: static mixer 1, reation kettle 2 No. 1, No. 1 reation kettle 3, No. 2 reation kettle 4, No. 2 reation kettle 5, No. 1 buffer tank 6, No. 2 buffer tank 7, No. 3 buffer tank 8, flash vessel 9, cooler 10, pump 11, 12, vacuum pump 13.

Detailed Description

The method for producing biodiesel by continuous transesterification according to the present invention will be described in further detail with reference to the accompanying drawings and the detailed description.

Referring to FIG. 1, for five examples, the relevant process parameters are shown in Table 1, and the method for producing biodiesel by continuous transesterification according to the present invention has the following operation steps:

metering the waste oil with the acid value less than 1mgKOH/g after removing free fatty acid by using a flow meter, metering methanol and a catalyst by using a metering pump, uniformly mixing the waste oil, the methanol and the catalyst according to the addition amount in the table 1 by using a static mixer 1, then feeding the mixture into a No. 1 reaction kettle 2, stirring the mixture in the kettle, introducing steam into a heating coil for heating, and carrying out ester exchange reaction on the materials at the temperature of 67-71 ℃;

TABLE 1

As can be seen from Table 1, the conversion rates of the transesterification reactions of the five examples of the present invention are all above 96%, and the conversion rate of example 3 is up to 97.5%, which is the best example.

Claims

1. A method for producing biodiesel by continuous ester exchange is characterized in that: the operation steps are as follows:

metering the waste oil and fat with the free fatty acid removed and the acid value of less than 1mgKOH/g by using a flow meter, metering methanol and a catalyst by using a metering pump, and mixing the waste oil and fat, the methanol and the catalyst according to the mass ratio of (38-48): (4.0-4.5): the material 1 is uniformly mixed by a static mixer (1) and then enters a No. 1 reaction kettle (2), the kettle is stirred and heated by introducing steam into a heating coil, so that the material is subjected to ester exchange reaction at the temperature of 67-71 ℃;

(II) the material after the reaction in the reaction kettle No. 1 (2) flows out from the bottom of the kettle and enters a precipitation kettle No. 1 (3), the material flows in a U shape under the action of a central clapboard in the kettle, because the glycerin generated by the reaction is insoluble in the biodiesel, and because the density of the glycerin is higher than that of the biodiesel, the glycerin is precipitated at the bottom of the kettle and is discharged, and the material flows out from the side surface of the upper part of the kettle and enters a reaction kettle No. 2 (4);

(III) because the ester exchange reaction is a reversible reaction process, after glycerin generated by the ester exchange reaction is discharged from the No. 1 precipitation kettle (3), the original ester exchange reversible reaction balance is broken, the subsequent reaction is facilitated to be continuously carried out in the direction of generating the biodiesel and the glycerin, and the conversion rate of the ester exchange reaction is improved; the materials are stirred after entering a No. 2 reaction kettle (4) and are heated by introducing steam into a heating coil, the temperature of the materials is kept at 67-71 ℃, the transesterification reaction is continuously carried out on methanol in the materials and a small amount of residual triglyceride in the waste oil, and the reacted materials flow out from the bottom of the No. 2 reaction kettle (4) and enter a No. 1 buffer kettle (6) provided with a liquid level meter;

fourthly, the materials in the No. 1 buffer kettle (6) are conveyed to a flash evaporator (9) with a plurality of layers of sieve plates arranged therein by a pump (11), under the condition that a vacuum pump (13) forms vacuum, most of excessive methanol in the materials is evaporated due to the reduction of boiling point and is led out from the top of the flash evaporator (9) to enter a cooler (10) for cooling, and the cooled methanol automatically flows into the No. 3 buffer kettle (8) for recycling;

fifthly, the material after most of methanol is separated by flash evaporation automatically flows to a No. 2 sedimentation kettle (5) with a clapboard in the center, because part of methanol is dissolved in glycerin generated after ester exchange reaction, the density difference between glycerin and biodiesel is reduced, the separation time of glycerin and biodiesel is longer, after most of methanol is removed by flash evaporation, the density difference between glycerin and biodiesel is improved, the separation of glycerin and biodiesel in the No. 2 sedimentation kettle (5) is accelerated, glycerin is discharged from the bottom of the No. 2 sedimentation kettle (5), and biodiesel containing part of methanol and very little glycerin is discharged from the side surface of the upper part of the No. 2 sedimentation kettle (5) and enters a No. 2 buffer kettle (7) with a liquid level meter;

and (VI) the materials in the No. 2 buffer kettle 7 are conveyed to a crude biodiesel dealcoholization procedure by a pump (12), most of glycerin is discharged in the No. 2 precipitation kettle (5), so that the glycerin content in the materials is reduced, and the possibility of reverse reaction between residual glycerin in the materials and biodiesel can be reduced or avoided in the subsequent continuous dealcoholization process of the materials, so that the transesterification conversion rate is integrally improved.