Method of removing volatiles from an elastomer

A method of continuously removing volatile hydrocarbons from a solution of elastomer and volatile hydrocarbons wherein said solution contains up to about 85 percent by weight of said hydrocarbons, said method comprising the steps in sequence of:

• (a) releasing the solution of elastomer and volatile hydrocarbons from a zone maintained at a temperature above normal boiling point of the volatile hydrocarbons and at an initial pressure at least sufficient to keep the volatile material in the liquid state, through four orifices, said orifice having an initial opening which is wider than the opening at the end of the orifices, into elongated conduits, which conduits are at a lower pressure than the initial pressure, said conduits each having a uniform minimum cross-section area of about 250 times orifice cross-section to about 10,000 times the orifice cross-section, whereby a portion of the volatile hydrocarbons is flashed into vapor and the remaining solution forms discrete crumbs of elastomer having volatile hydrocarbons entrapped therein, at a rate which produces a vapor velocity in the conduits of from 3 to 70 meters per second and a crumb concentration of from 0.25 to 25 percent by volume in the conduit, said crumb concentration and vapor velocity being such as to cause agglomeration of crumbs while limiting production of fines, thereby avoiding plugging of the conduit or adherence of crumbs to the walls thereof;
• (b) conducting the vapor and crumbs thus formed out of the ends of the conduits into an enclosure;
• (c) removing the vapors from the enclosure;
• (d) passing said crumbs, which maintain velocity from the conduit, from the enclosure to the screw of the first work section of a first extruder;
• (e) mechanically working said crumbs to produce a mass of elastomer and to increase the elastomer temperature;
• (f) passing said elastomer through a circumferential annular orifice into a zone of reduced pressure thereby causing hydrocarbon vapors to flash from the elastomer;
• (g) allowing said flashing vapors to escape through a tee-piece vent section located in a tee section formed by attaching a second extruder to said first extruder;
• whereby said flashing vapors proceed rearwardly to the end of the tee section, while simultaneously elastomer fines produced during the flashing operation are agglomerated and carried forward into the second extruder;
• (h) passing said elastomer having a lower content of volatile hydrocarbons to another work section in said second extruder whereby the elastomer is again worked to increase its temperature;
• (i) passing said elastomer through a circumferential annular orifice into a zone of reduced pressure thereby causing hydrocarbon vapors to flash from the elastomer;
• (j) allowing said flashing vapors to escape through a tee-piece vent section located in a tee-section formed by attaching a third extruder to said second extruder, whereby said flashing vapors proceed rearwardly to the end of the tee-section while simultaneously elastomer fines produced during the flashing operation are agglomerated and carried forward into the third extruder;
• (k) admixing antioxidant, oil, or a mixture thereof to the elastomer through an inlet in a work section of said third extruder;
• (l) passing said mixture of elastomer with antioxidant, oil, or mixture thereof through a circumferential annular orifice to a zone of reduced pressure thereby causing hydrocarbon vapors to flash from said mixture;
• (m) allowing said vapors to escape through a vent equipped with a single screw, wherein said screw has a sufficiently large pitch and small root diameter to reduce the vapor velocity to less than about 6.0 meters per second, thereby minimizing entrainment of fines in the vapor;
• (n) passing said elastomer through a second circumferential annular orifice in said extruder to a zone of reduced pressure thereby again causing hydrocarbon vapors to flash from the elastomer;
• (o) allowing said vapors to escape through a second vent section equipped with a single screw, wherein said screw has a sufficiently large pitch and small root diameter to reduce the vapor velocity to less than about 6.0 meters per second, thereby minimizing entrainment of fines in the vapor;
• (p) adding water to a work section in said third extruder;
• and
• (q) discharging the elastomer from the end of said extruder at a volatile hydrocarbon content of less than about 1.0 percent by weight.