What's the manufacturing process and application of polyether polyols?
Polyether Polyols Production:
In the polyurethane industry, polyether polyols are mainly used for polyurethane foam plastics, including polyoxypropylene polyols and polytetramethylene ether glycols.
1. Main Raw Materials:
- Organic oxides and cyclic compounds such as furans;
- Initiators;
- Catalysts.
Examples of organic oxides and cyclic compounds include epichlorohydrin, epichloropropane, epoxy propane, tetrahydrofuran, etc.
Initiators are low molecular weight compounds containing hydroxyl, amino, or both hydroxyl and amino groups, such as propylene glycol, glycerol, trimethylolpropane, ethylenediamine, pentaerythritol, xylitol, sucrose, bisphenol A, bisphenol S, tris(2-hydroxyethyl) isocyanurate, and methylenedianiline.
Catalysts are divided into anionic, cationic, and metal complex types. Commonly used catalysts in the polyurethane industry include alkali metal hydroxides as anionic catalysts and Lewis acids as cationic catalysts. Potassium hydroxide is commonly used.
2. Synthesis:
- Pretreatment of Raw Materials: Initiators and catalysts are usually pre-mixed to form alkoxide, which is then added to the reaction vessel after vacuum dehydration.
- Ring-opening Polymerization Reaction: This reaction is exothermic and requires timely removal of reaction heat to prevent oxidation reactions. Dry nitrogen gas is introduced before the reaction to prevent oxidation.
- Post-treatment Process: Mainly includes neutralization, adsorption, dehydration, filtration, distillation, etc.
Types of Common Polyether Polyols:
1. Polyoxypropylene Glycol:
- Also known as polypropylene glycol (PPG).
- Prepared in glass-lined or stainless steel reaction vessels.
- Starting materials (1,2-propylene glycol or 1,2-diol) and catalyst (potassium hydroxide) mixture is added to the catalyst preparation vessel, heated to 80-100°C, and the solvent in the catalyst is removed under vacuum to promote alcoholysis. Then the catalyst is transferred to the reaction vessel, heated to 90-120°C, and propylene oxide is added to maintain a pressure of 0.07-0.35 MPa. Continuous polymerization of propylene oxide occurs at this temperature and pressure until a certain molecular weight is reached. After residual propylene oxide is evaporated, the polyether mixture is transferred to a neutralization vessel, neutralized with acidic substances, and then filtered, refined, and stabilized to obtain the product.
2. Polytetramethylene Ether Glycol (PTMEG):
- Polymerized from tetrahydrofuran in the presence of a cationic catalyst.
- Production process: Tetrahydrofuran is added to the reaction vessel, cooled to below -5°C, and sulfonic acid catalyst is added dropwise under vigorous stirring. After adding a measured amount of water, the temperature is raised to 70-90°C, unreacted tetrahydrofuran is distilled off, and after settling, neutralization, filtration, and vacuum pumping, polytetramethylene ether glycol is obtained.
3. Tetrahydrofuran-Oxide Propylene Copolymer Glycol:
- Copolymerized from tetrahydrofuran and propylene oxide under the catalysis of Lewis acids.
- Produced through neutralization, water washing, dehydration, and filtration.
4. Special Polyether Polyols:
- Includes reactive polyether polyols, flame-retardant polyether polyols, grafted polyether polyols, polytetramethylene glycols, and heterocyclic modified polyether polyols.
Storage and Toxicity:
Polyether polyols containers can be made of steel, aluminum, polyethylene, or polypropylene. Storage temperature should not exceed 70°C, and containers are recommended to be filled with nitrogen gas to prevent moisture absorption and oxidation. Polyether polyols are not subject to flammable liquid storage regulations but should be kept away from groundwater or surface water as they are not easily biodegradable.
General neutral polyether polyols have negligible toxicity when ingested orally or in contact with skin, eyes, or mucous membranes, so personal protective measures are not necessary during use. However, amine-based polyether polyols may irritate the skin and eyes due to their alkalinity, so safety glasses and gloves should be worn during operation.