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Since their commercial introduction in the early 1940s, silicone defoamers have been continuously evolving. There has been significant interest in their effectiveness as a defoamer in brownstock washing operations, but there continue to be concerns with issues of silicone carryover. New technologies that use state-of-the-art silicone compounds and emulsification packages along with improvements in manufacturing have led to the next generation of both silicone water-based emulsions and concentrates defoamers. Silicones provide several important physical characteristics used for pulp washing, including excellent application, wet-out, thermal stability and broad compatibility with a wide range of other additives. Typically effective at far lower concentrations than competing mineral oil-based antifoams, silicone usage levels can range from 1/3 to 1/30 of the active ingredient volume required from oil-based additives. Improved washing efficiencies have translated into a more consistent cleaner pulp to the kraft machines.

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									                                                                                                                          defoaming
                                                                                                                    technology




By ALAN B. ROSENBERG

A new dispersible and rinse-able silicone-based brownstock
defoamer has been developed by Buckman


REDUCE THE CARRYOVER


                              S
                                       ince their commercial introduction in the early      products are extremely rinse-able, and will go with the
                                       1940s, silicone defoamers have been continuously     aqueous phase of black liquor, which will prevent down-
                                       evolving. There has been significant interest in     stream silicone carryover and buildup.
                              their effectiveness as a defoamer in brownstock washing            A review of more than 20 different pulps, all utiliz-
                              operations, but there continue to be concerns with issues     ing silicone defoamers, was done to determine silicone
                              of silicone carryover.                                        carryover. It was found that these pulps contained
                                   The first silicone defoamers were based on polydim-      between 2-30 ppm silicone and averaged 11 ppm in
                              ethylsiloxane (silicone fluid or oil) dispersed in water or   downstream samples. Ten of these applications were
                              light oil. Silicone fluids worked well but tended to cause    replaced by a new silicone technology developed by
                              spots and runnability concerns in papermaking. In 1963        Buckman that uses next generation delivery packages
                              the first anti-foams with hydrophobic particles (hydro-       and advanced manufacturing techniques. The silicone
                              phobic silica) in oil were patented. The next evolution in    levels for these applications were reduced 50-85%. This
                              silicone defoamers was in the early 1970s when hydro-         does not say that the levels of silicone are completely
                              phobic waxes like ethylene bis stearamide dispersed in        gone but that the amounts have been dramatically
                              oils were developed. These types of defoamers were very       reduced and are not creating any downstream deposit
                              effective, but the oil crisis during the middle 1970s made    issues. This new chemistry has proven extremely cost
                              these too expensive and resulted in a push for reduc-         efficient toward all wood species and all type of wash-
                              tion of the oil content. The solution to this problem was     ers. Since being introduced, it has helped several cus-
                              simple: just add water. This led to the water-extended        tomers improve their washing efficiencies and reduce
                              (water in oil emulsion) and water-based (oil in water         their operational costs.
                              emulsion) defoamers.
                                   The development of silicone-based defoamers has          SILICONE BACKGROUND
                              continued using different emulsifiers and modified
                              silicone oils. During the last 15 years, silicone emulsion    Silicones provide several important physical character-
                              defoamers that caused less surface disturbances have          istics used for pulp washing, including excellent applica-
                              been used for pulping with some success. These products       tion, wet-out, thermal stability, and broad compatibility
                              provided better washing, reduced biological oxygen            with a wide range of other additives. For example, silicone
                              demand (BOD) in effluent, and reduced deposits. The one       polyethers are highly surface-active silicone materials
                              negative was that many mills still experienced some level     that can be used in pulp washing formulations as effec-
                              of silicone deposition downstream of the washers that         tive surfactants and, as a result of their surface-active
                
								
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