A method for preparing biodiesel from waste oil and fat catalyzed by glycerol zinc

Abstract

The invention discloses a method for preparing biodiesel from waste oil and fat by catalyzing glycerol zinc, wherein the raw material waste oil and fat is subjected to pretreatment, glycerol esterification reaction, transesterification reaction, and post-treatment to obtain BD100 biodiesel; the glycerol esterification reaction and transesterification reaction processes both use a glycerol zinc catalyst, the glycerol zinc catalyst reacts with free fatty acids to form fatty acid zinc, and homogeneous catalysis of the glycerol esterification and transesterification reaction processes is realized, and fatty acid zinc reacts with glycerol in the later stage of the reaction to regenerate glycerol zinc, which has the advantages of easy separation of heterogeneous catalysts and the characteristics of high efficiency of homogeneous catalysts. The invention is based on the amphoteric catalytic characteristics of glycerol zinc, ingeniously combines the conversion characteristics of glycerol zinc and fatty acid zinc, couples the glycerol esterification reaction of waste oil and fat with the transesterification reaction, realizes the homogeneous catalytic reaction process of the heterogeneous catalyst and the heterogeneous separation process, has the characteristics of fast reaction rate and catalyst recyclability, is suitable for industrial production, and can stably produce BD100 biodiesel.

Description

Technical Field

[0001] The invention belongs to the technical field of oil chemical industry, and particularly relates to a method for preparing biodiesel from waste oil by catalyzing glycerol zinc. Background Art

[0002] Biodiesel is a clean and green fuel because of its sustainability, low sulfur content and biodegradability. At present, waste oil is the main raw material of my country's current biodiesel companies. However, waste oil contains a large amount of free fatty acids, which must be pre-treated by acid reduction before obtaining biodiesel through base-catalyzed transesterification. At present, the industrial production of biodiesel usually adopts a two-step method of sulfuric acid-catalyzed esterification combined with homogeneous alkali (KOH, NaOH, etc.) catalyzed transesterification to prepare biodiesel. This method has common problems such as large amount of sulfuric acid wastewater, severe equipment corrosion, high water washing cost, and low biodiesel yield.

[0003] Glycerol esterification is an effective method for reducing acidity. It can reduce the acidity of high-acid oils and fats to below 1 mgKOH / g, reducing acidity more thoroughly while avoiding the problems of large amounts of sulfuric acid wastewater, equipment corrosion, and low biodiesel yield. The byproduct glycerol after ester exchange can be refined and recycled as a raw material for glycerol esterification.

[0004] However, in the actual production process, the glycerol esterification method still has problems such as high energy consumption (generally the reaction temperature is 220℃-240℃), large oil evaporation loss, and more glycerol polymerization, which leads to high organic matter content in glycerol esterification wastewater, low glycerol recovery rate, and low biodiesel yield; in addition, the ester exchange reaction process uses homogeneous alkali (KOH or NaOH) catalysis, and there are still problems such as easy saponification of oils, low biodiesel yield, difficulty in catalyst recovery, and high glycerol refining cost. Summary of the invention

[0005] In view of the above technical problems existing in the prior art, the purpose of the present application is to provide a method for preparing biodiesel from waste oil and fat catalyzed by glycerol zinc. In the method of the present invention, the glycerol esterification reaction and the transesterification reaction are both carried out under the catalysis of glycerol zinc, and the glycerol zinc can react with the fatty acids in the raw material waste oil and fat to generate soluble fatty acid zinc, thereby the zinc element exists in the form of fatty acid zinc to realize homogeneous catalytic esterification. The present invention further controls the acid value of the feed liquid after the glycerol esterification reaction within a certain range, which is conducive to the continued homogeneous catalysis of part of the zinc element in the transesterification reaction. After the reaction is completed, the acid value is below 0.5 mgKOH / g, and the zinc element is basically converted into glycerol zinc and precipitated, realizing the homogeneous catalytic reaction process and heterogeneous separation process of the heterogeneous catalyst.

[0006] The technical solution adopted in this application is:

[0007] A method for preparing biodiesel from waste oil and fat catalyzed by glycerol zinc comprises the following steps: the raw material waste oil and fat is sequentially subjected to the processes of pretreatment, glycerol esterification reaction, transesterification reaction, and post-treatment to obtain BD100 biodiesel; the pre-treatment process uses an organic extractant to extract the waste oil and fat, and after filtering and removing impurities, removes the organic extractant to obtain the glycerol esterification raw material, and the organic extractant is reused in the raw material pre-treatment process; the glycerol esterification reaction and the transesterification reaction are both carried out under the catalysis of glycerol zinc, and the glycerol zinc catalyst reacts with free fatty acids to form fatty acid zinc, realizing homogeneous catalysis of the glycerol esterification and transesterification reaction processes, and in the later stage of the reaction, the fatty acid zinc reacts with glycerol to regenerate glycerol zinc, which has the advantages of easy separation of heterogeneous catalysts and the characteristics of high efficiency of homogeneous catalysts. The post-treatment process comprises four processes: catalyst sedimentation separation, flash dealcoholization, glycerol sedimentation separation, and distillation purification. The feed liquid after the transesterification reaction is subjected to the post-treatment process to obtain a high-quality BD100 biodiesel product, and the separated glycerol zinc catalyst, methanol, and glycerol are reused in the biodiesel production process.

[0008] Furthermore, the organic extractant used in the pretreatment process is n-hexane.

[0009] Furthermore, the waste oil includes at least one of soap stock acidified oil and kitchen waste oil, and the waste oil contains free fatty acids, and the acid value thereof is in the range of 20-180 mgKOH / g.

[0010] Furthermore, the glycerol esterification reaction process is to mix the pretreated waste oil with glycerol and glycerol zinc catalyst for reaction, the reaction temperature is 160-200°C, preferably 165-170°C, the amount of glycerol is 10-25wt% of the oil weight, preferably 12-15wt%, the amount of catalyst is 1-3wt% of the oil weight, preferably 1.5-2.0wt%, and the reaction time is 0.5-2h, preferably 1-1.5h.

[0011] Furthermore, the acid value of the feed solution after the glycerol esterification reaction is controlled within the range of 5-20 mgKOH / g.

[0012] Furthermore, the transesterification reaction process is to mix the feed liquid methanol after the glycerol esterification reaction, and the reaction is carried out under a nitrogen atmosphere. The reaction temperature is 100-150°C, preferably 130-140°C, the reaction pressure is 0.4-1.1MPa, preferably 0.8-1.0MPa, the alcohol-oil molar ratio of methanol to the initial raw material waste oil is 20:1-35:1, preferably 28-30:1, and the reaction time is 1-3h, preferably 1.5-2h.

[0013] Furthermore, the acid value of the feed solution after the transesterification reaction is controlled to be below 1 mgKOH / g, more preferably below 0.5 mgKOH / g.

[0014] Furthermore, the glycerol zinc catalyst is prepared by reacting zinc acetate dihydrate with glycerol and deionized water at 140-160° C., and the molar ratio of zinc acetate dihydrate, glycerol and deionized water is controlled at 1:(70-80):(5-7); the reaction temperature is preferably 150° C., and the molar ratio of zinc acetate dihydrate, glycerol and deionized water is preferably 1:75:6.

[0015] The beneficial effects achieved by the present invention are:

[0016] (1) Based on the amphoteric catalytic characteristics of zinc glycerol, the present invention skillfully combines the conversion characteristics of zinc glycerol and fatty acid zinc, couples the waste oil glycerol esterification reaction with the ester exchange reaction, and realizes the homogeneous catalytic reaction process and heterogeneous separation process that traditional heterogeneous catalysts do not have. It has the characteristics of good raw material universality, green process, fast reaction rate, high product yield, recyclable catalyst, and suitability for industrial production, and can stably produce BD100 biodiesel.

[0017] (2) The present invention uses a simple synthetic glycerol zinc as a catalyst, which is applied to the catalytic esterification and ester exchange reaction of waste oil and fat to prepare biodiesel, realizing acid-base integrated catalysis, avoiding the occurrence of side reactions such as oil and fat saponification reaction, reducing glycerol polymerization, and simplifying the glycerol separation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart of preparing biodiesel from waste oil and fat catalyzed by glycerol zinc;

[0019] Figure 2 This is a SEM image of the glycerol zinc catalyst obtained in Example 1;

[0020] Figure 3 This is the TEM image of the glycerol zinc catalyst obtained in Example 1. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0022] Example 1: Preparation of Catalyst

[0023] 8.00 g of zinc acetate dihydrate, 200 ml of glycerol, and 4 ml of deionized water (molar ratio 1:77:6.22) were heated and stirred at 160°C for 1 hour, and the solid was collected by filtration, washed with deionized water and ethanol, and dried to constant weight to obtain a glycerol zinc catalyst. The SEM and TEM analysis results of the obtained glycerol zinc are as follows: Figure 2 , Figure 3 Its performance parameters are shown in Table 1.

[0024] Table 1. Performance parameters of zinc glycerol catalyst

[0025]

[0026] Example 2: Glycerol esterification reaction of waste oil catalyzed by zinc glycerol

[0027] After preheating 500g palmitic acid oil (acid value of 113mgKOH / g) to 170°C, glycerol (125g, 25% of the weight of the raw oil) and glycerol zinc catalyst (10g, 2% of the weight of the raw oil) were added to carry out glycerol esterification reaction. The reaction temperature was controlled at 170°C and the reaction time was 2 hours. The final acid value was less than 1mgKOH / g oil. The reacted material was filtered to separate glycerol zinc (the recovery rate of glycerol zinc can be stabilized at 95%). After washing with deionized water and ethanol, drying and recovery, the glycerol esterification reaction was continued. The experimental results of the glycerol zinc catalyzed glycerol esterification reaction of palmitic acid oil are shown in Table 2:

[0028] Table 2. Experimental results of glycerol zinc catalyzed palmitic acid oil glycerol esterification reaction

[0029]

[0030]

[0031] Example 3: Transesterification of waste oils catalyzed by zinc glycerol catalyst:

[0032] Into an autoclave were added 40 g of glycerol esterified liquid (fatty acid content was 10% of the oil weight), 43.63 g of methanol (alcohol-oil molar ratio was 30:1), and 1.2 g of glycerol zinc (3% of the oil weight). The autoclave was pressurized to 1.1 MPa with nitrogen and then heated to 140°C for ester exchange reaction. The reaction time was 2 hours. After the reaction, the biodiesel yield was 90.1%.

[0033] Example 4: Preparation of biodiesel, comprising the following steps (process flow chart as shown in Figure 1 shown):

[0034] 1) Pretreatment step: The biodiesel raw material used in Example 4 is waste oil (its fatty acid distribution is shown in Table 3), and its pretreatment steps are as follows: 500mL of waste oil is heated to liquid state and extracted with an equal volume of normal hexane, filtered to remove solid impurities and then flashed to remove normal hexane to obtain glyceride esterification raw material (flash vacuum degree is 0.01MPa, flash temperature is 60°C). The distribution of fatty acid composition of waste oil after pretreatment and the corresponding indicators of waste oil before and after pretreatment are shown in Table 4:

[0035] Table 3. Distribution of fatty acids in waste cooking oil

[0036]

[0037] Table 4. Comparison of waste oil before and after pretreatment

[0038]

[0039] 2) Glycerol esterification reaction: 500g of pretreated waste oil is preheated to 170°C, and then glycerol (glycerol dosage is 20% of the raw oil weight, 100g) and glycerol zinc catalyst (catalyst dosage is 3% of the oil weight, 15g) are added to carry out glycerol esterification reaction. The reaction temperature is controlled at 170°C, the reaction time is 1 hour, and the final acid value is 20mgKOH / g; 3) Transesterification reaction: After the glycerol esterification reaction, the feed liquid is cooled to 60°C and then transported to a high-pressure reactor, and methanol (methanol dosage to alcohol-oil molar ratio of raw waste oil is 30:1) is added. After being pressurized to 1.1MPa by nitrogen, the temperature is raised to 140°C for transesterification reaction. The reaction time is 2 hours, and the final acid value is less than 0.5mgKOH / g. After the reaction is completed, the biodiesel yield is about 92%.

[0040] 4) Post-treatment: After the ester exchange, the glycerol zinc catalyst is separated by sedimentation, and the recovery rate of glycerol zinc reaches 96%, which can be reused in the glycerol esterification reaction; the material from which the catalyst is separated is flash-de-alcoholized while hot (flash vacuum degree 0.01MPa, flash temperature 60°C), and the crude methanol removed can be reused in the ester exchange reaction after methanol distillation; the dealcoholized material is further precipitated, and the upper layer of crude methyl ester is distilled at a pressure of 500Pa to obtain a biodiesel product, and the quality analysis results of the obtained biodiesel are shown in Table 5; the lower layer of crude glycerol can be distilled to obtain refined glycerol, which is used for glycerol esterification reaction and catalyst preparation; the plant asphalt and glycerol asphalt obtained in the bottom of the tower after the distillation of crude methyl ester and crude glycerol can be further utilized as resources.

[0041] Table 5. Biodiesel product analysis results

[0042]

[0043] In summary, the glycerol zinc in the present invention has high catalytic activity and high catalytic stability in catalyzing the glycerol esterification and transesterification reaction of waste oil and fat, and the BD100 biodiesel finally obtained complies with the GB 25199-2017 standard.

[0044] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be regarded as being limited to the specific forms described in the embodiments.

Claims

1. A method for preparing biodiesel from waste oil and fat catalyzed by zinc glycerol, characterized in that The method comprises the following steps: the raw material waste oil is sequentially subjected to the processes of pretreatment, glycerol esterification reaction, ester exchange reaction and post-treatment to obtain BD100 biodiesel; the pre-treatment process uses an organic extractant to extract the waste oil, and after filtering to remove impurities, the organic extractant is removed to obtain the glycerol esterification raw material, and the organic extractant is reused in the raw material pre-treatment process; the glycerol esterification reaction and the ester exchange reaction are both carried out under the catalysis of glycerol zinc, so as to realize the homogeneous catalytic reaction process of the zinc element in the reaction and the heterogeneous separation process in the subsequent post-treatment; the post-treatment process comprises four processes of catalyst sedimentation separation, flash dealcoholization, glycerol sedimentation separation and distillation purification, and the feed liquid after the ester exchange reaction is subjected to the post-treatment process to obtain a high-quality BD100 biodiesel product, and the glycerol zinc catalyst, methanol and glycerol separated at the same time are reused in the biodiesel production process; The glycerol esterification reaction and the transesterification reaction are both carried out under the catalysis of glycerol zinc, and the glycerol zinc catalyst reacts with free fatty acids to form fatty acid zinc, thereby realizing homogeneous catalysis of the glycerol esterification and transesterification reaction processes, and in the later stage of the reaction, the fatty acid zinc reacts with glycerol to regenerate glycerol zinc; The waste oil comprises at least one of soap stock acidified oil and kitchen waste oil, and the waste oil contains free fatty acids, and the acid value thereof is in the range of 20-180 mgKOH / g; The glycerol esterification reaction process is to mix the pretreated waste oil with glycerol and glycerol zinc catalyst for reaction, the reaction temperature is 160-200°C, the amount of glycerol is 10-25wt% of the oil weight, the amount of catalyst is 1-3wt% of the oil weight, and the reaction time is 0.5-2h; The acid value of the feed liquid after the glycerol esterification reaction is controlled within the range of 5-20 mgKOH / g; The transesterification reaction process is to mix the feed liquid methanol after the glycerol esterification reaction under a nitrogen atmosphere, the reaction temperature is 100-150°C, the reaction pressure is 0.4-1.1MPa, the alcohol-oil molar ratio of methanol to the initial raw material waste oil is 20:1-35:1, and the reaction time is 1-3h; The acid value of the feed solution after the ester exchange reaction is controlled below 1 mgKOH / g.

2. The method for preparing biodiesel from waste oil and fat catalyzed by zinc glycerol as claimed in claim 1, characterized in that The organic extractant used in the pretreatment process is n-hexane.

3. The method for preparing biodiesel from waste oil and fat catalyzed by zinc glycerol as claimed in claim 1, characterized in that The glycerol esterification reaction process is to mix the pretreated waste oil with glycerol and glycerol zinc catalyst for reaction, the reaction temperature is 165-170°C, the amount of glycerol is 12-15wt% of the oil weight, the amount of catalyst is 1.5-2.0wt% of the oil weight, and the reaction time is 1-1.5h.

4. The method for preparing biodiesel from waste oil and fat catalyzed by zinc glycerol as claimed in claim 1, characterized in that The transesterification reaction process is to mix the liquid methanol after the glycerol esterification reaction and react it under a nitrogen atmosphere, the reaction temperature is 130-140°C, the reaction pressure is 0.8-1.0MPa, the alcohol-oil molar ratio of methanol to the initial raw material waste oil is 28-30:1, and the reaction time is 1.5-2h.

5. The method for preparing biodiesel from waste oil and fat catalyzed by zinc glycerol as claimed in claim 1, characterized in that The acid value of the feed solution after the ester exchange reaction is controlled below 0.5 mgKOH / g.

6. The method for preparing biodiesel from waste oil and fat catalyzed by zinc glycerol as claimed in claim 1, characterized in that The glycerol zinc catalyst is prepared by reacting zinc acetate dihydrate with glycerol and deionized water at 140-160° C., and the molar ratio of zinc acetate dihydrate, glycerol and deionized water is controlled at 1: (70-80): (5-7).

7. The method for preparing biodiesel from waste oil and fat catalyzed by zinc glycerol as claimed in claim 6, characterized in that The reaction temperature for preparing the glycerol zinc catalyst is 150° C., and the molar ratio of zinc acetate dihydrate, glycerol, and deionized water is 1:75:6.

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