Liquid purification or separation – Processes – Ion exchange or selective sorption
Patent
1995-07-07
1998-07-07
Cintins, Ivars
Liquid purification or separation
Processes
Ion exchange or selective sorption
210694, 210797, B01D 1500
Patent
active
057763470
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for reducing the content of organic solvent in cellulose-reactive hydrophobing agents and use of the products obtained. More specifically, the present invention relates to dispersing a hydrophobing agent in water and thereafter contacting it with a sorbent or a gas. By the method of the invention the solvent is transferred from the hydrophobing agent to the aqueous phase and then from the aqueous phase to the sorbent or the gas. The aqueous dispersions containing cellulose-reactive hydrophobing agents prepared according to the invention are used for hydrophobation of paper.
Many kinds of paper are contacted with liquids, primarily aqueous solutions or water vapour. Since the fibres are water-absorbent (hydrophilic), they will absorb water, which reduces the paper strength. This effect can be counteracted by coating the fibres with a water-repellent (hydrophobic) substance, which reduces the possibility of liquid penetrating into the finally-dried web or sheet. Examples of hydrophobated papers are liquid carton board, fine paper and kraft liner.
Hydrophobation is generally performed by adding the hydrophobing agent to the suspension of fibres and water (the stock), so-called stock hydrophobation. To permit rapid and uniform admixture to the stock, the hydrophobing agent is normally dispersed in water.
Especially effective hydrophobing agents are cellulose-reactive hydrophobing agents, since these agents are bonded covalently and hence more strongly to the cellulose fibres than other hydrophobing agents. Thus, alkyl ketene dimers (AKD) are often used to make liquid carton board lactic acid resistant.
In the preparation of an alkyl ketene dimer, organic solvents are used, among other things, for accelerating dimerisation. A portion of the solvents may remain in the alkyl ketene dimer, which may then cause problems before, during or after the use of the alkyl ketene dimer in aqueous dispersions in the paper mills. When storing dispersions, the organic solvents may volatilize and impair the working environment. During the making of hydrophobated paper, the major portion of the residual organic solvents will be transferred to the white water system. The proportion of organic solvent accompanying the stock out on to the wire of the papermaking machine will evaporate, primarily in the drying section, or accompany the finished paper. In the latter case, problems may arise when using the hydrophobic paper as packaging material for solid or liquid foods, tobacco goods and medicines.
It is known to use thermal methods as an attempt to remove the organic solvent in connection with the synthesis. Heating increases the volatility of the solvent as well as the solubility in the melted hydrophobing agent. Cooling reduces the volatility of the solvent as well as the solubility in the melted hydrophobing agent. These opposite effects have made it most difficult to reduce the content of solvent effectively.
According to the present invention there is provided a method for reducing the content of organic solvent in cellulose-reactive hydrophobing agents. Hereby there is achieved a reduction in the proportion of solvent that can be transferred to paper or board, when hydrophobating such materials. Hereby the formation of bonds between the cellulose chains and the cellulose-reactive hydrophobing agent is also enhanced.
The invention thus relates to a method for reducing the content of organic solvent in cellulose-reactive hydrophobing agents, as defined in the claims. According to the inventive method a cellulose-reactive hydrophobing agent and an aqueous dispersion thereof can be prepared where the total content of organic solvent in the hydrophobing agent and the dispersion, respectively, is less than about 0.1% by weight. More specifically, the hydrophobing agent is an alkyl ketene dimer and the solvent is toluene.
The aqueous dispersions containing cellulose-reactive hydrophobing agents prepared according to the inventive method are used for hydrophobation of paper. By the present me
REFERENCES:
patent: 2369919 (1945-10-01), Sauer
patent: 4522686 (1985-06-01), Dumas
Lindgren Erik
Magnusson Jeppe
Cintins Ivars
Eka Nobel AB
Mancini Ralph J.
Morris Louis A.
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