WO2005066219A1

WO2005066219A1 - Process for oxidizing linear low molecular weight polyethylene

Info

Publication number: WO2005066219A1
Application number: PCT/US2004/009853
Authority: WO
Inventors: Manfred K. Seven
Original assignee: Honeywell International Inc.
Priority date: 2003-04-01
Filing date: 2004-03-31
Publication date: 2005-07-21

Abstract

The invention provides a process for the oxidation of waxes or more particularly to a process for producing an emulsifiable, oxidized polyolefin wax.

Description

PROCESS FOR OXIDIZING LINEAR LOW MOLECULAR WEIGHT POLYETHYLENE

BACKGROUND OF THE INVENTION The present invention relates to the oxidation of waxes or more particularly to a process for producing an emulsifiable, oxidized polyolefin wax.

It is known that polyolefin waxes, such as polyethylene waxes can be oxidized.

Such oxidation products of waxes and processes for preparing them are described, for example, in U.S. patent 3,278,513. The starting materials are generally reacted by treating their melts with oxygen or oxygen-containing gas mixtures. The oxidation of highly linear, crystalline polyethylene waxes usually requires catalytic agents in order to obtain reasonably commercially viable oxidation rates and high quality oxidized waxes. The catalytic agents add costs, complexity and often interfere with the ultimate application of theproducts as well as may reduce overall quality.

Highly linear low molecular weight polyolefin waxes such as those manufactured using Ziegler and metallocene catalysts are difficult to oxidize to yield satisfactory high quality oxidized products. Oxidized polyolefins are useful in many applications requiring more polarity than that offered by the parent homopolymer. For example, oxidized waxes are extensively used in emulsions for coatings and polish and as lubricants in the processing of polymers such as PVC, as auxiliaries for plastics processing or for producing aqueous dispersions, for use in cleaners, in textile processing, for waterproofing and for coating citrus fruits. , An important feature of highly linear waxes, such as those produced by Ziegler and metallocene catalysts can be relatively high crystallinity, melting point and lack of branch points along the polymer backbone. These features, either alone or in combination, make normal oxidation more difficult. Long oxidation times and high temperatures to drive the oxidation while yielding oxidized products, often results in inferior products of limited use. Such waxes can have poor color, high viscosities which are sometimes higher than the parent homopolymers, and poor emulsifiability. To overcome these disadvantages of long oxidation times, and high temperatures with attendant quality problems it is customary to use catalysts to both initiate and speed up the oxidation process. As catalysts, pre-oxidized polyethylenes, peroxides, inorganic and organic metal salts, inorganic and organic acids and ozone have been used. Some of these catalysts while useful in initiating and accelerating the oxidation nevertheless have drawbacks such as adding extra costs and complications, contamination factors with the catalyst, discoloration of the wax from the catalysts and generally interfering with end use properties and applications. Disadvantages which have been found in the oxidation of wax-like polyolefins prepared using metallocenes are the formation of high molecular weight by-products, and gel-like, crosslinked by-products. This can lead to a rapid increase in the viscosity of the reaction mixture during the reaction and as a result efficient dispersion of the wax with oxygen is hindered and the reaction rate is reduced. Furthermore, deposits are formed on the walls and internal fittings of the oxidation reactor resulting in a deterioration of the quality of the products. This behavior is observed particularly when the reaction is carried out in an economically advantageous manner using air as oxidant and at atmospheric pressure or slight superatmospheric pressure. Oxidation of such difficult to oxidize feedstock waxes as produced with Ziegler and metallocene catalyst based products without the addition of catalytic agent would therefore be highly , desirable.

It has now been found that specific oxidation process operating conditions can be used to manufacture high quality oxidized wax products without the use of catalytic agents as previously described. Wax feedstocks derived from Ziegler and/or metallocene based processes as well as conventional high pressure process based products can be oxidized via this process with equal effectiveness. The process operating conditions according to this invention are selected to allow oxidation to be conducted on a commercial scale without the use of oxidation catalytic agents. The resulting products are of high quality.

DESCRIPTION OF THE INVENTION

The invention provides a process for producing an oxidized polyolefin, which is preferably emulsifiable, which comprises charging an agitated flow of an oxygen containing gas into a molten polyolefin homopolymer or copolymer, in the absence of an oxidation catalyst, while maintaining a temperature in the range of from about 130 °C to about 160 °C, and a pressure of from about 50 to about 150 psig, wherein the gas is charged at a rate of from about .5 to about 2 liters per minute per kilogram of polyolefin.

The invention also provides an emulsifiable, oxidized polyolefin produced according to the process which comprises charging an agitated flow of an oxygen containing gas into a molten polyolefin homopolymer or copolymer, in the absence of an oxidation catalyst, while maintaining a temperature in the range of from about 130 °C to about 160 °C, and a pressure of from about 50 to about 150 psig, wherein the gas is charged at a rate of from about .5 to about 2 liters per minute per kilogram of polyolefin.

The polyolefin feedstocks which may be used may be one or more homopolymers or copolymers of alpha-olefins with ethylene. Suitable polyethylene wax raw materials are homopolymers of ethylene or copolymers of ethylene with one or more alpha-olefins. The alpha-olefins used are linear or branched olefins having 3 to 18 carbon atoms, preferably 3 to 8 carbon atoms. The preferred polyolefin is a polyethylene homopolymer, which may be a linear low density polyethylene homopolymer, a linear high density polyethylene homopolymer or a polyethylene containing copolymer, such as a copolymer of polyethylene and a C₃ to C₈ alpha- olefin. Examples of such olefins are propene, 1-butene, 1-hexene, 1-octene or 1- octadecene. Usually the polyolefin has a number average molecular weight in the range of from about 800 to about 6,000. Preferred are ethylene homopolymers and copolymers of ethylene with propene or 1-butene. The copolymers comprise 70-99.9% by weight, preferably 80-99% by weight, of ethylene.

Suitable polyethylene waxes used as raw material for the oxidation may be obtained by thermal degradation of high molecular weight polyethylene or by free- radical polymerization of ethylene by a known high pressure process, by metal- catalyzed homopolymerization of ethylene or metal-catalyzed copolymerization of ethylene with alpha-olefins. Suitable metal catalysts are those of the Ziegler-Natta type or metallocene compounds. The latter contain titanium, zirconium or hafnium atoms as active species and are generally used in combination with co- catalysts, e.g. organoaluminum or boron compounds, preferably aluminoxane compounds. The polymerization is carried out in the presence of hydrogen as molar mass regulator. One polymerization process which employs metallocene catalysts is described in EP-A-321 851. Suitable feedstock waxes may be formed by high pressure processes using oxygen and/or peroxides, thermally degraded polyethylene waxes, Fischer Tropsch waxes and linear and branched paraffin waxes. One method of preparing thermally degraded polyolefins is described in U.S. patent 2,928,797.

In carrying out the process of this invention, the polyolefin feedstock material is first charged to a reaction vessel and heated to the melting point. The reaction is conducted while maintaining a temperature in the range of from about 130 °C to about 160 °C, preferably from about 135 °C to about 145 °C, and more preferably from about 140 °C to about 145 °C. The reaction is exothermic and therefore heating and cooling must be respectively done during the reaction in order to keep the reaction temperature within these ranges. Below these temperatures the rate of oxidation is undesirably slow. Above these temperatures, the quality of the resulting product is degraded, as principally manifested by poor color. The vessel is simultaneously maintained at a pressure of from about 50 to about 150 psig, preferably about 80 psig to about 140 psig and more preferably from about 90 psig to about 110 psig. While lower pressures can he used, the higher air flow rates required for compensation tend to make oxygen uptake less efficient due to excessive foaming and slugging in the liquid/gas medium. An oxygen containing gas such as oxygen, air, or air provided with an enriched oxygen concentration, is charged directly into contact with the hot, melted materials at the desired rate of flow, with vigorous agitation. The gas flows at a rate of from about .5 to about 2 liters per minute per kilogram of polyolefin, preferably from about .8 to about 1.2 liters per minute per kilogram of polyolefin. The preferred medium is air as the use of pure oxygen is more hazardous and expensive. For efficient operation of the process on a commercial scale air is much preferred. The flow rate is measured at standard conditions of 25 °C and 1 atmosphere of pressure. An important feature of the invention is that the oxygen containing gas is charged into the molten polyolefin under high agitation conditions. The more intensive the agitatipn is, the better are the results obtained, because the mixture of the two raw materials is thereby kept more homogeneous and brought into closer contact with the oxidant gas. This may be achieved, for example, with a sparging device to produce fine bubbles which are then dispersed with an impeller, such as a turbine of the Rushton type. The reaction is conducted for from about 3 hours to about 12 hours. In practice, to achieve the objectives of the process, the oxidation needs to be conducted in such manner as to oxidize the waxes at a rate of approximately 2.5 - 3.5 acid number units per hour. At this rate, generation of unwanted side reactions such as intermolecular and crosslinking types are almost totally suppressed. An important feature of the invention is that the reaction is conducted in the absence of-any oxidation catalysts. The oxidation of the polyolefin waxes can be carried out batchwise or continuously. In the case of the batchwise procedure, oxygen or oxygen-containing gas is passed into the molten wax raw material, if necessary with removal of the heat of reaction.

When the desired degree of oxidation has been attained, introduction of the gas is stopped, and the resulting oxidized polyolefin is discharged from the vessel. The process can also be carried out continuously, in which case the low molecular weight polyolefin to be oxidized is continuously charged to the reaction vessel and mixed with the oxidized low molecular weight polyolefin present in the vessel in the desired proportions. The desired degree of oxidation will vary depending on the properties desired in the final product. The oxidation would generally be continued at least until a product having acceptable emulsifiability has been obtained. In general, the degree of oxidation may be determined by the acid number of the product. 5 The resulting emulsifiable, oxidized polyolefin usually has an acid number of from about 14 to about 22. The oxidized waxes produced^' according to the invention produce clear or pale yellow aqueous emulsions with good clarity and stability which do not separate or form a surface "cream" and typically have less than 1% by weight of non-emulsifiable particles. The resulting emulsifiable, l o oxidized polyolefin also has a Klett color of 80 or less, preferably 50 or less. An aqueous emulsion of the oxidized polyolefin has a Klett clarity of 100 or less, preferably 50 or less.

The following non-limiting examples serve to illustrate the invention.

15

EXAMPLE 1

This example describes the oxidation of a linear highly crystalline high melting polyethylene wax produced via a Ziegler catalyst system. 0 The wax feedstock was a Type 840, a linear highly crystalline high melting polyethylene wax produced via a Ziegler catalyst, which is commercially available from Honeywell International Inc. It had a viscosity, at 140°C of 630 cps, a penetration hardness of 0.2 dmm, a density of 0.9811 g/cm³, and a Mettler Drop 5 Pt. 131.6 °C. The oxidation was carried out in a pressure reactor equipped with a sparging device for distributing air, a turbine impeller and means to control pressure and temperature. The following operating conditions for oxidation were: temperature =140 °C, Air flow of 1.2 liters/min/kg of wax feedstock at a pressure of 130 psig. The resulting oxidized wax had the following properties: an acid number of 20 mg/g KOH, a viscosity @ 140°C of 125 cps, a hardness of 0.2 dmm, a Mettler drop point of 123.9 °C, a total oxidation time of 7.25 hours, acid number per hour = 2.76. The resulting color is white to off white.

This example clearly shows the advantages of this process. The low oxidation temperature used results in exceptionally low discoloration of products. The rapid rate of oxidation is responsible for retention of a high drop point, exceptional hardness and low viscosity. The absence of any catalyst which could interfere with applications. A rapid oxidation rate resulting in an exceptionally efficient time cycle for completing the oxidation.

EXAMPLE 2

This example describes the oxidation of a linear highly crystalline high melting but lower viscosity wax produced by a Ziegler type catalyst system.

The wax feedstock was a linear, highly crystalline, high melting point, low viscosity polyethylene wax produced by a Ziegler catalyst. The wax has a viscosity @ 140 °C of 85 cps, a Mettler drop point of 126.9 °C, a penetration hardness of 0.4 dmm, and a density of 0.970 g/cm³.

The following operating conditions were used for the oxidation:

Temperature = 145 °C, air flow =1.2 liters/min/kg of wax feedstock charged and a pressure of 125 psig.

The resulting oxidized wax had the following properties: a final acid number of 36.9 mg/KOH/g, a viscosity @ 140°C of 44 cps, a hardness of 1.8 dmm, a Mettler drop point of 113.8 °C, total oxidation time was 8.5 hours, the acid number/hr was 4.3 and the color was white to off white.

This example demonstrates the usefulness of the process in oxidizing even a very low viscosity feedstock wax without attendant discoloration or resulting in products of high viscosity or total gelation. Also, the acid number of the final product is very high, thus indicating that the wax is highly functional. This is an unexpected result in- a process not employing any catalytic agents. Normally, when very high acid number products are desired, the attendant long oxidation times causes the product to discolor and increase in viscosity.

EXAMPLE 3

Example 2 is repeated except a linear highly crystalline high melting but lower viscosity wax produced by a Ziegler type catalyst system is used. Similar results are noticed.

While the present invention has been particularly shown and described with reference to preferred embodiments, it will be readily appreciated by those of ordinary skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. It is intended that the claims be interpreted to cover the disclosed embodiment, those alternatives which have been discussed above and all equivalents thereto.

Claims

What is claimed is:

1. A process for producing an oxidized polyolefin which comprises charging an agitated flow of an oxygen containing gas into a molten polyolefin homopolymer 5 or copolymer, in the absence of an oxidation catalyst, while maintaining a temperature in the range of from about 130 °C to about 160 °C, and a pressure of from about 50 to about 150 psig, wherein the gas is charged at a rate of from about .5 to about-2 liters per minute per kilogram of polyolefin. 0

2. The process of claim 1 wherein the polyolefin comprises a polyethylene homopolymer.

3. The process of claim 1 wherein the polyolefin comprises a low density polyethylene homopolymer.5

4. The process of claim 1 wherein the polyolefin comprises a high density polyethylene homopolymer.

5. The process of claim 1 wherein the polyolefin comprises a polyethylene o homopolymer having a number average molecular weight in the range of from about 800 to about 6,000.

6. The process of claim 1 wherein the polyolefin comprises a polyethylene containing copolymer.5

7. The process of claim 1 wherein the polyolefin comprises a copolymer of polyethylene and a C₃ to C₈ olefin.

8. The process of claim 1 wherein the temperature is maintained at a range of from about 135 °C to about 145 °C.

9. The process of claim 1 wherein the temperature is maintained at a range of from about 140 °C to about 145 °C.

10. The process of claim 1 wherein the pressure is maintained at a range of from about 80 psig to about 140 psig.

11. The process of claim 1 wherein the pressure is maintained at a range of from about 90 psig to about 110 psig.

12. The process of claim 1 wherein the gas is charged at a rate of from about .8 to about 1.2 liters per minute per kilogram of polyolefin.

13. The process of claim 1 wherein the temperature is maintained at a range of from about 135 °C to about 145 °C, the pressure is maintained at a range of from about 80 psig to about 140 psig and the gas is charged at a rate of from about .8 to about 1.2 liters per minute per kilogram of polyolefin.

14. The process of claim 1 wherein the temperature is maintained at a range of from about 140 °C to about 145 °C, the pressure is maintained at a range of from about 90 psig to about 110 psig, and the gas is charged at a rate of from about .8 to about 1.2 liters per minute per kilogram of polyolefin.

15. The process of claim 1 wherein the oxygen containing gas comprises air.

16. The process of claim 1 which is conducted for from about 3 hours to about 12 hours.

17. The process of claim 1 wherein the resulting, oxidized polyolefin has less than 1% by weight of nori-emulsifiable particles.

18. The process of claim 1 wherein the resulting, oxidized polyolefin has a Klett color of 80 or less and a Klett clarity of 100 or less when emulsified with water.

19. The process of claim 1 wherein the resulting, oxidized polyolefin has an acid number of from about 14 to about 22.

20. The process of claim 1 wherein oxygen or an oxygen containing gas is admitted to the reactor with a sparging device and dispersed with a turbine impeller.

21. The process of claim 1 wherein the polyolefin comprises a low density polyethylene homopolymer or a high density polyolefin homopolymer having a number average molecular weight in the range of from about 800 to about 6,000; wherein the temperature is maintained at a range of from about 140 °C to about ' 145 °C; wherein the pressure is maintained at a range of from about 90 psig to about 110 psig; wherein the oxygen containing gas comprises air which is charged at a rate of from about .8 to about 1.2 liters per minute per kilogram of polyolefin with a sparging device and a turbine impeller; which is conducted for from about 3 hours to about 12 hours.

22. A oxidized polyolefin produced according to claim 19 wherein the resulting oxidized polyolefin has less than 1% by weight of non-emulsifiable particles; and wherein the resulting emulsifiable, oxidized polyolefin has an acid number of from about 14 to about 22 and a Klett color of 80 or less and a Klett clarity of 100 or less when emulsified with water.

23. The oxidized polyolefin produced according to the process of claim 1.

24. The oxidized polyolefin produced according to the process of claim 21.

25. A process for producing an emulsifiable, oxidized polyolefin which comprises charging an agitated flow of an oxygen containing gas into a molten polyolefin homopolymer or copolymer, in the absence of an oxidation catalyst, while maintaining a temperature in the range of from about 130 °C to about 160 °C, and a pressure of from about 50 to about 150 psig, wherein the gas is charged at a rate of from about .5 to about 2 liters per minute per kilogram of polyolefin.