Mineral oils: processes and products – Chemical conversion of hydrocarbons – With prevention or removal of deleterious carbon...
Reexamination Certificate
2000-10-31
2002-04-16
Preisch, Nadine (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
With prevention or removal of deleterious carbon...
C208S04800Q, C585S950000
Reexamination Certificate
active
06372121
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the field of cracking of hydrocarbons. Specifically this invention is in the field of reducing undesired polymerization of carbonyl compounds in unit operations of hydrocarbon cracking processes.
BACKGROUND OF THE INVENTION
Pyrolysis is the transformation of a compound into one or more other substances by heat alone. In the petroleum and petrochemical industries, pyrolysis is useful for the processing of hydrocarbons. This process is often referred to as “cracking”. When the pyrolysis of hydrocarbons is conducted in the presence of steam, it is often referred to as “steam cracking”. The steam cracking of ethane, propane, naphthas, gas oils and other hydrocarbon feedstocks is a useful process for producing valuable olefins. As a byproduct of the steam cracking process, oxygenated compounds, including carbonyl compounds, are formed. These carbonyl compounds include, but are not limited to, aldehydes and ketones. The amount of carbonyl compounds formed in cracking operations can vary widely, but is typically from about 1 ppm to about 200 ppm in the gas stream with concentrations as high as about 1000 ppm occasionally being encountered because of the use of various feedstocks and cracking temperatures.
Byproducts of hydrocarbon cracking processes include the undesirable acid gases CO
2
and H
2
S. Therefore, it is normal for a hydrocarbon cracking plant to have an acid gas removal system to remove CO
2
and H
2
S from the cracked gas. Typically the acid gas removal system usually consists of passing the gas steam through a basic wash (pH greater than 7) to remove acidic components, including hydrogen sulfide and carbon dioxide gas. In the petroleum and petrochemical industries, unit operations involving basic washes are commonly carried out in equipment referred to as ‘caustic scrubbers’ or ‘caustic towers’. As an alternative to a caustic tower, about 5% of all ethylene cracking plants use amine, instead of caustic, to remove acid gases. These units are often referred to as “amine scrubbers” or “amine towers”.
In an acid gas removal system, some oxygenated compounds are also removed. It is known in the art of hydrocarbon processing that certain of these oxygenated compounds, especially carbonyl compounds and particularly acetaldehyde, will undergo polymerization in the presence of the base. In the acid gas removal system, the acetaldehyde polymer will settle on internal equipment surfaces leading to fouling and eventual plugging. Fouling and plugging of the internal equipment means the unit must be shut down to perform cleaning. Every time a unit operation has to be shut down for cleaning it means that a cost is incurred due to lost production, over and above, the actual cost to clean the equipment.
In addition to the caustic scrubbers and caustic towers where treatment is required to inhibit fouling caused by unwanted polymerization, there are other basic wash unit operations in hydrocarbon processing that also require treatment in order to prevent undesirable polymerization of carbonyl compounds. These other basic wash unit operations include, but are not limited to, amine systems to scrub acid gasses (using higher-boiling aminoalcohols such as, but not limited to, ethanolamine, diethanolamine and derivatives of amino alcohols such as, but not limited to methoxyethylamine), spent caustic oxidizers and benzene strippers. A spent caustic oxidizer converts sulfides into sulfates to allow caustic to be disposed of, or to be sold. A benzene stripper is a unit that uses hydrocarbon, often a high boiling mixture called “pyrolysis gasoline”, taken from other units in the ethylene plant, to wash “spent caustic”. “Spent caustic” is caustic that has been used in other unit operations, such as the caustic tower. The hydrocarbon “washes” residual benzene out of the spent caustic. The unit is called a benzene stripper because the benzene is stripped from the spent caustic.
Ten years ago the amount of undesired polymer that was formed in this way was usually insignificant. As hydrocarbon plants expanded their capacity, the amount of undesired polymer increased and the sheer volume of undesired polymer formed has now become a problem for more and more hydrocarbon plant operators.
Several materials are known and currently being used in the petroleum and petrochemical industries to mitigate carbonyl compound polymer caused fouling. These materials include dispersants, inhibitors, reducing agents and antioxidants.
U.S. Pat. No. 5,714,055 to Lewis et al. describes a method of inhibiting the formation of fouling deposits occurring on the surfaces of an alkaline scrubber used to wash acid gases generated during the manufacturing of olefins by using substituted aromatic amines selected from the group consisting of 2-aminophenol, 4-aminophenol, 4-aminobenzenesulfonic acid and salts thereof, 4-amino-o-cresol, 3-aminophenol, 2-aminobenzoic acid and salts thereof, 3-aminobenzoic acid and salts thereof, and 4-aminobenzoic acid and salts thereof.
U.S. Pat. No. 5,264,114 to Dunbar, describes and claims a method for inhibiting the formation and deposition of fouling materials during caustic washing of hydrocarbon gases contaminated with carbonyl compounds (one group of carbonyl compounds being aldehydes) which comprises: treating said hydrocarbon gases with an aqueous amine solution, wherein said aqueous amine solution comprises water and an amine compound having a concentration range of from about 2 ppm to about 5,000 ppm, and wherein the amine of said aqueous amine solution is selected from the group of organic compounds consisting of the formula RNH
2
and R
2
NH wherein R is selected from the group consisting of alkyl groups and aryl groups, before said caustic washing, to remove a significant amount of said carbonyl compounds and to thereby produce a treated hydrocarbon stream.
U.S. Pat. No. 5,194,143 to Roling describes and claims a method for inhibiting the formation of polymeric based fouling deposits during the basic washings of olefin-containing hydrocarbons contaminated with oxygenated compounds comprising adding to the wash about 1 to about 10,000 parts per million acetoacetate ester compound having the formula
CH
3
COCH
2
CO
2
C
x
H
y
wherein x is an integer from about 1 to about 8 and y is an integer from about 3 to about 17.
U.S. Pat. No. 4,952,301 to Awbrey describes and claims a method for inhibiting the formation of polymeric based fouling deposits which, in the absence of inhibition treatment, are formed during the basic washing of hydrocarbons contaminated with oxygen-containing compounds, said method comprising adding to the wash an inhibiting amount of an ethylenediamine compound of the formula
NH
2
(CH
2
CH
2
NH)
x
H
wherein x is an integer of from about 1 to about 10.
U.S. Pat. No. 4,673,489 to Roling describes and claims a method for inhibiting the formation and deposition of fouling materials during the basic washing of hydrocarbons contaminated with oxygenated compounds which comprises performing the wash of the hydrocarbon in the presence of a sufficient amount of hydroxylamine, of the formula NH
2
OH or an acid salt or mixtures thereof, for inhibiting the formation and deposition of foulant.
U.S. Pat. No. 5,220,104 to McDaniel et al. describes and claims a method for inhibiting the formation and deposition of fouling materials during basic washing of hydrocarbons contaminated with oxygenated compounds which comprises performing the washing of the hydrocarbons in the presence of a solution comprising a percarbonate compound in an amount sufficient to inhibit the formation and deposition of fouling materials.
U.S. Pat. No. 5,160,425 to Lewis describes and claims a method of inhibiting formation of polymeric fouling deposits during the caustic scrubbing of pyrolytically produced hydrocarbons contaminated with oxygen containing compounds with a basic washing solution having a pH greater than 7 comprising adding to the basic washing solution a sufficient amount of carbohydrazide for inhibiting formation of polymeric fouling materials.
U.S. P
Glath Raymond M.
McClain Robert D.
Patel Natu R.
Breininger Thomas M.
Brumm Margaret M.
Nalco/Exxon Energy Chemicals L.P.
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