Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2001-03-30
2003-01-21
Wood, Elizabeth D. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S300000, C502S325000, C502S326000, C502S328000, C502S329000, C502S332000, C502S333000, C502S339000
Reexamination Certificate
active
06509292
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
This invention relates to a process for selective hydrogenation of acetylene in an olefinic feed stream, particularly for ethylene purification. This invention also relates to a catalyst, its process of preparation and its use for the selective hydrogenation of acetylene, particularly for ethylene purification.
2. Prior Art
The manufacture of unsaturated hydrocarbons usually involves cracking various types of hydrocarbons and often produces a crude product containing hydrocarbon impurities that are more unsaturated than the desired product. These unsaturated hydrocarbon impurities are often very difficult to separate by fractionation from the desired product. A common example of this problem occurs with ethylene purification, in which acetylene is a common impurity. It is often difficult, industrially, to remove such undesirable, highly unsaturated hydrocarbons by hydrogenation without significant hydrogenation of the desired hydrocarbons. One example of this process is described in UK Pat. No. 916,056.
Two general types of gas phase selective hydrogenation processes for removing undesired, unsaturated hydrocarbons have come into use. One, known as “front-end” hydrogenation, involves passing the crude gas from the initial cracking step, after removal of steam and condensible organic material, over a hydrogenation catalyst. Despite the large hydrogen content of such gas, which is very greatly in excess of the quantity of acetylenes that are present and which quantity should be sufficient to hydrogenate a substantial part of those acetylenes, substantially complete hydrogenation of acetylene with sufficient selectivity to produce olefins of polymerization quality is often a problem. The high concentration of hydrogen present in the front-end systems requires a very selective catalyst that does not substantially hydrogenate the ethylene. Overhydrogenation can lead to a thermal excursion in reactors, known as “run-away”. Under “run-away” conditions, high temperatures are experienced, severe loss of ethylene occurs and catalyst damage takes place. In addition, furnace upsets in the front-end reactor system can result in swings of CO concentration from moderate levels to very low levels. Existing front-end catalysts cannot tolerate these swings in CO concentration very well and often are prone to “run-away”. In the front-end reactor system, the catalyst is also exposed to high space velocity operations 10,000-12,000 GHSV per bed. In the other type of gas phase selective hydrogenation, known as “tail-end” hydrogenation, the crude gas is fractionated and the resulting concentrated product streams are individually reacted with hydrogen in a slight excess over the quantity required for hydrogenation of the highly unsaturated acetylenes which are present. However, in tail-end use there is a greater tendency for deactivation of the catalyst, and consequently, periodic regeneration of the catalyst is necessary. Tail-end reactor systems operate at lower GHSV of 2500-5000 per bed. H2 addition can also be adjusted to maintain selectivity. However, formation of polymers is a major problem. Thermal excursion is not a problem.
A number of patents have discussed the selective hydrogenation of unsaturated hydrocarbons such as U.S. Pat. Nos. 4,126,645, 4,367,353, 4,329,530, 4,347,392 and 5,414,170.
The catalysts that are preferred for the selective hydrogenation reactions include palladium supported on an alumina substrate, as disclosed for example in U.S. Pat. Nos. 3,113,980, 4,126,645 and 4,329,530. Other gas phase palladium on alumina catalysts for the selective hydrogenation of acetylene compounds are disclosed, for example, in U.S. Pat. Nos. 5,925,799, 5,889,138, 5,648,576 and 4,126,645.
One of the problems with palladium on alumina catalysts is that under normal operating conditions not only is the acetylene hydrogenated, a substantial portion of the ethylene is also converted to ethane. In addition, these palladium on alumina catalysts often have relatively low stability due to the formation of large amounts of oligomers on the catalyst surface.
To overcome this problem, enhancers are added to the palladium which improve the catalyst properties. One common enhancer which is added to a palladium on alumina catalyst is silver. For example, conventional acetylene hydrogenation catalysts for ethylene purification comprising palladium and silver on a support material are disclosed in U.S. Pat. Nos. 4,404,124, 4,484,015, 5,488,024, 5,489,565 and 5,648,576. Specifically, U.S. Pat. No. 5,648,576 discloses a selective hydrogenation catalyst for acetylene compounds comprising from about 0.01 to 0.5 weight percent of palladium and, preferably, from about 0.001 to 0.02 percent by weight of silver. 80 percent or more of the silver is placed within a thin layer on the surface of the carrier body.
Catalysts comprising palladium, silver, an alkali metal fluoride and a support material, which are utilized for the hydrogenation of other feed stream impurities, such as dienes and diolefins, are disclosed, for example, in U.S. Pat. No. 5,489,565.
Catalysts comprising palladium and gold on a catalyst support which may be used for the hydrogenation of acetylenes and diolefins have also been suggested by U.S. Pat. Nos. 4,533,779 and 4,490,481. These patents disclose the use of a substantially greater amount of palladium than of gold, specifically 0.03 to about 1 percent by weight palladium and from 0.003 to 0.3 percent by weight gold. The ratio of the palladium to the gold is from 10:1 to about 2:1 as shown in Example 3 of both patents.
Other patents that disclose or suggest the use of palladium and gold on a carrier include U.S. Pat. No. 3,974,102 (isomerization of alpha-pinene) and U.S. Pat. No. 4,136,062 (oxidative dehydrogenation), FR 2,482,953 (U.S. Pat. No. 4,409,410 (selective hydrogenation of diolefins with silver and palladium)) and GB 802,100 (selective hydrogenation of acetylene with palladium and an element selected from the group consisting of copper, gold and silver, preferably silver).
A heterogeneous bimetallic palladium/gold catalyst for vinyl acetate production is disclosed in WO 97/44130. This catalyst is prepared by forming a first shell dispersion coating of colloidal palladium on a catalyst support surface and superimposing a second shell dispersion coating of colloidal gold metal on the first shell dispersion coating. An organometallic gold compound is employed to apply the gold dispersion on the catalyst support surface.
While conventional silver/palladium-based catalysts for the selective hydrogenation of acetylene have been useful, there are a number of problems that have been discovered from their use, including a relatively low tolerance to carbon monoxide concentration swings, lower selectivity than is desirable by the industry, and problems with high space velocity operation. Further, because the silver on these promoted catalysts reoxidizes quite easily during conventional preparation, transportation, installation and use, it is generally necessary to prereduce the silver-promoted catalyst in-situ before selective hydrogenation of the acetylene for the most efficient hydrogenation.
The catalysts of the invention are designed to address these problems and deficiencies in conventional ethylene purification catalysts.
Accordingly, it is an object of this invention to disclose a process for the selective hydrogenation of a C
2
and C
3
olefinic feed streams containing acetylenic impurities, particularly for ethylene purification.
It is a still further object of this invention to disclose a process for the front-end selective hydrogenation of acetylenic impurities, whereby the quantity of the desirable C
2
and C
3
olefins, particularly ethylene, is not substantially reduced.
It is a still further object of this invention to disclose process steps for the front end selective hydrogenation of a C
2
and C
3
olefinic feed stream containing acetylenic impurities, particularly for ethylene purification.
It is a still further object of the inve
Blankenship Steven A.
Fried, Jr. James E.
Perkins Jennifer A.
Voight Richard W.
Cox Scott R.
Sud-Chemie Inc.
Wood Elizabeth D.
LandOfFree
Process for selective hydrogenation of acetylene in an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for selective hydrogenation of acetylene in an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for selective hydrogenation of acetylene in an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3043171