Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Patent
1997-08-26
1999-01-12
Hampton-Hightower, P.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
528312, 528322, 528332, 528335, 528336, 528340, C08G 6928, C08G 6946, C08J 300, C08J 500
Patent
active
058591770
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process for single-stage postcondensation of polycondensates, especially polyamide 6.6 granulate, in a fluidized bed reactor using nitrogen (N.sub.2) as the carrier gas.
For producing filaments of polycondensates for industrial yarns, a thermal posttreatment in the solid state, generally known as postcondensation, is required in order to adjust the degree of polymerization. In the postcondensation of polyamide 6.6, the polyamide is typically treated with heat in a vacuum in granulate form, or an inert gas, as a rule dry nitrogen, is passed through the granulate. Some of the inert gas, laden with moisture and contaminants, is blown off after passing through the granulate bed. Dessicators, such as deep-freeze traps, silica gel, or molecular sieves, are often located in the inert-gas loop in order to dry the polymers. All the known processes for postcondensation of polyamide 66 require very long postcondensation times, as a rule more than 20 hours.
In postcondensation in the solid state, as a rule one begins with granulate that is not completely dry. Adjusting the moisture in a polyamide granulate by adding water is known. For instance, in the process of European Patent Disclosure EP-A 0 092 898, postcondensation is first done in at least two stages, and then in a conditioning phase a regulated quantity of water is added to the polyamide immediately before the melting in the extruder. With the known process, the water content in the polymer is meant to be adjusted as accurately as possible before the extrusion. However, adding water in metered fashion to the cooled granulate or to the hot extruder has the disadvantage that the metered dosage can fluctuate, or undesired temperature fluctuations can occur. As a rule, fractional streams pass from the extruder to a plurality of stations whose operation has to be stopped, for instance for changing spinning nozzles, thus necessitating a complicated adaptation of the metered addition of water. Both manual addition and metering using a pump are too inaccurate to prevent deviations in the quality of the resulting filament.
SUMMARY OF THE INVENTION
The object of the invention is to remove the water, which is contained in the prestored polymer and escapes from the polymer as a result of heating of the granulate, in a simple way.
Another object is to remove the reaction water thus produced.
A further object is to give the cooled polymer a certain predetermined moisture content. Thus by means of the invention, adding water upstream of the extruder can be eliminated.
Still another object is for the moisture content to be adjustable within wider ranges.
Another object is to remove the monomers, oligomers and contaminants contained in the carrier gas.
A further object is to prevent unnecessary consumption of nitrogen that would be used in order to replace moist nitrogen with dry nitrogen.
The objects of the invention are attained according to the invention in that a fractional stream of the carrier gas at a temperature of 20.degree. to 230.degree. C. is withdrawn from the main stream and passed through a gas scrubber column, filled with water, such that the fractional stream of conditioned carrier gas is returned to the main stream of the carrier gas with a dew point of 10.degree.-80.degree. C., (100% relative humidity).
A considerable advantage here is considered to be that when the hot fractional stream of carrier gas is introduced into the water upon cooling down, first all the components in the water, such as oligomers, that can condense out and resublimate are separated out. At the same time, the temperature of the thus-purified carrier gas is automatically predetermined by the temperature of the water in the scrubber column, and thus the dew point of the reflux to the reactor can be adjusted very accurately as well (saturation). The dew point in the reactor itself adapts to the head temperature of the scrubber as the process time increases.
This has the further particular advantage that the regulation can be ac
Berger Luzius
Stehr Hans
Zemp Niklaus
Hampton-Hightower P.
Rhodia Filtec AG
Striker Michael J.
LandOfFree
Process for subsequent condensation of polycondensates, in parti does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for subsequent condensation of polycondensates, in parti, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for subsequent condensation of polycondensates, in parti will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1517379