| Abstract: | A laboratory investigation of the possibilities for the reduction of odor from Kraft mill stack gases by lignin precipitation from oxidized Kraft black liquor and subsequent pyrolysis of the filtrate solids has been carried out. Samples of oxidized black liquor were acidified with sulphuric acid and the lignin precipitate extracted. The extraction scheme indicates that > 90% w/w of the sodium in the original black liquor samples can be retained in the filtrate after lignin removal at final pH 2.0. The evaporated filtrate solids containing the bulk of the black liquor inorganic chemicals were pyrolyzed and the evolved hydrogen sulphide, methyl mercaptan and dimethyl sulphide monitored by gas-chromatography. Gas-chromatograph traces displaying the increase and decrease of methyl mercaptant evolution levels on pyrolysis of the filtrate solids to increasing temperatures are shown. A thermogravimetric technique was used to investigate the decomposition rates of the extracted samples and these rates correlated with the levels of sulphur gases evolved on pyrolysis. Heats of combustion were determined by bomb calorimetry. Sulphur losses from the filtrate solids and the Kraft black liquor total solids are compared. The results show a significant decrease in the evolution of organo sulphur gases from samples of ligninextracted black liquor solids in comparison with original total solids samples, an increase in the level of hydrogen sulphide evolution however, presents a problem. |
