GB783666A - Improvements in method of cleaning equipment fouled with latex coagulum - Google Patents

Abstract

783,666. Cleaning rubber latex equipment: rubber solvents. UNITED STATES RUBBER CO. Nov. 28, 1955 [Feb. 17, 1955], No. 33985/55. Class 70. Equipment used for handling or processing rubber latex and which has become coated with a rubber coagulum, is cleaned by subjecting the coagulum to the action of a rubber solvent containing a small amount of a prooxidant softener for rubber in the presence of available oxygen, at an elevated temperature. In the apparatus shown, rubber latex containing ammonia as a preservative flows from a source 11 down a tower 10 against an upward current of moisture-saturated air or other suitable gas flowing via pipes 12 and 13, said air or gas sweeping the ammonia out of the latex so that deammoniated latex may be stored in a vessel 15. In due course two distinct forms of rubber are deposited in the tower, one of which is of soft buttery consistency and is easily removable and the other of which is of tough, stringy agglomerates that are difficult to remove. At frequent intervals the process is stopped and the buttery deposits in the tower 10 are removed by introducing a dilute aqueous solution of an aqueous alkali through an inlet 18 ; and delivering it by a pump 19 through a pipe 20 and heater 26 to the top of the tower 10. The alkali flows down the tower to loosen and dissolve said buttery deposits, the solution being then recirculated or discharged to waste through the line 21. At less frequent intervals, the more difficult to remove coagulum of rubber is treated with a chemical softener for rubber contained in a rubber solvent, the treatment being made in the presence of available oxygen and preferably at an elevated temperature as well as with mechanical agitation. The softener may be a pre-oxidant or an oxidation catalyst such as one of the mercaptans of which phenylhydrazine is preferred. The amount of softener used is from about 0À5 to about 5 per cent on the weight of the solvent. The solvents employable include all solvents for rubber and their mixtures. A trace of oxygen is supplied in the form of air or gaseous oxygen or in the form of a peroxy compound. The temperature should preferably be between 40‹ and 200‹C. Mechanical agitation may be caused by (a) refluxing the solution in which case the reflux leaches the coagulum, or (b) filling the tower with the solution and bubbling in air from the bottom of the tower, or (c) pumping the solution continuously from the bottom to the top of the tower, and (d) stirring, in the case of autoclaves or tanks. When the volume of cleaning liquid is large, the system preferably includes a solution vessel 28 connected to the cleaning liquid return line 24 by a line 29 and at its lower portion to the inlet side of the pump 19 by a line 30. The circulating cleaning liquid passes through the vessel 28 and chunks of coagulum loosened from the tower 10 settle at the bottom of the vessel 28. A breather line 31 which is open to the atmosphere is also connected to the top of the solution vessel 28. A reflux condenser 32 may be included in the breather line. Specification 775,536 is referred to.