Process for hydrogenating unsaturated polymers

Details Process for hydrogenating unsaturated polymers Process for hydrogenating unsaturated polymers

2000-11-21

2002-05-28

Lipman, Bernard (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S332800, C525S332900, C525S333100, C525S333200, C525S339000

Reexamination Certificate

active

06395841

ABSTRACT:

The present invention relates to a continuous hydrogenation process for hydrogenating unsaturated polymers.
BACKGROUND OF THE INVENTION
Unsaturated polymers have been previously hydrogenated using a variety of catalysts and conditions. Historically, typical hydrogenation catalysts have low reactivity and require high catalyst to polymer ratios, especially in hydrogenation of aromatic polymers. Improvements in catalytic hydrogenation have been achieved using various metals and supports. Group VIII metals on porous supports have been particularly useful in hydrogenating unsaturated polymers, especially aromatic polymers such as described in U.S. Pat. No. 5,612,422. However, these catalysts have been found to have a relatively short life span in that they deactivate upon contact with polar impurities, which are common to aromatic polymer feed streams. Additionally, previous hydrogenation processes have typically been performed as batch processes. However, batch processes are economically inefficient and product consistency is more difficult to attain.
WO99/64479 by Asahi discloses a method of hydrogenating vinyl aromatic-conjugated diene block copolymers using a fixed-bed reactor packed with a hydrogenation catalyst comprising a platinum group metal deposited on an inorganic support. However, the catalyst used provides low hydrogenation rates, requiring long reaction times.
Accordingly, it remains highly desirable to provide a continuous process of hydrogenating unsaturated polymers at high hydrogenation rates using a catalyst which is resistant to deactivation.
SUMMARY OF THE INVENTION
The present invention is a continuous process for hydrogenating an unsaturated polymer comprising:
contacting the unsaturated polymer with a hydrogenating agent in a fixed bed reactor, wherein the reactor is packed with a hydrogenation catalyst characterized in that the hydrogenation catalyst comprises a Group VIII metal component and at least one deactivation resistant component.
Surprisingly, the combination of the above hydrogenation catalyst and a fixed bed reactor provides an improved and very efficient continuous hydrogenation process, wherein the hydrogenation rate is high, steady stable performance is achieved, and the catalyst packing is resistant to deactivation upon exposure to impurities within the polymer; thus allowing for greater productivity during the useful life of the catalyst.
DETAILED DESCRIPTION OF THE INVENTION
The continuous process of the present invention hydrogenates aromatic polymers using a unique catalyst.
The process of the present invention is a continuous one, wherein a composition comprising an unsaturated polymer is continuously fed into a fixed bed reactor, wherein the unsaturated polymer is hydrogenated and continuously removed from the reactor. The fixed bed reactor is packed with a hydrogenation catalyst, herein after referred to as mixed hydrogenation catalyst, characterized in that it comprises an admixture of at least two components. The first component comprises any metal which will increase the rate of hydrogenation and includes nickel, cobalt, rhodium, ruthenium, palladium, platinum, other Group VIII metals, or combinations thereof. Preferably rhodium and/or platinum is used. However, platinum is known to be a poor hydrogenation catalyst for nitrites, therefore, platinum would not be preferred in the hydrogenation of nitrile copolymers. The second component used in the mixed hydrogenation catalyst comprises a promoter which inhibits deactivation of the Group VIII metal(s) upon exposure to polar materials, and is herein referred to as the deactivation resistant component. Such components preferably comprise rhenium, molybdenum, tungsten, tantalum or niobium or mixtures thereof.
The amount of the deactivation resistant component is at least an amount which significantly inhibits the deactivation of the Group VIII metal component when exposed to polar impurities within a polymer composition, herein referred to as a deactivation inhibiting amount. Deactivation of the Group VIII metal is evidenced by a significant decrease in hydrogenation reaction rate. This is exemplified in comparisons of a mixed or two component hydrogenation catalyst and a catalyst containing only a Group VIII metal component under identical conditions in the presence of a polar impurity, wherein the catalyst containing only a Group VIII metal component exhibits a hydrogenation reaction rate which is less than 75 percent of the rate achieved with the mixed hydrogenation catalyst.
Preferably, the amount of deactivation resistant component is such that the ratio of the Group VIII metal component to the deactivation resistant component is from 0.5:1 to 10:1, more preferably from 1:1 to 7:1, and most preferably from 1:1 to 5:1.
The catalyst can consist of the two components alone, but preferably the catalyst additionally comprises a support on which the components are deposited. The support can be any material which will allow good distribution of the components and produce an efficient catalyst which can be used in the continuous process of the present invention. Typically, the support will be a porous material produced from a material such as a silica, alumina, magnesium oxide or carbon, having a narrow pore size distribution.
The pore size distribution, pore volume, and average pore diameter of the support can be obtained via mercury porosimetry following the procedures of ASTM D-4284-83.
The pore size distribution is typically measured using mercury porosimetry. However, this method is only sufficient for measuring pores of greater than 60 angstroms. Therefore, an additional method must be used to measure pores less than 60 angstroms. One such method is nitrogen desorption according to ASTM D-4641-87 for pore diameters of less than about 600 angstroms. Therefore, narrow pore size distribution is defined as the requirement that at least 98 percent of the pore volume is defined by pores having pore diameters greater than 600 angstroms and that the pore volume measured by nitrogen desorption for pores less than 600 angstroms, be less than 2 percent of the total pore volume measured by mercury porosimetry. It has been surprisingly discovered that the use of supports having large pore diameters and narrow pore size distribution as described, are particularly advantageous in the process of the present invention.
The surface area can be measured according to ASTM D-3663-84. The surface area is typically from 10, preferably from 15 and most preferably from 50 to 100, preferably to 90 and most preferably to 85 m
2
/g.
In one embodiment, at least 98 percent of the pore volume is defined by pores having pore diameters greater than 300 angstroms and that the pore volume measured by nitrogen desorption for pores less than 300 angstroms, be less than 2 percent of the total pore volume measured by mercury porosimetry. In another embodiment, 98 percent of the pore volume is defined by pores having pore diameters greater than 200 angstroms and the pore volume for pores less than 200 angstroms is less than 2 percent of the total pore volume measured by mercury porosimetry.
The desired average pore diameter is dependent upon the polymer which is to be hydrogenated and its number average molecular weight (Mn). It is preferable to use supports having higher average pore diameters for the hydrogenation of polymers having higher molecular weights to obtain the desired amount of hydrogenation. For high molecular weight polymers (Mn&Dgr;200,000 for example), the typical desired surface area can vary from 15 to 25 m
2
/g and the desired average pore diameter from 3,000 to 4000 angstroms. For lower molecular weight polymers (Mn<200,000 for example), the typical desired surface area can vary from 45 to 85 m
2
/g and the desired average pore diameter from 200 to 700 angstroms.
The shape of the support is not particularly limited and can include spherical or cylindrical particles. Extrusion-molded supports with side cuts or ring-shaped supports can also be used. The size of the catalyst, in the case of spherical

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