Green and environment-friendly skim gum concentration process

Abstract

The invention discloses a green and environment-friendly skim glue concentration process, and relates to the technical field of skim glue. By adopting an overclocking vibrating membrane separation technology, the whole process is automatically controlled, the operation cost is low, the energy consumption is low, the occupied area is small, the content of dry glue in the separated skim liquor waste liquid is low, a large amount of strong acid does not need to be added for flocculation, the environmental protection pressure of skim liquor treatment is greatly reduced, the whole process is subjected to closed production, the process is simplified, and the method is environmentally friendly; the method can comprehensively replace the traditional process of strengthening acid treatment of the skim solution.

Description

Technical Field

[0001] The present invention relates to the technical field of skim latex, and particularly relates to a green and environment-friendly skim latex concentration process. Background Art

[0002] The rubber industry is one of the important basic industries of the national economy and also one of the important strategic materials of the country. High energy consumption and high pollution in the primary processing stage of natural rubber are worldwide problems; the extensive processing method severely restricts the development of the natural rubber industry. Therefore, it has become more urgent to carry out the primary processing of natural rubber in an environmentally friendly and cost-controllable manner.

[0003] For the concentration of skim latex, the mainstream process in the current market is acid addition and flocculation treatment, which occupies more than 95% of the market. However, this process has the following problems: 1) After flocculation, simple concentration is carried out, and repeated cleaning and drying are still required, with high labor intensity and low efficiency; 2) A large amount of flushing wastewater needs to be treated environmentally, resulting in serious pollution and a large floor area for environmental protection treatment equipment; 3) The skim latex contains 3-7% rubber (i.e., skim latex rubber), and a large amount of strong acid needs to be added for flocculation, causing serious environmental pollution, and a large amount of land is required for the environmental protection treatment of acid-containing sewage; 30 kg of 30% sulfuric acid is required for the flocculation of 1 ton of skim latex rubber, and a rubber factory with an annual output of 10,000 tons of concentrated latex needs to use 300 tons of 30% concentrated sulfuric acid for the treatment of skim latex rubber every year; 4) The use of a large amount of strong acid will cause the rubber quality to decline, and most of the skim latex rubber is treated as secondary rubber. Facing the above problems, there has been no complete solution since the industrialization of the skim latex industry nearly a hundred years ago. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art and provide a green and environment-friendly skim latex concentration process. The over-frequency vibration membrane separation technology is adopted, and the whole process is fully automated controlled, with low operating cost, low energy consumption, small floor area, and low dry rubber content in the separated skim latex waste liquid. There is no need to add a large amount of strong acid for flocculation, greatly reducing the environmental protection pressure of skim latex treatment. The separated skim latex concentrate can be used for the production of special rubbers; the present invention is a fully enclosed production process with simplified procedures and environmental friendliness, and can completely replace the traditional process of treating skim latex solution with strong acid.

[0005] The technical solution of the present invention is as follows:

[0006] A green and environment-friendly skim latex concentration process, comprising the following steps:

[0007] S1: Let the skim latex solution stand still and clarify to precipitate the gum and impurities therein;

[0008] S2: Take the upper-layer skim latex solution after clarification for preliminary filtration, then let it stand still and clarify, and take the upper-layer solution to obtain the pretreated skim latex;

[0009] S3: Feed the pretreated skim rubber into a pre-filter for filtration. After ensuring that there are no impurities and flocculation in the skim rubber during transportation, then transport it to the membrane barrel of the ultra-high frequency vibration membrane system. Through the reserved flow channel, control the liquid flow direction to enable the skim rubber to be fully filtered for the second time;

[0010] S4: Part of the skim rubber after the second filtration flows back to the pre-filter, mixes with the pretreated skim rubber and is filtered again, and then is transported to the membrane barrel of the ultra-high frequency vibration membrane system for full filtration;

[0011] S5: Repeat step S4 multiple times to obtain a skim rubber concentrate;

[0012] S6: Feed part of the skim rubber concentrate obtained in step S5 into the finished product tank, and the other part flows back to the membrane barrel of the ultra-high frequency vibration membrane system, mixes with the newly pretreated skim rubber for filtration. At this time, the system operates stably and continuous production of concentrated skim rubber can be carried out;

[0013] S7: Repeat step S6, and the concentrated skim rubber obtained in the finished product tank is the concentrated skim rubber.

[0014] Preferably, in step S1, the skim rubber solution is obtained by centrifuging natural rubber latex with a centrifuge.

[0015] Preferably, in step S2, the preliminary filtration is carried out in a self-cleaning filter, and the filter mesh aperture of the self-cleaning filter is 1 - 100 μm.

[0016] Preferably, in step S5, the dry rubber content in the skim rubber concentrate obtained after filtration is 20 - 35 wt.%.

[0017] Preferably, the ultra-high frequency vibration membrane system includes a membrane barrel and an excitation motor. A membrane sheet is arranged in the membrane barrel, and the excitation motor transmits through a torsion shaft to make the membrane barrel vibrate.

[0018] Preferably, the membrane sheet gap is 1 - 5 mm.

[0019] Preferably, the membrane sheet is made of PES material, and the aperture is 0.05 - 0.15 μm.

[0020] Preferably, the frequency of the excitation motor is 10 - 100 Hz.

[0021] Preferably, a metering pump is used to transport the skim rubber or the skim rubber concentrate to the ultra-high frequency vibration membrane system, the transport pressure is 0.1 - 0.2 MPa, and the temperature is 20 - 40 °C.

[0022] Preferably, when the skim rubber or the skim rubber concentrate is transported to the ultra-high frequency vibration membrane system, the flow rate is 1 - 3 m / s.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. In the green and environment-friendly rubber skim concentrate process of the present invention, the over-frequency vibration membrane separation technology is adopted to concentrate the rubber skim. The whole process is fully automated, with low operating costs, low energy consumption, small floor area, and low dry rubber content in the separated rubber skim waste liquid, eliminating the need to add a large amount of strong acid for flocculation, greatly reducing the environmental protection pressure of rubber skim treatment. The separated rubber skim concentrate can be used to produce special rubbers. The present invention features closed production throughout the process, simplified processes, and environmental friendliness. It is a revolutionary rubber skim concentration and separation process that can completely replace the traditional process of treating rubber skim solution with strong acid.

[0025] 2. The process of the present invention is highly energy-efficient and low-cost: it reduces the use of acidic solutions, with the production cost per ton reduced by approximately 200 - 300 yuan. Moreover, the products separated by the process of the present invention have excellent performance and can produce low-protein concentrated latex, significantly enhancing the quality and value.

[0026] 3. The traditional process of adding acid for flocculation to treat rubber skim requires a large amount of acidic solutions, resulting in high costs. Additionally, the latex in the rubber skim cannot be effectively utilized, and the acid-added solution is difficult to treat, causing serious environmental pollution problems. In contrast, the process of the present invention has a low maintenance frequency. After continuous operation for 1 - 2 months, it is only necessary to clean the membrane barrel of the over-frequency vibration membrane system with a cleaning agent, reducing the labor intensity of workers, decreasing the use of acidic solutions, and improving the working environment.

[0027] 4. The rubber content in the rubber skim solution obtained by centrifuging natural latex is low (usually only 5 - 15 wt.%), and the traditional extraction cost is relatively high. Moreover, it contains impurities such as proteins and ash, resulting in poor mechanical properties (low strength and elasticity) and insufficient aging resistance of the recovered rubber, making it difficult to be used in high-end products and having low added value. The rubber skim concentrate obtained by the process of the present invention has a rubber content of 20 - 35 wt.%, few impurities, good mechanical properties of rubber, high added value, and high economic recovery benefits.

[0028] 5. The traditional centrifuge has a good separation effect on rubber particles with a diameter > 2 μm, but has a low capture rate for small particle sizes (especially < 1 μm), resulting in a large amount of recoverable rubber still remaining in the rubber skim (accounting for 10 - 30 wt.% of the total rubber in the original latex), causing waste. The present invention can effectively utilize these small particle sizes, improving economic benefits.

[0029] 6. In the present invention, the dry rubber component (i.e., natural rubber) in the rubber skim waste liquid is very small, changing the original acid flocculation process, reducing costs, and being more environmentally friendly. Detailed Embodiments

[0030] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention.

[0031] (1) The natural latex contains the following components in the following contents:

[0032] 1) Natural rubber (rubber hydrocarbon, cis-1,4-polyisoprene):

[0033] Content: Dispersed in water in the form of latex particles, it is the main effective component of natural latex and determines its elasticity and mechanical properties.

[0034] 2) Water

[0035] Content: It is the continuous phase of natural latex and maintains the liquid dispersion state of natural latex.

[0036] 3) Non-rubber components

[0037] a) Proteins and nitrogen-containing substances: including the protective layer proteins (such as rubberin) on the surface of rubber particles, which affect the stability of latex and subsequent processing properties (such as vulcanization rate, aging resistance of products).

[0038] b) Carbohydrates (carbohydrates): including glucose, fructose, etc., which may affect the microbial stability of natural latex (prone to spoilage).

[0039] c) Ash (inorganic salts): mainly mineral ions such as potassium, magnesium, calcium, and phosphorus. Excessive content will cause an increase in the conductivity of natural latex and affect the electrical insulation of products.

[0040] d) Phospholipids and resins: Phospholipids (such as lecithin) act as natural emulsifiers to stabilize latex particles, and resinous substances (such as terpenes) affect the viscosity and processing properties of natural latex.

[0041] e) Others: small amounts of organic acids (such as acetic acid, formic acid, which affect the pH value), enzymes (such as protease, which may cause latex coagulation), etc.

[0042] (2) After the natural latex is centrifuged by a centrifuge, a latex serum solution and particulate matter are obtained. The latex serum solution includes the following components:

[0043] 1) Rubber hydrocarbon (natural rubber)

[0044] Content: Significantly lower than the original natural latex.

[0045] Traditional centrifuges mainly separate rubber particles with larger particle sizes (usually particle size > 1 - 2 μm), while the remaining rubber particles in the latex serum solution are small particle size rubber particles (particle size < 1 μm, even nano-scale), which are difficult to be captured by centrifugation.

[0046] 2) Water

[0047] Content: It is the continuous phase of the latex serum solution and accounts for a much higher proportion than concentrated latex.

[0048] 3) Non-rubber components

[0049] a) Proteins and nitrogenous substances: (higher content than in the original natural latex, as the proteins adsorbed on the surface of small-sized rubber particles enter the crepe latex during centrifugation), including hevein, enzymes, etc.

[0050] b) Carbohydrates (sugars): Exist in dissolved or minute particulate form.

[0051] c) Ash (inorganic salts): Mainly potassium, magnesium, calcium ions, etc., with strong water solubility and remaining in the liquid phase.

[0052] d) Phospholipids and resins: Stabilize small-sized rubber particles as emulsifiers, with some in colloidal dispersion.

[0053] e) Volatile fatty acids (VFA): Higher content than in the original natural latex, as centrifugation may damage some latex particles and release free fatty acids.

[0054] f) Preservatives (such as ammonia): If ammonia preservative is added to the original natural latex, the ammonia content in the crepe latex is 0.05 - 0.3 wt.%, maintaining a weak alkaline (pH 9 - 11).

[0055] (3) The particulate matter is mainly in the dispersed phase from micron to nanometer scale, specifically including the following components:

[0056] 1) Rubber particles

[0057] a) Small-sized rubber colloidal particles: The particle size is mostly 0.1 - 1 μm (the separation lower limit of traditional centrifuges is usually 1 - 2 μm, and smaller particles cannot be effectively separated), with a protective layer of proteins, phospholipids, etc. adsorbed on the surface, presenting a stable colloidal state.

[0058] b) Coagulated or damaged rubber microparticles: Rubber particles damaged by mechanical stress during centrifugation, or small coagulates formed by natural aggregation (particle size can reach several microns).

[0059] 2) Non-rubber solid impurities

[0060] a) Mechanical impurities: Bark debris, sediment, mycelia, etc. from the latex vessels of rubber trees or the tapping process, with a particle size usually > 5 μm (may remain if not fully filtered before centrifugation).

[0061] b) Protein aggregates: Flocculent precipitates or particles formed by some proteins due to pH changes or mechanical actions (particle size 1 - 10 μm).

[0062] c) Resin and wax particles: Terpene resins and waxes insoluble in water, presenting as minute crystals or oil droplets (particle size 0.5 - 5 μm).

[0063] 3) Colloidal dispersions

[0064] Colloidal particles of non - rubber components: such as protein - carbohydrate complexes, phospholipid micelles, etc., with a particle size < 0.1 μm, stably existing in the form of a colloidal solution and difficult to be separated by centrifugation.

[0065] Example 1

[0066] The green and environment - friendly latex concentrate process of this example includes the following steps:

[0067] S1: Let the latex solution stand still and clarify to precipitate the latex mud and impurities in it.

[0068] S2: Take the upper - layer clarified latex solution and send it into a self - cleaning bag - type filter with a filter mesh aperture of 100 μm for preliminary filtration to remove sediment, fibers, flocculent debris, etc., then let it stand still and clarify, take the upper - layer solution to obtain the pretreated latex.

[0069] S3: Send the pretreated latex into a pre - filter for filtration. After ensuring that there are no impurities and flocs in the transportation of the latex, then transport it to the membrane barrel of the ultra - frequency vibration membrane system through a metering pump. The transportation pressure is 0.2 MPa, the temperature is 40 °C, and the flow rate is 2 m / s. Control the liquid flow direction through the reserved flow channel to make the latex fully filtered for the second time. Among them, the ultra - frequency vibration membrane system includes a membrane barrel and an excitation motor. There is a PES - material membrane sheet with a gap of 2 mm in the membrane barrel, the aperture of the membrane sheet is 0.05 μm, and the frequency of the excitation motor is 90 Hz. The excitation motor transmits through a torsion shaft to make the membrane barrel vibrate.

[0070] S4: Part of the latex after the second filtration flows back to the pre - filter, mixes with the pretreated latex and is filtered again, and then is transported to the membrane barrel of the ultra - frequency vibration membrane system for full filtration.

[0071] S5: Repeat step S4, continuously filter and concentrate. The dry rubber content in the obtained latex concentrate is 33 wt.%.

[0072] S6: Send part of the latex concentrate obtained in step S5 into the finished - product tank, and the other part flows back to the membrane barrel of the ultra - frequency vibration membrane system to mix with the new pretreated latex for filtration. At this time, the system operates stably and continuous production of concentrated latex can be carried out.

[0073] S7: Repeat step S6. What is obtained in the finished - product tank is the concentrated latex, and the latex waste liquid is sent into the waste - liquid tank.

[0074] Detect the concentrated latex obtained in this example, and the detection results are shown in Table 1:

[0075] Table 1 Detection results of the concentrated latex obtained in Example 1

[0076]

[0077] Comparative Example 1

[0078] Comparative Example 1 adopts a traditional latex concentrate process, including the following steps:

[0079] (1) Raw material pretreatment: Remove impurities (such as sediment and fibers) in the latex solution through plate and frame filtration to avoid affecting the subsequent flocculation effect.

[0080] (2) Add dilute acid solution: Under stirring (rotation speed 50 r / min), slowly drop 10% sulfuric acid into the filtered latex (the dropping speed is about 10 L / min, adjusted according to the amount of latex); calculated based on the rubber content of the latex, about 10 L of 10% sulfuric acid is required per ton of latex.

[0081] (3) Endpoint control: When the pH of the latex drops to 4, the rubber particles are completely coagulated to form flocculent rubber masses; continue stirring for 10 min after the addition of acid is completed to ensure uniform acid distribution.

[0082] (4) Static settlement and separation: Stop stirring and let it stand overnight to allow the rubber masses to settle fully; then drain the upper layer of whey by siphon to obtain the bottom rubber masses (rubber content is 15 - 25 wt.%), and transfer to the next step for washing.

[0083] (5) Washing and dewatering of rubber masses; Add clear water (the amount of water is 2 times the volume of the rubber masses) to the rubber masses, stir evenly and let it stand for 30 min, then drain the washing water; repeat the washing multiple times until the pH of the washing water is close to neutral and the conductivity < 500 μS / cm; the washed rubber masses are dehydrated by a roll press to obtain usable rubber blocks, that is, the concentration of latex is completed.

[0084] The total time-consuming of the concentration process in Comparative Example 1 is 16.5 h (the core time-consuming is concentrated in the static settlement link, accounting for more than 60%). Cost estimation: 128 yuan / ton of latex (the main costs are sulfuric acid and labor, and there is no energy consumption but equipment time occupation in the static settlement stage). There are problems of long time, low efficiency and large quality fluctuation in industrial production. The core pain points of the concentration process in Comparative Example 1 lie in the time-consuming and labor dependence in the static settlement and washing links, and the loss of rubber particles in the separation process.

[0085] The vulcanized rubber prepared from the concentrated latex of Example 1 has better tensile strength, elongation at break and tear strength than the products of the traditional acid coagulation process. The tensile strength can reach more than 20 MPa, approaching the level of first-class natural rubber. The concentrated latex can be compatible with low-ammonia / ammonia-free preservatives (such as biological bacteriostatic agents), eliminating the ammonia removal process, improving the production environment, and the qualified rate of products is increased to 91%. It can also be used in high-end fields: the concentrated latex is suitable for products with high purity requirements such as medical catheters and condoms.

[0086] However, the products produced using the clarified glue of the concentrated glue of Comparative Example 1 have problems such as low strength and easy breakage; moreover, impurities (such as proteins and sugars) are not completely removed, which easily accelerates oxidation, mildew or moth-eaten, and the aging speed is fast (such as discoloration, stickiness, embrittlement); the water and heat resistance is insufficient, it is easy to expand in a humid environment, and peculiar smell or softening may be released at high temperature.

Claims

1. Green environmental protection type rubber cement concentrating process, characterized in that, It includes the following steps: S1: Let the crepe rubber solution stand still for clarification to precipitate the rubber clay and impurities therein; S2: Take the upper-layer crepe rubber solution after clarification for preliminary filtration, then let it stand still for clarification, and take the upper-layer solution to obtain the pretreated crepe rubber; S3: Send the pretreated crepe rubber into a pre-filter for filtration, and then transport it to the membrane barrel of the ultra-high-frequency vibration membrane system. Control the liquid flow direction through the reserved flow channel to enable the crepe rubber to be fully filtered for the second time; S4: Part of the crepe rubber after the second filtration flows back to the pre-filter, is mixed with the pretreated crepe rubber and then filtered again, and then is transported to the membrane barrel of the ultra-high-frequency vibration membrane system for full filtration; S5: Repeat step S4 multiple times to obtain a crepe rubber concentrate; S6: Send part of the crepe rubber concentrate obtained in step S5 into the finished product tank, and the other part flows back to the membrane barrel of the ultra-high-frequency vibration membrane system to be mixed with the new pretreated crepe rubber for filtration; S7: Repeat step S6, and the concentrated crepe rubber obtained in the finished product tank is the concentrated crepe rubber.

2. The green and environment-friendly latex concentrate process according to claim 1, wherein, In step S1, the crepe rubber solution is obtained by centrifuging natural rubber latex with a centrifuge.

3. The green environmental protection type glue clarification glue concentration process according to claim 1, characterized in that, In step S2, the preliminary filtration is carried out in a self-cleaning filter, and the mesh aperture of the self-cleaning filter is 1 - 100 μm.

4. The green and environment-friendly rubber latex concentrate process according to claim 1, characterized in that, In step S5, the dry rubber content in the crepe rubber concentrate obtained after filtration is 20 - 35 wt.%.

5. The green environmental protection type glue skim concentrate process according to claim 1, characterized in that, The ultra-high-frequency vibration membrane system includes a membrane barrel and an excitation motor. A membrane is arranged inside the membrane barrel, and the excitation motor transmits through a torsion shaft to make the membrane barrel vibrate.

6. The green environmental protection type glue skim concentrate process according to claim 5, characterized in that The membrane gap is 1 - 5 mm.

7. The green environmental protection type glue clarification glue concentration process according to claim 5, characterized in that, The membrane is made of PES material, and the pore diameter is 0.05 - 0.15 μm.

8. The green environmental protection type rubber latex concentrate process according to claim 5, characterized in that, The frequency of the excitation motor is 10 - 100 Hz.

9. The green environmental protection rubber latex concentrate process according to claim 1, wherein, Use a metering pump to transport the crepe rubber or the crepe rubber concentrate to the ultra-high-frequency vibration membrane system, the transport pressure is 0.1 - 0.2 MPa, and the temperature is 20 - 40 °C.

10. The green environmental protection type rubber latex concentrate process according to claim 9, characterized in that, When the crepe rubber or the crepe rubber concentrate is transported to the ultra-high-frequency vibration membrane system, the flow rate is 1 - 3 m / s.

Images