Preparation And Evaluation Of Polyether Modified Polysiloxane Defoamer

Flue-gas desulfurization systems(WFGD)are the most widely used in coal-fired power plants.The slurry foaming is a very common phenomenon in the absorber.The economical and effective way to solve this problem is to add appropriate defoamer which can quickly defoam and prohibit from foaming.Organosilicon defoamer and polyether modified polysiloxane defoamer are promising defoaming/antifoaming properties.Based on this,the detailed research was focused on getting the defoamers optimal formula and preparation method by the defoamers perfoemance evaluation.Firstly,in the paper an efficient organosilicon defoamer was prepared by an emulsification process with the silicone paste as the major component,the silicone paste was synthesized by the dimethyl silicone,fumed silica and vinyl-substituted MQ silicone resin,the Span60-Tween60 mixture as the emulsifying agent,and the hydroxypropyl methyl cellulose(HPMC)as the thickener.The effects of different component contents on the properties of the defoamer were investigated,to obtain the optimal defoamer composition and preparation method as follows: 21 wt% of the dimethyl silicone with a viscosity of 10 Pa·s,1.4 wt% of both fumed silica and vinyl-substituted MQ silicone resin,6.3 wt% of the mixed emulsifying agent with the HLB value of 10,and 0.5 wt% of the thickener.And then defoamer emulsion was shearing at 3000 r/min for 5 min.The results showed that the organosilicon defoamer was more promising defoaming/antifoaming properties than the commercial products,and moreover,it also had good centrifugal stability,thermostability and dilution stability.And then,polyether modified polysiloxane was synthesized to enhance performance of defoamer.The innovation methed of preparation of polyether modified polysiloxane was basd on hydrosilylation by the addition of low hydrogen content silicone and polyether F-6.The optimal experiment conditions were as follows: using 0.16% low hydrogen content silicone and polyether F-6 as raw material,the mol ratio of C=C and Si-H was 1:1.1,the catalyst concentration was 40 ?g/g,the optimal reaction temperature was 130 ? for 4 h,89.4% conversion of the Si-H was achieved.The polyether modified polysiloxane had clear yellow color and suitable viscosity.The product structure was characterized by FT-IR spectrum.Finally,excellent performance modified polysiloxane defoamer was made by adding polyether modified polysiloxane to the organosilicon defoamer.And the optimal mass fraction of polyether modified polysiloxane was 5%.At the same time,polyether modified polysiloxane could be used as a co-emulsifier to make the emulsification process easier.When the concentration of organosilicon defoamer's and of polyether modified polysiloxane defoamer's was 1.0 g/L,their surface tension values were 27.6 m N/m and 22.6 m N/m,respectively.The polyether modified polysiloxane defoamer's surface tension was lower,so that it had more efficient defoaming/antifoaming properties.Meanwhile two kinds of defoaming curves were formed by doing parallel experiments between organosilicon defoamer and polyether modified polysiloxane defoamer.Relative theoretical analysis upon this phenomenon was carried out.