Pretreatment method for waste grease used in preparation of hydrocarbon-based biodiesel

Abstract

A pretreatment method for waste grease used in the preparation of a hydrocarbon-based biodiesel. A cascaded process including a water vapor treatment, a low-carbon alcohol treatment and reduced-pressure distillation is utilized, and the pretreatment method comprises the following process steps: first performing a water vapor treatment on waste grease by using high-temperature water vapor; then cooling same by using a transition tank, separating by-products, and then conveying same into a low-carbon alcohol treatment tank; introducing a low-carbon alcohol / nitrogen gas mixture for a deacidification reaction; and finally performing reduced-pressure distillation, with an intermediate fraction obtained therefrom being used as a raw material for the production of a hydrocarbon-based biodiesel. The pretreatment method removes or significantly decreases organic chlorine, phospholipids, metal elements and other impurities in waste grease which affect the activity and lifetime of a catalyst used in the production process of a hydrocarbon-based biodiesel, prolongs the service life of a catalyst used in the preparation of a hydrocarbon-based biodiesel from waste grease, improves the process stability, and solves the problem of organic chlorine, phospholipids, metal elements and other impurities in waste grease affecting the lifetime of a catalyst and equipment in the existing hydrocarbon-based biodiesel production techniques.

Description

A pretreatment method for waste oil and fat for producing hydrocarbon-based biodiesel Technical Field

[0001] The invention relates to the technical field of methods for processing raw materials for producing organic chemical product biodiesel, and in particular to a pretreatment method for waste grease used for preparing hydrocarbon-based biodiesel. Background Art

[0002] With the development of society, people's demand for energy continues to increase, and non-renewable fossil energy is rapidly being consumed. Hydrocarbon-based biodiesel has become a focus of attention because it has the same chemical structure as diesel, similar calorific value, and higher cetane number.

[0003] The primary raw material for domestic biodiesel production is waste animal and plant oils and fats, hereinafter referred to as waste oils or waste fats. While biodiesel production recycles biomass energy resources, impurities in waste oils and fats also impact biodiesel production to varying degrees. In addition to fatty acids and glycerides, waste oils and fats also contain impurities such as organochlorine, phospholipids, and metals. Typical impurity levels in commercially available waste oils and fats are shown in Table 1. During the production of hydrocarbon-based biodiesel, the colloids and phospholipids in waste oils and fats are susceptible to coking on the catalyst and the inner walls of the production equipment under high temperature and high pressure. This increases the pressure drop across the catalyst bed, reduces catalyst activity, and affects the heat transfer efficiency and production stability of the equipment. In addition to phospholipids, chlorine in waste oils and fats, after hydrogenation, forms chloride ions, which adsorb onto the catalyst, poisoning it and corroding the piping of production equipment. Consequently, the complex composition of waste oils and fats significantly impacts the continuous production of hydrocarbon-based biodiesel and hinders the development of waste oils and fats as green biomass energy. Existing pretreatment methods for waste grease generally use simple physical sedimentation or centrifugal separation technologies. These pretreatment technologies can only separate mechanical impurities such as water and food residues, and cannot reduce or remove impurities such as organic chlorine elements, phospholipids, and metal elements in waste grease that affect the life of hydrocarbon-based biodiesel production equipment and catalysts.

[0004] Currently, the commercialized process for producing hydrocarbon-based biodiesel from oil and fat hydrogenation primarily utilizes the HEFA (Hydroprocessed Esters and Fatty Acids) pathway. For example, the SRJET (Solution to Jet Fuel) technology developed by the Sinopec Research Institute of Petrochemicals involves using waste oil and fat hydrogenation catalysts to first saturate C=C bonds through hydrogenation, followed by hydrodeoxygenation via three reaction pathways: direct hydrodeoxygenation, hydrodecarbonylation, and hydrodecarboxylation. Glyceryl groups in the waste oil and fat are converted into low-value-added propane during the hydrodeoxygenation process. Technical requirements for the waste oil and fat used are as follows: chlorine content <50 ppm, phosphorus content <5 ppm, and total metal content less than 50 ppm, with iron ions ≤20 ppm, calcium ions ≤10 ppm, and sodium ions ≤10 ppm, all of which are lower than typical impurity levels for waste oil and fat currently on the market.

[0005] Table 1 Typical waste oil and grease indicators on the current market

[0006] Summary of the Invention

[0007] The purpose of the present invention is to provide a pretreatment method for waste grease for producing hydrocarbon-based biodiesel, so as to solve the problem in the prior art that waste grease affects catalysts and equipment in the production of hydrocarbon-based biodiesel.

[0008] To achieve the above objectives, the present invention provides a method for pretreating waste oils and fats for producing hydrocarbon-based biodiesel, and the operating steps are as follows:

[0009] (1) First, the waste grease is fed into an industrial centrifuge to separate the flocculent matter and the water dispersed in the waste grease, which has a density greater than that of the waste grease;

[0010] (2) The waste grease after impurity removal is then heated to 110-350°C in a preheater;

[0011] (3) The material is pumped into a steam treatment tank for steam treatment, with the waste grease entering from the top of the steam treatment tank and the steam entering from the bottom of the steam treatment tank to ensure sufficient contact between the waste grease and the steam; the steam treatment conditions are a reaction pressure of 3 to 10 MPa, a steam treatment reaction temperature of 110 to 350°C, a reaction time of 1 to 10 hours, and a waste grease to liquid water volume ratio of 20:1 to 1:20;

[0012] (4) After the water vapor treatment is completed, it is sent to the transition tank to be cooled to 35-60 ° C and kept warm. After standing and separating the liquid, the lower layer of liquid is discharged; the transition tank body needs to be treated with acid corrosion resistance or made of corrosion-resistant materials;

[0013] (5) Pumping the upper layer of the transition tank into the low-carbon alcohol treatment tank, and adding a catalyst, the catalyst dosage is 100 to 10000 ppm of the mass of the material after water vapor treatment in the tank, and at the same time continuously passing a low-carbon alcohol / nitrogen mixed gas into the tank body from the bottom of the low-carbon alcohol treatment tank for deacidification reaction, the reaction temperature is 35 to 65 ° C, and the reaction time is 8 to 36 hours; the low-carbon alcohol / nitrogen mixed gas is obtained by passing nitrogen into liquid low-carbon alcohol, so that the nitrogen and low-carbon alcohol are mixed and overflowed; the low-carbon alcohol is one of methanol or ethanol; the volume ratio of the low-carbon alcohol liquid volume to the fatty acid ester / fatty acid mixture in the transition tank is 10:1 to 1:10;

[0014] (6) After the deacidification reaction is completed, the reaction product including fatty acid ester and a small amount of fatty acid is obtained by standing and separating the layers and draining the lower liquid.

[0015] (7) The reaction product is subjected to vacuum distillation at a temperature of 120 to 380° C. and a pressure of less than 3000 Pa. The obtained intermediate fraction is a raw material that can be used for the production of hydrocarbon-based biodiesel; the distillation range of the intermediate fraction is 150 to 300° C. and the pressure is less than 3000 Pa.

[0016] In the step (2), the waste oil is heated to 180-280° C. in a preheater.

[0017] The conditions for the steam treatment in step (3) are a reaction pressure of 5 to 8 MPa; a steam treatment reaction temperature of 180 to 280° C., a reaction time of 3 to 8 hours, and a volume ratio of waste oil and liquid water of 5:1 to 1:5.

[0018] In the step (4), the steam-treated product is cooled to 40-50° C. in a transition tank and kept warm.

[0019] The catalyst added in step (5) is one or a mixture of Aspergillus niger fermentation lipase and Candida lipase, and is in the form of solid or liquid.

[0020] The amount of catalyst used in step (5) is 500 to 5000 ppm of the mass of the product after water vapor treatment in the tank;

[0021] The deacidification reaction temperature in step (5) is 40-50°C.

[0022] In the step (5), the volume ratio of the low-carbon alcohol liquid to the fatty acid ester / fatty acid mixture in the transition tank is 10:3 to 3:10, and the reaction time is 12 to 24 hours.

[0023] The temperature of the reduced pressure distillation in step (7) is 180-280° C. and the pressure is less than 1000 Pa.

[0024] In the step (7), the distillation range of the intermediate fraction is 180-260° C., and the pressure is less than 1000 Pa.

[0025] The above-mentioned pretreatment method for waste oil and fat for producing hydrocarbon-based biodiesel has the following technical characteristics and beneficial effects:

[0026] 1. Glycerol is recovered from waste oil through water vapor treatment, avoiding direct hydrogenation of waste oil to convert glycerol into low-value-added propane.

[0027] 2. Through water vapor treatment, the waste oil is freed from phospholipids and colloids that can easily cause the catalyst bed to coke.

[0028] 3. Chlorine and metal elements can be effectively removed or significantly reduced by treating waste grease with water vapor.

[0029] 4. The deacidification reaction is carried out through a low-carbon alcohol / nitrogen mixture, which not only improves the distillability of the raw materials, but also reduces the acid value of the raw materials and the material requirements of subsequent process devices and equipment.

[0030] 5. Through vacuum distillation, the metal elements in the raw materials can be further reduced or removed, so that the impurity content in the raw materials is within the limit of the catalyst and equipment for producing hydrocarbon-based biodiesel, effectively extending the operating cycle of the hydrogenation unit.

[0031] 6. After pretreatment, the raw materials have reduced steric hindrance and viscosity due to the removal of glycerol groups, making it easier for them to fully contact with the active sites of the catalyst, which is beneficial to the hydrogenation reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG1 is a schematic diagram of a process flow of a pretreatment method for waste oil and fat for producing hydrocarbon-based biodiesel according to the present invention.

[0033] Figure numerals: waste oil after centrifugation 1, water vapor 2, water vapor treatment product 3, water vapor treatment by-product 4, insulated water vapor treatment product 5, catalyst 6, low-carbon alcohol / nitrogen mixed gas 7, deacidification product 8, water vapor treatment tank A, transition tank B, low-carbon alcohol treatment tank C, vacuum distillation device D.

[0034] It should be noted that Figure 1 is only a flow chart for illustrating the method for treating waste grease in the present invention. Only the necessary parts of the process are drawn. For the sake of simplicity and clarity, other necessary facilities such as instruments, gas reflux equipment, preheaters, pumps and valves are omitted. DETAILED DESCRIPTION

[0035] The following is a further detailed description of a method for pretreating waste oils and fats for producing hydrocarbon-based biodiesel according to the present invention in conjunction with the accompanying drawings and specific embodiments.

[0036] 1 , the pretreatment method for waste oil and fat for producing hydrocarbon-based biodiesel of the present invention has the following operating steps:

[0037] (1) First, the waste grease is fed into an industrial centrifuge to separate the flocculent matter and the water dispersed in the waste grease, which has a density greater than that of the waste grease;

[0038] (2) heating the waste grease after impurity removal to 110-350° C., preferably 180-280° C., in a preheater;

[0039] (3) Pumping the material into a steam treatment tank for steam treatment, the waste grease enters from the top of the steam treatment tank and the steam enters from the bottom of the steam treatment tank, so that the waste grease and the steam are fully in contact; the steam treatment conditions are: reaction pressure 3-10 MPa, preferably 5-8 MPa; steam treatment reaction temperature 110-350°C, preferably 180-280°C; reaction time 1-10 hours, preferably 3-8 hours; waste grease and liquid water volume ratio 20:1-1:20, preferably 5:1-1:5;

[0040] (4) After the water vapor treatment is completed, the tank is sent to a transition tank and cooled to 35-60°C and kept warm, preferably 40-50°C, and the lower layer of liquid is discharged after standing and separating the liquid; the transition tank body needs to be treated with acid corrosion resistance or made of corrosion-resistant materials;

[0041] (5) Pumping the upper layer of the transition tank material into the low-carbon alcohol treatment tank, and adding a catalyst, the catalyst is one of Aspergillus niger fermentation lipase and Candida lipase or a mixture of the two, in the form of solid or liquid, and the catalyst dosage is 100 to 10,000 ppm of the mass of the material after water vapor treatment in the tank, preferably 500 to 5,000 ppm, and simultaneously continuously passing a low-carbon alcohol / nitrogen mixed gas into the tank body from the bottom of the low-carbon alcohol treatment tank for deacidification reaction, the low-carbon alcohol is one of methanol or ethanol; the reaction temperature is 35 to 65° C., preferably 40 to 50° C., and the reaction time is 8 to 36 hours, preferably 12 to 24 hours; the low-carbon alcohol / nitrogen mixed gas is obtained by passing nitrogen into liquid low-carbon alcohol to mix and overflow with the nitrogen; the volume ratio of the low-carbon alcohol liquid volume to the fatty acid ester / fatty acid mixture in the transition tank is 10:1 to 1:10, preferably 10:3 to 3:10;

[0042] (6) After the deacidification reaction is completed, the reaction product including fatty acid ester and a small amount of fatty acid is obtained by standing and separating the layers and draining the lower liquid.

[0043] (7) The reaction product is subjected to vacuum distillation at a temperature of 120 to 380° C., preferably 180 to 280° C., and a pressure of <3000 Pa, preferably <1000 Pa; the obtained intermediate fraction is a raw material that can be used for the production of hydrocarbon-based biodiesel; the distillation range of the intermediate fraction is 150 to 300° C., preferably 180 to 260° C., and the pressure is <3000 Pa, preferably <1000 Pa.

[0044] The specific implementation of the present invention is further described in detail below through three specific examples.

[0045] The indicators of waste grease used in the examples are shown in Table 2:

[0046] Table 2 Waste grease indicators

[0047] Example 1

[0048] The first step is to use an industrial centrifuge to remove floccules and liquids with a density greater than that of the waste grease;

[0049] In the second step, the waste oil after impurities removal is preheated to 180°C in a preheater and then pumped into the top of the steam treatment tank, where it comes into countercurrent contact with the steam introduced from the bottom. The oil-water volume ratio is 2:1, and the reaction is carried out at 5MPa and 180°C for 3 hours.

[0050] In the third step, the product of the second step was kept at 50° C., 500 ppm (based on the mass of the product of the second step) of Aspergillus niger fermentation lipase was added, and the reaction was carried out under the flow of methanol / nitrogen mixed gas, with the volume ratio of the product of the second step to the volume of methanol being 2:3, and the reaction was carried out for 10 hours;

[0051] In the fourth step, after the reaction is completed, the product is subjected to reduced pressure distillation, and the distillate at 180-230° C. is collected under 1000 Pa. The content of organic chlorine, metal elements, and phospholipids in the product is determined using a microcoulometric chlorine analyzer, an inductively coupled plasma emission spectrometer, and a molybdenum blue colorimetric method (referring to GB / T 5537-2008).

[0052] The results of the middle fraction analysis were as follows: organochlorine content was 19.06 ppm, phospholipid content was not detected, calcium was not detected, iron was not detected, sodium was not detected, and tin was not detected. The results are listed in Table 3.

[0053] Example 2

[0054] The first step is to use an industrial centrifuge to remove floccules and liquids with a density greater than that of the waste grease.

[0055] In the second step, the waste oil after impurities removal is preheated to 230°C in a preheater and then pumped into the top of the steam treatment tank, where it comes into countercurrent contact with the steam introduced from the bottom. The oil-water volume ratio is 5:2, and the reaction is carried out at 8MPa and 230°C for 5 hours.

[0056] In the third step, the product of the second step was kept at 50° C., 2000 ppm (based on the mass of the product of the second step) of Aspergillus niger fermentation lipase was added, and the reaction was carried out under the flow of methanol / nitrogen mixed gas, with the volume ratio of the product of the second step to the volume of methanol being 3:5, and the reaction was carried out for 18 hours;

[0057] In the fourth step, after the reaction is completed, the product is subjected to reduced pressure distillation, and the distillate at 180-230°C is collected under 800 Pa. The content of organic chlorine, metal elements, and phospholipids in the product is determined using a microcoulometric chlorine analyzer, an inductively coupled plasma emission spectrometer, and a molybdenum blue colorimetric method (referring to GB / T 5537-2008).

[0058] The results of the middle fraction analysis were as follows: organic chlorine content was 13.38 ppm, phospholipid content was not detected, calcium was not detected, iron was not detected, sodium was not detected, and tin was not detected. The results are listed in Table 3.

[0059] Example 3

[0060] The first step is to use an industrial centrifuge to remove floccules and liquids with a density greater than that of the waste grease.

[0061] In the second step, the waste oil after impurities removal is preheated to 280°C in a preheater and then pumped into the top of the steam treatment tank, where it comes into countercurrent contact with the steam introduced from the bottom. The oil-water volume ratio is 1:1, and the reaction is carried out at 8MPa and 280°C for 8 hours.

[0062] In the third step, the product of the second step was kept at 50° C., 4000 ppm (based on the mass of the product of the second step) of Aspergillus niger fermentation lipase was added, and the reaction was carried out under the flow of methanol / nitrogen mixed gas, with the volume ratio of the product of the second step to the volume of methanol being 5:2, and the reaction was carried out for 24 hours;

[0063] In the fourth step, after the reaction is completed, the product is subjected to reduced pressure distillation, and the distillate at 180-260° C. is collected under 600 Pa. The content of organic chlorine, metal elements, and phospholipids in the product is determined using a microcoulometric chlorine analyzer, an inductively coupled plasma emission spectrometer, and a molybdenum blue colorimetric method (referring to GB / T 5537-2008).

[0064] The results of the middle fraction analysis were as follows: organochlorine content was 8.06 ppm, phospholipid content was not detected, calcium was not detected, iron was not detected, sodium was not detected, and tin was not detected. The results are listed in Table 3.

[0065] Table 3 Summary of indicators tested in the examples

[0066] The above examples, through the application of the present invention, achieved significant purification results for waste oils and fats. The organic chlorine content after treatment was significantly reduced, and no phospholipids, calcium, iron, sodium, or tin were detected. This kept the impurity content in the feedstock within the limits of the catalyst and equipment required for producing hydrocarbon-based biodiesel, effectively extending the operating cycle of the hydrogenation unit. Example 3 achieved the lowest organic chlorine content of 8.06 ppm, making it the optimal example.

[0067] The above embodiments are all preferred implementation examples of the present invention. In addition, the present invention can also be implemented in other ways. Without departing from the concept of the present invention, any obvious replacement is within the scope of protection of the present invention. Industrial Applicability

[0068] The present invention discloses a pretreatment method for waste oil and fat for producing hydrocarbon-based biodiesel. The method utilizes a serial process of water vapor treatment, low-carbon alcohol treatment, and vacuum distillation. The process steps are as follows: first, the waste oil and fat is subjected to water vapor treatment using high-temperature water vapor; then, the waste oil and fat is cooled in a transition tank, by-products are separated, and then the waste oil and fat is fed into a low-carbon alcohol treatment tank. A low-carbon alcohol / nitrogen mixture is introduced for deacidification reaction; and finally, the waste oil and fat is subjected to vacuum distillation. The intermediate fraction obtained is used as a raw material for hydrocarbon-based biodiesel production. The present invention can remove or significantly reduce impurities such as organic chlorine elements, phospholipids, and metal elements in the waste oil and fat that affect the activity and life of the catalyst used in the hydrocarbon-based biodiesel production process, thereby increasing the service life and process stability of the catalyst for producing hydrocarbon-based biodiesel from waste oil and fat. This solves the problem in existing hydrocarbon-based biodiesel production technologies where impurities such as organic chlorine elements, phospholipids, and metal elements in the waste oil and fat affect the life of the catalyst and equipment, and thus has industrial applicability.

Claims

1. A pretreatment method for waste oil and fat used to produce alkyl biodiesel, characterized in that: the operation The steps are as follows: (1) First, feed the waste grease into an industrial centrifuge to separate the flocs and the water dispersed in the waste grease with a density greater than that of the waste grease; (2) Then, heat the waste grease after impurity removal to 110 - 350 °C through a preheater; (3) Pump the material into a water-vapor treatment tank for water-vapor treatment. The waste grease enters from the top of the water-vapor treatment tank, and steam is introduced from the bottom of the water-vapor treatment tank to ensure sufficient contact between the waste grease and the water vapor. The conditions for water-vapor treatment are: reaction pressure 3 - 10 MPa, water-vapor treatment reaction temperature 110 - 350 °C, reaction time 1 - 10 hours, and the volume ratio of waste grease to liquid water is 20:1 - 1:20; (4) After the water-vapor treatment, send it into a transition tank to cool to 35 - 60 °C and keep it warm. After standing and liquid separation, drain the lower-layer liquid; the tank body of this transition tank needs to be treated against acid corrosion or made of corrosion-resistant materials; (5) Pump the upper-layer material in the transition tank into a lower-carbon alcohol treatment tank and add a catalyst. The dosage of the catalyst is 100 - 10000 ppm of the mass of the material after water-vapor treatment in the tank. At the same time, continuously introduce a lower-carbon alcohol / nitrogen mixture from the bottom of the lower-carbon alcohol treatment tank into the tank body for deacidification reaction. The reaction temperature is 35 - 65 °C, and the reaction time is 8 - 36 hours; this lower-carbon alcohol / nitrogen mixture is obtained by introducing nitrogen into liquid lower-carbon alcohol to make the nitrogen and lower-carbon alcohol mix and overflow; this lower-carbon alcohol is one of methanol or ethanol; the volume ratio of the lower-carbon alcohol liquid to the fatty acid ester / fatty acid mixture in the transition tank is 10:1 - 1:10; (6) After the deacidification reaction, let it stand for stratification and drain the lower-layer liquid, and then obtain a reaction product including fatty acid esters and a small amount of fatty acids; (7) Subject the reaction product to vacuum distillation. The temperature of vacuum distillation is 120 - 380 °C, and the pressure < 3000 Pa. The obtained intermediate fraction is the raw material that can be used for the production of alkyl biodiesel; the distillation range of this intermediate fraction is 150 - 300 °C, and the pressure is < 3000 Pa. In step (2), the waste grease is heated to 180 - 280 °C through a preheater.

2. The pretreatment method of waste oil and fat for preparing alkyl biodiesel according to claim 1, characterized in that: In step (3), the conditions for water-vapor treatment are: reaction pressure 5 - 8 MPa; water-vapor treatment reaction temperature 180 - 280 °C, reaction time 3 - 8 hours, and the volume ratio of waste grease to liquid water is 5:1 - 1:

5.

3. The pretreatment method of waste grease for preparing alkyl biodiesel according to claim 1, characterized in that: In step (4), the water-vapor treatment product is cooled to 40 - 50 °C and kept warm in the transition tank.

4. The pretreatment method of waste oil and fat for preparing alkyl biodiesel according to claim 1, characterized in that: In step (5), the added catalyst is one or a mixture of two of Aspergillus niger fermented lipase and Candida lipase, and the form is solid or liquid.

5. The pretreatment method of waste grease for preparing alkyl biodiesel according to claim 1, characterized in that: In step (5), the dosage of the catalyst is 500 - 5000 ppm of the mass of the product after water-vapor treatment in the tank; 6. The pretreatment method of waste oil and fat for preparing alkyl biodiesel according to claim 1, characterized in that: In step (5), the deacidification reaction temperature is 40 - 50 °C.

7. The pretreatment method of waste grease for preparing alkyl biodiesel according to claim 1, characterized in that: In step (5), the volume ratio of the lower-carbon alcohol liquid to the fatty acid ester / fatty acid mixture in the transition tank is 10:3 - 3:10, and the reaction time is 12 - 24 hours.

8. The pretreatment method of waste oil and fat for preparing alkyl biodiesel according to claim 1, characterized in that: In step (7), the temperature of vacuum distillation is 180 - 280 °C; the pressure < 1000 Pa.

9. The pretreatment method of waste oil and fat for preparing alkyl biodiesel according to claim 1, characterized in that: In step (7), the distillation range of the intermediate fraction is 180 - 260 °C, and the pressure is < 1000 Pa.

10. The pretreatment method of waste oil and fat for preparing alkyl biodiesel according to claim 1, characterized in that: ​

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