Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Patent
1989-06-22
1991-04-23
Spear, Frank
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
210651, 210652, 2101952, 210259, B01D 6120
Patent
active
050097890
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for separation of synthetic water soluble polymers by a filtration process into two solutions, one of which is recirculated for re-polymerization. The invention also relates to a plant comprising a polymerization reactor and a unit for separation of produced synthetic water soluble polymers.
Natural polymers such as proteins, latex of natural rubber, cellulose etc often have very well defined molecular weights. In contrast to this synthetic polymers usually have a broad molecular weight distribution and in many cases only the fractions containing polymer of high molecular weight have the for the intended use desired favourable properties. It is not always possible to control polymer synthesis with available technology in order to obtain only the desired high molecular weight fractions. In addition to undesired low molecular weight polymer and byproducts, unreacted monomers are also often present in the synthesized resins.
The present invention offers a method for separation of synthetic water soluble polymers to obtain the desired high molecular weight fractions with advantageous properties and the method further includes recirculation of the low molecular weight fraction to a polymerization step.
The molecular weight of synthetic polymers depends on several variables such as monomers, type of polymer reaction, reaction time and temperature etc. For polymers in solution the molecular weight distribution nearly always has the form of a curve. The curve will of course vary from polymer to polymer and may have one or more peaks. It has, for example, been found that water soluble urea-formaldehyde resins have a molecular weight distribution with two clearly defined and specific peaks. According to the present method the desired high molecular weight fraction of such a resin can be separated from the undesired ones which can be re-used.
The method of the present invention is generally applicable to separation of desired high molecular weight fractions of any water soluble synthetic resin. However, the method is particularly advantageous for water soluble resins used in paper production and the following discussion will thus be directed, although not limited, to such resins.
Water soluble resins used in paper production are for example urea-formaldehyde resins, melamine-formaldehyde resins and polyamidoamine-epichlorohydrin resins. These resins are used as wet strength agents for paper and it has been found that the effect on the wet strength is obtained only by the high molecular weight fraction. The low molecular weight fraction is not retained in the paper, but circulated in the closed white water system. For formaldehyde based resins the high temperature of the water results in hydrolysis of this low molecular weight fraction and release of free formaldehyde which may cause environmental problems. Polyamidoamine-epichlorohydrin resins have a higher molecular weight than the formaldehyde based resins and the low molecular weight fraction of this resin also has a lower effect on the wet strength. Further, these resins contain monomeric chlorinated byproducts which also may cause environmental problems.
When the above described resins are treated according to the method of the invention solutions of high molecular weight polymers are obtained which give a very good wet strength effect and which also give a considerable reduction of formaldehyde and other non-desired compounds in the water and air at paper mills.
Since urea-formaldehyde resins are the predominant wet strength resins and also those which tend to cause the severest environmental problems their upgrading according to the invention is of particular importance and these resins will thus be discussed more in detail. As stated above, free formaldehyde is released from urea-formaldehyde resins at paper production due to hydrolysis. Further, the utilized original resins always contain free formaldehyde as well and this is accumulated and circulated in the white water system. Since all concentrated solutions obtai
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patent: 3565256 (1971-02-01), Coeffler
patent: 3567031 (1971-03-01), Loeffler
patent: 4159251 (1979-06-01), Wrasidlo et al.
patent: 4308121 (1981-12-01), Hazen
patent: 4340702 (1982-07-01), Huddleston, Jr. et al.
Chemical Abstracts 103:124428k.
Chemical Abstracts 103:23285f.
Helmer Ulla K. E.
Stensio Karl-Erland M.
EKA Nobel
Philpitt Fred
Spear Frank
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