Kitchen waste oil recovery treatment method

Abstract

The invention relates to a kitchen waste oil recovery treatment method, which comprises: S1, carrying out multi-field synergistic pretreatment: sequentially carrying out ultrasonic wave and high-frequency pulse electric field treatment on waste oil to break an emulsion layer, adding magnetic nanoparticles to adsorb polar impurities, and carrying out magnetic field separation to obtain high-purity oil; s2, supercritical catalytic reaction: under the CO2 supercritical condition, using a core-shell structure composite catalyst to synchronously perform transesterification reaction and glycerol dehydration reaction; s3, dynamic membrane separation: separating biodiesel and glycerol in real time through an intelligent membrane assembly; s4, gradient utilization of energy: recovering reaction waste heat to drive membrane distillation to concentrate wastewater, and using tail gas CO2 for carbonation reaction to generate calcium carbonate. Through four core technologies of multi-field collaborative pretreatment, low-temperature supercritical catalysis, dynamic membrane separation and energy gradient utilization, triple limitations on efficiency, cost and environmental protection in the prior art are remarkably broken through.

Description

Technical Field

[0001] The present invention relates to the technical field of resource utilization of waste grease, and particularly relates to a method for recycling and treating kitchen waste grease. Background Art

[0002] The resource utilization of kitchen waste grease is of great significance for ensuring food safety, alleviating energy shortage and achieving the "dual carbon" goal. According to statistics, about 12 million tons of kitchen waste grease are generated in China every year. If all are converted into biodiesel, it can replace about 8 million tons of fossil diesel and reduce CO2 emissions by 16 million tons. However, there are significant defects in the existing technologies:

[0003] Serious pollution in the acid catalysis method: Although the traditional acid-catalyzed transesterification process can achieve a biodiesel yield of 88-92%, 1.2-1.5 tons of sulfuric acid are consumed for every 1 ton of grease treated, generating strongly acidic wastewater (pH < 2), which requires complex sewage treatment facilities. The environmental protection cost accounts for more than 35% of the total operating cost.

[0004] Low efficiency in the bio-enzymatic method: Although lipase catalysis avoids chemical pollution, limited by the kinetics of enzymatic reactions, it takes 12-24 hours to react at 40-60°C to reach a 90% conversion rate, and the cost of enzyme preparations is as high as 300-500 yuan per ton of grease, seriously restricting the economy.

[0005] Excessive energy consumption in the supercritical technology: Although the supercritical methanol method can complete the reaction within 1-2 hours, it needs to maintain a high temperature of 300-350°C and a high pressure of 20-30 MPa. The unit energy consumption reaches 335 kWh / t, and the equipment investment is 2-3 times that of the conventional process, making it difficult to be applied on a large scale.

[0006] Difficult glycerol separation: When separating biodiesel and glycerol by the traditional distillation method, the mixture needs to be heated to above 250°C, resulting in a glycerol purity of only 95-97%, and the energy consumption accounts for 25% of the total process, and the by-products are not highly utilized.

[0007] Existing technologies (such as CN105255932A using microwave pretreatment + acid catalysis, and US9783738B2 using immobilized enzyme catalysis) have not been able to synchronously solve the problems of pollution, efficiency, energy consumption and by-product utilization. Summary of the Invention

[0008] The present invention utilizes a multi-field collaborative pretreatment technology. Through the synergistic effect of ultrasonic cavitation and high-frequency pulsed electric field, the purity of grease is increased to 98.7%, and the acid value is reduced to 0.6 mgKOH / g. A core-shell structure composite catalyst is developed to reduce the supercritical reaction temperature from 280 °C to 180 °C and shorten the reaction time to 2.5 hours. An integrated dynamic membrane separation and energy cascade utilization system is implemented to achieve a biodiesel yield of 96.3% and a glycerol purity of 99.5%. Through CO2 carbonization technology, negative carbon emissions are achieved, breaking through the triple limitations of traditional processes in terms of efficiency, cost, and environmental protection.

[0009] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0010] A method for recycling and treating kitchen waste grease includes the following steps:

[0011] Step S1. Multi-field collaborative pretreatment: Pass the waste grease through ultrasonic waves and high-frequency pulsed electric fields in sequence to break the emulsion layer, then add magnetic nanoparticles to adsorb polar impurities, and obtain high-purity grease after magnetic separation.

[0012] Step S2. Supercritical catalytic reaction: Under the supercritical condition of CO2, use a core-shell structure composite catalyst to simultaneously carry out transesterification reaction and glycerol dehydration reaction.

[0013] Step S3. Dynamic membrane separation: Real-time separate biodiesel and glycerol through an intelligent membrane module.

[0014] Step S4. Energy cascade utilization: Recover the waste heat of the reaction to drive membrane distillation to concentrate wastewater, and use the tail gas CO2 for carbonation reaction to generate calcium carbonate.

[0015] Further, the parameters of the ultrasonic pretreatment are: frequency 20 - 40 kHz, power density 0.5 - 1.2 W / cm 2 , treatment time 10 - 15 minutes, and the transducer material is titanium alloy.

[0016] Further, the parameters of the high-frequency pulsed electric field pretreatment are: electric field strength 20 - 25 kV / cm, pulse frequency 50 - 80 kHz, treatment time 30 - 60 seconds, the electrode material is titanium alloy mesh, pore diameter 0.1 mm, and spacing 2 cm.

[0017] Further, the magnetic nanoparticles are Fe3O4@SiO2-COOH, where the Fe3O4 core particle size is 15 - 20 nm, the SiO2 shell layer thickness is 5 - 8 nm, the surface carboxyl density is 2.5 mmol / g, the dosage is 0.3 - 0.8 g / L, and the magnetic field strength is 0.8 T.

[0018] Furthermore, the core-shell structured composite catalyst is composed of TiO2 nanorods, ZSM-5 molecular sieves and immobilized lipase, where:

[0019] The length of the TiO2 nanorods is 400 - 600 nm, and the diameter is 80 nm;

[0020] The Si / Al ratio of the ZSM-5 molecular sieve is 40 - 60;

[0021] The lipase loading is 15 - 25 mg / g, and it is immobilized by glutaraldehyde cross-linking.

[0022] Furthermore, the conditions of the supercritical catalytic reaction are as follows: temperature 175 - 185 °C, pressure 4.5 - 5.5 MPa, molar ratio of alcohol to oil 6:1, catalyst dosage 1.2 - 1.8 wt%, and reaction time 2.5 - 3.5 hours.

[0023] Furthermore, the intelligent membrane module is a PVDF-g-PSSA membrane, with a grafting rate of 20 - 30%, a molecular weight cut-off of 4000 - 6000 Da, an operating pressure of 0.3 - 0.5 MPa, and a temperature of 60 - 70 °C.

[0024] Furthermore, the energy cascade utilization system includes:

[0025] A plate heat exchanger for recovering waste heat, with a heat recovery efficiency of ≥ 75%;

[0026] A membrane distillation system for treating wastewater, with a fresh water recovery rate of 60 - 70%;

[0027] The pressure of the CO2 carbonation reaction is 0.4 - 0.6 MPa, the temperature is 35 - 45 °C, and the residence time is 25 - 35 minutes.

[0028] Furthermore, the biodiesel yield is ≥ 96%, the acid value is ≤ 0.5 mg KOH / g, and the glycerol content is ≤ 0.02%; the glycerol purity is ≥ 99.5%, and the calcium carbonate purity is ≥ 97%.

[0029] Furthermore, the unit energy consumption is ≤ 180 kWh / t, the carbon emission is ≤ -120 kg CO2 / t, and the acid value of the pretreated oil is ≤ 0.8 mg KOH / g.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention constructs a full-chain process for the efficient resource utilization of kitchen waste oil and grease through four core technologies: multi-field collaborative pretreatment, low-temperature supercritical catalysis, dynamic membrane separation, and cascaded energy utilization. Among them, ultrasonic waves and pulsed electric fields cooperate to break the emulsion layer, the catalyst reduces the supercritical reaction temperature from 280 °C to 180 °C, the intelligent membrane separates biodiesel and glycerol in real time, and negative carbon emissions are achieved through CO2 carbonization. Compared with the traditional process, the biodiesel yield is increased by 9%, the energy consumption is reduced by 45%, the treatment cost is reduced by 38%, and the by-products glycerol and calcium carbonate both meet the industrial-grade standards, significantly breaking through the triple limitations of the existing technology in terms of efficiency, cost, and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts.

[0033] Figure 1 It is a logic block diagram of the treatment method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0035] 1. Multi-field collaborative pretreatment system

[0036] Technical principle: Through ultrasonic cavitation effect (30 kHz high-frequency vibration destroys the emulsion interface film), pulsed electric field-induced droplet coalescence (20 kV / cm strong electric field promotes oil-water separation), and selective adsorption of magnetic nanoparticles (targeted capture of polar impurities by Fe3O4@SiO2-COOH), a three-stage purification chain of "demulsification - coalescence - adsorption" is formed.

[0037] Implementation steps:

[0038] Ultrasonic treatment:

[0039] Equipment: Titanium alloy ultrasonic reactor (frequency 20 kHz, power density 0.5 W / cm 2 )

[0040] Parameters: The waste oil and grease pass through the reactor at a flow rate of 30 L / h, and the treatment time is 15 minutes.

[0041] Effect: The Zeta potential of the emulsion layer increased from -35 mV to -12 mV, and the oil droplet size increased from 5 - 8 μm to 15 - 20 μm;

[0042] Demulsification by pulsed electric field:

[0043] Equipment: Bipolar pulsed power supply (electric field strength 25 kV / cm, pulse frequency 80 kHz);

[0044] Parameters: Waste grease stays between titanium alloy meshes with an electrode spacing of 2 cm for 30 seconds;

[0045] Effect: The conductivity decreased from 2.8 mS / cm to 0.5 mS / cm, and the water content in the oil phase decreased from 28% to 1.2%;

[0046] Purification by magnetic adsorption:

[0047] Material: Fe3O4@SiO2-COOH nanoparticles (Fe3O4 particle size 15 nm, carboxyl density 2.5 mmol / g);

[0048] Parameters: Dosage 0.3 g / L, separated for 10 minutes under a magnetic field strength of 0.8 T;

[0049] Effect: The removal rate of polar impurities is 98.7%, and the acid value of the oil after pretreatment is 0.6 mg KOH / g.

[0050] Innovative synergy: Free radicals generated by ultrasonic cavitation and pulsed electric field synergistically reduce the interfacial tension, increasing the magnetic particle adsorption efficiency by 30%; The purity of the oil after pretreatment reaches 98.7%, providing a clean raw material for subsequent low-temperature catalysis.

[0051] 2. Supercritical catalytic reaction system

[0052] Technical principle: Acidic sites (TiO2) and basic sites (ZSM-5) of the core-shell catalyst (TiO2 nanorods@ZSM-5@immobilized lipase) synergistically catalyze the transesterification reaction. Supercritical CO2 (180 °C, 5 MPa) is used as the reaction medium to reduce the mass transfer resistance and simultaneously promote the dehydration of glycerol to produce acrolein.

[0053] Implementation steps:

[0054] Catalyst preparation:

[0055] Hydrothermal synthesis of TiO2 nanorods (180 °C, 24 h) → In-situ growth of ZSM-5 (Si / Al = 60) → Cross-linking and immobilization of lipase with glutaraldehyde (25 mg / g);

[0056] Characterization: BET specific surface area 380 m 2 / g, average pore diameter 4.2 nm, thermal stability with inactivation rate <5% at 200 °C;

[0057] Reaction process:

[0058] Equipment: 316L stainless steel autoclave (volume 1L, temperature resistance 300°C, pressure resistance 10MPa);

[0059] Parameters: temperature 180°C, pressure 5MPa, methanol / oil = 6:1, catalyst dosage 1.2wt%;

[0060] Operation: continuous feeding, residence time 2.5 hours;

[0061] Effect: biodiesel yield 96.5%, glycerol dehydration conversion rate 92.8%, by-product acrolein <0.08%.

[0062] Innovation synergy: supercritical CO2 as the reaction medium reduces the mass transfer resistance, increasing the enzymatic reaction rate by 4 times; the synergistic effect of the acidic sites of the catalyst and the enzyme active center breaks through the thermodynamic limitation of low-temperature reactions.

[0063] 3. Dynamic membrane separation system

[0064] Technical principle: PVDF-g-PSSA intelligent membrane (grafting rate 28%, molecular weight cut-off 5000Da) realizes the efficient separation of biodiesel and glycerol through the selective adsorption of glycerol by sulfonic acid groups, and at the same time the catalyst is recycled through the membrane pores.

[0065] Implementation steps:

[0066] Preparation of intelligent membrane:

[0067] Grafting process: SSA monomer concentration 1.5mol / L, APS initiator 0.5mol / L, grafting rate 28%;

[0068] Membrane performance: water flux 85L / (m 2 ·h)(0.1MPa), oil rejection rate 99.9%.

[0069] Separation process:

[0070] Separation of biodiesel: operating pressure 0.5MPa, temperature 70°C, methyl ester purity 99.6% Glycerol recovery: the liquid after the membrane is concentrated by reverse osmosis to 80%, and glycerol with a purity of 99.5% is obtained by vacuum distillation (120°C / 1kPa).

[0071] Innovation synergy: the coupling of membrane separation and reaction shortens the overall process, and the service life of the catalyst is extended to 500 hours; the selective separation of glycerol increases the resource utilization rate of by-products to 99%

[0072] 4. Energy cascade utilization system

[0073] Technical principle: The waste heat of the reaction (180 °C) drives the membrane distillation to concentrate the wastewater, and the CO2 tail gas (5 MPa) reacts with Ca(OH)2 to produce high-purity calcium carbonate, realizing the recycling of carbon.

[0074] Implementation steps:

[0075] Waste heat recovery:

[0076] Heat exchanger: Plate-type titanium alloy heat exchanger, with a heat recovery efficiency of 78%;

[0077] Membrane distillation: Feed temperature 75 °C, fresh water recovery rate 65%, TDS of concentrated water 28000 ppm;

[0078] CO2 carbonization:

[0079] Reaction parameters: CO2 pressure 0.5 MPa, temperature 40 °C, Ca(OH)2 concentration 10%, reaction time 30 minutes;

[0080] Product: Calcium carbonate purity 97.2%, particle size 1 - 2 μm (SEM analysis).

[0081] Innovative synergy: The utilization of waste heat increases the energy efficiency ratio of the system by 40%, and the CO2 resource utilization realizes a negative carbon emission of -120 kg / t; the calcium carbonate by-product can be used as a papermaking filler, improving economic benefits.

[0082] Full-process collaborative verification

[0083] Pilot test data:

[0084] Treatment scale: 50 kg / h

[0085] Operating parameters:

[0086] Pretreatment: Ultrasonic + pulsed electric field + magnetic adsorption

[0087] Reaction: 180 °C, 5 MPa, catalyst 1.5 wt%

[0088] Separation: Membrane module treatment capacity 50 L / h

[0089] Product indicators:

[0090]

[0091] Innovative synergy effect:

[0092] Catalyst reusability: The adsorption efficiency of magnetic nanoparticles is still >95% after 50 cycles of use;

[0093] Membrane life: The flux decline of the PVDF-g-PSSA membrane is <10% after continuous operation for 500 hours;

[0094] Economy: The sales revenue of by-product calcium carbonate accounts for 25% of the total profit.

[0095] The present invention constructs a full-chain process for the efficient resource utilization of kitchen waste oil and fat through four core technologies, namely multi-field collaborative pretreatment, low-temperature supercritical catalysis, dynamic membrane separation, and cascaded energy utilization. Among them, ultrasonic waves and pulsed electric fields are used in combination to break the emulsion layer, the catalyst reduces the supercritical reaction temperature from 280 °C to 180 °C, the intelligent membrane separates biodiesel and glycerol in real time, and negative carbon emissions are achieved through CO2 carbonization. Compared with the traditional process, the yield of biodiesel is increased by 9%, the energy consumption is reduced by 45%, the treatment cost is reduced by 38%, and the by-products glycerol and calcium carbonate both meet the industrial grade standards, significantly breaking through the triple limitations of the existing technology in terms of efficiency, cost, and environmental protection.

[0096] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0097] In addition, it should be understood that although this specification is described according to the embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for recycling and treating kitchen waste grease, characterized in that, It includes the following steps: Step S1. Multi-field collaborative pretreatment: The waste grease is successively passed through ultrasonic waves and high-frequency pulsed electric fields to break the emulsion layer, and then magnetic nanoparticles are added to adsorb polar impurities. After magnetic separation, high-purity grease is obtained; Step S2. Supercritical catalytic reaction: Under the supercritical conditions of CO2, a core-shell structured composite catalyst is used to simultaneously carry out transesterification reaction and glycerol dehydration reaction; Step S3. Dynamic membrane separation: The biodiesel and glycerol are separated in real time through an intelligent membrane module; Step S4. Energy cascade utilization: The waste heat of the reaction is recovered to drive membrane distillation to concentrate the wastewater, and the tail gas CO2 is used for carbonation reaction to generate calcium carbonate.

2. The method according to claim 1, characterized in that The parameters of the ultrasonic pretreatment are as follows: frequency 20 - 40 kHz, power density 0.5 - 1.2 W / cm 2 , treatment time 10 - 15 minutes, and the transducer material is titanium alloy.

3. The method according to claim 1, wherein The parameters of the high-frequency pulsed electric field pretreatment are: electric field strength 20 - 25 kV / cm, pulse frequency 50 - 80 kHz, treatment time 30 - 60 seconds, the electrode material is titanium alloy mesh, the pore diameter is 0.1 mm, and the spacing is 2 cm.

4. The method according to claim 1, wherein The magnetic nanoparticles are Fe3O4@SiO2-COOH, where the Fe3O4 core particle size is 15 - 20 nm, the SiO2 shell layer thickness is 5 - 8 nm, the surface carboxyl density is 2.5 mmol / g, the dosage is 0.3 - 0.8 g / L, and the magnetic field strength is 0.8 T.

5. The method according to claim 1, characterized in that, The core-shell structured composite catalyst consists of TiO2 nanorods, ZSM-5 molecular sieves and immobilized lipase, where: The length of the TiO2 nanorods is 400 - 600 nm, and the diameter is 80 nm; The Si / Al ratio of the ZSM-5 molecular sieve is 40 - 60; The lipase loading amount is 15 - 25 mg / g, and it is immobilized by glutaraldehyde crosslinking.

6. The method according to claim 1, characterized in that The conditions of the supercritical catalytic reaction are: temperature 175 - 185 °C, pressure 4.5 - 5.5 MPa, molar ratio of alcohol to oil 6:1, catalyst dosage 1.2 - 1.8 wt%, and reaction time 2.5 - 3.5 hours.

7. The method according to claim 1, wherein The intelligent membrane module is a PVDF-g-PSSA membrane, the grafting rate is 20 - 30%, the cut-off molecular weight is 4000 - 6000 Da, the operating pressure is 0.3 - 0.5 MPa, and the temperature is 60 - 70 °C.

8. The method according to claim 1, wherein The energy cascade utilization system includes: A plate heat exchanger recovers waste heat, and the heat recovery efficiency ≥ 75%; A membrane distillation system treats wastewater, and the fresh water recovery rate is 60 - 70%; The pressure of the CO2 carbonation reaction is 0.4 - 0.6 MPa, the temperature is 35 - 45 °C, and the residence time is 25 - 35 minutes.

9. The method according to claim 1, wherein The biodiesel yield ≥ 96%, the acid value ≤ 0.5 mgKOH / g, and the glycerol content ≤ 0.02%; the glycerol purity ≥ 99.5%, and the calcium carbonate purity ≥ 97%.

10. The method according to any one of claims 1-9, characterized in that, The unit energy consumption ≤ 180 kWh / t, the carbon emission ≤ -120 kgCO2 / t, and the acid value of the grease after pretreatment ≤ 0.8 mgKOH / g.

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