Patent Application
20080011687
The phrase “silica/silicate” is intended to include silica, silicate, and mixtures thereof. The method of the invention is applicable to any aqueous system where silica/silicate scale must be inhibited, the most typical of which are cooling towers, boilers, aqueous sugar concentrate evaporated during sugar production, drive fluids used to enhance oil recovery, and a aqueous systems undergoing controlled temperature reduction in geothermal processes.
According to the invention, a scale inhibiting amount of an ester of (A) a carboxylic acid functional polymer obtained by polymerizing an ethylenically unsaturated carboxylic monomer or copolymerizing the ethylenically unsaturated carboxylic monomer with one or more additional ethylenically unsaturated monomers and (B) a hydroxyl functional polyether obtained by reacting an alkyl alcohol with one or more alkylene oxides. Since the carboxylic acid functional polymer will usually have more than one carboxyl group, most or all of the carboxyl groups will react with the terminal hydroxyl groups of the hydroxyl functional polyether molecules.
The esters used in this invention can be prepared by the method described in French patent 2776285 A1, Guicquero, et al., published Sep. 24, 1999, which disclosed these esters as base catalyzed partial esters obtained by reacting a polycarboxylic acid obtained by polymerizing an unsaturated acid and a polyether containing a free hydroxyl group capable of reacting with one carboxylic function of the carboxylic acid, used as dispersants for cement compositions and mineral particle aqueous suspensions. The French patent 2776285 A1 is hereby incorporated by reference for its teachings of preparation of the partial esters.
The following examples are presented to illustrate a few embodiments of the invention. All parts and percentages are by weight unless otherwise indicated.
A static test was first employed to demonstrate the improved property of silica/silicate scale inhibition of the esters of the present invention compared with a control and other scale inhibitors. The control had no silica scale inhibitor. The comparative silica scale inhibitors were Acumer 5000 and Good-rite K-XP212. A high silica solution was prepared by mixing deionized water, sodium silicate solution (a) and a calcium chloride and magnesium chloride solution (b), which were prepared from Analytical Reagent grade chemicals (unless otherwise stated):
(a) Sodium Silicate Solution
The solution as such contained 10,000 ppm as silica (SiO2)
(b) Calcium/Magnesium Solution
The solution as such contained 8,000 ppm of calcium (Ca) and 4,860 ppm of magnesium (Mg).
The final composition of the test solutions was as follows:
Sodium silicate solution (a) was added to 183 mL of deionized water (in a stirred plastic beaker. Then 2 mL of inhibitor or 2 mL of water (for the blank) was added. The pH was adjusted to 7 with diluted hydrochloric acid and sodium hydroxide. Then solution (b) was added and the pH was adjusted to 8 or 9. The final test solution was rapidly transferred into a plastic bottle and placed in an oven at 40° C. Samples of solution were taken over time and filtered through a 0.2 μm filter before being analyzed for silica in solution according to the standard Hach method.
Performance, with respect to silica/silicate inhibition, was also determined by use of the formula: % Inhibition=[Si(inhib)−Si(blank)]/[Si(initial)−Si(blank)]×100
While the invention has been described and illustrated in detail herein, various alternatives and modifications should become readily apparent to those skilled in this art without departing from the spirit and scope of the invention.
