1. Characteristics and application background of liquid potassium silicate
As an important inorganic silicon compound, liquid potassium silicate plays a key role in many fields due to its unique chemical properties. Taking the HLKL-1 liquid potassium silicate produced by Tongxiang Hengli Chemical Co., Ltd as an example, its modulus is 2.20-2.40. It has the characteristics of high transparency and strong alkalinity. It is widely used in inorganic coatings, potash fertilizers, catalysts, soap fillings, refractory materials and other fields. In the production process, the key to ensuring product quality is to avoid excessive polymerization or gelation, which is not only related to the performance stability of the product, but also directly affects the production efficiency and market competitiveness of the enterprise.
2. Basic principles of polymerization and gelation of liquid potassium silicate
(I) Polymerization reaction mechanism
The main component of liquid potassium silicate is potassium silicate (K₂O・nSiO₂・mH₂O), and there are complex silicate anions in its aqueous solution. Under certain conditions, these anions will undergo polymerization through the formation of silicon-oxygen bonds (Si-O-Si) to form polysilicates with different degrees of polymerization. The modulus (M) is an important indicator for measuring the ratio of the amount of silicon dioxide to potassium oxide in potassium silicate. For liquid potassium silicate with a modulus of 2.20-2.40, the degree of polymerization of its silicon-oxygen tetrahedron is at a medium level, and the controllability of the polymerization reaction is crucial.
(II) Causes of gelation
Gelation is the result of excessive polymerization. When the molecular chains of polysilicates continue to grow and cross-link to form a three-dimensional network structure, the system will change from liquid to gel. This process is usually affected by a combination of factors, including temperature, concentration, pH value, impurity content, and stirring conditions. Once gelation occurs, the fluidity and performance of liquid potassium silicate will be severely reduced, and may even fail to meet customer application requirements.
3. Key factors affecting polymerization and gelation during production
(I) Raw material purity and ratio
Silicon dioxide raw materials: The purity of silicon dioxide raw materials (such as quartz sand) used to produce liquid potassium silicate directly affects the quality of the product. If the raw materials contain impurity ions such as iron, aluminum, and calcium, these impurities may act as catalysts or cross-linking centers for polymerization reactions, accelerate the polymerization reaction, and increase the risk of gelation. For example, excessive iron content (such as more than 0.01%) will significantly reduce the stability of liquid potassium silicate. Tongxiang Hengli Chemical Co., Ltd strictly controls the iron content ≤0.01% during the production process based on this consideration.
Ratio of potassium oxide to silicon dioxide: Accurate control of modulus is the core of producing qualified liquid potassium silicate. The calculation of modulus is based on the ratio of the amount of potassium oxide (K₂O) to silicon dioxide (SiO₂). If the ratio is inaccurate, the charge balance of silicon-oxygen tetrahedrons in the system may be destroyed, thereby inducing abnormal polymerization. During the production process, precise metering and chemical reaction control are required to ensure that the modulus is within the target range of 2.20-2.40.
(II) Reaction temperature and time
The influence of temperature: Temperature is an important factor affecting the polymerization reaction rate. Increasing the temperature will accelerate the molecular movement rate and increase the chance of collision between reactant molecules, thereby accelerating the polymerization reaction. In the preparation process of liquid potassium silicate, if the high temperature and high pressure reaction process is adopted, if the temperature is not properly controlled, the polymerization reaction may be out of control, and high molecular weight polysilicates may be quickly generated, and even gelation may occur. For example, when the reaction temperature exceeds 120°C, the polymerization reaction rate may increase sharply, and special attention should be paid to real-time monitoring and regulation of temperature.
Control of reaction time: Reaction time is closely related to the degree of polymerization. At a certain temperature, the degree of polymerization gradually increases with the extension of reaction time. If the reaction time is too long, the molecular chain of polysilicate will continue to grow and eventually form a gel. Therefore, it is necessary to determine the optimal reaction time through experiments to ensure that the silica reacts fully while avoiding excessive polymerization. For liquid potassium silicate with a modulus of 2.20-2.40, the reaction time usually needs to be controlled within the range of 8-12 hours. The specific time needs to be adjusted according to the reaction equipment and raw material characteristics.
(III) Solution concentration and pH value
Effect of concentration: The higher the concentration of liquid potassium silicate solution, the greater the concentration of silicate anions per unit volume, the greater the probability of intermolecular collision, and the faster the polymerization reaction rate. When the concentration exceeds a certain threshold (such as Baume greater than 46.0), the viscosity of the system increases significantly, the mass transfer and heat transfer efficiency decreases, and it is easy to cause local overheating and uneven polymerization reaction, which in turn triggers gelation. The Baume degree of HLKL-1 liquid potassium silicate produced by Tongxiang Hengli Chemical Co., Ltd is controlled at 44.0-46.0, which is in a relatively safe concentration range, but it is still necessary to pay close attention to changes in concentration during the production process.
pH value regulation: Potassium silicate solution is strongly alkaline, and the pH value will affect the existence form of silicate anions. Under high pH conditions, silicate anions mainly exist in the form of monomers or oligomers, and the polymerization reaction rate is slow; when the pH value decreases, the dissociation degree of silicate decreases, and silicate colloidal particles are easily formed. These particles will serve as the core of the polymerization reaction and promote the formation and cross-linking of polysilicate. Therefore, during the production process, it is necessary to maintain the pH value of the system stable by adding alkaline substances such as potassium hydroxide. Generally, the pH value is controlled between 12-13 to inhibit excessive polymerization.
(IV) Stirring and mass transfer effect
Stirring is an important means to ensure the uniformity of the reaction system. In the production process of liquid potassium silicate, if the stirring is not sufficient, the raw material concentration, temperature and pH value in the local area may be uneven, thereby causing local excessive polymerization. For example, in the dead corner of the reactor or near the stirring paddle, material retention and over-reaction may occur, forming a gel core and gradually spreading to the entire system. Therefore, it is necessary to select a suitable agitator type and stirring rate to ensure that the materials are fully mixed during the reaction process and improve the mass transfer and heat transfer efficiency. An anchor stirrer or paddle stirrer is usually used, and the stirring rate is controlled at 30-60 rpm to balance the mixing effect and energy consumption.
(V) Impurities and catalysts
In addition to the impurity ions in the raw materials, the choice of production equipment materials will also introduce impurities. For example, if the reactor is made of ordinary carbon steel, under strong alkaline conditions, iron ions may dissolve and enter the solution, accelerating the polymerization reaction. Therefore, stainless steel or enamel reactors are usually used to reduce the introduction of impurities. In addition, certain metal ions (such as sodium ions and calcium ions) may act as catalysts to promote polymerization reactions and need to be removed as much as possible during raw material pretreatment and production.
4. Key technical measures to avoid excessive polymerization or gelation
(I) Raw material pretreatment and quality control
Select high-purity raw materials: select quartz sand with low impurity content such as iron and aluminum as silica raw materials, and conduct strict chemical analysis on the raw materials to ensure that their purity meets production requirements. At the same time, use high-quality potassium hydroxide or potassium carbonate as potassium source to avoid the introduction of impurity ions.
Precisely control the raw material ratio: Use advanced metering equipment (such as electronic scales, flow meters) to accurately control the feeding amount of potassium oxide and silicon dioxide to ensure that the modulus is within the target range. During the production process, online analytical instruments can be used to monitor the modulus and concentration of the solution in real time, and adjust the raw material ratio in time.
(II) Optimize reaction process parameters
Segmented temperature control process: Use a segmented temperature control strategy to appropriately increase the temperature (such as 100-110℃) at the beginning of the reaction to accelerate the dissolution and initial polymerization reaction of silicon dioxide; in the middle and late stages of the reaction, gradually reduce the temperature (such as 80-90℃) to slow down the polymerization reaction rate and avoid over-polymerization. In this way, the degree of polymerization can be better controlled while ensuring the reaction efficiency.
Strictly control the reaction time: According to the characteristics of the raw materials and the performance of the reaction equipment, the optimal reaction time window is determined through experiments. During the production process, set up a time relay or automatic control system to ensure that the reaction time is accurately controllable and avoid excessive reaction time due to human operating errors.
Control solution concentration and pH value: During the reaction process, regularly monitor the Baume degree and pH value of the solution, and adjust them by adding deionized water or potassium hydroxide solution. When the Baume degree is close to the upper limit (46.0), add deionized water to dilute it in time; when the pH value is lower than 12, add an appropriate amount of potassium hydroxide solution to maintain the alkaline environment of the system.
(III) Strengthen stirring and equipment design
Optimize the stirring system: According to the volume and material characteristics of the reactor, select the appropriate type and installation position of the agitator. For example, for large reactors, multi-layer stirring paddles or combined agitators (such as turbine agitators on the upper layer and anchor agitators on the lower layer) can be used to improve the mixing effect of materials in different areas. At the same time, the speed and direction of the stirring paddle are reasonably designed to avoid vortexes and material retention.
Improve the structure of the reactor: Use a reactor design with a smooth inner wall and no dead corners to reduce the adhesion and retention of materials on the reactor wall. For example, the bottom of the reactor can be designed to be conical or elliptical to facilitate the discharge and cleaning of materials; a guide tube is set in the reactor to guide the flow direction of the material and improve the mixing uniformity.
Introducing ultrasonic or mechanical vibration: During the stirring process, ultrasonic or mechanical vibration devices can be introduced to further enhance the mixing and mass transfer effects of the materials through energy input. Ultrasonic waves can produce cavitation effects, destroy agglomerates and gel nuclei in the materials, and inhibit excessive polymerization reactions; mechanical vibrations can reduce the adhesion of materials to the stirring paddle and the reactor wall, and improve the uniformity of the reaction system.
(IV) Adding stabilizers and inhibitors
The role of stabilizers: Adding an appropriate amount of stabilizers, such as organic alcohols (methanol, ethanol), polyols (ethylene glycol, propylene glycol) or polyethylene glycol, to the liquid potassium silicate solution. These stabilizers can form hydrogen bonds with silicate anions, hinder the formation of silicon-oxygen bonds, and thus inhibit the polymerization reaction. The amount of stabilizer added is usually 0.5%-2% of the solution mass, and the optimal addition ratio needs to be determined through experiments.
Selection of inhibitors: For liquid potassium silicate with a low modulus (such as M=2.20-2.40), a small amount of acid salt (such as potassium dihydrogen phosphate, potassium bicarbonate) can be added as an inhibitor. Acid salts can neutralize some hydroxide ions and appropriately reduce the pH value of the solution, but the amount of addition must be strictly controlled to avoid the precipitation of silica colloid due to too low pH value. Generally speaking, the amount of acid salt added does not exceed 0.1% of the mass of potassium oxide in the solution.
(V) Real-time monitoring and process control
Online analysis technology: Use online infrared spectrometers, viscometers and other analytical instruments to monitor the composition, viscosity, degree of polymerization and other parameters of the reaction system in real time. For example, infrared spectroscopy can detect the characteristic absorption peaks of silicon-oxygen bonds in real time to determine the degree of polymerization; the viscometer can reflect the changes in the fluidity of the solution in real time. When the viscosity increases abnormally, timely measures can be taken to adjust the process parameters.
Automatic control system: Establish an automatic control system based on PLC (programmable logic controller) or DCS (distributed control system), and include key process parameters such as temperature, pressure, concentration, pH value, stirring rate, etc. into the scope of automatic control. Through the preset control algorithm and threshold, the operating status of the heating/cooling device, feeding pump, agitator and other equipment is automatically adjusted to achieve stable control of the production process and reduce the impact of human operation errors on product quality.
(VI) Post-processing and storage management
Filtration and clarification: After the reaction is completed, the liquid potassium silicate solution is filtered to remove undissolved impurity particles and possible gel particles. Plate and frame filter, centrifugal filter or membrane filtration equipment can be used to ensure the transparency and purity of the product. The filtered solution can be further clarified, such as static sedimentation or adding flocculants to remove tiny suspended matter.
Storage condition control: Liquid potassium silicate should be stored in sealed plastic barrels or stainless steel tanks to avoid contact with air. The storage environment should be cool and dry, with the temperature controlled within the range of 5-30℃, avoiding direct sunlight and high temperature environment. During storage, the product quality is regularly inspected. If there are signs of gelation, it should be processed or scrapped in time to prevent unqualified products from entering the market.
5. Practical experience
Tongxiang Hengli Chemical Co., Ltd, as a professional manufacturer of inorganic silicon products, has accumulated rich experience in the production process of liquid potassium silicate. The company always pays attention to the control of product quality, and has established a complete quality management system by introducing advanced production equipment and testing instruments. In terms of avoiding excessive polymerization or gelation of liquid potassium silicate, the company has taken the following measures:
Strict raw material control: Select high-purity quartz sand and potassium hydroxide as raw materials, and establish long-term cooperative relationships with high-quality suppliers to ensure the stability of raw material quality. At the same time, each batch of raw materials is strictly inspected before entering the factory to prevent unqualified raw materials from being put into production.
Optimized production process: The self-developed segmented temperature control reaction process and efficient stirring system are adopted to achieve precise control of the polymerization reaction. Through years of process optimization, the company can stably produce liquid potassium silicate products with a modulus of 2.20-2.40 and excellent performance.
Perfect testing methods: Equipped with advanced chemical analysis instruments and physical performance testing equipment, each link in the production process is monitored and analyzed in real time. For example, by measuring the Baume degree, density, silica content, potassium oxide content and other indicators of the solution, the process parameters can be adjusted in time to ensure that the product quality meets the standard requirements.
Personalized solutions: According to the different needs of customers, the company can provide customized liquid potassium silicate products and solutions. In the process of communicating with customers, the company's technical personnel will fully understand the customer's application scenarios and performance requirements, recommend suitable product models to customers, and provide professional technical support to help customers solve problems encountered during use.
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