| 摘要 |
An improved displacement washing process for recovering processing chemicals from a porous medium, particularly wood pulp, is described. The effective mobility of a displacing solution, typically a more dilute solution of the chemical sought to be recovered, is reduced such that it is less than the mobility of the solution to be recovered. In a pulp mill washing system, consumption of wash water may be reduced 0.6 tons of water per ton of pulp produced without reducing chemical recovery. Conversely, chemical effluent from the washer could be reduced by 50% without increasing wash water requirement. Mobility is proportional to the permeability of the porous medium with respect to the solution of interest and inversely proportional to the viscosity of that solution. Mobility of the wash solution relative to the solution to be displaced is preferrably reduced by the addition of a soluble, high molecular weight polymer, greater than 106, until the ratio of the mobility of the wash solution to that of the chemical rich solution is in the range of 0.05-2.0, preferably within the range of 0.2-1. As examples, copolymers of acrylamide and acrylic acid, carboxypolymethylene, polyacrylic acid and deacetylated chitin have been found to be effective in reducing mobility. The presence of 6-10 ppm of a copolymer of acrylamide and acrylic acid of MW greater than 106 in the wash solution of a brownstock washer can double the efficiency of the washer.
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