Multi-bed selective hydrogenation of acetylenes

Details Multi-bed selective hydrogenation of acetylenes Multi-bed selective hydrogenation of acetylenes

1996-05-03

2000-01-04

Langel, Wayne

Chemistry of hydrocarbon compounds

Adding hydrogen to unsaturated bond of hydrocarbon, i.e.,...

Hydrocarbon is contaminant in desired hydrocarbon

585263, 585265, C07C 508, C07C 509

Patent

active

060111887

DESCRIPTION:

BRIEF SUMMARY
This invention relates to hydrogenation and in particular to the selective catalytic hydrogenation of acetylene in the presence of olefins.
Olefins are often produced by reforming or cracking a hydrocarbon feedstock such as naphtha: as a result of the production process, small proportions of acetylene and other more highly unsaturated compounds are often formed. It is normally desirable to remove the acetylene before further processing of the olefin product.
While it is often possible to effect partial separation by fractionation, removal of the acetylene to very low levels by fractionation is often difficult. Consequently it is more usual to selectively hydrogenate the acetylene in the presence of the olefins, for example using a supported palladium catalyst as described in U.S. Pat. No. 4,329,530.
Since the hydrogenation reaction is exothermic, and low hydrogenation temperatures are required in order to minimise the hydrogenation of the olefins present, the selective hydrogenation is normally effected using a series of adiabatic catalyst beds with inter-bed cooling. Alternatively an isothermal bed, followed by one or more adiabatic beds, is sometimes employed with the temperature in the isothermal bed maintained essentially constant by means of suitable heat exchange means within the bed to extract the heat of reaction into a suitable coolant: again it is normal to operate the beds at successively decreasing bed temperatures, and so inter-bed cooling is required.
A series of beds, rather than a single bed, is normally used to keep the temperature to a minimum since as the temperature increases, the hydrogenation becomes less selective and an increasing amount of the olefins become hydrogenated. Furthermore as the temperature increases, there is a risk of run-away reactions occurring. Thus in operation, part of the desired hydrogenation is effected in a first catalyst bed, without an undue temperature rise, and then the product from the first bed is cooled and passed through a second catalyst bed in order to effect further hydrogenation. Further catalyst beds, with inter-bed cooling, may be employed: the number of beds used will normally depend on the acetylene and content of the feed and the desired acetylene content of the product. Typically there may be a total of 2 to 5 beds. Using typical selective hydrogenation catalysts such as a support impregnated with small amounts, eg 0.02 to 0.5% by weight, of palladium, the catalyst bed inlet temperature is generally in the range 50-100.degree. C., particularly 50-90.degree. C. As is well known, it is generally desirable to have a small proportion of carbon monoxide, eg 200-1500 ppm by volume, in the gas stream subjected to selective hydrogenation.
The hydrogenation catalyst generally gradually loses activity over a period of use: often this loss of activity is a result of poisoning of the catalyst with impurities, particularly sulphur, iron, and/or arsenic compounds, in the feed and by formation of organic compounds, such as polymers, which accumulate on the surface of the catalyst. Consequently, as the catalyst activity decreases it is the normal practice to increase the temperature at which the feed is fed to the first bed. For example during the normal life of the catalyst the inlet temperature may gradually be increased from an initial value of about 60.degree. C. to an "end-of-life" inlet temperature of about 90.degree. C. One consequence of this is that, as the activity of the catalyst decreases and the inlet temperature is increased to compensate for the loss of activity, the proportion of olefins hydrogenated gradually increases.
We have devised a method whereby the increasing effective loss of olefins resulting from such increased unwanted hydrogenation as the catalyst activity declines may be minimised.
In the present invention, in order to compensate for the decline of catalyst activity, instead of increasing the temperature at which the mixture is fed to the first bed and providing cooling so that the product from the first bed is cooled before i

REFERENCES:
patent: 3412169 (1968-11-01), Clark
patent: 3471582 (1969-10-01), Lupfer
patent: 3656911 (1972-04-01), Hobbs
patent: 4236219 (1980-11-01), Killebrew, Jr. et al.
patent: 4249908 (1981-02-01), Funk
patent: 5254758 (1993-10-01), Hiles et al.

Affiliated with

Also associated with

Rating

Multi-bed selective hydrogenation of acetylenes does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Multi-bed selective hydrogenation of acetylenes, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multi-bed selective hydrogenation of acetylenes will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1073878