Acidulation of tall oil soap with phosphoric acid

The use of H 3 PO 4 instead of H 2 SO 4 affords a novel approach to eliminate the input of sulphur into the pulp mill's chemical recovery system. Laboratory soap acidulation experiments have shown the availability of H 3 PO 4 soap acidulation approach,as providing the avoidance of adding about 27 kg sulphur (as S) per tonne of soap into the chemical recovery system of the kraft pulp mill. Under prevailing pricing of H 3 PO 4 and NaOH, the phosphoric acid approach would have a higher chemical cost than the sulphuric acid approach, by a margin of about US$8 per tonne of soap processed. Small changes in the commodity pricing of H 3 PO 4 and/or NaOH would render the H 3 PO 4 soap acidulation method to be economically competitive.