Polyamide beads and method for the production thereof

Abstract

Certain polyamide beads or granules are useful as a sustaining material for underground natural or artificial cracks of the earth's crust essentially employed for the extraction of hydrocarbons such as crude oil or natural gas; such polyamide beads have a spherical or ellipsoidal shape and have a surface free of concave portions, advantageously having a uniform shape, and having a mean diameter lower than or equal to 1.7 mm and a porosity lower than 0.1 ml/g, and are produced using a particular cutting device/extruder.

1 .- 17 . (canceled) 
     
     
         18 . Polyamide beads of substantially spherical or ellipsoidal shape, the surface of which does not comprise concave portions, having an average diameter less than or equal to 1.7 mm and a porosity measured according to the mercury porosity measurement method of less than 0.1 ml/g. 
     
     
         19 . The polyamide beads as defined by  claim 18 , wherein the polyamide comprises a reinforcing filler and/or a bulking filler. 
     
     
         20 . The polyamide beads as defined by  claim 19 , wherein the weight concentration of reinforcing and/or bulking fillers ranges from 5% to 90%. 
     
     
         21 . The polyamide beads as defined by  claim 18 , having an average diameter ranging from 0.8 mm to 1.5 mm. 
     
     
         22 . The polyamide beads as defined by  claim 21 , having an average diameter ranging from 0.9 mm to 1.3 mm. 
     
     
         23 . The polyamide beads as defined by  claim 19 , wherein the reinforcing and/or bulking fillers are selected from the group consisting of glass fibers, aramid fibers, ceramic fibers, mineral fibers, clays, kaolin, silica, alumina, molecular sieves, glass beads, ceramic beads, fillers and plant fibers. 
     
     
         24 . The polyamide beads as defined by  claim 18 , wherein the polyamide is selected from the group consisting of polyamide 6, polyamide 6,6, polyamide T6, polyamide 4,6, copolyamides of these polyamides and semi-crystalline semi-aromatic polyamides. 
     
     
         25 . The polyamide beads as defined by  claim 24 , wherein the polyamide is a polyamide 66 or a copolyamide 6,6/6. 
     
     
         26 . The polyamide beads as defined by  claim 18 , wherein the polyamide contains additives selected from the group consisting of additives for stabilization to oxidation and to light, pigments, dyes, mattifying agents, flame retardants, plasticizers and crosslinking agents. 
     
     
         27 . A method for the production of the polyamide beads as defined by  claim 18 , comprising introducing a polyamide or polyamide-based composition into a granulating device having an underwater pelletizer, the diameter of the die holes ranging from 0.3 mm to 1.7 mm, the temperature of the cooling liquid ranging from 70° C. to 100° C., and wherein the polyamide or the polyamide composition is fed into the die with establishment of at least 80% of the nominal feed pressure no later than 5 seconds after the start of feeding the die holes with thus molten polymer or material. 
     
     
         28 . The method as defined by  claim 27 , wherein the polyamide or polyamide composition is fed into the underwater granulating device by means of a feed device comprising a single-screw or twin-screw extruder combined with a gear pump. 
     
     
         29 . The method as defined by  claim 27 , wherein the throughput of the polyamide in the die is from 3 and 15 kg/h per hole. 
     
     
         30 . The method as defined by  claim 29 , wherein the throughput of the polyamide in the die is from 5 and 12 kg/h per hole. 
     
     
         31 . The method as defined by  claim 27 , wherein the rotational speed of the cutting means of the underwater pelletizer granulating apparatus ranges from 3,000 to 6,000 rpm. 
     
     
         32 . A proppant for underground cracks of the earth in the extraction of hydrocarbons, comprising the polyamide beads as defined by  claim 18 . 
     
     
         33 . Apparatus for conducting the method as defined by  claim 27 , comprising a granulating device including an underwater pelletizer which comprises:
 one means of cutting, with a die, for die holes having a diameter from 0.3 mm to 1.7 mm;   one means of feeding, under pressure, the polyamide or polyamide-based composition to the cutting means through the die holes, including means for controlling the pressure such that the polyamide or polyamide composition is fed into the die with establishment of at least 80% of the nominal feed pressure no later than 5 seconds after the start of the feeding of the die holes with thus molten polymer or material; and   a fluid circuit comprising means for controlling the temperature of the cooling liquid at a temperature ranging from 70° C. to 100° C.   
     
     
         34 . The apparatus as defined by  claim 33 , wherein the feed means comprises a single-screw or twin-screw extruder combined with a gear pump. 
     
     
         35 . The apparatus as defined by  claim 33 , wherein the feed means comprises a means for controlling the throughput of the polyamide in the die permitting a throughput from 3 to 15 kg/h per hole. 
     
     
         36 . The apparatus as defined by  claim 35 , wherein the feed means comprises a means for controlling the throughput of the polyamide in the die permitting a throughput from 5 to 12 kg/h per hole. 
     
     
         37 . The apparatus as defined by  claim 33 , wherein the cutting means comprises a rotating knife driven by a rotary drive at a rotational speed of from 3,000 and 6,000 rpm.