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Title:
ENDLESS ROPE
Document Type and Number:
WIPO Patent Application WO/2003/102295
Kind Code:
A1
Abstract:
Endless rope (10) containing primary strands (12), the primary strands (12) containing laid-up secondary strands (14), the laid-up secondary strands (14) containing rope yarns (16), wherein the primary strands (12) have been laid up from 3,4 or 6 secondary strands (14), wherein the rope (10) contains a splice in at least every primary strand (12) and wherein the rope (10) preferably has been laid up from 3, 4 or (1+6) primary strands (12) or, alternatively, has been braided from 8 or 12 primary strands (12).

Inventors:
SMEETS PAULUS JOHANNES HYACINT (NL)
DIRKS CHRISTIAAN HENRI PETER (BE)
Application Number:
PCT/NL2003/000396
Publication Date:
December 11, 2003
Filing Date:
May 27, 2003
Export Citation:
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Assignee:
DSM IP ASSETS BV (NL)
SMEETS PAULUS JOHANNES HYACINT (NL)
DIRKS CHRISTIAAN HENRI PETER (BE)
International Classes:
D04C1/00; D04C1/12; D07B1/02; (IPC1-7): D07B1/02; D04C1/12
Foreign References:
US2181344A1939-11-28
US2281036A1942-04-28
US4170921A1979-10-16
US5901632A1999-05-11
US2600395A1952-06-17
Attorney, Agent or Firm:
Mooij, Johannes Jacobus (Postbus 9, MA Geleen, NL)
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Claims:
The invention claimed is:
1. A process for the selective hydrogenation of the di¬ olefins and acetylenic compounds contained within a propylene rich stream, comprising the steps of: (a) feeding (1) a first stream comprising propylene, diolefins and acetylenic compounds and (2) a second stream containing hydrogen to a distillation column reactor into a feed zone; (b) concurrently in said distillation column reactor (i) contacting said first and second streams in a distillation reaction zone with a hydrogenation catalyst prepared in a form to act as a distillation structure thereby reacting essentially all of said diolefins and acetylenic compounds with said hydrogen to form propylene and other hydrogenated products in a reaction mixture, and (ii) separating the propylene contained in said first stream and the propylene formed by the reaction of said diolefins and said acetylenic compounds from said reaction mixture by fractional distillation; and (c) withdrawing the separated propylene from step (b) (ii) along with any propane and lighter compounds, including any unreacted hydrogen, from said distillation column reactor as overheads.
2. The process according to claim 1 wherein substantially all of said diolefins and acetylenic compounds have three carbon atoms and substantially all of said diolefins and acetylenic compounds are converted to propylene.
3. The process according to claim 1 wherein said hydrogenation catalyst comprises 0.1 to 5.0 wt% palladium oxide on alumina extrudates.
4. The process according to claim 1 wherein hydrogen is contained in said second stream in an amount to provide a mole ratio of hydrogen to said diolefins and acetylenic compound of from 1.05 to 2.
5. 5.
6. The process according to claim 1 wherein the overhead pressure of said distillation column reactor is between 240 and 315 psig.
7. The process according to claim 1 wherein said first and second streams are combined before feeding to said distillation column reactor.
8. The process according to claim 1 wherein essentially no oligomerization of said propylene, diolefins or acetylenic compounds occurs.
9. The process according to claim 3 wherein said hydrogenation catalyst is contained in the pockets of a cloth belt which is twisted with distillation wire to form a catalytic distillation structure and placed into said distillation column reactor.
10. The process according to claim 1 additionally comprising (d) withdrawing any C4 or higher boiling compounds from said distillation column reactor as bottoms.
11. A process for the selective hydrogenation of methyl acetylene and propadiene contained in a propylene rich stream while suppressing the oligomerization of said methyl acetylene, said propadiene and said propylene, comprising the steps of: (a) feeding (1) a first stream comprising propylene, propadiene and methyl acetylene and (2) a second stream containing hydrogen to a distillation column reactor into a feed zone; (b) concurrently in said distillation column reactor (i) contacting said first and second streams in a distillation reaction zone at a pressure of between 240 and 315 psig with extrudates of 0.3 wt% palladium oxide on alumina contained in the pockets of a cloth belt which is twisted with distillation wire to form a catalytic distillation structure, thereby reacting essentially all of said methyl acetylene and said propadiene with said hydrogen to form propylene and in a reaction mixture, and (ii) separating the propylene contained in said first stream and the propylene formed by the reaction of said propadiene and said methyl acetylene with said hydrogen from said reaction mixture by fractional distillation to prevent oligomerization; and (c) withdrawing the separated propylene from step (b) (ii) along with any propane and lighter compounds, including any unreacted hydrogen, from said distillation column reactor as overheads.
12. The process according to claim 11 additionally comprising (d) withdrawing any C4 or higher boiling compounds from said distillation column reactor as bottoms.
Description:
SELECTIVE HYDROGENATION OF DIENES AND ACETYLENES IN C 3 STREAMS BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to the selective hydrogenation of di-olefins acetylenic compounds in a propylene rich stream. More particularly the invention relates to a process utilizing a supported palladium oxide catalyst as both the catalyst and as a distillation structure for the simultaneous reaction and separation of the reactants and reaction products. Related Art Mixed refinery streams often contain a broad spectrum of olefinic compounds. This is especially true of products from either catalytic cracking or thermal cracking processes. These olefinic compounds comprise ethylene, acetylene, propylene, propadiene, methyl acetylene, butenes, butadiene, etc. Many of these compounds are valuable, especially as feed stocks for chemical products. Ethylene, especially is recovered. Additionally, propylene and the butenes are valuable. However, the olefins having more than one double bond and the acetylenic compounds (having a triple bond) have lesser uses and are detrimental to many of the chemical process in which the single double bond compounds are used, for example polymerization.

Hydrogenation is the reaction of hydrogen with a carbon- carbon multiple bond to "saturate" the compound. This reaction has long been known and is usually done at superatmospheric pressures and moderate temperatures using an excess of hydrogen over a metal catalyst. Among the metals known to catalyze the hydrogenation reaction are platinum, rhenium, cobalt, molybdenum, nickel, tungsten and palladium. Generally, commercial forms of catalyst use supported oxides of these metals. The oxide is reduced to the active form either prior to use with a reducing agent

or during use by the hydrogen in the feed. These metals also catalyze other reactions, most notably dehydrogenation at elevated temperatures. Additionally they can promote the reaction of olefinic compounds with themselves or other olefins to produce dimers or oligomers as residence time is increased.

Selective hydrogenation of hydrocarbon compounds has been known for quite some time. Peterson, et al in "The Selective Hydrogenation of Pyrolysis Gasoline" presented to the Petroleum Division of the American Chemical Society in September of 1962, discusses the selective hydrogenation of C and higher di-olefins. Boitiaux, et al in "Newest Hydrogenation Catalyst", Hydrocarbon Processing, March 1985, presents an over view of various uses of hydrogenation catalysts, including selective hydrogenation of a propylene rich stream. US Patent No. 5,087,780 discloses the hydroisomerization of mixed C 4 streams and the hydrogenation of butadiene.

As noted in the Boitiaux article, selective hydrogenation of a propylene rich cut from a steam cracker or catalytic cracker is mandatory for high-purity propylene production. This cut contains some methyl acetylene and propadiene (MAPD) which must be removed. Partial hydrogenation of the methyl acetylene and propadiene produces additional propylene resulting in propylene yields greater than 100%. Prior art vapor phase reactions results in catalyst deactivation, while in the liquid phase some Cg and Cg olefins are formed. The new catalyst described in the Boitiaux article while an improvement still produced about 0.15 wt% (1500 ppm) C 6 oligomer content when the residual propadiene is within the specifications for polymerization grade propylene. h e use of a solid particulate catalyst as part of a distillation structure in a combination distillation column reactor for various reactions is described in U.S. Pat. No.s: (etherification) 4,232,177; 4,307,254; 4,336,407; 4,504,687; 4,918,243; and 4,978,807; (di erization) 4,242,530; (hydration) 4,982,022; (dissociation) 4,447,668;

and (aromatic alkylation) 4,950,834 and 5,019,669. Additionally U.S. Pat. No.s 4,302,356 and 4,443,559 disclose catalyst structures which are useful as distillation structures. It is an advantage of the present process that the di¬ olefins (dienes) and acetylenic compounds contained within the propylene stream are converted to propylene with very little if any formation of oligomers of propylene.

SUMMARY OF THE INVENTION Briefly, the present invention comprises the selective hydrogenation of acetylenic compounds and di-olefins contained within a propylene rich stream to purify the stream and obtain greater amounts of the propylene. The propylene rich stream is fed to a distillation column reactor into a reaction distillation zone containing a supported palladium oxide catalyst in the form of a catalytic distillation structure. Hydrogen is provided as necessary to support the reaction and to reduce the oxide and maintain it in the hydride state. The distillation column reactor is operated at a pressure such that the reaction mixture is boiling in the bed of catalyst. If desired, a bottoms stream containing any higher boiling material may be withdrawn to effectuate a complete separation. Essentially all of the acetylenic materials and propadiene are converted to propylene. Additionally, there is very little, if any, hydrogenation of the propylene to propane. There is no loss of propylene.

More preferably the present invention is a process for the selective hydrogenation of the di-olefins and acetylenic compounds contained within a propylene rich stream, comprising the steps of:

(a) feeding (1) a first stream comprising propylene, di-olefins and acetylenic compounds and (2) a second stream containing hydrogen to a distillation column reactor into a feed zone;

(b) concurrently in said distillation column reactor

(i) contacting said first and second streams in a distillation reaction zone with a hydrogenation catalyst

capable of acting as a distillation structure thereby reacting essentially all of said di-olefins and acetylenic compounds with said hydrogen to form propylene and other hydrogenated products in a reaction mixture, and (ii) separating the propylene contained in said first stream and the propylene formed by the reaction of said di-olefins and said acetylenic compounds from said reaction mixture by fractional distillation and

(c) withdrawing the separated propylene from step (b) (ii) along with any propane and lighter compounds, including any unreacted hydrogen, from said distillation column reactor as overheads. Optionally the process may include withdrawing any C 4 or higher boiling compounds from said distillation column reactor as bottoms. Although the reaction may be described as taking place in a mixed phase (the mixture is boiling) there is unexpectedly no oligomerization noted. This may be attributed to the fact that the propylene is boiled upward away from the catalyst continuously, reducing the residence time in the reaction distillation zone.

DESCRIPTION OF THE PREFERRED EMBODIMENT The hydrogenation reactions have been described as reversible. See for example the Peterson article cited above. Additionally, the same catalysts are known to promote the dehydrogenation reaction at elevated temperatures (above about 900°F) . In the instant process where the catalyst serves as a distillation component, the equilibrium is constantly disturbed, thus driving the reaction toward the hydrogenation. As described the catalytic material employed in the hydrogenation process is in a form to serve as distillation packing. Broadly stated, the catalytic material is a component of a distillation system functioning as both a catalyst and distillation packing, i.e., a packing for a distillation column having both a distillation function and a catalytic function.

The reaction system can be described as heterogenous since the catalyst remains a distinct entity. The

catalyst may be employed as palladium oxide, preferably 0.1 to 5.0 weight %, supported on an appropriate support medium such as alumina, carbon or silica, e.g., 1/8" alumina extrudates, preferably in bags as described herein or as conventional distillation packing shapes as Raschig rings, Pall rings, saddles or the like.

It has been found that placing the supported catalyst into a plurality of pockets in a cloth belt, which is supported in the distillation column reactor by open mesh knitted stainless steel wire by twisting the two together into a helix, allows the requisite flows, prevents loss of catalyst, allows for normal swelling if any, of the catalyst and prevents breakage of the extrudates through mechanical attrition. This novel catalyst arrangement is described in detail in commonly owned US Patent No. 4,242,530 and US Pat. No. 4,443,559 which are incorporated herein.

The cloth may be of any material which is not attacked by the hydrocarbon feeds or products or catalyst under the conditions of the reaction. Cotton or linen may be useful, but fiber glass cloth or TEFLON cloth is preferred. A preferred catalyst system comprises a plurality of closed cloth pockets arranged and supported in the distillation column reactor by wire mesh intimately associated therewith.

A new catalyst structure developed for use in hydrogenations is described in US Serial No. 790,771, filed 06/22/92 which is incorporated herein in its entirety. Briefly the new catalyst structure is a catalytic distillation structure comprising flexible, semi-rigid open mesh tubular material, such as stainless steel wire mesh, filed with a particulate catalytic material said tubular material having two ends and having a length in the range of from about one-half to twice the diameter of said tubular material, a first end being sealed together along a first axis to form a first seam and a second end being sealed together along a second axis to form a second seam wherein the plane of the first seam along the axis of said

tubular material and the plane of the second seam along the axis of said tubular material bisect each other at an angle of about 15 to 90°.

The particulate catalyst material may be a powder, small irregular chunks or fragments, small beads and the like. The particular form of the catalytic material in the cloth pockets is not critical, so long as sufficient surface area is provided to allow a reasonable reaction rate. The sizing of catalyst particles can be best determined for each catalytic material (since the porosity or available internal surface area will vary for different material and of course affect the activity of the catalytic material) .

A catalyst suitable for the present process is 3.0 wt%

PdO on 1/8" AI2O 3 (alumina) extrudates, hydrogenation catalyst, supplied by United Catalysts Inc. designated as

G68F. Typical physical and chemical properties of the catalyst as provided by the manufacturer are as follows:

TABLE I Designation G68F Form spheres

Nominal size 3x6 Mesh

Pd. wt% 3.0

Support High purity alumina

The catalyst is believed to be the hydride of palladium which is produced during operation.

The hydrogen rate to the reactor must be sufficient to maintain the catalyst in the active form because hydrogen is lost from the catalyst by hydrogenation. The hydrogen rate must be adjusted such that it is sufficient to support the hydrogenation reaction and replace hydrogen lost from the catalyst but kept below that required for hydrogenation of propylene and to prevent flooding of the column which is understood to be the "effectuating amount of hydrogen " as that term is used herein. Generally the mole ratio of hydrogen to acetylenic compounds in the feed to the fixed bed of the present invention will be about 1.05 to 2.5 preferably 1.4 to 2.0. The presence of hydrogen feed as described herein does not adversely effect the physical

operation of the catalytic distillation system.

The present invention carries out the method in a catalyst packed column which can be appreciated to contain a vapor phase and some liquid phase as in any distillation. The success of the catalytic distillation approach lies in an understanding of the principles associated with distillation. First, because the reaction is occurring concurrently with distillation, the initial reaction products are removed from the reaction zone as quickly as possible. Second, because all the components are boiling the temperature of reaction is controlled by the boiling point of the mixture at the system pressure. The heat of reaction simply creates more boil up, but no increase in temperature at a given pressure. Third, the reaction has an increased driving force because the reaction products have been removed and cannot contribute to a reverse reaction (LeChatelier's Principle).

As a result, a great deal of control over the rate of reaction and distribution of products can be achieved by regulating the system pressure. Also, adjusting the throughput (residence time = liquid hourly space velocity -1 ) gives further control of product distribution and to a degree control of the side reactions such as oligomerization. The temperature in the reactor is determined by the boiling point of the liquid mixture present at any given pressure. The temperature in the lower portions of the column will reflect the constitution of the material in that part of the column, which will be higher than the overhead; that is, at constant pressure a change in the temperature of the system indicates a change in the composition in the column. To change the temperature the pressure is changed. Temperature control in the reaction zone is thus effected by a change in pressure; by increasing the pressure, the temperature in the system is increased, and vice versa.

The distillation column reactor is operated at a pressure such that the reaction mixture is boiling in the

bed of catalyst. A "froth level" may maintained throughout the catalyst bed by control of the bottoms and/or overheads withdrawal rate which improves the effectiveness of the catalyst thereby decreasing the height of catalyst needed. As may be appreciated the liquid is boiling and the physical state is actually a froth having a higher density than would be normal in a packed distillation column but less than the liquid without the boiling vapors.

In the present process the hydrocarbon stream is rich in propylene such as a C 3 cut from the gas plant of a fluid catalytic cracking unit or a steam cracker. A typical analysis of such a stream is given in Table II below.

TABLE II

The propylene containing feed and the hydrogen may be fed to the distillation column rector separately or they may be mixed prior to feeding. A mixed feed is fed below the catalyst bed or at the lower end of the bed. Hydrogen alone is fed below the catalyst bed and the C 3 stream is

fed below the bed up to about the lower one-third of the bed. The pressure selected is that which maintains the dienes and acetylenes in the catalyst bed wile allowing the propylene and lighter to distill overhead. Any unreacted hydrogen exits overhead with the C 3 's.

The pilot unit used was a 1 inch laboratory column fifteen feet in height. The catalyst, 240 grams of 0.3 wt% PdO on 1/8 inch alumina extrudates) was placed in two inch pouches of distillation wire mesh packing to form the catalytic distillation structures described in the U.S. Serial No. 07/790,771 incorporated herein. The catalytic distillation structures were loaded into the middle ten feet of the column with the lower and upper 2.5 feet filled with inert distillation packing. The propylene rich feed and hydrogen were started to the column and heat added to initiate the reaction. The overhead pressure was maintained at between 240 and 315 psig. In the pilot unit no bottoms were taken, and an equilibrium amount of 0 4 *3 + of about 15 vol% was present in the lower section of the column as indicated by a constant temperature of about 140°F. The constant temperature also indicated that no build up of heavier materials occurred as a result of any oligomerization. If there were any residual diene the bottoms temperature would have increased as the heavies built up, thus indicating total selective removal of the dienes and acetylenes. In commercial or larger scale units a bottoms draw would probably be included to effectuate the separation of the C 4 's + from the propylene product. Table II below gives the results from the pilot unit run.

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