| Double metal cyanide complex catalysts (DMC) are dispersing in low unsaturated polyether polyol product (PPG), the residual catalyst catalyzes allophanate formation when a polyether polyol is reacted with an isocyanate and also promotes the formation of undesirable volatile by-products during storage, which can have a bad effect on the properties of polyurethane products. Using chemical method, adsorption method and membrane separation method, an investigation about removing DMC catalyst from low unsaturated polyether polyol was done here, and the effect, process, model were explored, which can provide reliable method and craft for the purification of polyether polyols.Firstly, the process of separation Zn2+, Co2+ from polyether polyols by chemical method was investigated, using strong alkali solution of KOH and NH3/NH4Cl buffer solution as the treatment agent, affter treating with KOH the Zn2+ removal rate is 64.4%, the Co2+ removal rate is 90.8%, and after treating with NH3/NH4Cl, the Zn2+ removal rate is 82.3%, the Co2+ removal rate is 51.1%. The effect of strong alkali treatment method is comparatively good. When the mass ratio of PPG:KOH was 10:1, and 1.6wt.% of magnesium silicate based on the amount of polyol was added, the treated polyol indicated:Zn2+, Co2+<1.0μg·g-1, K+< 10μg·g.Secondly, the process of separation Zn2+, Co2+ from polyether polyols by adsorption was investigated, in which Zn2+, Co2+were removed from the polyether polyols. The experiment show that the optimum sort of adsorbents was chelating fiber and activated clay as composite adsorbent, and the proportion to the mass ratio was 1:1, and the removal rate of Zn2+, Co2+ were 97.1% and 74.2%, respectively. The adsorption mechanism, the optimum adsorption conditions of chelating fiber adsorbent and the reusing tests were studied. The results showed that the optimal conditions were obtained as:the amount of chelating fiber added was 3.33 parts by weight per each 100 parts by weight of the polyether polyols treated and the polyether polyols were adsorbed for 40 min at 60℃, in which conditons the removal rate of Zn2+, Co2+ were the highest,77.1% and 40.5%, respectively. The chelating fiber was reused 4 times, and the removal rate of Zn2+, Co2+ were 74.1% and 26.4%, yet. Using IR, XRD. SEM characterization methods the result that the chelating fiber had better adsorption selectivity was analyzed and obtained.Finally, flat membrane ultrafiltration was applied to purification of low unsaturated degree polyether polyols. which flat membrane prepared from polyethersulphone(PES). Crude polyether polyols were used as polyols/hexane miscella in a 1:1 proportion. The separation effect was very good, and at the most of testing time the intercepting rate of Zn-+ Co2+ were more than 90% and the content of Zn2+, Co2+ were less than 1.0μg·g-1. The reject was analysed that it contained DMC catalysts using IR. The optimal operating conditions of ultrafiltration were determined:molecular weight cut-off 150kDa, diluting by hexane in a 1:1 proportion, operating pressure 0.5MPa, flow speed 40L·h-1. The contaminated membrane was ultrasonic cleaned by means of deionized water,2%o sodium hydroxide solution, and hexane, respectively. The results showed that good effect can be obtained by 2%o sodium hydroxide solution, the permeate flux can be recovered to 66.4%. Based on this experiment data, using a mathematic resistance model describing membrane flux as a function of pressure and flow rate was established, and the model parameters were got by fitting the experimental data. The resullts showed that the predicted results of membrane flux as a function were in good agreement with the experimental results well, with a relative error varying between 0.13%～14.02%. Using this model, flux change can be predicted and the basis was prvided for designing the industrial equipment. |
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