Example 1
APoly-E-caprolactam granulate in the form of chips 2.5
mm. in diameter and 2.5 mm. thick is extracted in counter
current flow with water at 95° C. in an extraction column
of 4 meters length and 150 mm. diameter. The rate of discharge is 6 kg./h. of chips calculated on the dry weight,
which corresponds to a time of sojourn of about 71/2
hours. In the process, the content of extractable constituents decreases from 10.2 to 1.3 percent by weight.
Pure water is fed into the bottom of the column from a
leveling vessel and 9.3 l./h. lactam solution with a content
of 6.2% of extract are drawn off at the top of the column
by means of a dosing pump.
Example 2
Poly-E-caprolactam chips having a grain size of 2.5 mm.
are extracted with water at 95° C. in an extraction apparatus of 8 meters length comprising six parallel tubes of
150 mm. diameter. The column is provided with an in
termediate tapping point for lactam solution at a height
of 2 meters from the bottom end. A total quantity of 22
kg./h. of chips (calculated on the dry state) is drawn off
in equal amounts at the bottom from all six tubes. In the
process, the content of extractable constituents is lowered
from 10.5 to 0.5%. Pure water is fed into the bottom of
the column from a leveling vessel, and a total quantity of
9 l./h. of a 22% lactam solution are drawn off at the top
of the column in equal quantities from each tube by means
of a six-part pump. Through the intermediate tapping, a
quantity of 16 l./h. of a 2.2% solution is likewise drawn
off by means of a six-part pump. The lactam solution contains caprolactam in monomeric and oligomeric form.
In both examples water-white poly-E-caprolactam was
recovered which had not in the least discolored.
We claim as our invention:
1.’ A continuous process for the removal of monomeric
and oligomeric caprolactam from granulated highly polymerized poly-E-caprolactam including fiber-forming
grades while preventing its yellowing and for the concentration and recovery of said caprolactam, which comprises
countercurrently washin g a compact layer of said granules,
having an average grain size of substantially 2.5 mm.,
with a liquid which is a solvent for said caprolactam but
.a non-solvent for the polymer, in an extract or consisting
essentially of a vertical cylindrical tube having a ratio of
inside diameter to height of at least 1:5 and having a plu rality of solvent outlets at varying heights, the topmost
outlet being disposed near the top of said extractor; said
washing ‘being carried out by continuously feeding substantially 6 to 22 kg./h. of said granules into said extrac
tor from the top and allowing the compact layer formed
to slide downward while continuously feeding solvent into
said extractor at its bottom and allowing it to travel upward; continuously drawing off portions of said solvent,
now containing monomeric and oligomeric caprolactam,
at said varying heights, but at all times fully covering said
compact layer with solvent, in total amounts of substantially 9 to 25 1./h. and containing said caprolactam in
quantities up to 22 percent; continuously drawing off
washed granules at the bottom of said extractor; and recovering the monomers and oligomers from their solution.
2. A continuous process for the removal of monomeric
and oligomeric caprolactam from granulated highly polymerized poly-E-caprolactam including fiber-forming
grades while preventing its yellowing and for the concentration and recovery of said caprolactam, which comprises
countercurrently washing a compact layer of said granules, having an average grain size of substantially 2.5 mm.,
with a liquid which is a solvent for said caprolactam but
a non-solvent for the polymer, in an extract or consisting
essentially of a vertical cylindrical tube having a ratio of
inside diameter to height of 1:5 to 1:40 and a ratio of
height to inside diameter not exceeding 1:100, said extractor having a plurality of solvent outlets at varying
heights, the topmost outlet being disposed near the top of
said extractor; said washing being carried out by con
tinuously feeding substantially 6 to 22 kg./ h. of said granules into the top of said extractor and allowing the com
pact layer formed to slide downward while continuously
feeding solvent into said extractor at its bottom and allow
ing it to travel upward; continuously drawing off portions
of said solvent, now containing monomeric and oligomeric caprolactam, at said varying heights but at all times
fully covering said compact layer with said solvent, in
total amounts of substantially 9 to 25 l./h. and containing said caprolactam in quantities up to 22 percent; continuously drawing off washed granules at the bottom of
said extractor; and recovering the monomers and oligomers from their solution.
3. The process as defined in claim 2, wherein said
counter-current extraction is carried out in an extractor
consisting of a plurality of parallel vertical cylindrical
tubes.
4. A continuous process for the removal of monomeric
and oligomeric caprolactam from granulated highly polymerized poly-E-caprolactam including fiber-forming
grades while preventing its yellowing and for the concentration and recovery of said caprolactam, which comprises
countercurrently washing a compact layer of the granules,
having an average grain size of 2.5 mm. with water below
its boiling point in an extractor consisting essentially of a
vertical cylindrical tube having a ratio of inside diameter
to height of at least 1:5 and having a plurality of water
outlets at varying heights, the topmost outlet ‘being disposed near the top of said extractor; said washing being
carried out by continuously feeding substantially 6 to 22
kg./h. of said granules in the extractor at its top and allowing the compact layer formed to slide downward while
continuously feeding hot water into said extractor from
its bottom and allowing it to travel upward; continuously
withdrawing portions of said water, now containing monomeric and oligomeric caprolactam, at said varying
heights but at all times fully covering said compact layer
with water, in total amounts of substantially 9 to 25 l./h.
and containing said caprolactam in quantities up to 22
percent; continuously drawing off washed granules at the
bottom of said extractor; and recovering the monomers
and oligomers from their aqueous solution.
5. A continuous process for the removal of monomeric
and oligomeric caprolactam from granules of highly polymerized poly-E-caprolactam including fiber-forming
grades while preventing its yellowing and for the concentration and recovery of said caprolactam, which comprises
washing a compact layer of the granules, having an
average grain size of substantially 2.5 mm., with water of
substantially 90-95° C. at atmospheric pressure in an extractor consisting essentially of a vertical cylindrical tube
provided with heating means and having a ratio of inside
diameter to height of 1:5 to 1:40 and a ratio of height to
inside diameter not exceeding 100:1; said extractor having a plurality of outlets at varying heights, the topmost
outlet being disposed near the top of said extractor; said
washing being carried out by continuously feeding substantially 6 to 22 kg./h. of said granules into the extractor
from the top and allowing the compact layer formed to
slide downward while continuously feeding water at said
temperatures into the bottom of said extractor and allow
irig it to travel upwards while maintaining said temperatures; continuously withdrawing water, now containing dis
solved monomeric and oligomeric caprolactam, at said
varying heights but at all times fully covering said compact layer with water, in total amounts of substantially 9
to 25 l./h. and containing said caprolactam in quantities
upto 22 percent; continuously drawing off washed granules at the bottom of said extractor; and recovering the
monomers and oligomers from their solution.
References Cited