Plastic and nonmetallic article shaping or treating: processes – Formation of solid particulate material directly from molten... – By vibration or agitation
Patent
1994-09-16
1995-12-26
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Formation of solid particulate material directly from molten...
By vibration or agitation
264 13, 425 6, B29B 910, B05B 900
Patent
active
054785090
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for forming polymer particles from a solution of polymer by evaporating the solvent from the solution.
Many prior art methods are known for the recovery of a polymer from its solution; however, there are many disadvantages to these methods such as inefficient use of energy, safety and health hazards, use of inert gas and mechanical problems.
U.S. Pat. No. 3,450,183 to Robert A. Hinton discloses a method for drying a polymer where the polymer solution is flashed below the melting point of the polymer to obtain an essentially dry or solid flash residue. The problem is that the method is only operable with those polymers that will flash to form an essentially dry solid, whereas if the polymer solution upon flashing retains enough solvent to be a sticky mass, the equipment will become all fouled up. A rubbery polymer solution is one example wherein after several stages of flash the rubber solution reaches a viscous stage which still is not dry, yet it cannot be pumped or handled otherwise either.
Another method is disclosed in U.S. Pat. No. 3,251,428 where a slurry of polyolefin is sprayed into a fluidised bed of polyolefin particles. The slurry coats the particles, then the hot vaporous solvent used to fluidise the bed vaporises any solvent remaining in the coating. Problems arise, however, when the polymer bed becomes too sticky to fluidise. Safety hazards are increased due to the use of the hydrocarbon as a fluidising medium. The system, as well, is generally inefficient energy-wise.
EP Patent 2271 to William R. King discloses a process where the polymer solution is introduced into a maintained bed of mechanically agitated polymer particles. This process requires the passage of an inert gas countercurrent to the polymer particles and the presence of initial solid particles (preferably of the same type of polymer as that which is to be recovered) to create a seed bed for the polymer particles to be treated.
This patent also claims a two-stage drying system where in addition to the disclosed purge column a conventional holding polisher is added in order to obtain better desolventizing yields. There are however, many disadvantages to use the teaching of this patent. The use of the countercurrent inert gas carries the fine particles to the top of the purge column which obliges to separate said fine particles from the inert gas in order to recycle the inert gas. Moreover it is necessary to stir the bed to prevent channeling of the inert gas. The movement of the bed causes agglomerates to form and float to the top of the bed. Eventually the entire bed is composed of large masses which defeat the purpose of the purge column and plug the product outlet opening. There are vortex problems arising in the purge column as mentioned in the patent. It is necessary to use a seed feed of polymer particles. There are mechanical problems due to the passage from the purge column to the holding polisher when the two-stage system is used. There are problems relating to the discharge of the polymer which is very sticky at the working temperatures. Furthermore, the long residence times often lead to the degradation of the polymer.
It is an object of the present invention to provide a continuous process for forming polymer particles from a solution of polymer which does not have the above identified drawbacks.
The present invention relates to a continuous process for recovering polymer particles from a solution of polymer by evaporating the solvent from the solution which process is characterised by introducing the solution of a polymer into at least two agitated vessels connected in series and further by removing substantially all the solvent by successively treating the solution into the first agitated vessel and treating the resulting polymer into the second agitated vessel.
Furthermore, the invention relates to an apparatus for performing the aforesaid process for recovering polymer particles.
The present invention overcomes the problems involved in the prior art methods of recovering
REFERENCES:
patent: 4778835 (1988-10-01), Sittel et al.
patent: 4923646 (1990-05-01), Kinsley, Jr.
Feder Fred R.
King William R.
Mlinaric Jean M.
Naveau Jean
Caddell Michael J.
Cheairs M. Norwood
Fina Research S.A.
Theisen Mary Lynn
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