The thermal stabilities of four kraft black liquors were determined by measuring the change in viscosity during time exposed to temperatures from 94.3 to 136.9 °C and for solids contents from 60.2 to 73.5% BLS (black liquor solids). The data were generated by using a Haake RV12 concentric cylinder viscometer designed to operate at temperatures as high as 300 °C and at pressures as high as 40 bars. The viscosities of the black liquors tested were shown to decrease with increased exposure time at elevated temperatures, and the rate of the change was a strong function of both the solids content and the exposure temperature. The extent of the decrease in viscosity ranged from 7.6 to 48% after 8 h at the exposure temperature. Chemical analysis indicated that the black liquors continued to undergo chemical reactions at the conditions tested and that the reactions probably involved the lignin.
A dual chamber capillary viscometer (DCCV) has been designed and constructed to measure steady shear viscosity of concentrated polymer solutions at temperatures above the solution normal boiling point. Projected equipment capabilities are as follows: Shear rate: 102≤γ̇≤104 s−1, Viscosity: 10−1≤η≤104 Pa s, Temperature: 300 ≤T≤520 K. Equipment design and results using Newtonian viscosity standards and various Newtonian polymer solutions are presented. Viscosity results determined with Newtonian standards are within ±5% or better of the reported values and two different concentrated polymer solutions and a paper coating (a suspension of clay in a starch-water solution) were used to test the equipment capabilities over wide ranges of shear rate, viscosity, and temperature. The ranges of equipment capabilities tested to date are Shear rate: 300≤γ≤5500 s−1, Viscosity: 0.12≤η≤7.5 Pa s, Temperature: 299≤T≤399 K.
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