Patent ID: 7172677

Claim:
A method for inhibiting calcium salt scale formation in chemical pulping processes comprising adding an effective scale inhibiting amount of at least one phosphonate to the alkaline aqueous mixture in the digester of said chemical pulping process, wherein said at least one phosphonate is selected from compounds having the formula: X 2 NCH 2 PO 3 M 2 (I), compounds having the formula: amine oxides of phosphonates of formula (I), or mixtures thereof; wherein M is independently selected from hydrogen, alkali metal, alkaline earth metal or ammonium, X is independently selected from H, R, or â€”CH 2 PO 3 M 2 wherein R is an alkyl group or â€”NX 2 substituted alkyl group having 2 to 6 carbon atoms, Râ€² is an alkyl group having 1 to 17 carbon atoms and Râ€² is optionally branched and optionally unsaturated, and Y is selected from â€”PO 3 M 2 , H or Râ€²; with the proviso that: a) said scale inhibiting composition does not contain a nonionic surfactant, and b) that when said phosphonate is only N(CH 2 PO 3 M 2 ) 3 , the amount of said phosphonate on an active acid basis in the range of from about 500 to about 1000 ppm based on the weight of total liquor charged to said digester.