Polyether Polyol Production Process

The main raw materials for the production of polyether polyols are starting agents, epoxides, catalysts, catalyst removers or deactivators, and post-treatment agents.

The starting agents are low molecular compounds containing hydroxyl groups and low molecular compounds containing amino groups or hydroxyl and amino groups. Commonly used are propylene glycol, glycerol, trimethylolpropane, PTMEG, ethylenediamine pentaerythritol, xylitol, triethylenediamine, sorbitol, sucrose, bisphenol A, bisphenol S, tris(2-hydroxyethyl) isocyanate, toluenediamine, etc.; when using aromatic or heterocyclic polyol or polyamine starter, the above structure will be introduced into the polyether polyol structure, which can make the generated polyurethane material have better dimensional stability, and Heat and flame resistance. These starting agents include bisphenol A, bisphenol S, tris(2-hydroxyethyl) isocyanate, toluenediamine, etc. The variation of starting agent species can synthesize polyether polyol with different functionalities, different chemical structures and different functions to meet the diverse changes and performance requirements of polyurethane products.

Epoxides mainly use organic oxides and furan-like cyclic compounds, including propylene oxide, ethylene oxide, epichlorohydrin and tetrahydrofuran.

There are three types of catalysts, i.e. anionic, cationic and metal complexed. Commonly used in the polyurethane industry are alkali metal hydroxides for anionic catalysts and Lewis acids for cationic catalysts. The former is used for the preparation of low molecular weight common polyether polyols, while the latter is used for the preparation of high molecular weight polyether polyols and tetrahydrofuran ring-opening co-polymerization of special polyether polyols. Metal-based complexation catalysts are used for the synthesis of ultra-high molecular weight polyether polyols. Polyether polyols for polyurethane are synthesized with only a few applications, the most commonly used being potassium hydroxide.

The selection of different catalysts determines the different process routes used to produce polyether polyols. At present, there are three main types of catalysts that are most used by polyether polyol producers.

(1) Alkali metal, hydroxide or alkaline earth metal (hydrogen) oxide represented by KOH

Due to the residual alkali metal or alkaline earth metal ions affect the production of PU and product performance, the process requires maximum removal of metal ions, energy and material consumption in the production process, the yield is not ideal production of high drilling degree of polyether polyol for hard foam when energy and material consumption is particularly high. But the synthesis process is mature, catalytic production of soft foam, hard foam, highly reactive polyether polyol with good storage stability, good compatibility stability in the combination of polyether, the combination of material foaming performance interference is small and other advantages, most companies are still using.

(2) Organic amines represented by dimethylamine

Dimethylamine catalysis is mainly used in the synthesis of polyether polyol for hard foam. This process has the advantages of no catalyst removal, low energy consumption, and less or no amine catalyst can be added to the PU foam formulation. However, because a certain amount of amine involved in the reaction is not removed, the storage stability of the produced polyether polyol is poor, and the foam stability is also poor, thus limiting the scope of use and time frame of its composites.

(3) Multi-component high-activity bimetallic cyanide complexation catalysts (MMC)

Unlike the above 2 types of catalysts, the bimetallic cyanide complexation catalyst synthesizes polyether polyol, and the ring-opening polymerization reaction of epoxide has an obvious induction period, but due to its extremely high activity, the production cycle can be greatly shortened, and the purpose of energy expansion and consumption reduction can be achieved without increasing equipment. The process produces polyether polyol products without post-treatment in most cases, which improves both production efficiency and product yield, and also produces low unsaturation products with high relative molecular mass. These polyether polyols are mostly used in the CASE polyether polyols field.

These three types of catalyst-catalyzed processes for the synthesis of polyether polyols vary in their scope of application and product performance. In addition, there are many manufacturers of polyether polyols, many of which have dedicated production technologies. The development of polyether polyol production and application technologies are inextricably linked, and their patent holders often bundle development and promotion applications. There are many quality control indexes for polyether polyol products, but even if the measured values of the indexes are similar for different manufacturers' products, their user processing and application processes are different, and they need to use their own application technologies to ensure the quality of the manufactured products with polyether polyol as the base material.

The typical process flow of polyether polyol is mainly composed of three processes, namely, polymerization process, neutralization process and purification process.

(1) Polymerization process

Two-stage polymerization process is used for the production of polyether polyols. The first stage polymerization is based on glycerol as the starting agent and propylene oxide as the raw material, and the continuous polymerization reaction is carried out under the action of catalyst to produce the lower molecular weight polyol intermediate. The second stage polymerization is based on the monomer propylene oxide (or propylene oxide/ethane oxide mixture) and polyol intermediates as raw materials, and the intermittent polymerization reaction is carried out under the action of catalyst to produce high molecular weight polyether polyol.

Production of low molecular weight polyol intermediates, are used in continuous polymerization process; and the production of polyether polyol using intermittent polymerization process.

Polymerization kettle has two types, one type is with stirring polymerization kettle; the other type is with jet distribution tube polymerization kettle.

(2) Neutralization process

Phosphoric acid is generally used as a neutralizing agent to neutralize the alkali in the polymerization reaction solution, and the phosphate made can be used as agricultural fertilizer; hydrochloric acid can also be used as a neutralizing agent. However, the former is widely used and has outstanding advantages.

(3) Purification process

The water in the crude polyol is removed by two methods. One is to continuously pump the crude polyol from the intermediate storage tank into the purification process, remove the saline phase in the agglomerator, and the organic phase of polyol from the chromatography will enter the refining tower to further remove water. The other is dehydration by vacuum in the neutralization tank, and the dehydrated neutralized liquid is filtered to get polyether polyol filter residue. The polyether polyol filter residue is mixed with water extraction and stirring, and after the residue is layered, the aqueous polyether polyol phase is pumped back to the neutralization tank intermittently, and the filter residue is sent outside the boundary area for incineration.

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