Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By contact with solid sorbent
Reexamination Certificate
2001-11-30
2004-01-20
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By contact with solid sorbent
C585S809000, C585S820000, C585S826000
Reexamination Certificate
active
06680419
ABSTRACT:
FIELD OF THE INVENTION
The field of this invention relates to use of heterogeneous adsorbents in purification of relatively impure olefins such as are typically produced by thermal cracking of suitable hydrocarbon feedstocks. More particularly, this invention concerns purification by passing an olefinic process stream, containing small amounts of acetylenic impurities, and optionally carbon oxides and/or other organic components which are, typically, impurities in cracked gas, through a particulate bed of heterogeneous adsorbent comprising a metal supported on a high surface area carrier, under conditions suitable for adsorption of alkynes. Beneficially, a limited amount of dihydrogen is fed into the bed during treatment of the olefinic process stream thereby increasing capacity of the adsorbent for acetylenics.
Beneficially, a sub-stoichiometric amount of dihydrogen is admixed with the olefinic process stream fed into the bed thereby increasing capacity of the adsorbent for acetylenics.
Processes according to this invention are particularly useful where the olefin being purified is ethylene and/or propylene formed by thermal cracking of hydrocarbon feedstocks.
BACKGROUND OF THE INVENTION
As is well known, olefins, or alkenes, are a homologous series of hydrocarbon compounds characterized by having a double bond of four shared electrons between two carbon atoms. The simplest member of the series, ethylene, is the largest volume organic chemical produced today. Olefins including, importantly, ethylene, propylene and smaller amounts of butadiene, are converted to a multitude of intermediate and end products on a large scale, mainly polymeric materials.
Commercial production of olefins is, almost exclusively, accomplished by pyrolysis of hydrocarbons in tubular reactor coils installed in externally fired heaters. Thermal cracking feed stocks include streams of ethane, propane or a hydrocarbon liquid ranging in boiling point from light straight-run gasoline through gas oil. Because of the very high temperatures employed, commercial olefin processes invariably coproduce significant amounts of acetylene and methyl acetylene. Required separation of the acetylene from the primary olefin can, considerably, increase the plant cost.
In a typical ethylene plant the cracking section represents about 25 percent of the cost of the unit while the compression, heating, dehydration, recovery and refrigeration sections represent the remaining about 75 percent of the total. This endothermic process is carried out in large pyrolysis furnaces with the expenditure of large quantities of heat which is provided in part by burning the methane produced in the cracking process. After cracking, the reactor effluent is put through a series of separation steps involving cryogenic separation of products such as ethylene and propylene. The total energy requirements for the process are thus very large and ways to reduce it are of substantial commercial interest. In addition, it is of interest to reduce the amount of methane and heavy fuel oils produced in the cracking processor to utilize it other than for its fuel value.
Hydrocarbon cracking is carried out using a feed which is ethane, propane or a hydrocarbon liquid ranging in boiling point from light straight-run gasoline through gas oil. Ethane, propane, liquid naphthas, or mixtures thereof are preferred feed to a hydrocarbon cracking unit. Hydrocarbon cracking is, generally, carried out thermally in the presence of dilution steam in large cracking furnaces which are heated by burning, at least in part, methane and other waste gases from the olefins process resulting in large amounts of NOx pollutants. The hydrocarbon cracking process is very endothermic and requires large quantities of heat per pound of product. However, newer methods of processing hydrocarbons utilizes at least to some extent catalytic processes which are better able to be tuned to produce a particular product slate. The amount of steam used per pound of feed in the thermal process depends to some extent on the feed used and the product slate desired. Typically, steam pressures are in the range of about 30 lbs per sq in to about 80 lbs per sq in, and amounts of steam used are in the range of about 0.2 pounds of steam per pound of feed to 0.7 pounds of per pound of feed. The temperature, pressure and space velocity ranges used in thermal hydrocarbon cracking processes to some extent depend upon the feed used and the product slate desired which are well known as may be appreciated by one skilled in the art.
The type of furnace used in the thermal cracking process is also well known. However the ceramic honeycomb furnace which is described in U.S. Pat. No. 4,926,001, the contents of which patent are specifically incorporated herein by reference, is an example of a new type of cracking which could have a special utility for this process.
Several methods are known for separation of an organic gas containing unsaturated linkages from gaseous mixtures. These include, for instance, cryogenic distillation, liquid adsorption, membrane separation and the so called “pressure swing adsorption” in which adsorption occurs at a higher pressure than the pressure at which the adsorbent is regenerated. Cryogenic distillation and liquid adsorption are common techniques for separation of carbon monoxide and alkenes from gaseous mixtures containing molecules of similar size, e.g., nitrogen or methane. However, both techniques have disadvantages such as high capital cost and high operating expenses. For example, liquid adsorption techniques suffer from solvent loss and need a complex solvent make-up and recovery system.
Molecular sieves which selectively adsorb carbon monoxide from gaseous mixtures by chemisorption are also known. U.S. Pat. Nos. 4,019,879 and 4,034,065 refer to use of high silica zeolites, which have relatively high selectivities for carbon monoxide, in the pressure swing adsorption method. However, these zeolites only have moderate capacity for carbon monoxide and more particularly require very low vacuum pressures to recover the adsorbed gases and/or to regenerate the zeolite.
U.S. Pat. No. 4,717,398 describes a pressure swing adsorption process for selective adsorption and subsequent recovery of an organic gas containing unsaturated linkages from gaseous mixtures by passing the mixture over a zeolite ion-exchanged with cuprous ions (Cu I) characterized in that the zeolite has a faujasite type crystalline structure (Y).
U.S. Pat. No. 6,215,037 in the name of Joel Padin, Curtis L. Munson and Ralph T. Yang provides a selection of specific zeolites said to be useful for selective adsorption of dienes from mono-olefins. In particular, the adsorbents are ion-exchanged zeolites of the group consisting of zeolite X, Zeolite Y and zeolite LSX in a form having exchangeable cationic sites. According to the patent, essentially all cationic sites of the ion-exchanged zeolite must contain silver cation or copper cation for the selective separation of diene from mono-olefin which the same number of carbon atoms.
Kokai JP Number 50929-1968 describes a method of purifying vinyl compounds containing up to about 10 percent by weight of acetylene compounds including ethyl acetylene, vinyl acetylene and phenyl acetylene whereby the acetylene compounds are adsorbed in an adsorption agent of 1-valent and/or 0-valent copper and/or silver supported on inert carrier such as &dgr;-alumina, silica or active carbon. However, it is well known that acetylene and these acetylene compounds react with copper and/or silver to from copper acetylide or silver acetylide. Both the acetylide of copper and silver are unstable compounds. Because they are explosive under some conditions their possible formation presents safety problems in operation and in handling adsorbent containing such precipitates.
German Disclosure Document 2059794 describes a liquid adsorption process for purification of paraffinic, olefinic and/or aromatic hydrocarbons with an adsorption agent consisting in essence of a complex of a copper (Cu I)-salt with
Foral Michael J.
Satek Larry C.
Ventura Diadema N.
BP Corporation North America Inc.
Griffin Walter D.
Henes James R.
Nguyen Tam M.
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