Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2000-08-16
2002-03-05
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S312000, C528S319000, C528S320000, C528S322000, C528S323000, C528S332000, C528S335000, C528S336000
Reexamination Certificate
active
06353085
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for producing polyamides by polymerization of lactams in the presence of metal oxides as heterogeneous catalysts.
The hydrolytic polymerization process is one of the most important processes for producing polyamides from lactams. Acidic catalysts are known to speed up the lactam polymerization.
For instance, the use of mono- and bifunctional acids in the hydrolytic polymerization of caprolactam for the purpose of chain regulation has the advantage that the space-time yield can be improved compared with base-regulated polyamide. EP-A 0 462 476 concerns the use of dicarboxylic acids in nylon-6 production. However, acidic compounds, such as terephthalic acid, adipic acid or isophthalic acid, react with the amino end groups of the resulting polymer chains and thus have a decisive influence on the number of end groups available for condensation and on the rate of the polycondensation. The amount of reactive acidic regulator which can be used is therefore limited by the desired final molecular weight and the required space-time yield when condensing in the melt and in the solid phase.
Acidic, condensation-capable regulators reduce not only the space-time yield of the polymerization but also the amino end group number and thus compromise the dyeing properties of polyamides and especially of nylon fibers, since amino end groups play a leading role in binding dyes to the polymer in numerous applications.
2. Description of the Related Art
GB-B 1 148 508 proposes adding acidic salts, such as TiCl
2
, AlCl
3
, SiCl
4
and FeCl
3
, to the reaction mixture to speed up the hydrolytic polymerization process.
DE-C 2 554 788 mentions the use of the metal oxides TiO
2
, V
2
O
5
, CrO
3
, MnO
2
, CuO, CuO
2
, CoO
3
, MoO
3
and WO
3
in finely divided form as catalysts, optionally under the additional effect of ionizing radiation. The catalysts, which are used in an amount from 0.1 to 50% by weight, are discharged from the reactor together with the polymer melt and remain in the polymer. The disadvantages of using the abovementioned salts and metal oxides depend on the type of catalyst. For instance, the end product may discolor or the mechanical and rheological properties of the polymer may deteriorate badly. It is also known that the deterioration of the property profile of the polymers becomes noticeable in spinning applications at very low catalyst or filler concentrations.
DD 280 766 proposes the use of a catalyst system which is composed of calcium carbonate, barium sulfate and TiO
2
and which is coated with a silica gel ester mixture to prevent discoloration of the end product. In this case too the catalyst remains in the product in an amount from 2 to 10% by weight, which again has an adverse effect on processing and product properties in the case of spinning applications in particular.
Moreover, with all the abovementioned catalysts and catalyst mixtures which contain metal oxides and remain in the end product, a comparatively pronounced light and heat instability has to be assumed, since uncoated, reactive metal oxides are known to possess a pronounced photocatalytic effect and to speed up the degradation of the polymer.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for producing polyamides from lactams with an improved space-time yield and improved polymerization economics without the abovementioned product and processing properties being adversely affected.
We have found that this object is achieved according to the invention by a process for producing polyamides by polymerization of lactams in the presence of metal oxides as heterogeneous catalysts, which comprises the metal oxides being used in a form which permits mechanical removal from the reaction mixture and being removed from the reaction mixture in the course of or on completion of the polymerization. The catalysts can be used in the form of pellets, extrudates, fixed beds or catalyst-coated packing elements or internals.
DETAILED DESCRIPTION OF THE INVENTION
The use of metal oxides or metal oxide mixtures as fixed bed catalysts in the polymerization reactor significantly speeds up the molecular weight buildup compared with no fixed bed catalyst being present, whereby the polymerization may advantageously be carried out at reduced temperature and reduced water content.
The reaction mixture is separated from the catalyst material before or after attainment of the desired final viscosity.
To produce polyamide according to the invention, all known monomers can be polymerized in the presence of the catalysts of the invention. In a preferred embodiment of the process of the invention, the starting monomer used is &egr;-caprolactam. Hereinbelow “caprolactam” is preferably “&egr;-caprolactam”.
As heterogeneous catalysts there can be used known metal oxides, such as zirconium oxide, aluminum oxide, magnesium oxide, cerium oxide, lanthanum oxide and preferably titanium dioxides and also beta-zeolites and sheet-silicates. Particular preference is given to titanium dioxide in the anatase form. The titanium dioxide is preferably at least 70% by weight, particularly preferably at least 90% by weight, especially essentially completely, in the anatase form. Silica gel, zeolites and doped metal oxides, examples of dopants used being ruthenium, copper or fluoride, have also been found to provide a considerable improvement in the reaction of the reactants mentioned. Suitable catalysts are especially notable for the fact that they are Brönsted acid. According to the invention, the heterogeneous catalyst has a macroscopic form which permits mechanical separation of the polymer melt from the catlyst, for example by means of sieves or filters. The invention proposes the use of the catalyst in extrudate or pellet form or as a coating on packing elements.
In another embodiment, the lactam is reacted with homogeneously dissolved acidic cocatalysts or a mixture of different catalytically active compounds in the presence of the abovementioned heterogeneous catalysts. The cocatalysts used are preferably acidic catalysts selected from organic mono- and dicarboxylic acids, inorganic acids, their salts or mixtures thereof, for example the abovementioned carboxylic acids, terephthalic acid, adipic acid, propionic acid and isophthalic acid, or oxygen-containing phosphorus compounds, especially phosphoric acid, phosphorous acid, hypophosphorous acid, their alkali metal and alkaline earth metal salts and ammonium salts, or oxygen-containing sulfur compounds, especially sulfuric acid and sulfurous acid.
The process of the invention is batch or preferably continously operated. The monomers and the desired comonomers, the chain regulators and the catalysts are melted and mixed either in the polymerization reactor, preferably prior to heating to the reaction temperature, or in a separate makeup vessel prior to being introduced into the reactor. The water content of the starting mixture is within the range from 0 to 20% by weight, preferably within the range from 0 to less than 10% by weight, particularly preferably within the range from 0.005 to 1% by weight.
The way the process is carried out according to the invention can be characterized by temperature-time and pressure-time profiles, which depend on the reactants and catalysts used. The time dependence of pressure and temperature is directly dependent on the progress of the reaction, on the desired molecular weight distribution, or the viscosity of the end product, and on the amount of water to be removed from the reaction mixture.
The molecular weight buildup can be improved if the reaction mixture passes sequentially through a plurality of process phases or stages each having different process parameter (pressure, temperature and residence time) settings. The pressure and temperature time-courses within and between the phases are not necessarily constant or discontinuous, but can also change monotonously and continuously, respectively.
Two-phase Process
Preferably, the po
Fuchs Eberhard
Hildebrandt Volker
Mohrschladt Ralf
Pipper Gunter
BASF - Aktiengesellschaft
Hampton-Hightower P.
Keil & Weinkauf
LandOfFree
Method for producing polyamides does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing polyamides, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing polyamides will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2857267