A method of preparing modified heteropolysaccharides in buffered brine and their use for oil recovery

Claim 1

A process for producing a heteropolysaccharide product stabilized against loss of pyruvate content, free of cell debris and having improved filterability which comprises : (a) preparing an aqueous solution which contains (i) from about 200 to about 30,000 parts per million by weight, of a heteropolysaccharide product produced by the bacterial fermentation of bacteria of the genus Xanthomonas, and (ii) at .least about 0.5 weight percent of at least one inorganic salt to obtain a saline heteropolysaccharide solution; (b) adding a buffer, said buffer being characterized by having a pH and a buffer capacity such that the saline heteropolysaccharide solution has an initial pH of about 6.5 to 10.0 and a pH of about 6.0 to 9.5 during heating; (c) heating said saline heteropolysaccharide solution to a temperature of at least about 100°C; . (d) maintaining said saline heteropolysaccharide solution at a temperature of at least about 100°Cj ( e ) maintaining said saline heteropolysaccharide at a pH of from about 6.0 to 9.5 during the heat treatment; and (f) removing or separating the proteinaceous materials and/or residual whole bacterial cells or other cell debris from the saline and heat-treated heteropolysaccharide product to thereby obtain a modified heteropolysaccharide capable of imparting a viscosity of at least 4.0 centipoises to an aqueous test solution containing 2 weight percent NaCl and 0.2 weight percent CaC1 2 when said modified heteropolysaccharide is added to said solution at a concentration of approximately 600 parts per million, by weight, as measured on a Brookfield viscosimeter with a UL adapter at 60 rpm at 25°C and said modified heteropolysaccharide is further capable of imparting a filterability such that more than 1000 ml of a different aqueous test solution containing 8.8 weight percent salt comprised of NaCl and CaCl 2 on a 10:1 weight ratio and approximately 600 parts per million concentration, by weight, of said modified heteropolysaccharide will pass without plugging through a Millipore filter having a diameter of 13 mm and a pore size of about 5 microns at a constant pressure drop of about 1.55 psig.