High pressure polymerization reactorAfter long-term operation, stubborn dirt such as polymers, catalysts, and carbides are prone to remain inside. If not thoroughly cleaned, it can lead to cross contamination, decreased reaction efficiency, and even equipment damage. The following systematically introduces the cleaning work of high-pressure polymerization reactors from four dimensions: residue analysis, cleaning method selection, operation steps, and safety control.
1、 Preparation before cleaning: Clarify the type of residue and equipment status
Analysis of residual components
Polymer residues, such as polyethylene, polypropylene, etc., have strong adhesion and are prone to clogging pipelines.
Catalyst residue: such as Ziegler Natta catalyst (containing titanium and chlorine), which is corrosive.
Carbide: A hard deposit produced by the decomposition of materials during high-temperature reactions, with a hardness of HRC60 or higher.
Inorganic salts: such as sodium chloride, a byproduct of the reaction, are prone to moisture absorption and agglomeration.
Analysis method: Take residual samples from the kettle, determine the polymer type through infrared spectroscopy (IR), and detect the metal element content through X-ray fluorescence spectroscopy (XRF).
Equipment status assessment
Check sealing: Confirm that there are no leaks in the kettle body, mixing shaft, valves, and other parts to prevent cleaning solution from seeping into the motor or bearings.
Assess dirt thickness: Measure the residual thickness using an endoscope or ultrasonic thickness gauge. If it exceeds 5mm, mechanical cleaning should be prioritized.
Confirm material compatibility: The material of the kettle body (such as stainless steel 316L, Hastelloy) should be compatible with the cleaning agent to avoid corrosion.
2、 Cleaning method selection: chemical cleaning vs physical cleaning
Choose a suitable cleaning solution based on the type of residue and equipment conditions:
1. Chemical cleaning method
Applicable scenarios: Polymer and catalyst residues, dirt thickness<3mm.
Common cleaning agents:
Alkaline cleaning agent (such as NaOH solution): dissolves acidic polymers such as polyester and polyamide, with a concentration of 5% -10%, and a temperature of 80-100 ° C.
Acidic cleaning agents (such as HNO ∝+HF mixture): To remove inorganic salts and metal oxides, the concentration must be strictly controlled (<5%) to avoid corrosion.
Solvent based cleaning agents (such as xylene, NMP): dissolve polyolefin residues, but are flammable and highly toxic, and should be used in a closed system.
Operation points:
Circulating cleaning: By using a bottom circulation pump to make the cleaning agent flow, the cleaning efficiency is improved.
Segmented heating: gradually raise the temperature from room temperature to the optimal reaction temperature of the cleaning agent (such as alkaline cleaning agents divided into three stages of 30 ° C → 60 ° C → 90 ° C).
PH monitoring: Real time detection of the pH value of the cleaning solution. Acidic cleaning agents need to maintain a pH<2, while alkaline cleaning agents need to maintain a pH>12.
2. Physical cleaning method
Applicable scenarios: carbides, hard dirt, or residues after chemical cleaning.
Common techniques:
High pressure water jet cleaning: pressure of 150-300MPa, water flow rate of 20-50L/min, equipped with a rotating nozzle to cover the dead corners of the kettle body.
Dry ice blasting cleaning: using -78 ° C dry ice particles to impact dirt, suitable for heat sensitive equipment (such as PTFE lined kettles).
Ultrasonic cleaning: frequency 20-40kHz, power density 0.5-1W/cm ², suitable for local cleaning of small components such as agitator blades.
Operation points:
Distance control: The high-pressure water jet nozzle should be 50-100mm away from the kettle wall to avoid direct impact and metal fatigue.
Angle adjustment: Dry ice blasting needs to impact dirt at a 45 ° angle and use shear force to peel off sediment.
Time optimization: Ultrasonic cleaning should not exceed 30 minutes per cycle to prevent equipment overheating.
3、 Standardized cleaning process (taking chemical cleaning as an example)
preprocessing
Empty the material from the kettle and replace it with nitrogen until the oxygen content is less than 2%.
Disassemble detachable components (such as agitator blades and thermometer sleeves) and clean them separately.
First cleaning (alkaline cycle)
Prepare a 5% NaOH solution and inject it into the kettle until the volume reaches 80%.
Start the circulation pump, raise the temperature to 90 ° C, and maintain it for 6-8 hours.
Discharge waste liquid and rinse with deionized water until pH=7.
Second cleaning (acid descaling)
Inject a mixture of 3% HNO ∝+1% HF and circulate for 2-4 hours at a temperature of 50 ° C.
Focus on cleaning the bottom of the kettle and the root of the stirring shaft, as inorganic salts are prone to accumulate here.
Final rinsing and drying
Rinse with deionized water until the conductivity is less than 10 μ S/cm.
Dry with hot nitrogen gas (120 ° C) for 2 hours to avoid corrosion caused by residual moisture.
Acceptance Criteria
Visual inspection: There is no visible residue on the kettle wall, and it appears metallic in color.
Wipe test: Use a white cotton cloth to wipe the kettle wall, and the cotton cloth should be free of color spots.
Particle size detection: Take a drainage sample from the bottom of the kettle, with a particle diameter of<100 μ m.
4、 Key points of safety control
personal protection
Operators are required to wear gas masks (for organic solvents), acid and alkali resistant gloves, and goggles.
Before entering the kettle for cleaning, oxygen content testing (>19.5%) and toxic gas analysis (such as CO<20ppm) are required.
Equipment protection
Before cleaning, disconnect the motor power supply and hang a "Do Not Close" sign.
Isolate and protect sensitive components (such as pressure sensors) to prevent the intrusion of cleaning solution.
emergency response
Leakage of acidic cleaning solution: Immediately neutralize with sodium bicarbonate and collect the waste liquid in a dedicated container.
Personnel contact with cleaning agents: For skin contact, rinse with plenty of water for 15 minutes. For eye contact, seek medical attention immediately.
5、 Suggestions for optimizing cleaning effectiveness
Establish a cleaning database: record the type of residue, cleaning agent formula, and time parameters for each cleaning, and optimize subsequent plans.
Adopting composite cleaning: first, high-pressure water jet is used to remove large dirt, and then chemical cleaning is used to dissolve small residues, increasing efficiency by 40%.
Regular maintenance: Conduct a deep cleaning every 200 batches to avoid the accumulation of dirt and shorten the lifespan of the equipment.
By scientifically selecting cleaning methods, strictly following operating procedures, and strengthening safety control, significant improvements can be madeHigh pressure polymerization reactorThe cleaning efficiency ensures the long-term stable operation of the equipment.