Method for preparing pure biodiesel from kitchen waste oil by enzyme catalytic desulfurization

Abstract

The invention relates to the technical field of catalysis, and particularly discloses a method for preparing pure biodiesel from kitchen waste oil through enzyme catalytic desulfurization. The method comprises the following steps: adding a Sm2O3 / ZrO2 solid acid catalyst into the kitchen waste oil for pretreatment to obtain pretreated waste oil, and then adding lipase into the pretreated waste oil for catalyzing transesterification to obtain the biodiesel. According to the method for preparing the pure biodiesel from the kitchen waste oil through enzyme catalytic desulfurization, in-situ esterification and synchronous desulfurization of free fatty acid can be completed in a single-step reaction, the stability of a conversion reaction is effectively improved, the production process is simplified, and the conversion efficiency of preparing the biodiesel from the kitchen waste oil is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalysis technology, more particularly, it relates to a method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil. BACKGROUND

[0002] With the increasing prominence of global energy crisis and environmental problems, the large-scale production and application of biodiesel as a renewable, low-pollution green energy has become a research hotspot in the energy field.

[0003] The booming development of urban catering industry has led to an increasing amount of kitchen waste and kitchen waste oil produced by catering and food processing enterprises. Kitchen waste oil can be converted into biodiesel mainly composed of aliphatic hydrocarbons through appropriate chemical conversion. The annual output of kitchen waste oil in China exceeds 5 million tons. How to efficiently convert and recycle kitchen waste oil is of great significance to resource recycling, environmental governance and energy export.

[0004] At present, lipase as a biological catalyst is widely used in the conversion of oil and fat, especially in the production of biodiesel. However, for the above-mentioned related technology, the inventors found that the complex composition characteristics of kitchen waste oil often face the problems of acid value and sulfur pollution in the process of conversion into biodiesel. The lipase is extremely sensitive to the acid value of the reaction system. High FFA environment (acid value 15-20 mgKOH / g) will cause the destruction of the enzyme active center, directly leading to enzyme catalytic conversion rate <70%, and easily causing equipment corrosion and waste acid pollution; and sulfur compounds (150-300 ppm) will specifically bind to the active center of lipase, poison the enzyme active center, and significantly shorten the service life of the enzyme. In the prior art, the desulfurization and esterification processes are usually carried out separately. After independent desulfurization by hydrogenation desulfurization, adsorption desulfurization and other methods, esterification reaction is carried out. This not only increases the production process and equipment investment, but also causes energy consumption and loss of raw materials due to the transfer of intermediate environment materials, increases the production cost, and seriously restricts the industrialization application process of kitchen waste oil. SUMMARY

[0005] In order to reduce the influence of high acid value and sulfur compounds of kitchen waste oil on the conversion reaction, simplify the production process, and improve the conversion efficiency of kitchen waste oil for preparing biodiesel, the present application provides a method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil.

[0006] The present application provides a method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil, which adopts the following technical scheme: A method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil, comprising the following steps: S1: adding Sm2O3 / ZrO2 solid acid catalyst to the kitchen waste oil for pretreatment to obtain pretreated waste oil; S2: adding lipase to the pretreated waste oil to catalyze the transesterification reaction to obtain biodiesel.

[0007] The inventors designed a specific Sm2O3 / ZrO2 solid acid catalyst, the surface hydroxyl group of ZrO2 forms Brønsted acid sites (acid amount 0.68 mmol / g) which can protonate the carboxyl group in free fatty acid (FFA), and efficiently catalyze the esterification reaction of FFA in kitchen waste oil with methanol to generate ester, thereby significantly reducing the acid value in the kitchen waste oil raw material. This process effectively reduces the problem of low conversion rate caused by the destruction of the enzyme active center in the high FFA environment during direct enzyme catalysis.

[0008] Further, Sm2O3 provides strong Lewis acid sites, and the empty orbital of Lewis acid (Sm 3+ ) can form a coordination bond with the sulfur atom lone pair of electrons in sulfur-containing compounds (such as mercaptans, sulfides, thiophenes, etc.), realizing selective adsorption of sulfides, and finally removing them through the reaction medium methanol. This process effectively prevents the poisoning of the lipase active center by sulfides.

[0009] By adopting the above technical solution, a specific Sm2O3 / ZrO2 solid acid catalyst is selected, and Sm2O3 and ZrO2 cooperate to complete the in-situ esterification of free fatty acid in kitchen waste oil and simultaneous efficient desulfurization in a single-step reaction in the pretreatment stage. The traditional multi-step process of esterification, desulfurization, and enzyme catalysis is simplified to two steps, without the need for an independent desulfurization process, reducing the process and cost, shortening the reaction time, and effectively preventing the poisoning of the lipase active center by high acid value and sulfur compounds, thereby effectively improving the efficiency of the subsequent enzyme catalytic conversion reaction. In addition, the present application does not produce waste acid emissions by in-situ esterification of free fatty acid in kitchen waste oil, is green and environmentally friendly, and meets the requirements of sustainable development.

[0010] Optionally, the preparation method of the Sm2O3 / ZrO2 solid acid catalyst comprises the following steps: Dissolve ZrOCl2·8H2O in water, add ammonia water for co-precipitation, filter, wash, and dry to obtain Zr(OH)4 precursor; Immerse the Zr(OH)4 precursor in Sm(NO3)3 solution, stir, filter, dry, and calcine to obtain the Sm2O3 / ZrO2 solid acid catalyst.

[0011] Optionally, the Sm2O3 content in the Sm2O3 / ZrO2 solid acid catalyst is 5-15 wt%.

[0012] Optionally, the specific surface area of the Sm2O3 / ZrO2 solid acid catalyst is ≥100 m 2 / g, and the acid center density is ≥0.6 mmol / g.

[0013] The inventors prepared Zr(OH)4 precursor by co-precipitation method, Sm(NO3)3 impregnation and calcination to prepare Sm2O3 / ZrO2 solid acid catalyst, the co-precipitation method ensures the high specific surface area of the ZrO2 carrier, and after Sm(NO3)3 impregnation and calcination, Sm2O3 is uniformly loaded on the ZrO2 to form a synergistic catalyst structure, in which Sm2O3 provides strong Lewis acid sites, and the surface hydroxyl groups of ZrO2 form Brønsted acid sites, providing reactive centers for in-situ esterification of free fatty acids and simultaneous desulfurization in a single-step reaction.

[0014] By adopting the above technical scheme, the preparation process of the Sm2O3 / ZrO2 solid acid catalyst is stable, the repeatability is high, the acid site type and density of the catalyst can be accurately controlled, the specific surface area is high, the exposure of active sites is increased, the mass transfer efficiency is improved, and the esterification and desulfurization dual functional catalytic performance is ensured.

[0015] Optionally, the pretreatment of the kitchen waste oil in step S1 includes the following steps: The Sm2O3 / ZrO2 solid acid catalyst and methanol are added to the kitchen waste oil, and the stirring reaction is carried out at 70-80°C and 200-400rpm for 1-2h to obtain pretreated waste oil.

[0016] By adopting the above technical scheme, the uniformity of the reaction system is ensured under the temperature and stirring parameters, the contact between the catalyst and the substrate is promoted, the esterification reaction efficiency of methanol as a reactant of the esterification reaction and FFA to generate methyl ester is improved, efficient esterification and desulfurization conversion can be completed within 1-2h of pretreatment time, which is more than 50% shorter than the traditional step-by-step process (4h), greatly improving the conversion efficiency, and also reducing the waste acid pollution and sulfur pollution problems caused by concentrated sulfuric acid catalysis, meeting the requirements of green environmental protection.

[0017] Optionally, the addition amount of the Sm2O3 / ZrO2 solid acid catalyst in step S1 is 1-3wt% of the kitchen waste oil.

[0018] Optionally, the addition amount of the methanol is 10-20wt% of the kitchen waste oil.

[0019] Optionally, the acid value in the pretreated waste oil is ≤1.5mgKOH / g, and the sulfur content is ≤15ppm.

[0020] By adopting the above technical scheme, 1-3wt% of Sm2O3 / ZrO2 solid acid catalyst is used, which can not only ensure the reduction rate of the acid value of the kitchen waste oil and the desulfurization efficiency in the pretreatment process, but also reduce the occurrence of side reactions, balancing the conversion efficiency and economy.

[0021] Optionally, the amount of lipase added in step S2 is 1-3 wt% of the pretreated waste oil.

[0022] In summary, the present application has the following advantages: 1. Since the present application uses Sm2O3 / ZrO2 solid acid catalyst for pretreatment of kitchen waste oil, the strong Lewis acid sites of Sm2O3 and the Brønsted acid sites of ZrO2 synergistically act in the single-step pretreatment process to simultaneously complete in-situ esterification of free fatty acids and desulfurization, thereby reducing the problems of reduced conversion reaction efficiency and equipment corrosion caused by reduced enzyme catalytic activity due to high acid value of kitchen waste oil, reducing the toxic effect of sulfide compounds on lipase, eliminating the need for an additional desulfurization process, reducing the process and cost, and shortening the reaction time.

[0023] 2. The Sm2O3 / ZrO2 solid acid catalyst prepared by co-precipitation method, Sm(NO3)3 impregnation and calcination in the present application has high specific surface area and stability, improves mass transfer efficiency, and the catalyst can be reused, and still maintains excellent acid value reduction rate and sulfur removal rate after multiple uses, effectively improving the production efficiency of kitchen waste oil conversion to biodiesel, and has both economy and practicality.

[0024] 3. The method for preparing pure biodiesel from kitchen waste oil in the present application does not emit waste acid, reduces waste acid pollution and sulfur pollution problems, realizes green and environmentally friendly production, and meets the requirements of green and environmentally friendly production. DETAILED DESCRIPTION

[0025] The present application will be further described in detail below in combination with examples and comparative examples. Preparation example of solid acid catalyst

[0026] Preparation example 1 The preparation method of the Sm2O3 / ZrO2 solid acid catalyst comprises the following steps: S1: Dissolve ZrOCl2·8H2O in water, add ammonia water, adjust the pH to 9, and fully co-precipitate to obtain a mixture containing precipitate, filter the mixture, wash and dry the precipitate to obtain Zr(OH)4 precursor; S2: Impregnate the Zr(OH)4 precursor in a 8 wt% Sm(NO3)3 solution according to a solid-liquid ratio of 1:2, stir for 2 h to ensure uniform loading, then filter and dry to obtain a pre-catalyst; S3: Calcine the pre-catalyst at 550℃ for 3 h to obtain Sm2O3 / ZrO2 solid acid catalyst, the Sm2O3 content in the Sm2O3 / ZrO2 solid acid catalyst is 5 wt%, the specific surface area is 113 m 2 / g, and the acid center density was 0.62 mmol / g as determined by NH3-TPD.

[0027] Preparation Example 2 A preparation method of the Sm2O3 / ZrO2 solid acid catalyst included the following steps: S1: ZrOCl2·8H2O was dissolved in water, ammonia water was added, and the pH was adjusted to 9 to obtain a mixture containing precipitates after sufficient coprecipitation. The precipitates were washed and dried after filtration to obtain a Zr(OH)4 precursor; S2: The Zr(OH)4 precursor was immersed in a 10wt% Sm(NO3)3 solution at a solid-liquid ratio of 1:2, stirred for 2.5 h to ensure uniform loading, and then filtered and dried to obtain a pre-catalyst; S3: The pre-catalyst was calcined at 550°C for 3 h to obtain a Sm2O3 / ZrO2 solid acid catalyst. The Sm2O3 content in the Sm2O3 / ZrO2 solid acid catalyst was 9.8wt%, the specific surface area was 118m 2 / g, and the acid center density was 0.65 mmol / g as determined by NH3-TPD.

[0028] Preparation Example 3 A preparation method of the Sm2O3 / ZrO2 solid acid catalyst included the following steps: S1: ZrOCl2·8H2O was dissolved in water, ammonia water was added, and the pH was adjusted to 9 to obtain a mixture containing precipitates after sufficient coprecipitation. The precipitates were washed and dried after filtration to obtain a Zr(OH)4 precursor; S2: The Zr(OH)4 precursor was immersed in a 17wt% Sm(NO3)3 solution at a solid-liquid ratio of 1:2, stirred for 3 h to ensure uniform loading, and then filtered and dried to obtain a pre-catalyst; S3: The pre-catalyst was calcined at 550°C for 3 h to obtain a Sm2O3 / ZrO2 solid acid catalyst. The Sm2O3 content in the Sm2O3 / ZrO2 solid acid catalyst was 15wt%, the specific surface area was 124m 2 / g, and the acid center density was 0.69 mmol / g as determined by NH3-TPD. Example Example 1

[0029] A method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil included the following steps: S1: 1g of the Sm2O3 / ZrO2 solid acid catalyst prepared in Preparation Example 2 was added to 100g of kitchen waste oil, 15g of methanol was added, and the mixture was stirred at 75°C and 300rpm for 1.5h to obtain pretreated waste oil. The acid value of the kitchen waste oil used was 16.5mgKOH / g, and the sulfur content was 240ppm. S2: To 100 g of the pretreated waste oil, 1 g of lipase and 600 g of methanol were added, and the catalytic transesterification reaction was stirred at 50°C and 200 rpm for 6 h, to obtain biodiesel after rectification, wherein the lipase was selected from Novozyme, and the model number was 400238. Example 2

[0030] A method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil, comprising the following steps: S1: To 100 g of the kitchen waste oil, 1 g of the Sm2O3 / ZrO2 solid acid catalyst prepared in Preparation Example 2, and 20 g of methanol were added, and the stirring reaction was carried out at 80°C and 200 rpm for 1 h to obtain pretreated waste oil, wherein the acid value of the kitchen waste oil used was 16.5 mgKOH / g, and the sulfur content was 240 ppm; S2: To 100 g of the pretreated waste oil, 2 g of lipase and 600 g of methanol were added, and the catalytic transesterification reaction was stirred at 50°C and 200 rpm for 6 h, to obtain biodiesel after rectification, wherein the lipase was selected from Novozyme, and the model number was 400238. Example 3

[0031] A method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil, comprising the following steps: S1: To 100 g of the kitchen waste oil, 1 g of the Sm2O3 / ZrO2 solid acid catalyst prepared in Preparation Example 2, and 10 g of methanol were added, and the stirring reaction was carried out at 70°C and 400 rpm for 2 h to obtain pretreated waste oil, wherein the acid value of the kitchen waste oil used was 16.5 mgKOH / g, and the sulfur content was 240 ppm; S2: To 100 g of the pretreated waste oil, 3 g of lipase and 600 g of methanol were added, and the catalytic transesterification reaction was stirred at 50°C and 200 rpm for 6 h, to obtain biodiesel after rectification, wherein the lipase was selected from Novozyme, and the model number was 400238. Example 4

[0032] A method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil, which is different from Example 1 in that the addition amount of the Sm2O3 / ZrO2 solid acid catalyst in step S1 is 2 g, and the other steps are the same as those in Example 1. Example 5

[0033] A method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil, which is different from Example 1 in that the addition amount of the Sm2O3 / ZrO2 solid acid catalyst in step S1 is 3 g, and the other steps are the same as those in Example 1. Example 6

[0034] A method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil, which differs from example 1 in that the amount of Sm2O3 / ZrO2 solid acid catalyst added in step S1 is 0.5 g, and the other steps are the same as in example 1. Example 7

[0035] A method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil, which differs from example 1 in that the amount of Sm2O3 / ZrO2 solid acid catalyst added in step S1 is 3.5 g, and the other steps are the same as in example 1. Example 8

[0036] A method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil, which differs from example 1 in that the Sm2O3 / ZrO2 solid acid catalyst in step S1 is prepared by preparation example 1, and the other steps are the same as in example 1. Example 9

[0037] A method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil, which differs from example 1 in that the Sm2O3 / ZrO2 solid acid catalyst in step S1 is prepared by preparation example 3, and the other steps are the same as in example 1. Comparative example

[0038] Comparative example 1 A method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil, which differs from example 1 in that the Sm2O3 / ZrO2 solid acid catalyst in step S1 is replaced by 5 g of concentrated sulfuric acid with a concentration of 98%, and the other steps are the same as in example 1.

[0039] Comparative example 2 A method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil, which differs from example 1 in that the Sm2O3 / ZrO2 solid acid catalyst in step S1 is replaced by an equal amount of pure ZrO2 catalyst with a specific surface area of 80 m 2 / g, and the other steps are the same as in example 1.

[0040] Comparative example 3 A method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil, which differs from example 1 in that the Sm2O3 / ZrO2 solid acid catalyst in step S1 is replaced by an equal amount of γ-Al2O3 solid acid catalyst with a specific surface area of 120 m 2 / g, and the other steps are the same as in example 1. Performance detection test

[0041] The acid value reduction rate (%) and sulfur removal rate (%) of the pretreated waste oil obtained before and after pretreatment by the method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil of Examples 1-9 and Comparative Examples 1-3 were measured, respectively; the acid value, sulfur content and triglyceride content in the product biodiesel obtained by the method for preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil of Examples 1-9 and Comparative Examples 1-3 were measured, respectively, and each group of tests was performed 3 times, the average of the 3 test results was taken as the final result and recorded in Table 1.

[0042] 1. Determination of acid value: according to the relevant provisions of GB / T 5530-2005, 2g of pretreated waste oil sample and product biodiesel sample were taken, 50mL of ethanol-ether mixture was added, 1ml of phenolphthalein indicator with a concentration of 1% was added dropwise, after shaking, 0.1mol / L KOH ethanol standard solution was used for titration until the pink color did not fade within 30s, and the KOH consumption volume was recorded; The calculation formula of acid value (mgKOH / g) is: acid value = (VxCx56.1) / m, wherein V is the KOH consumption volume (mL), C is the KOH concentration (mol / L), and m is the oil sample mass (g); Acid value reduction rate = (initial acid value of kitchen waste oil - acid value of pretreated waste oil) / initial acid value of kitchen waste oil x 100%; 2. Sulfur content determination: detected by GS-SDC method, instrument is Agilent 8890 gas chromatograph (GC) equipped with 355 sulfur chemiluminescence detector (SDC), chromatographic column is HP-5 Sulfur capillary column (30m), sulfur chemiluminescence detection is carried out at detector 800℃ in quantitative mode; Sulfur removal rate (%) = (initial sulfur content of kitchen waste oil - sulfur content of pretreated waste oil) / initial sulfur content of kitchen waste oil x 100%; 3. Triglyceride: detected by GS-SDC method; 4. The catalysts used in Examples 1, Examples 8-9 (prepared by Preparation Examples 1-3) and Comparative Examples 2-3 were recovered after pretreatment reaction, and were repeatedly used for multiple times under the same conditions, and the activity retention rate of the catalysts after 5 times of repeated use was recorded.

[0043] Table 1

[0044] According to the performance detection results of the examples in Table 1, compared with the traditional catalyst in the process of preparing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil, the kitchen waste oil is pretreated by the Sm2O3 / ZrO2 solid acid catalyst of the application, the strong Lewis acid site of Sm2O3 and the Brønsted acid site of ZrO2 synergistically act, and the in-situ esterification of free fatty acids and desulfurization are simultaneously completed in the single-step pretreatment process, the acid value reduction rate is all > 90%, the sulfur removal rate is all > 94%, it is confirmed by XPS that the sulfides are adsorbed on the Sm site, the Sm2O3 / ZrO2 solid acid catalyst has excellent stability, the activity is still ≥ 90.0% after 5 cycles, the final product biodiesel has high quality, all meet the requirements of national standard GB25199, the acid value is ≤ 0.5 mgKOH / g, the sulfur content is ≤ 1 ppm, and the triglyceride is ≤ 0.25%. The method of the application reduces the problems of reduced conversion reaction efficiency and equipment corrosion caused by the reduction of enzyme catalytic activity caused by high acid value of kitchen waste oil, reduces the toxic effect of sulfide compounds on lipase, does not need an additional desulfurization process, reduces the process and cost, shortens the reaction time, effectively improves the production efficiency of kitchen waste oil to biodiesel, and has economy and practicability.

[0045] The specific embodiments are only an explanation of the application, and are not a limitation of the application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, as long as the modifications are within the scope of the claims of the application, and are protected by the patent law.

Claims

1. A method for preparing pure biodiesel from enzymatic catalytic desulfurization of kitchen waste oil, characterized in that, The method comprises the following steps: S1: adding Sm2O3 / ZrO2 solid acid catalyst to the kitchen waste oil for pretreatment to obtain pretreated waste oil; S2: adding lipase to the pretreated waste oil to catalyze ester exchange reaction to obtain biodiesel.

2. The method of claim 1, wherein the method of producing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil is characterized by, The preparation method of the Sm2O3 / ZrO2 solid acid catalyst comprises the following steps: ZrOCl2·8H2O is dissolved in water, ammonia water is added for co-precipitation, and Zr(OH)4 precursor is obtained after filtration, washing and drying; The Zr(OH)4 precursor is immersed in Sm(NO3)3 solution, stirred, filtered, dried and calcined to obtain Sm2O3 / ZrO2 solid acid catalyst.

3. The method of producing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil according to claim 1 or 2, characterized in that, The Sm2O3 / ZrO2 solid acid catalyst has a Sm2O3 content of 5-15 wt%, a specific surface area of ≥100 m 2 / g, and an acid center density of ≥0.6 mmol / g.

4. The method of producing pure biodiesel by enzymatic catalytic desulfurization of kitchen waste oil according to claim 1 or 2, characterized in that, The specific surface area of the Sm2O3 / ZrO2 solid acid catalyst is ≥100 m 2 / g, and the acid center density is ≥0.6 mmol / g.

5. The method of producing pure biodiesel by enzymatic catalytic desulphurization of kitchen waste oil as claimed in claim 1, wherein, The kitchen waste oil is pretreated in step S1, which comprises the following steps: Sm2O3 / ZrO2 solid acid catalyst and methanol are added to the kitchen waste oil, and stirring reaction is carried out at 70-80℃ and 200-400rpm for 1-2h to obtain pretreated waste oil.

6. The method of producing pure biodiesel by enzymatic catalytic desulphurization of kitchen waste oil as claimed in claim 1 or 5, wherein, The addition amount of the Sm2O3 / ZrO2 solid acid catalyst in step S1 is 1-3wt% of the kitchen waste oil.

7. The method of claim 5, wherein the method is characterized by, The addition amount of the methanol is 10-20wt% of the kitchen waste oil.

8. The process for the preparation of pure biodiesel by enzymatic catalytic desulphurization of kitchen waste oil as claimed in claim 1, wherein, The addition amount of the lipase in step S2 is 1-3wt% of the pretreated waste oil.

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