Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Patent
1995-12-28
1997-10-07
Acquah, Samuel A.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
528325, 528326, 528335, 528336, 528339, 528340, 528347, 528348, C08G 6914, C08G 6926, C08G 6928
Patent
active
056749732
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/EP 94/01998 Jun. 20, 1994.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved process for the continuous production of polyamides from a mixture of at least one lactam and water and, if required, other monomer units and/or conventional additives and fillers under polyamide-forming conditions, where the mixture of the starting materials is heated in liquid phase in a first reaction zone until a conversion of at least 70% is reached, and undergoes adiabatic decompression and further polymerization in another reaction zone.
The invention also relates to low molecular weight polycaprolactam having a molecular weight in the range from 3000 to 1400 g/mol, to the use of this polycaprolactam for the production of granular polycaprolactam and high molecular weight polycaprolactam, and to a process for producing high molecular weight polycaprolactam from this low molecular weight polycaprolactam.
2. Description of the Related Art
DE-A 24 43 566 describes a process for the continuous production of polyamides by progressive movement of a mixture of one or more lactams and 1-15% by weight of water and, where appropriate, other polyamide-forming compounds, in which the mixture of the starting materials is heated in a first reaction zone to 210.degree.-330.degree. C., and the polycondensation mixture is adiabatically decompressed in another reaction zone and subsequently polymerization is completed in further reaction stages to give high molecular weight polyamides, where heated under pressures which are above the appropriate vapor pressures of the starting materials and prevent the formation of a vapor phase for from 5 minutes to 2 hours, preferably 10 minutes to 1 hour, until a conversion of at least 70%, and preferably 80%, is reached; pressures of 1-11 bar, preferably 1-6 bar, and immediately thereafter is heated in a third reaction zone, preferably together with the steam formed in the decompression, with input of heat and evaporation of most of the water under the pressure after decompression or a lower pressure, within less than 10 minutes, preferably less than 5 minutes, to 250.degree.-350.degree. C., preferably 260.degree.-280.degree. C., and reaction zone and polymerization is completed in further reaction stages to give high molecular weight polyamides.
However, the disadvantage of this process is that the melt viscosity of the resulting polycaprolactam is too high. Thus, a high melt viscosity usually gives rise to problems in conveying the melt and dissipating the heat of reaction. These problems usually result in caking within the reactor system which leads, inter alia, to reductions in quality. Furthermore, the space-time yield of the process disclosed in DE-A 24 43 566 is too low. In addition, low molecular weight polycaprolactam cannot be obtained with a conversion of more than 85% as disclosed in DE-A 24 43 566.
It is an object of the present invention to provide an improved process for producing polyamides which does not have these disadvantages.
SUMMARY OF THE INVENTION
We have found that this improved process for producing polyamides is achieved by a process for the continuous production of polyamides from a mixture of at least one lactam and water and, if required, other monomer units and/or conventional additives and fillers under polyamide-forming conditions, where the mixture of the starting materials is heated in liquid phase in a first reaction zone until a conversion of at least 70% is reached, and undergoes adiabatic decompression and further polymerization in another reaction zone, wherein, in the first reaction zone, 0.5-7% by weight of water are employed, the temperature is increased to the range from 220.degree. to 310.degree. C., and polymerization is carried out until a conversion of at least 85% is reached and, in the second reaction zone, after the decompression further polymerization is carried out in the range from 215.degree. to 300.degree. C. without heat input.
We have furthermore found low mole
REFERENCES:
patent: 4049638 (1977-09-01), Doerfel et al.
Hildenbrand Peter
Kleinke Andreas
Pipper Gunter
Acquah Samuel A.
BASF - Aktiengesellschaft
Hampton Hightower P.
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