Method for co-producing lactic acid and crude oil by utilizing perishable garbage

Abstract

The invention relates to the technical field of organic waste resource utilization, and discloses a method for co-production of lactic acid and crude grease by using perishable garbage, and the method comprises the following steps: step a, preparing the perishable garbage into slurry; b, feeding the slurry into an electrochemical reactor for electrochemical treatment; c, carrying out acidification treatment on the generated fatty acid salt to recover crude oil; and step d, carrying out lactic acid fermentation on the residual liquid rich in the small molecular sugar after the crude oil is recovered to obtain the lactic acid. The anode region and the cathode region which are separated by the ion selective diaphragm are arranged in the electrochemical reactor, and acid and alkali are respectively generated in situ in the two regions by utilizing water electrolysis and are directly used for hydrolysis of polysaccharide and saponification of grease, so that chemical reagents such as sulfuric acid and caustic soda do not need to be additionally added; the introduction of extra impurity ions such as sulfate radicals and sodium ions into the system is avoided, the load of subsequent product separation and wastewater treatment is reduced, and the process flow is simplified.

Description

Technical Field

[0001] This invention relates to the field of testing instrument technology, specifically a method for co-producing lactic acid and crude oil using perishable waste. Background Technology

[0002] Perishable waste, typically referring to food waste, kitchen waste, and fruit and vegetable waste, contains abundant organic components such as carbohydrates, proteins, and oils. It is a potential raw material for producing high-value-added bio-based chemicals (such as lactic acid) and biofuels (such as biodiesel precursors). Therefore, effective resource recovery of perishable waste can not only reduce its environmental impact but also enhance its value, aligning with the requirements of a circular economy and sustainable development.

[0003] In existing technologies, the process routes for converting perishable waste into lactic acid and oil products typically involve complex pretreatment steps. Due to the high moisture content, complex composition, and heterogeneity of perishable waste raw materials, direct processing is difficult. One technical approach, to facilitate subsequent processing or increase reactant concentration, first involves mechanical dehydration or thermal drying of the high-moisture perishable waste. However, since the moisture content of perishable waste is typically as high as 70% to 90%, thermal drying requires a significant amount of thermal energy, directly resulting in high operating costs and poor economic efficiency for the entire process.

[0004] In the pretreatment stage, chemical pretreatment is usually required to convert large organic molecules in waste into smaller molecules that can be utilized later. For example, strong acids (such as sulfuric acid) are used under high temperature and pressure to hydrolyze carbohydrates such as starch and cellulose to produce fermentable sugars. At the same time, strong alkalis (such as sodium hydroxide) are often used to carry out saponification reactions to separate and recover the oil components, converting the oils into easily separable fatty acid salts.

[0005] However, the exogenous chemical reagents such as sulfuric acid and sodium hydroxide used extensively in the chemical pretreatment steps need to be neutralized to adjust the pH value after completing their catalytic or reactive functions, thus meeting the requirements of subsequent biological fermentation steps. This series of neutralization processes introduces a large number of inorganic salt ions into the system, such as sulfate ions and sodium ions, ultimately forming high-salt, high-chemical-oxygen-demand (COD) wastewater. Treating this high-salt wastewater is difficult and costly, and the high salt concentration can exert osmotic pressure inhibition on subsequent microbial fermentation processes, reducing fermentation efficiency and posing a risk of secondary environmental pollution. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for co-producing lactic acid and crude oil from perishable waste. This method solves the problems of high energy consumption due to thermal drying of wet waste and high-salt wastewater and secondary pollution caused by the use of chemical reagents for pretreatment in the process of co-producing lactic acid and crude oil from perishable waste.

[0007] To achieve the above objectives, the present invention provides a method for co-producing lactic acid and crude oil from perishable waste.

[0008] The method includes the following steps:

[0009] Step a: Pre-treat the perishable waste and prepare it into a slurry;

[0010] Step b: The slurry is fed into an electrochemical reactor for electrochemical treatment. In the anode region of the electrochemical reactor, hydrogen ions (H+) are generated through water electrolysis. + The hydrogen ions are used to perform in-situ acid hydrolysis of the polysaccharides in the slurry to generate small molecule sugars. The reaction principle can be expressed as follows:

[0011]

[0012] Simultaneously, oxygen (O2) is produced by the electrolysis of water at the anode:

[0013] 2H2O-4e - →4H - +O2↑

[0014] In the cathode region of the electrochemical reactor, hydroxide ions (OH-) are generated through water electrolysis. - The hydroxide ions are used to saponify the oils in the slurry in situ to generate water-soluble fatty acid salts and glycerol. The reaction principle can be expressed as follows:

[0015] (RCOO)3C3H5+3OH - →3RCOO - +C3H5(OH)3;

[0016] Simultaneously, hydrogen gas (H2) is produced by the electrolysis of water at the cathode.

[0017] 2H2O+2e - →2OH - +H2↑

[0018] Step c: Separate the slurry after the electrochemical treatment and acidify the fatty acid salts generated therein to recover crude oil;

[0019] Step d: The liquid remaining after recovering the crude oil, which is rich in the small molecule sugars, is subjected to lactic acid fermentation to obtain lactic acid.

[0020] In one specific embodiment, the anode and cathode regions of the electrochemical reactor are separated by an ion-selective membrane, a structure designed to prevent direct neutralization of hydrogen ions generated in the anode region with hydroxide ions generated in the cathode region.

[0021] In one specific embodiment, the electrochemical reactor is a vertical tower structure, with the slurry entering from the bottom and the treated liquid flowing out from the top.

[0022] Furthermore, in an embodiment employing the vertical tower structure, the electrochemical treatment includes: utilizing oxygen generated in the anode region and hydrogen generated in the cathode region to form an upward airflow within the reactor, which is used to perform air stripping mixing of the slurry; simultaneously, utilizing hydrogen microbubbles generated in the cathode region to combine with the generated fatty acid salt molecules, and through air stripping flotation, transporting and enriching the fatty acid salt in the upper part of the electrochemical reactor.

[0023] In another specific embodiment, based on the vertical tower structure, the electrochemical treatment further includes: dynamically controlling the electric field of the slurry by applying periodically reversing voltages or asymmetric pulse voltages to the electrodes.

[0024] Specifically, the dynamic electric field modulation is used to change the surface charge state of amphoteric impurities such as proteins and peptides in the slurry. By controlling the local pH environment, the amphoteric impurities are made to carry positive or negative charges, and the electric field force is used to drive them to undergo electrophoretic migration, thereby achieving the purification and separation of the amphoteric impurities.

[0025] Preferably, the step of recovering crude oil includes: collecting the product rich in the fatty acid salts, and acidifying it by adding an acidic substance or introducing carbon dioxide gas, so that the fatty acid salts are converted into water-insoluble free fatty acids, followed by oil-water separation. The principle of the acidification reaction can be expressed as follows:

[0026] RCOO - +H + →RCOOH↓

[0027] Preferably, before the lactic acid fermentation in step d, the method further includes solid-liquid separation of the liquid rich in small molecule sugars to remove unreacted solid residues.

[0028] In one specific embodiment, after performing the solid-liquid separation to remove unreacted solid residue, the liquid rich in small molecule sugars is neutralized by the acidic liquid generated in the anode region and the alkaline liquid generated in the cathode region of the electrochemical reactor to adjust its pH value to a preset range.

[0029] Preferably, the pretreatment step in step a includes at least one of sorting, crushing and pulping the perishable waste.

[0030] This invention provides a method for co-producing lactic acid and crude oil from perishable waste. It has the following beneficial effects:

[0031] 1. This invention sets up an anode region and a cathode region separated by an ion-selective membrane in an electrochemical reactor, and uses water electrolysis to generate acids and bases in situ in the two regions respectively, which are directly used for the hydrolysis of polysaccharides and the saponification of oils. Therefore, there is no need to add chemical reagents such as sulfuric acid and caustic soda, avoiding the introduction of additional sulfate ions, sodium ions and other impurity ions into the system, reducing the load on subsequent product separation and wastewater treatment, and simplifying the process flow.

[0032] 2. This invention utilizes hydrogen and oxygen, byproducts of the electrolysis process, to achieve gentle mixing of the slurry through a gas-lift circulation formed by the rising gas, replacing external mechanical stirring devices. Simultaneously, hydrogen microbubbles generated at the cathode act as flotation agents, efficiently enriching the in-situ generated fatty acid salts to the upper part of the reactor. This enrichment effect separates the target product from the large volume of liquid phase and concentrates it into a small volume of foam phase. Therefore, in subsequent recovery steps, only this small volume of concentrated material needs to be processed, avoiding phase separation or solvent extraction of the entire slurry, thus reducing the material transportation, processing load, and energy consumption in the subsequent product recovery process.

[0033] 3. This invention utilizes the principle of electrophoresis to actively migrate and separate amphoteric impurities such as proteins and peptides in the slurry by applying a dynamic electric field. Therefore, it can directionally remove substances that may inhibit the subsequent lactic acid fermentation process, thereby obtaining a purer small-molecule sugar liquid. This provides a more suitable substrate environment for subsequent bio-fermentation steps and helps maintain the stability of the fermentation process. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] To better understand the present invention, the above content will be described in detail below with reference to specific embodiments.

[0037] Please see the appendix Figure 1 , Figure 1 This is a schematic diagram of a method for co-producing lactic acid and crude oil from perishable waste according to an embodiment of the present invention. The method includes the following steps;

[0038] Step a, Pretreatment and Slurry Preparation

[0039] First, the collected perishable waste is sorted to remove non-organic or large, inert impurities such as bones, plastics, and metals, in order to protect subsequent equipment and improve reaction efficiency. Then, the sorted organic material is fed into a crusher or pulper, where an appropriate amount of water is added for processing, forming a homogeneous slurry with a preset solids content (e.g., 5%-15% w / w) and good flowability. The purpose of this step is to transform solid, heterogeneous waste into a fluid form suitable for pumping and wet chemical reactions.

[0040] Step b, electrochemical treatment

[0041] The slurry prepared in the previous step is pumped from the bottom into a vertical tower electrochemical reactor. Upon application of direct current, a synergistic effect occurs inside the reactor:

[0042] In the anode region, hydrogen ions generated by water electrolysis create a localized acidic environment, causing the macromolecular polysaccharides in the slurry to hydrolyze in situ into soluble small-molecule sugars.

[0043] In the cathode region, hydroxide ions generated by water electrolysis create a localized alkaline environment, causing the oils in the slurry to be saponified in situ into water-soluble fatty acid salts.

[0044] In this process, the hydrogen and oxygen produced byproducts at both electrodes serve as an internal driving force, mixing the slurry through air stripping. Fatty acid salts generated in the cathode region are selectively enriched to the liquid surface at the top of the reactor via air stripping flotation, forming a stable foam layer. Simultaneously, by applying a dynamic electric field, peptide impurities such as proteins can be migrated and separated using electrophoresis, further purifying the main liquid phase.

[0045] Step c: Crude oil recovery

[0046] A layer of foam rich in fatty acid salts is continuously or intermittently skimmed from the top of the electrochemical reactor. The collected foam is then acidified, for example, by introducing carbon dioxide gas or adding an acidic liquid generated in the reactor's anode zone, to convert the water-soluble fatty acid salts into water-insoluble free fatty acids. The acidified mixture will naturally separate into layers, with the target product, crude oil, on top. The crude oil can then be collected using gravity separation, centrifugation, or other oil-water separation techniques.

[0047] Step d, lactic acid production

[0048] The treated bulk liquid phase, rich in small-molecule sugars and glycerol generated in step b, is extracted from the upper part of the electrochemical reactor. First, unreacted solid residues (such as lignin) are removed by pressure filtration or sedimentation to obtain a clear liquid. Then, the pH of the clear liquid is adjusted to a suitable neutral range for microbial growth using acid-base liquids generated in the reactor's anode and cathode zones. Finally, the adjusted clear liquid is used as a fermentation substrate in a bioreactor, inoculated with lactic acid-producing bacteria, and fermented under suitable conditions to convert sugars and glycerol into lactic acid. After fermentation, the lactic acid product is extracted using conventional downstream separation and purification techniques.

[0049] In a specific embodiment:

[0050] First, the collected perishable waste materials undergo a sorting process. This process aims to remove non-target components from the material, including but not limited to: plastic products, metals, glass, stones, textiles, and large bones. This step is used to prevent mechanical damage to subsequent crushing and conveying equipment and to reduce the content of inert substances entering the reaction system.

[0051] After sorting, the organic materials are fed into crushing equipment for particle size reduction. Suitable crushing equipment includes hammer crushers or shear crushers. After crushing, the particle size is controlled within a preset range. In one embodiment, the material is crushed to a maximum particle size of less than 50 mm; in another embodiment, it is crushed to a maximum particle size of less than 20 mm.

[0052] The crushed material is mixed with water to prepare a fluid slurry. In one embodiment, the water used is process circulating water. The mixed material is then fed into a pulper or wet mill for homogenization to form a uniform suspension.

[0053] In the process of preparing the slurry, the total solids content is controlled by adjusting the amount of water added. The total solids content is calculated as follows:

[0054]

[0055] Where, m solid For the quality of dry matter in perishable waste, m water The amount of water added is determined by the specific conditions. In one embodiment, the total solids content of the slurry is adjusted to a range of 3% to 20% (w / w). In another preferred embodiment, the total solids content is adjusted to a range of 5% to 15% (w / w). Simultaneously, the viscosity of the slurry is adjusted to be within the range of 500-2000 mPa·s at a specific shear rate to ensure stable delivery by pump. The final product of this pretreatment and slurry preparation stage serves as the feed for subsequent electrochemical treatment steps.

[0056] In one embodiment, the main body of the electrochemical reactor is a vertically arranged tower-type container with a cylindrical structure, made of 316L stainless steel, polypropylene, or carbon steel with an anti-corrosion coating. The height-to-diameter ratio (length-to-diameter ratio) of the tower-type container is set in the range of 3:1 to 10:1 to facilitate effective gas circulation and self-stratification.

[0057] The lower part of the tower-type container is equipped with a slurry inlet for introducing the slurry to be treated from the bottom. At the top, there is at least one liquid outlet and one foam outlet. The liquid outlet is used to discharge the treated liquid phase rich in small-molecule sugars, while the foam outlet is used to collect fatty acid salt foam accumulated on the liquid surface.

[0058] Inside the tower-shaped vessel, an ion-selective membrane is installed. The membrane divides the vessel's interior into an anodic and a cathode region. The function of the ion-selective membrane is to prevent the formation of H₂ in the anodic region. + OH generated in the cathode region + A neutralization reaction occurs directly, thereby maintaining independent pH environments in both regions. In one embodiment, the membrane is a tubular or plate membrane arranged along the longitudinal axis of the container. This membrane may be a cation exchange membrane (e.g., Nafion). TM A series of perfluorosulfonic acid membranes or anion exchange membranes.

[0059] An anode is disposed within the anode region. To adapt to the acidic and strongly oxidizing environment within the anode region, the anode can be made of a material with high electrocatalytic activity and chemical stability in the oxygen evolution reaction. In one embodiment, the anode is a size-stable anode, specifically constructed by coating a titanium substrate with one or more layers of noble metal oxides, such as iridium dioxide (IrO2), ruthenium dioxide (RuO2), or mixtures thereof. Furthermore, the anode can be plate-like, mesh-like, or porous.

[0060] A cathode is disposed within the cathode region. To adapt to the alkaline and reducing environment within the cathode region, the cathode can be made of a material with low hydrogen evolution overpotential and good conductivity. In one embodiment, the cathode material is 316L stainless steel, nickel, or an electrode with a platinum layer electroplated on a titanium substrate. The cathode can also be plate-shaped or mesh-shaped, and is arranged parallel to or coaxially with the anode, maintaining a fixed electrode spacing between them, which can range from 5 mm to 50 mm. The anode and cathode are respectively connected to the positive and negative terminals of a DC power supply via wires.

[0061] In one embodiment, after the prepared slurry is fed into the electrochemical reactor through the slurry inlet, the electrochemical treatment process is carried out by applying a constant DC voltage to the anode and cathode.

[0062] Within the anode region, water undergoes an electrochemical oxidation reaction on the anode surface, generating hydrogen ions (H+). + (and oxygen). The chemical equation for this reaction is as follows:

[0063] 2H2O-4e - →4H + +O2↑

[0064] The hydrogen ions generated in this process accumulate near the anode, creating a locally acidic environment that lowers the pH to between 1.5 and 4.0. Under these acidic conditions, macromolecules of polysaccharides such as starch and cellulose in the slurry undergo in-situ acid-catalyzed hydrolysis, breaking their glycosidic bonds to generate smaller sugar molecules, primarily glucose. A representative reaction formula for this hydrolysis process is as follows:

[0065]

[0066] Meanwhile, within the cathode region, water undergoes an electrochemical reduction reaction on the cathode surface, producing hydroxide ions and hydrogen gas. The chemical equation for this reaction is as follows:

[0067] 2H2O+2e - →2OH - +H2↑

[0068] The hydroxide ions generated in this process accumulate in the region near the cathode, creating a locally alkaline environment that raises the pH value in this area to the range of 10.0 to 12.5. Under these alkaline conditions, triglycerides (oils) in the slurry undergo in-situ saponification, producing water-soluble fatty acid salts and glycerol. A representative reaction formula for this saponification process is as follows:

[0069] (RCOO)3C3H5+3OH - →3RCOO - +C3H5(OH)3

[0070] Simultaneously with the aforementioned reaction, oxygen and hydrogen bubbles continuously generated on the anode and cathode surfaces move upwards from the bottom of the reactor. These rising bubbles reduce the apparent density of the fluid in their respective areas, thereby initiating overall slurry circulation within the reactor, i.e., gas mixing. This mixing method eliminates the need for external mechanical stirring components, reducing equipment complexity and energy consumption.

[0071] In addition, the hydrogen microbubbles generated in the cathode region are also used for gas stripping flotation of the generated fatty acid salts. Fatty acid salt anions (RCOO) -The nonpolar hydrocarbon chain (R) of the gas makes it hydrophobic and allows it to adsorb onto the surface of equally hydrophobic hydrogen bubbles. This complex, consisting of gas and fatty acid salt, has a lower overall density than the surrounding slurry, thus floating against gravity. Through this mechanism, the fatty acid salt is directionally transported to the top of the reactor and aggregates there to form a stable foam layer, thereby achieving in-situ separation and enrichment of the saponification products from the bulk liquid phase.

[0072] In one specific embodiment, the operating parameters for the electrochemical treatment are set as follows: the applied voltage is 3V to 15V; the operating current density is 20 to 200mA / cm². 2 The reaction temperature is maintained between 30℃ and 80℃; the hydraulic residence time (HRT) of the slurry in the reactor is 2 to 24 hours. The formula for calculating the HRT is:

[0073]

[0074] Where V is the effective working volume of the reactor, and Q is the volumetric flow rate of the slurry.

[0075] In a preferred embodiment, the electrochemical treatment process further includes applying a dynamic electric field to purify and separate amphoteric impurities such as proteins and peptides in the slurry. This control is an additional or alternative operation based on the aforementioned steady-state DC electric field.

[0076] Proteins and polypeptides are amphoteric substances because their structures contain both amino (-NH2) and carboxyl (-COOH) groups. In aqueous solutions, the net charge state of these molecules depends on the pH of the solution and their isoelectric point. When the pH is below the isoelectric point, the molecules are more protonated and thus carry a positive charge; when the pH is above the isoelectric point, the molecules are more deprotonated and thus carry a negative charge. In an electric field, charged molecules migrate under the influence of the electric field force; this is called electrophoresis.

[0077] At this point, the pH gradient already formed in the electrochemical reactor (acidic at the anode and alkaline at the cathode), combined with an externally applied dynamic electric field, is used to drive these amphoteric impurities to undergo controlled electrophoretic migration.

[0078] In one extended embodiment, the electrode polarity can be periodically reversed. The voltage polarity applied to the anode and cathode is periodically switched using a programmable DC power supply or an H-bridge circuit. For example, in one cycle, electrode 1 is the anode and electrode 2 is the cathode; but in the next cycle, electrode 1 switches to cathode and electrode 2 switches to anode. The reversal period can be set from 1 minute to 60 minutes. This allows impurities to migrate back and forth within the reactor, preventing over-accumulation on a single electrode surface that could lead to electrode passivation.

[0079] Another method for dynamic electric field control is to apply an asymmetric pulsed electric field. This method outputs a non-constant pulsed voltage waveform through a power controller. This waveform consists of a series of pulses, and its characteristic parameters can be defined by the pulse period T, pulse width Ton, and duty cycle D, as shown in the following formula:

[0080]

[0081] In one embodiment, the pulse frequency (f = 1 / T) ranges from 1 Hz to 1 kHz, and the duty cycle D ranges from 10% to 90%. By adjusting these parameters, the magnitude and direction of the average electric field force applied to the impurities can be precisely controlled, thereby enabling selective separation of impurities at different isoelectric points.

[0082] Therefore, through the aforementioned dynamic electric field regulation, amphoteric impurities such as proteins and peptides in the slurry are driven to undergo electrophoretic migration. In one embodiment, these impurities migrate to the electrode surface and undergo electrochemical oxidation or reductive degradation; in another embodiment, they migrate and accumulate in a specific region within the reactor, and are subsequently discharged through a dedicated outlet, thereby improving the purity of the liquid phase bulk rich in small molecule sugars flowing out of the liquid outlet.

[0083] Furthermore, in the electrochemical treatment step, fatty acid salt foam layers enriched at the top of the electrochemical reactor are collected through air stripping flotation and then collected via the foam outlet. This collection operation can be carried out continuously or intermittently, and the collected material is subsequently sent to a separate acidification and separation unit to recover crude oil.

[0084] In one embodiment, acidification is achieved by adding an acidic substance. Specifically, a hydrogen-rich acidic liquid (anolyte) generated in the anode region of the electrochemical reactor is pumped into the acidification and separation unit and mixed with collected fatty acid salt foam. The pH of the system is monitored during mixing until it is adjusted to below 6.0, or in a specific example, to a range of pH 3.0 to 5.0.

[0085] In another embodiment, the acidification process is achieved by introducing carbon dioxide (CO2) gas. CO2 gas is introduced from the bottom of the acidification and separation unit, causing it to disperse in the fatty acid salt foam and react with water to produce carbonic acid (H2CO3). The hydrogen ions generated by the ionization of carbonic acid are used to neutralize the fatty acid salt. The reaction equation for this process is as follows:

[0086]

[0087] H2CO3+RCOO - →RCOOH↓+HCO3 -

[0088] Regardless of the acidification method used, the core chemical transformation process involves converting water-soluble fatty acid salts (in the form of anionic RCOO) into salts. - The fatty acid (in its original form) is converted into water-insoluble free fatty acid (RCOOH). The chemical equation for this conversion can be uniformly expressed as:

[0089] RCOO - +H + →RCOOH↓

[0090] Because the product has low solubility in the aqueous phase, it will precipitate out in the oil phase.

[0091] After acidification, the mixture is left to stand in the acidification and separation unit or undergoes phase separation through physical means. Since the density of free fatty acids is less than that of water, the mixture separates into two phases: an upper oil phase (i.e., crude fat) and a lower acidic aqueous phase. Finally, the upper crude fat is separated from the lower aqueous phase using equipment such as gravity decanting, a centrifuge, or an oil-water separator, thereby obtaining the first target product.

[0092] After the crude oil is recovered, the liquid phase exiting the electrochemical reactor is rich in small-molecule sugars and glycerol generated during the electrochemical treatment steps. This liquid will be used as a raw material for preparing lactic acid fermentation substrates.

[0093] First, the liquid rich in small-molecule sugars undergoes solid-liquid separation to remove unreacted or incompletely hydrolyzed solid residues. These residues primarily consist of lignin, some hemicellulose, and other insoluble organic or inorganic particles. In one embodiment, solid-liquid separation is achieved using a plate and frame filter press or a horizontal screw centrifuge to separate the liquid from the solid residues. The product of this step is a clear liquid, i.e., a sugar solution with most of the suspended solids removed.

[0094] The pH of the clarified sugar solution was then adjusted to suit conditions for subsequent microbial fermentation. In one specific embodiment, the target pH range was set to 6.0 to 7.5. This pH adjustment process utilized the acidic liquid (anolyte) and alkaline liquid (catholyte) generated by the electrochemical reactor itself.

[0095] The specific control operation is as follows: The clarified sugar solution is placed in a mixing tank equipped with a stirring system and an online pH monitoring system. Based on the real-time value measured by the pH monitoring system, alkaline liquid collected from the cathode area of ​​the electrochemical reactor or acidic liquid collected from the anode area is quantitatively added to the clarified sugar solution via a metering pump and mixed until the pH value of the liquid stabilizes within the preset target range. The essence of this neutralization reaction is the reaction between hydrogen ions and hydroxide ions:

[0096] H + +OH - →H2O

[0097] This method achieves pH neutralization and regulation through internal material circulation, without the need for additional external acid or alkali chemicals.

[0098] Therefore, after the above solid-liquid separation and pH adjustment steps, the final liquid obtained is a qualified lactic acid fermentation substrate. This substrate has the characteristics of clear composition, low solid phase impurity content and moderate pH value, and can be directly fed into subsequent bio-fermentation units.

[0099] Once the fermentation substrate, prepared in the previous step and with its pH value adjusted to the preset range, is transported into the bio-fermentation tank, it can be used for lactic acid fermentation.

[0100] Before fermentation begins, a lactic acid-producing microbial strain is inoculated into the fermentation substrate. In one embodiment, the strain used is *Lactobacillus casei* or other microorganisms capable of converting hexoses and pentoses into lactic acid. The inoculation amount, by volume, is 5% to 15% (v / v) of the fermentation substrate.

[0101] After inoculation, fermentation is carried out under the set process conditions. The main biochemical reaction during fermentation is the conversion of carbohydrates (taking glucose as an example) into lactic acid, and its chemical reaction formula is as follows:

[0102] C6H 12 O6→2CH3CH(OH)COOH

[0103] The fermentation process is carried out under anaerobic or microaerobic conditions, with the fermentation temperature controlled within the range of 35℃ to 42℃.

[0104] During fermentation, the pH of the fermentation broth continuously decreases due to the continuous production of lactic acid. To maintain microbial activity, a pH adjuster is added to the fermenter to maintain the pH of the fermentation broth within the range of 5.5 to 6.5. In one embodiment, the pH adjuster used is calcium carbonate (CaCO3) slurry. Calcium carbonate reacts with the generated lactic acid to produce calcium lactate, which has high solubility, as shown in the following reaction formula:

[0105] 2CH3CH(OH)COOH+CaCO3→(CH3CH(OH)COO)2Ca+H2O+CO2↑

[0106] The fermentation process continues until the sugar in the substrate is consumed to below a predetermined residual concentration, or the concentration of lactic acid (in the form of calcium lactate) reaches a target value. In one embodiment, the fermentation cycle is 48 to 72 hours.

[0107] After fermentation, the resulting fermentation broth undergoes post-processing. First, microbial cells and other solid impurities are removed from the broth using methods such as centrifugation or membrane filtration. Then, the clarified calcium lactate solution is acidified, for example, by adding sulfuric acid, to convert calcium lactate into free lactic acid and generate calcium sulfate precipitate. After removing the calcium sulfate precipitate by filtration, the resulting crude lactic acid solution undergoes further purification steps such as decolorization, distillation, or ion exchange to finally obtain the target product, lactic acid.

Claims

1. A method for co-producing lactic acid and crude oil from perishable waste, characterized in that, Includes the following steps: Step a: Pre-treat the perishable waste and prepare it into a slurry; Step b: The slurry is fed into an electrochemical reactor for electrochemical treatment. The anode region of the electrochemical reactor is used to perform in-situ acid hydrolysis of the polysaccharides in the slurry to generate small molecule sugars, and the cathode region is used to perform in-situ saponification of the oils in the slurry to generate fatty acid salts. Step c: Separate the slurry after the electrochemical treatment and acidify the fatty acid salts generated therein to recover crude oil; Step d: The liquid remaining after recovering the crude oil, which is rich in the small molecule sugars, is subjected to lactic acid fermentation to obtain lactic acid.

2. The method for co-producing lactic acid and crude oil from perishable waste according to claim 1, characterized in that, In step b, the electrochemical reactor is a vertical tower structure, the slurry enters from the bottom of the electrochemical reactor, and the treated liquid flows out from the top.

3. The method for co-producing lactic acid and crude oil from perishable waste according to claim 2, characterized in that, The electrochemical treatment includes: using oxygen generated in the anode region and hydrogen generated in the cathode region to perform gas stripping and mixing of the slurry, and using hydrogen generated in the cathode region to perform gas stripping flotation of the generated fatty acid salt, so as to enrich the fatty acid salt in the upper part of the electrochemical reactor.

4. The method for co-producing lactic acid and crude oil from perishable waste according to claim 2, characterized in that, The electrochemical treatment further includes: dynamically controlling the electric field of the slurry by periodically reversing the electrode polarity or applying an asymmetric pulsed electric field.

5. The method for co-producing lactic acid and crude oil from perishable waste according to claim 4, characterized in that, The dynamic electric field modulation is used to change the surface charge state of amphoteric impurities such as proteins and peptides in the slurry and drive the amphoteric impurities such as proteins and peptides in the slurry to undergo electrophoretic migration, thereby purifying and separating the amphoteric impurities.

6. The method for co-producing lactic acid and crude oil from perishable waste according to claim 1, characterized in that, In step c, the step of recovering crude oil includes: collecting the product rich in the fatty acid salt, adding acidic substances or introducing carbon dioxide gas for acidification, so that the fatty acid salt is converted into free fatty acids and then separating oil and water.

7. The method for co-producing lactic acid and crude oil from perishable waste according to claim 1, characterized in that, In step d, before lactic acid fermentation, the liquid rich in small molecule sugars is first subjected to solid-liquid separation to remove unreacted solid residue.

8. The method for co-producing lactic acid and crude oil from perishable waste according to claim 7, characterized in that, After removing the unreacted solid residue, the liquid is neutralized by the acidic liquid generated in the anode region and the alkaline liquid generated in the cathode region of the electrochemical reactor to adjust the pH value of the liquid rich in small molecule sugars.

9. The method for co-producing lactic acid and crude oil from perishable waste according to claim 1, characterized in that, The anode and cathode regions of the electrochemical reactor are separated by an ion-selective membrane.

10. The method for co-producing lactic acid and crude oil from perishable waste according to claim 1, characterized in that, In step a, the pretreatment step includes: sorting, crushing and pulping the perishable waste.

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