High-efficiency defoaming agent for environment-friendly anaerobic digestion system and preparation method and application thereof

Abstract

The application provides an environment-friendly high-efficiency defoaming agent for an anaerobic digestion system, and belongs to the technical field of defoaming agents.The application comprises the following components in percentage by mass: 15-20% of a solid defoaming component, 35-50% of an oil-state defoaming agent component, 30-40% of water, 4% of a composite emulsifier and 1% of a thickening agent; the solid defoaming component is one of calcium soap, glycerol monostearate and biocarbon of biogas residue; the oil-state defoaming agent component is glycerol trioleate or mineral oil; the compounding relationship of the solid defoaming component and the oil-state defoaming agent component does not comprise the compounding of calcium soap and mineral oil.The application is prepared by using components without biological toxicity and containing no silicon, and the obtained environment-friendly high-efficiency defoaming agent for the anaerobic digestion system has no biological toxicity, does not damage the gas production efficiency of the anaerobic digestion system, has high foam inhibition effect and foam reduction rate, and does not pollute the biogas combustion system after use.

Description

Technical Field

[0001] This invention relates to the field of defoamer technology, and in particular to an environmentally friendly, high-efficiency defoamer for anaerobic digestion systems and its preparation method. Background Technology

[0002] Foaming in anaerobic digestion systems: Foaming in anaerobic digestion systems refers to the phenomenon where biogas produced in an anaerobic reactor cannot be smoothly discharged from the liquid phase, forming a dispersed system in the liquid. Eventually, this system accumulates on the liquid surface to form a stable viscous layer or fills the entire reactor, causing rapid volume expansion.

[0003] Anaerobic digestion (AD) is the core technology for biogas engineering, which can convert waste biomass into biogas. It offers dual advantages: pollution reduction, environmental protection, greenhouse gas emission reduction, and renewable energy development. Therefore, biogas engineering has steadily progressed towards industrialization and commercialization in recent years. However, anaerobic digestion systems are highly susceptible to foaming events, especially when food waste is present in the feed substrate, where the foaming rate in the reactor can reach as high as 94%. The resulting side effects, such as decreased gas production, biogas slurry overflow, and blockage of pumps and gas outlet pipes, pose significant economic and operational challenges to the operation of anaerobic digester plants.

[0004] Common defoaming methods are mainly divided into four categories: physical methods, mechanical methods, biological methods, and chemical methods. Among them, chemical methods use defoamers to defoam, which can disrupt the foam film, achieving high defoaming efficiency in a short time and even suppressing foam for a period of time. Research on defoamers has mainly progressed through the development stages of organic, polyether, organosilicon, and polyether-modified organosilicon types. Organic defoamers are generally suitable for systems with low foaming capacity, have a low rate of breaking dense foam, and can easily affect the foaming system. Polyether defoamers have low surface tension and good defoaming and foam-suppressing properties, making them suitable for industries such as fermentation, food, detergents, and fiber processing. However, previous studies have found that they are toxic to anaerobic digestive microorganisms and can inhibit the gas production efficiency of anaerobic digestion systems. Organosilicon, due to its unique molecular structure, has low surface tension and chemical inertness, and is often used as a defoamer in industries such as papermaking, wastewater treatment, petroleum processing, and fermentation. However, silicone defoamers contain siloxanes, which may form siloxanes in anaerobic digestion systems. When siloxanes are mixed with biogas, silicon precipitates are produced during biogas combustion, which can cause engine wear.

[0005] In the prior art, such as the invention patent with publication number CN113384921A, a polyether defoamer and its preparation method are disclosed: the polyether defoamer is formulated by at least one of polyethylene glycol, modified polyethylene glycol or polyethylene glycol 6000 distearate, at least one of glycerol, polyglycerol or polyoxyethylene modified polyoxypropylene amine ether, propylene oxide and additives, thereby improving the traditional polyether defoamer and enhancing its performance.

[0006] The invention patent with publication number CN116271998A discloses a method for preparing and applying a highly efficient and low-toxicity defoamer for bio-fermentation: it is composed of raw materials such as silicone paste, polyether, emulsifier, thickener, deionized water, and preservative. By adjusting the type and ratio of silicone oil, polyether, and emulsifier, a variety of emulsion-type defoamers are compounded for comparison of dispersibility and stability.

[0007] The invention patent with publication number CN116351108A discloses an environmentally friendly polyether ester defoamer for landfill leachate and its preparation method: the environmentally friendly polyether ester defoamer for landfill leachate is prepared by adjusting the proportions of polyether polyol, composite emulsifier, catalyst and the types and proportions of fatty acids.

[0008] The aforementioned invention patent, CN113384921A, describes a polyether defoamer suitable for systems such as papermaking, fermentation, and desulfurization. Compared to traditional defoamers, it features high-temperature and strong alkali resistance, thus overcoming the weaknesses of common polyether defoamers such as polyol-type, fatty acid ester-type, and amine ether-type defoamers, which have poor sustained defoaming and foam-suppressing effects. However, the high-temperature and strong alkali resistance features achieved by this invention are not inherent characteristics of anaerobic digestion systems or features that defoamers need to achieve. More importantly, previous research has found that polyether defoamers have a toxic effect on microorganisms in anaerobic systems, inhibiting their gas production. Therefore, polyether defoamers cannot be used in anaerobic digestion systems.

[0009] The aforementioned invention patent, CN116271998A, describes a silicone-polyether composite emulsion defoamer for erythritol bio-fermentation. Currently, defoamers suitable for erythritol fermentation are mainly divided into two types: silicone and polyether. This composite defoamer avoids the disadvantages of single defoamers and possesses advantages such as low toxicity, high temperature resistance, and resistance to stratification, meeting the needs of pure-culture fermentation and ease of use. However, erythritol is the only polyol in the sugar alcohol industry produced through aerobic fermentation, which is fundamentally different from anaerobic systems. Furthermore, the key cultivation conditions for erythritol fermentation, such as osmotic pressure, temperature, pH, and dissolved oxygen, differ from those in anaerobic digestion systems. In addition, anaerobic digestion systems convert biomass waste into biogas, and silicone defoamers may generate siloxanes during anaerobic digestion, which can mix into the biogas and cause silicon precipitation during combustion, leading to equipment wear. Therefore, the silicone-polyether composite defoamer for erythritol bio-fermentation is not suitable for anaerobic digestion systems.

[0010] The aforementioned invention patent, CN116351108A, is applicable to defoaming of leachate from municipal solid waste landfills. It aims to address the problem of foam generation impacting the surrounding environment, human health, and subsequent leachate treatment, providing an environmentally friendly polyether ester defoamer that is easily biodegradable, has a long foam-suppressing time, and does not pollute water bodies after use. However, this differs from the purpose of defoaming in anaerobic digestion systems. This invention is used before leachate treatment systems to pre-defoam in the landfill, reducing surrounding pollution and the difficulty of subsequent treatment. Anaerobic digestion is a microbial-mediated biochemical process where biomass waste is converted into biogas under anaerobic conditions. The adaptability of the microorganisms and the organic matter conversion process need to be considered. Polyether defoamers inhibit the gas production effect of anaerobic digestion systems and therefore cannot be directly applied.

[0011] In summary, the defoamers commonly used in the defoaming industry are not suitable for anaerobic digestion systems. There is an urgent need to develop new defoamers that are suitable for anaerobic digestion systems, have high defoaming efficiency, are non-biotoxic, and do not negatively impact subsequent biogas combustion systems. Summary of the Invention

[0012] In view of this, in order to develop a defoamer suitable for anaerobic digestion systems, with high defoaming efficiency, no biotoxicity, and no impact on subsequent biogas combustion systems, this invention provides an environmentally friendly high-efficiency defoamer for anaerobic digestion systems. It is formulated with non-biotoxic and silicon-free components. The resulting environmentally friendly high-efficiency defoamer for anaerobic digestion systems is non-biotoxic, will not impair the gas production efficiency of anaerobic digestion systems, and has high foam suppression and foam reduction rates. It will not pollute biogas combustion systems after use.

[0013] To achieve the above objectives, the present invention provides the following technical solution:

[0014] An environmentally friendly, high-efficiency defoamer for anaerobic digestion systems comprises the following components by weight percentage:

[0015] 15%-20% solid defoamer component, 35%-50% oil-based defoamer component, 30%-40% water, 4% compound emulsifier and 1% thickener;

[0016] The environmentally friendly anaerobic digestion system uses a highly efficient defoamer that is non-toxic and silicone-free;

[0017] The solid defoaming component is one of calcium soap, glyceryl monostearate, and biochar from biogas residue.

[0018] The oil-based defoamer component is trioleic acid glyceride or mineral oil;

[0019] The compounding relationship between the solid defoaming component and the oil-based defoamer component does not include the compounding of the calcium soap and the mineral oil.

[0020] Preferably, the composite emulsifier is Span80 and Tween60, mixed in a mass ratio of 7:3.

[0021] Preferably, the thickener is hydroxypropyl methylcellulose.

[0022] On the other hand, the present invention provides a method for preparing the above-mentioned environmentally friendly anaerobic digestion system high-efficiency defoamer, comprising the following steps:

[0023] (1) The composite emulsifier is mixed in water and fully dissolved;

[0024] (2) After adding the oil-based defoaming component until it is completely dissolved, perform intermittent short-time homogenization.

[0025] (3) After adding solid defoaming components until completely dissolved, perform intermittent short-time homogenization, adding water as needed during the process;

[0026] (4) Dissolve the thickener in water to obtain a thickener solution. Add the thickener solution and mix evenly. Perform intermittent short-time homogenization until fully mixed and homogenized to obtain an environmentally friendly high-efficiency defoamer for anaerobic digestion systems.

[0027] Preferably, in step (2), the intermittent short-time homogenization operation conditions are: 5000-10000 r / min for 1-2 intermittent short-time homogenizations.

[0028] Preferably, in step (3), the intermittent short-time homogenization operation conditions are: 10000-15000 r / min for 3-5 intermittent short-time homogenizations.

[0029] Preferably, in step (4), the intermittent short-time homogenization operation conditions are: 10000-15000 r / min for 1-2 intermittent short-time homogenizations.

[0030] Furthermore, the present invention also provides the application of the above-mentioned high-efficiency defoamer for environmentally friendly anaerobic digestion systems or the high-efficiency defoamer for environmentally friendly anaerobic digestion systems prepared by the above-mentioned method in anaerobic digestion systems, wherein the volume percentage of the defoamer is 0.05-0.5% (the ratio of the volume of the defoamer to the volume of sludge in the reactor).

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] This invention provides an environmentally friendly, high-efficiency defoamer for anaerobic digestion systems. It is formulated with non-biotoxic and silicon-free components. The resulting environmentally friendly, high-efficiency defoamer for anaerobic digestion systems is non-biotoxic, will not impair the gas production efficiency of anaerobic digestion systems, and has high foam suppression and foam reduction rates. It will not pollute biogas combustion systems after use.

[0033] Specifically:

[0034] 1) It does not use antifoaming agents that are toxic to the growth and reproduction of anaerobic digestive system microorganisms, and has no biotoxicity;

[0035] 2) Do not use defoamer components that affect the anaerobic digestion gas production system and subsequent biogas combustion system;

[0036] 3) The selected single solid defoamer component is compounded with the single oil liquid defoamer component to obtain a composite defoamer, which has sufficient hydrophobicity, good diffusion and adsorption properties, and has good defoaming and foam suppression performance.

[0037] 4) Highly targeted and simple preparation method. Attached Figure Description

[0038] Figure 1 The effect of different dosages of defoamer components on the gas production performance of anaerobic digestion;

[0039] Figure 2 The effect of different dosages of defoamer components on the foaming volume of anaerobic sludge;

[0040] Figure 3 Diagram of the apparatus for testing foaming potential;

[0041] Figure 4 This is a comparison chart showing the defoaming effect of the defoamer of the present invention at a dosage of 0.05% with that of a commercial silicone defoamer. Detailed Implementation

[0042] Given that most existing research focuses on defoamers for industries such as power generation, papermaking, coatings, and fermentation, no defoamers specifically designed for anaerobic digestion systems have been found. Anaerobic digestion systems have many unique characteristics compared to other systems:

[0043] Firstly, this system is a microbial-mediated biochemical process, so any defoamer that is toxic to the growth and reproduction of microorganisms cannot be used;

[0044] Secondly, the system converts biomass waste into biogas, so any defoamer components that could affect the biogas production of the anaerobic digestion system cannot be used; furthermore, the biogas produced by anaerobic digestion will subsequently enter the biogas combustion system, so any defoamer components that could affect the combustion system cannot be used.

[0045] The above conditions limit the applicability of currently available mainstream defoamers in anaerobic digestion systems.

[0046] In view of the above reasons, this invention considers the complexity and variability of anaerobic digestion systems and improves upon the limitations of existing technologies. First, it identifies potential single-component liquid defoamer with sufficient hydrophobicity and sharp edges, good diffusivity, and surface activity. Then, it excludes defoamer components with biotoxicity or those affecting biogas combustion. Next, based on biotoxicity, it conducts preliminary screening of other potential defoamer components. Finally, this invention combines the screened single-component solid defoamer with oil-based defoamer components to form oil-solid mixtures, explores the defoaming performance of each mixture, and screens out highly efficient and environmentally friendly defoamers with high defoaming and foam-suppressing efficiencies.

[0047] Therefore, the present invention provides an environmentally friendly, high-efficiency defoamer for anaerobic digestion systems, comprising the following components by weight percentage:

[0048] 15%-20% solid defoamer component, 35%-50% oil-based defoamer component, 30%-40% water, 4% compound emulsifier and 1% thickener;

[0049] The environmentally friendly anaerobic digestion system uses a highly efficient defoamer that is non-biotoxic and silicone-free.

[0050] Given the limitations mentioned above, this invention selects non-biotoxic and silicone-free raw materials to formulate defoamers, thereby obtaining highly efficient and environmentally friendly defoamers with high defoaming and foam-suppressing efficiencies.

[0051] In this invention, the solid defoaming component is one of calcium soap, glyceryl monostearate, and biochar from sludge residue.

[0052] Calcium soap can be synthesized directly from edible oil and calcium oxide under the catalysis of hydrogen peroxide. Its preparation method includes the following steps:

[0053] (1) Add 50g of cooking oil and 7g of calcium oxide powder to a beaker and stir well;

[0054] (2) Add an appropriate amount of water and stir to react for a certain period of time;

[0055] (3) Add 10 mL of catalyst H2O2 and heat the reaction at 90-95℃. During the process, add an appropriate amount of water (oil-water ratio 1:4.5) and continue heating the reaction for 4.0-6.0 h.

[0056] (4) After cooling, dry in an oven;

[0057] (5) After drying, grind and pass through a 100-mesh sieve. The product is calcium soap.

[0058] Biochar from biogas residue can be prepared from biogas residue that has been modified with sodium hydroxide activator. The preparation method includes the following steps:

[0059] (1) Crush the dried biogas residue and add 1 mol / L sodium hydroxide solution at a ratio of 1 g: 2.5 mL, and let it stand for 24 h;

[0060] (2) Discard the supernatant and place it in a 105℃ oven to dry completely;

[0061] (3) Heating was performed in a high-temperature tubular furnace under nitrogen purging conditions, with the heating parameter set to 5℃·min. -1 The pyrolysis temperature was set to 550℃, and the heating time was set to 1 hour.

[0062] (4) After the product has cooled, wash it with dilute hydrochloric acid and pure water respectively;

[0063] (5) Dry in a 105℃ oven;

[0064] (6) Grind and crush the material, and pass it through a 100-mesh sieve. The product is biochar made from biogas residue.

[0065] You can choose commercially available glyceryl monostearate; there are no special requirements.

[0066] In this invention, the oil-based defoamer component is trioleic acid glyceride or mineral oil, and commercially available finished products can be selected; there are no special requirements in this regard.

[0067] In this invention, the composite emulsifier is a mixture of Span80 and Tween60.

[0068] In this invention, the mass ratio of Span80 to Tween60 is 7:3.

[0069] In this invention, the thickener is hydroxypropyl methylcellulose (HPMC), and any commercially available finished product is acceptable; there are no special requirements.

[0070] The environmentally friendly, high-efficiency defoamer for anaerobic digestion systems provided by this invention has the following advantages:

[0071] 1) It does not affect biogas utilization.

[0072] Currently, commonly used silicone defoamers and composite defoamers such as polyether-modified silicone defoamers all use silicon-containing substances as raw materials. Although they have good defoaming effects in systems such as wastewater treatment, bio-fermentation, and papermaking, silicone-containing defoamers can generate siloxanes in anaerobic digester reactors, leading to silicon precipitation in subsequent biogas combustion systems and affecting equipment lifespan. Therefore, this invention, in developing a novel defoamer for anaerobic digestion systems, avoids using silicon-containing substances as defoaming components, thus preventing adverse effects on biogas quality and equipment in subsequent gas utilization systems.

[0073] 2) The defoaming component is non-biotoxic and does not affect gas production.

[0074] Based on the selection principles of defoaming components and the foaming potential of individual substances, solid defoaming components (calcium soap, glyceryl monostearate, and biochar from sludge were initially selected as usable solid defoaming components) and oil-based defoaming components (glyceryl trioleate and mineral oil were selected as usable oil-based defoaming components, respectively). Since other studies on the use of biochar in anaerobic digestion systems have shown that it does not inhibit the methanogenesis efficiency of the system, the biotoxicity of glyceryl trioleate, mineral oil, calcium soap, and glyceryl monostearate was tested in batch reaction flasks. This also re-verified the biotoxicity of polyethers in anaerobic digestion systems.

[0075] On the other hand, the present invention provides a method for preparing the above-mentioned environmentally friendly anaerobic digestion system high-efficiency defoamer, comprising the following specific steps:

[0076] (1) At room temperature, mix 4% of the composite emulsifier Span80 and Tween60 in a mass ratio of 7:3, dissolve them in 1 / 3 of the water, add them to a beaker, and stir thoroughly until dissolved;

[0077] (2) After stirring evenly, add 35%-50% of the oil-based defoaming component trioleic acid glyceride or one of mineral oils, stir evenly until completely dissolved, and homogenize intermittently for short periods of 5000-10000r / min 1-2 times.

[0078] (3) Add 15%-20% of solid defoaming component calcium soap, glyceryl monostearate, or biochar from biogas residue, stir evenly, and homogenize intermittently for short periods at 10,000-15,000 r / min 3-5 times, adding 1 / 3 water as needed during the process.

[0079] (4) Dissolve 1% HPMC in 1 / 3 water at 60℃ to obtain a thickener solution. Add the solution to a beaker and stir until homogenized. Then, intermittently homogenize the solution 1-2 times at 10000-15000r / min until it is fully mixed and homogenized. This will give you an environmentally friendly high-efficiency defoamer for anaerobic digestion systems.

[0080] Furthermore, the present invention also provides the application of the above-mentioned environmentally friendly high-efficiency defoamer for anaerobic digestion systems or the environmentally friendly high-efficiency defoamer for anaerobic digestion systems prepared by the above-mentioned method in anaerobic digestion systems, wherein the amount of defoamer is 0.05-0.5% (the ratio of the volume of defoamer to the volume of sludge in the reactor, such as 0.05-0.5 ml of defoamer for 100 mL of sludge).

[0081] The research approach of this invention will be explained in detail below with reference to the accompanying drawings and the specific screening process.

[0082] 1. Research Approach

[0083] 1.1 Selection and preparation of defoaming components

[0084] 1.1.1 Characteristics of High-Efficiency Defoamers for Environmentally Friendly Anaerobic Digestion Systems

[0085] 1) It is insoluble in the medium system and has good stability;

[0086] 2) It easily diffuses and spreads in the medium;

[0087] 3) When foam overflows from the digestive fluid, the defoamer molecules should be easily adsorbed onto the foam liquid film;

[0088] 4) The defoamer components should contain hydrophobic solid particles. The oil phase and the hydrophobic particles work together to achieve a better defoaming effect.

[0089] To meet the above characteristics, the overall idea of ​​this invention is to screen out solid defoaming components and oil-based defoaming components that have defoaming properties and have no negative impact on the gas production efficiency of anaerobic digestion systems, and then add emulsifiers, thickeners and water to form an oil-solid mixture, which is a new type of defoamer.

[0090] 1.1.2 Selection of defoaming components:

[0091] The selection principles for solid defoaming components are: sufficient hydrophobicity to allow dehumidification at oil-water and air-water interfaces (i.e., a large contact angle); insoluble or sparingly soluble in the foaming system; large specific surface area; and good adsorption properties. The selection principles for oil-based defoaming components are: low surface tension; insoluble in the foaming system; not easily degraded by microorganisms; and good diffusivity.

[0092] Based on the selection principles of the above-mentioned single defoaming components, solid and oily substances that can meet the selection principles are sought. These substances are then used as defoaming components in compound novel defoamers by purchasing commercially available drugs or preparing them in-house.

[0093] 1.2 Initial screening of single defoaming components

[0094] 1) Initial screening for biotoxicity: Batch experiments of a single defoaming component were conducted in batch bottles. The cumulative gas production was used to verify whether the gas production of anaerobic digestion was inhibited by a single defoaming component. Single defoaming components that did not have a negative impact on the gas production of anaerobic digestion were selected as solid defoaming components and oil-based defoaming components, respectively.

[0095] 2) Initial screening of foaming potential: The foaming potential of the single defoaming component selected in 1.1.2 was determined by adding effervescent tablets. Different types and dosages of defoaming components were added to the experimental group, and the foaming potential of the experimental group was compared with that of the control group to analyze whether it has defoaming and foam-suppressing properties.

[0096] 1.3 Formulation of novel defoamers

[0097] 1) Compound formulation: The solid defoaming component and oil-based defoaming component that have been screened for biotoxicity and foaming potential in 1.1.2 are compounded with emulsifier, thickener and water to obtain a new defoamer. By adjusting the proportion of different components (especially solid defoaming component and water), the reasonable range of the proportion of different components is gradually narrowed to obtain the formulation table of the new defoamer.

[0098] 2) Foaming potential screening: Based on the obtained formula table, different types and different component ratios of new defoamers were compounded one by one, and the defoaming and foam suppression performance of the compounded oil-solid mixture was analyzed by adding effervescent tablets. Finally, the best performance was selected from several different formulations to become the environmentally friendly high-efficiency defoamer for anaerobic digestion systems.

[0099] 2. Selection and preparation process of defoaming components

[0100] 2.1 Solid defoaming components

[0101] 1) Calcium soap

[0102] Metallic soaps are particles of insoluble fatty acid salts. When oil is present in a medium, these solid particles can adhere to the surface of oil droplets and act as defoamers. Under weakly alkaline conditions, when fatty acids in the oil react with calcium ions to form calcium soaps in situ, solid soap particles are observed on the surface of the oil droplets. These small particles facilitate the droplets' entry into the air-water interface, leading to bridging instability at the foam film or plateau boundary. Therefore, this type of solid component is chosen as a potential defoamer.

[0103] The preferred preparation method is as follows: Calcium metal soap is directly synthesized using edible oil and calcium oxide under the catalysis of hydrogen peroxide. 50g of edible oil and calcium oxide powder are added to a three-necked flask and stirred until homogeneous. An appropriate amount of water is added, and the mixture is stirred for a certain time. Then, the catalyst H2O2 is added, and the mixture is heated to react. An appropriate amount of water is added, and the reaction is continued until the mixture is allowed to cool. The precipitate is then dried in an oven. The preparation conditions are: 50g of edible oil, temperature 90–95℃, time 4.0–6.0h, catalyst (H2O2) dosage 10mL, material ratio (calcium oxide dosage) 50:7, and oil-water ratio (water addition) 1:4.5.

[0104] 2) Biochar from biogas residue

[0105] Biochar has a large specific surface area and a well-developed pore structure. In previous defoamer screening experiments conducted by our research group, we found that biochar from biogas residue had a relatively weak foam suppression effect, but it showed good foam reduction efficiency at three different dosage levels and could promote foam breakage, second only to organosilicon defoamers. Although biochar defoamers alone have poor spreadability in the system, resulting in mediocre defoaming effects, they may have good effects as a solid defoaming component in compound defoamers. Therefore, this solid component was also selected for future use.

[0106] The preferred preparation method is as follows: The dried biogas residue is pulverized, and sodium hydroxide activator is added at a ratio of 1g:2.5mL. After standing for 24 hours, the supernatant is discarded, and the residue is further dried completely in an oven at 105℃. The residue is then heated in a high-temperature tube furnace under nitrogen atmosphere, with the heating parameter set to 5℃·min. -1 The pyrolysis temperature was set to 550℃, and the heating time was set to 1 hour. After the product cooled, it was washed with dilute hydrochloric acid and pure water respectively, dried in an oven at 105℃, ground and pulverized through a 100-mesh sieve, and the product was biochar.

[0107] 3) Glyceryl monostearate (commercially available)

[0108] Glyceryl monostearate is a white or pale yellow waxy solid, insoluble in water, but forms a stable hydrated dispersion in water, melting into a pale yellow transparent liquid. Glyceryl monostearate possesses one lipophilic long-chain aliphatic carbon group and two hydrophilic hydroxyl groups, making it a nonionic surfactant with an HLB value of 3.8–4.0. In oil-water systems, it interacts simultaneously with both the oil and water phases; this dual interaction reduces the interfacial tension between oil and water. It is speculated that it may possess antifoaming properties, therefore it was also selected as a solid component for testing, and the following experiments were conducted to confirm this.

[0109] 2.2 Oil-based defoaming components (commercially available)

[0110] 1) Tributyl phosphate

[0111] Tributyl phosphate, an early defoamer used in the metal processing industry, has strong defoaming power but poor foam suppression effect. It has also been studied in the fermentation of *Cyclocarya paliurus*, where it can quickly eliminate foam, but its foam suppression effect is poor. It can achieve rapid defoaming with minimal impact on the bacterial cells in the culture medium. Therefore, it is proposed to explore its use as the oil component in a compound defoamer.

[0112] 2) Trioleic acid glycerides

[0113] Triolein is an ester-type organic compound. According to literature review, when a mixture of triolein / oleic acid is dropwise dispersed in a solution containing a small amount of calcium ions, solid calcium oleate particles form and aggregate on the droplet surface, resulting in an antifoaming effect. Therefore, we attempted to use it as the oil-based component in a compound defoamer.

[0114] 3) Mineral oil

[0115] Early mineral oil-based defoamers contained a single active ingredient, using mineral oil as a carrier. While they possessed some defoaming ability after the addition of appropriate thickeners and emulsifiers, their foam-suppressing performance was poor. Later, single-element mineral oil defoamers evolved towards compound formulations, with the potential to enhance their defoaming performance by incorporating solid hydrophobic defoaming components into mineral oil. Therefore, this study explored its use as an oil-based component in compound defoamers.

[0116] 4) Polyether

[0117] Polyethers, as second-generation defoamers, offer advantages such as strong foam suppression, odorless and non-toxic properties, ease of use, easy dispersibility, and good thermal and chemical stability. They are commonly used in fermentation, food, detergent, and fiber processing industries and have already been commercially deployed, demonstrating good defoaming effects in other systems. However, their disadvantage is a low foam breaking rate; if foam suddenly and rapidly forms in a foaming system, they cannot quickly and effectively break the foam. This invention also considers using them as an oil-based component in compound defoamers.

[0118] 3. Initial screening of single defoaming components

[0119] 3.1 Initial screening for biotoxicity

[0120] 3.1.1 Initial screening methods and procedures for biotoxicity

[0121] After identifying the various solid and oily components in Sections 2.1 and 2.2, we first conducted biotoxicity verification on each of them. Since biochar from sludge has been shown in various studies to have no inhibitory effect on the methanogenic efficiency of the system, this study did not repeat the verification. Instead, we conducted batch experiments on four oily defoaming components: trioleate, mineral oil, tributyl phosphate, and polyether, as well as two solid defoaming components: calcium soap and glyceryl monostearate, and measured their cumulative gas production in the batch reaction flasks.

[0122] Determination method: Sludge was taken from a sample prepared according to 1.5 g VS·d -1 ·L -1 A mesophilic anaerobic digester, after a period of stable operation, was equipped with 19 batch bottles of 500 mL each, one blank control group without any additives, and the remaining experimental groups were treated with 0.05%, 0.1%, and 0.5% of trioleate, mineral oil, tributyl phosphate, polyether, calcium soap, and glyceryl monostearate, respectively. All reaction bottles were purged with nitrogen for 3 minutes to remove oxygen and ensure anaerobic conditions. They were then sealed with perforated rubber stoppers. A short silicone tube attached to the rubber stopper served as the gas outlet for the reactor, connected to a gas sampling bag. An extended silicone tube was used for purging with nitrogen. The batch bottles were incubated in a 37°C water bath. The gas production during the batch process was periodically measured to determine whether the products exhibited biotoxicity.

[0123] 3.1.2 Summary of cumulative gas production (e.g.) Figure 1 (As shown)

[0124] like Figure 1 As shown, the gas production curves of each reactor revealed that the cumulative gas production of the experimental group with added tributyl phosphate and polyether was lower than that of the control group, and the greater the dosage, the greater the inhibition. This indicates that these two types of substances have a potential inhibitory effect on gas production in the anaerobic digestion system. It also verifies that polyether defoamers, which are widely used in other systems, have biotoxicity in the anaerobic digestion system. Therefore, neither tributyl phosphate nor polyether can be used as oil-based defoaming components in the formulation of novel defoamers.

[0125] The gas production of the experimental groups with the other four defoaming components mentioned above was not negatively affected. The gas production of the experimental group with mineral oil was not significantly different from that of the control group. The gas production of the experimental groups with trioleate, calcium soap and glyceryl monostearate was even slightly higher than that of the control group, indicating that none of these four components inhibited gas production.

[0126] In summary, after initial screening for biotoxicity, trioleic acid glycerides and mineral oil can be used as oil-based defoaming components, while calcium soap, glyceryl monostearate, and biochar from biogas residue can be used as solid defoaming components in the formulation of novel defoamers.

[0127] 3.2 Initial screening of foaming potential (e.g.) Figure 2 (As shown)

[0128] 3.2.1 Foaming potential of oil-based defoaming components

[0129] Place 2g of Liduxin brand Vitamin C effervescent tablet powder at the bottom of a 250mL graduated cylinder. Pour 100mL of sludge into the graduated cylinder, and immediately add 0.05%, 0.1%, and 0.5% V / V of the solution respectively. 污泥 The defoamer was used, and the change in foam volume from foam formation to complete disappearance was observed. The changes in foam volume over time after adding effervescent tablets were shown in the experimental groups with different types and dosages of defoaming components. Figure 2 As shown in ac:

[0130] like Figure 2 As shown in Figure ac, the foam volume changes revealed that the foam volume of the experimental groups adding trioleic acid ester and mineral oil was consistently lower than that of the control group at almost every moment, and this was also related to the dosage. The experimental group adding trioleic acid ester showed better results. Although tributyl phosphate also has a good antifoaming effect, it is not considered in later compounding due to its biotoxicity.

[0131] 3.2.2 Foaming potential of solid defoaming components

[0132] Place 2g of Liduxin brand Vitamin C effervescent tablet powder at the bottom of a 250mL graduated cylinder. Pour 100mL of sludge into the graduated cylinder, and immediately add 0.05%, 0.1%, and 0.5% V / V of the solution respectively. 污泥 The defoamer was used, and the change in foam volume from foam formation to complete disappearance was observed. The changes in foam volume over time after adding effervescent tablets were shown in the experimental groups with different types and dosages of defoaming components. Figure 2 As shown in df:

[0133] The changes in foam volume revealed that the defoaming rate of the experimental group with biochar added was not significantly different from that of the control group. The foam volume of the experimental group with glyceryl monostearate added was lower than that of the control group for most of the time, but the inhibition amount was not significant. Calcium soap showed greater foam inhibition and a shorter defoaming time. Considering that the effectiveness of solid defoaming components used alone might be affected by diffusion issues, which could be compensated for by combining them with liquid components with good diffusion properties, all three substances were selected as alternative solid defoaming components.

[0134] 4. Combination of defoaming components

[0135] 4.1 Exploration of component ratios and determination of formulation

[0136] The raw materials of the novel defoamer include: solid defoaming components (calcium soap, biochar from biogas residue, or one of glyceryl monostearate), oil-based defoaming components (glyceryl trioleate or one of mineral oils), a composite emulsifier (Span 80 + Tween 60), a thickener (HPMC), and water. Considering the defoaming effect and form of the defoamer, the optimal mixing ratio was explored by adjusting the mass proportions of the solid defoaming components and water. Solid and oil-based components are the main defoaming components; theoretically, a higher proportion of these two types of components results in better defoaming effect. However, during preparation, it was found that when the mass proportion of solid components exceeded 20%, the defoamer had extremely poor flowability and could not be used normally. Simultaneously, when the mass proportion of water exceeded 45%, the components of the defoamer could not blend smoothly, resulting in stratification. Therefore, the proportion of solid components was reduced to 15%–20%, and the proportion of water was reduced to 30%–40%.

[0137] Therefore, the mass percentage of the fixed composite emulsifier (Span 80 to Tween 60 in a mass ratio of 7:3) is 4%, and the mass percentage of the thickener HPMC is 1%. This means the sum of the mass percentages of the solid defoamer, oil-based defoamer, and water is 95%. The main changes are made to the mass percentages of the solid components and water. The mass percentages of water are determined to be 30%, 35%, and 40%; the mass percentages of the solid components are determined to be 15% and 20%, and the percentage of the oil-based components is determined accordingly. The following formulation table was developed:

[0138] Table 1. Raw material formulation of high-efficiency defoamer for environmentally friendly anaerobic digestion systems.

[0139]

[0140] 4.2 Defoamer compounding and foaming potential screening

[0141] The two oil-based defoaming components screened in the previous stage—mineral oil and trioleate—and the three solid defoaming components—calcium soap, glyceryl monostearate, and biochar—can theoretically be combined in any way to produce six different oil-solid mixtures as novel defoamers. These different types are denoted as AF.

[0142] A – Calcium soap + trioleic acid glycerides;

[0143] B – Glyceryl monostearate + Glyceryl trioleate;

[0144] C—biochar from biogas residue + trioleic acid glycerides;

[0145] D – Calcium soap + mineral oil;

[0146] E – Glyceryl monostearate + mineral oil;

[0147] F – Biochar from biogas residue + mineral oil

[0148] By compounding the six types of defoamers from AF according to the formulations in Table 1, 36 defoamers can be obtained. Using these 36 defoamers as the research object, the immediate defoaming efficiency and continuous defoaming efficiency were calculated by measuring the foam volume in the foaming potential experiment of adding effervescent tablets to evaluate their defoaming and foam suppression performance.

[0149] Specifically, the main instruments and materials for the foaming potential experiment are: a 250mL graduated cylinder and Lidu Shen brand Vitamin C effervescent tablets.

[0150] Test conditions: 37℃ water bath;

[0151] Test medium: Sludge from a mesophilic anaerobic digester that has been operating for a long time;

[0152] Specific testing methods: As shown in the example... Figure 3The foaming potential experimental apparatus described above involves adding 100 ml of sludge to a 250 mL graduated cylinder, adding effervescent vitamin C tablets as a foaming agent, and recording the foam volume V1 (mL) when the foam reaches its maximum volume. Subsequently, defoamers of 0.05% V / V, 0.1% V / V, and 0.5% V / V are added respectively. The foam volume V2 (mL) is recorded immediately after adding the defoamer, and again after 1 hour, the foam volume V3 (mL). The immediate and continuous defoaming efficiencies are calculated according to formulas (1) and (2), respectively.

[0153] Instant defoaming efficiency = (V1 - V2) / V1 × 100% (1)

[0154] Continuous defoaming efficiency = (V2 - V3) / V2 × 100% (2)

[0155] Table 2 shows the defoaming effects of 36 defoamers formulated according to the method of the present invention at different dosages, and uses them as examples; the defoaming effect of commercially available silicone DF280 defoamer is used as a comparative example. Figure 4 Furthermore, a comparison graph is provided showing the defoaming effect of five implementation methods (A4, B4, C4, E4, and F4) with that of commercially available silicone DF280 defoamer at a dosage of 0.05% over time, with the combination of 20% solid components and 45% liquid components.

[0156] Table 2. Defoaming efficiency of different types of defoamers at various dosages.

[0157]

[0158]

[0159]

[0160] As shown in Table 2 above, the defoaming effects of the six defoamers obtained by compounding mineral oil and calcium soap according to the formula in Table 1 are not always better than those of the comparative example. Therefore, this invention excludes the scheme of compounding mineral oil and calcium soap. From the fact that the defoaming effects of the remaining 30 defoamers in the table are significantly better than those of the comparative example, it can be seen that the environmentally friendly high-efficiency defoamer for anaerobic digestion systems provided by this invention has both better immediate and sustained defoaming efficiency than the comparative example.

[0161] The above are merely preferred embodiments of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concept, should be covered within the scope of protection of the present invention.

Claims

1. A highly efficient defoamer for environmentally friendly anaerobic digestion systems, characterized in that, By mass percentage, it includes the following components: 15%-20% solid defoamer component, 35%-50% oil-based defoamer component, 30%-40% water, 4% compound emulsifier and 1% thickener; The environmentally friendly anaerobic digestion system uses a highly efficient defoamer that is non-toxic and silicone-free; The solid defoaming component is one of glyceryl monostearate and biochar from biogas residue. The oil-based defoamer component is trioleic acid glyceride or mineral oil.

2. The environmentally friendly, high-efficiency defoamer for anaerobic digestion systems according to claim 1, characterized in that, The composite emulsifier is a mixture of Span80 and Tween60 in a mass ratio of 7:

3.

3. The environmentally friendly, high-efficiency defoamer for anaerobic digestion systems according to claim 1 or 2, characterized in that, The thickener is hydroxypropyl methylcellulose.

4. A method for preparing an environmentally friendly, high-efficiency defoamer for an anaerobic digestion system according to any one of claims 1-3, characterized in that, Includes the following steps: (1) The composite emulsifier is mixed in water and fully dissolved; (2) After adding the oil-based defoaming component until it is completely dissolved, perform intermittent short-term homogenization. (3) After adding solid defoaming components until completely dissolved, perform intermittent short-time homogenization, adding water as needed during the process; (4) Dissolve the thickener in water to obtain a thickener solution. Add the thickener solution and mix evenly. Perform intermittent short-time homogenization until fully mixed and homogenized to obtain an environmentally friendly high-efficiency defoamer for anaerobic digestion systems.

5. The preparation method of a high-efficiency defoamer for an environmentally friendly anaerobic digestion system according to claim 4, characterized in that, In step (2), the intermittent short-time homogenization operation conditions are: 5000-10000 r / min for 1-2 intermittent short-time homogenizations.

6. The method for preparing an environmentally friendly, high-efficiency defoamer for an anaerobic digestion system according to claim 4, characterized in that, In step (3), the intermittent short-time homogenization operation conditions are: 10000-15000 r / min for 3-5 intermittent short-time homogenizations.

7. The preparation method of a high-efficiency defoamer for an environmentally friendly anaerobic digestion system according to claim 4, characterized in that, In step (4), the intermittent short-time homogenization operation conditions are: 10000-15000 r / min for 1-2 intermittent short-time homogenizations.

8. The application of the environmentally friendly high-efficiency defoamer for anaerobic digestion systems prepared by any one of the environmentally friendly high-efficiency defoamers for anaerobic digestion systems according to any one of claims 1-3 or any one of claims 4-7 in an anaerobic digestion system, characterized in that, The volume percentage of the defoamer used is 0.05-0.5%.

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