Patent Application
20130172654
The present invention is a process for removing oxygenated contaminants from an hydrocarbon stream. In a specific embodiment said hydrocarbon stream comprises olefins.
Olefins are traditionally produced from petroleum feedstocks by catalytic or steam cracking processes. These cracking processes, especially steam cracking, produce light olefin(s), such as ethylene and/or propylene, from a variety of hydrocarbon feedstock. Ethylene and propylene are important commodity petrochemicals useful in a variety of processes for making plastics and other chemical compounds.
The limited supply and increasing cost of crude oil has prompted the search for alternative processes for producing hydrocarbon products. The MTO process produces light olefins such as ethylene and propylene as well as heavy hydrocarbons such as butenes. Said MTO process is the conversion of methanol or dimethylether by contact with a molecular sieve. The interest in the methanol to olefin (MTO) process is based on the fact that methanol can be obtained from coal or natural gas by the production of synthesis gas which is then processed to produce methanol.
The effluent produced by a MTO process is a complex mixture comprising the desired light olefins, unconverted oxygenates, by-product oxygenates, heavier hydrocarbons and large amounts of water. The separation and purification of this mixture to recover the light olefins and other valuable by-products is critical to the overall efficiency and cost effectiveness of the process. In particular, it is important that the purification scheme produces products that are substantially free of impurities, which could adversely effect downstream processing. For example, certain oxygenate components present in the effluent from an oxygenate conversion process, particularly aldehydes and ketones, may cause problems in olefin recovery operations and in derivative manufacturing processes that feed and react C4+ hydrocarbons. There is therefore a need to ensure that the effluent purification scheme effectively removes aldehydes and ketones from the olefinic and C4+ hydrocarbon components while at the same time minimizing loss of useful product.
WO 2006-048098 A1 describes a method for removing oxygen-containing organic compounds from mixtures of various hydrocarbon compounds. A liquid phase containing hydrocarbons and oxygenates is supplied to a first column to produce a light fraction comprising the oxygenates and a bottom fraction. Said light fraction and a gaseous mixture of hydrocarbons and oxygenates are then supplied to a second column. A separation by distillation into a light and a heavy hydrocarbon fraction takes place in said second column, wherein an additional solvent is fed to the upper part of said second column which dissolves the oxygenates prior to discharging them in the bottom product of said second column. As a result, an oxygenate-free hydrocarbon product exits the head of the second column and a mixture of oxygenates, solvents and remaining hydrocarbons is removed from the bottom of the second column. The solvent can be partially or completely regenerated and recycled to the extractive distillation column. The solvent can be an alcohol such as methanol, ethanol, propanol or diethyleneglycol or N-Methyl-Pyrrolidone (NMP). The examples are made with methanol and NMP.
US 20030045655 A1 provides a method of extracting an oxygenate from an olefin containing stream. The method comprises contacting the olefin containing stream with an extractant; and separating the contacted olefin containing stream and extractant using extractive distillation. Preferably, the extractant is a polar liquid composition at 1 atm., having an average boiling point of at least 38° C. at 1 atm. More preferably, the polar liquid composition comprises at least 75 wt. % water, alcohol, or a mixture thereof. The extractants are also desirably polar compositions. Such compositions preferably contain compounds such as water, monohydric alcohols, polyhydric alcohols, or mixtures thereof. Preferred monohydric alcohols include ethanol and propanol. Preferred polyhydric alcohols include glycols. Preferred glycols include ethylene glycol and triethylene glycol. It is desirable that the extractant contains at least about 75 wt. % water, monohydric alcohol, and or polyhydric alcohol, preferably at least about 85 wt. %, more preferably at least about 90 wt. %, and most preferably at least about 95 wt. %. Water is most preferred as the extractant.
US 20030098281 A1 describes a method of controlling water and/or oxygenate concentrations of an olefin stream. The method includes contacting the olefin stream with a liquid absorbent. The liquid absorbent is selected from the group consisting of a polyol, amine, amide, nitrile, heterocyclic nitrogen containing compound, and mixtures thereof.
WO 03 020678 A2 describes a method of removing dimethyl ether from an olefin stream made from an oxygenate to olefin reaction process, comprising: contacting oxygenate with a molecular sieve catalyst to form an olefin stream, wherein the olefin stream comprises ethylene, propylene, dimethyl ether and C4+ olefin and higher boiling point hydrocarbons, separating the olefin stream into a first stream comprising the ethylene, propylene and dimethyl ether and a second stream comprising the C4+ olefin and higher boiling point hydrocarbons, and separating the dimethyl ether present in the first stream using extractive distillation. The extractants are desirably polar compositions. Such compositions preferably contain compounds such as water, monohydric alcohols, polyhydric alcohols, or mixtures thereof. Preferred monohydric alcohols include ethanol and propanol. Preferred polyhydric alcohols include glycols. Preferred glycols include ethylene glycol and tri-ethylene glycol. It is desirable that the extractant contains at least about 75 wt. % water, monohydric alcohol, and or polyhydric alcohol, preferably at least about 85 wt. %, more preferably at least about 90 wt. %, and most preferably at least about 95 wt. %. Water is most preferred as the extractant.
WO 03 020670 A1 provides a method for removing oxygenated components such as acetaldehyde, CO2 and/or water from an olefin stream. It explains it is desirable to remove such oxygenated components, since they may poison catalysts that are used to further process olefin composition. In addition, the presence of certain oxygenated compounds, such as acetaldehyde, can cause fouling in other olefin purification units, e.g., acid gas treating units. This prior art provides a method of treating an ethylene and/or propylene containing stream. The method comprises providing an olefin stream containing ethylene, propylene, C4+ olefins and acetaldehyde. The olefin stream is separated into a first fraction and a second fraction, wherein the first fraction comprises at least a majority of the ethylene and/or propylene present in the olefin stream, and the second fraction comprises at least a majority of the C4+ olefins and acetaldehyde present in the olefin stream. The first fraction is then acid gas treated. The olefin stream is separated by distillation, preferably, the distillation is extractive distillation using an extractant. The preferred extractant is a polar composition having an average boiling point of at least 38° C. at 1 atm. Methanol is one type of preferred extractant.
WO 03 020672 A1 describes method of removing dimethyl ether from an ethylene and/or propylene containing stream. The olefin stream is passed to a water absorption column, methanol is used as the water absorbent. Methanol and entrained water, as well as some oxygenated hydrocarbon, is recovered as the bottoms stream of said water absorption column, an overhead olefin is recovered and sent to a distillation column. The distillation column separates ethylene and propylene, as well as lighter boiling point components from the dimethyl ether and heavier boiling point components, including C4+ components and methanol remaining from the methanol wash. Additional methanol is added to the distillation column to reduce clathrate and/or free water formation in the distillation column. The ethylene and propylene containing stream exits the distillation column as overhead and the heavier boiling point components which include the dimethyl ether and C4+ components exit the distillation column as the bottoms. Ethylene and propylene then flow to a caustic wash column.
WO 03 033438 A1 describes a method for processing an olefin stream containing oxygenates and water, comprising: providing an olefin stream containing oxygenates and water; dewatering the olefin stream; compressing the dewatered olefin stream; washing the olefin stream with methanol to remove at least a portion of the oxygenate from the olefin stream; contacting the methanol washed olefin stream with water; and fractionating the water contacted olefin stream. The olefin stream is the effluent of an MTO process.
US 2006 258894 A1 relates to a process for extracting oxygenates from a hydrocarbon stream, typically a fraction of the condensation product of a Fischer-Tropsch reaction, while preserving the olefin content of the condensation product. The oxygenate extraction process is a liquid-liquid extraction process that takes place in an extraction column using a polar organic solvent, such as methanol, and water as the solvent, wherein the polar organic solvent and water are added separately to the extraction column.
US 2009 048474 A1 relates to a process for the production of alkene(s) from a feedstock comprising at least one monohydric aliphatic paraffinic primary (or secondary) alcohol(s), consisting of ethanol or propanol(s) or a mixture thereof, characterised by the following steps;
1. the monohydric aliphatic paraffinic primary (or secondary) alcohol(s) are converted into the corresponding same carbon number alkene(s) in a reactive distillation column at elevated pressure and temperature so that the heads stream extracted from the top of the said reactive distillation column comprises essentially the said alkene(s),
2. the heads stream from step 1 is then cooled to a temperature sufficient to condense at least part of the alkene(s) with the highest boiling point,
3. at least part of the condensed alkene(s) from step 2 are then recycled back into the said reactive distillation column, as a reflux return,
4. simultaneously the remaining alkene(s) are recovered.
The present invention is a process for removing oxygenated contaminants and water from an hydrocarbon stream comprising:
introducing the contaminated hydrocarbon stream in a gaseous phase in an absorption zone,
contacting said hydrocarbon stream in said absorption zone with an absorbent capable to absorb water and oxygenated contaminants at conditions effective to produce,
The hydrocarbon stream comprising oxygenated contaminants and water can be a stream in a refinery or a chemical plant. The hydrocarbon may comprise olefins.
In an embodiment the hydrocarbon stream comprising oxygenated contaminants and water is the effluent produced by a MTO process. Said hydrocarbon stream is a complex mixture comprising the desired light olefins, unconverted oxygenates, by-product oxygenates, heavier hydrocarbons and large amounts of water.
As regards the oxygenated contaminants one can cite alcohols such as methanol, ethanol, C3 alcohols; ethers such as dimethyl ether, diethylether and methyl ethyl ether; carboxylic acids such as acetic acid, propanoic acid and butyric acid; aldehydes such as acetaldehyde; ketones such as acetone; and esters such as methyl esters. Particularly problematic oxygenate contaminants in the MTO process are dimethyl ether (DME) and acetaldehyde.
The hydrocarbon stream comprising oxygenated contaminants and water can be available at low pressure such as 1 to 3 bars absolute and may comprise a high proportion of water. Advantageously said hydrocarbon stream is successively compressed and cooled in one or more steps to remove the major part of water and further fed to the absorption zone. The pressure of the absorption zone is advantageously ranging from 5 to 40 bars absolute and preferably from 10 to 30 bars absolute.
In the previous compression steps the recovered water contains a part of the oxygenated contaminants and hydrocarbons dissolved. In an embodiment the water recovered upon each cooling further to a compression step is sent to a water stripping column to produce an overhead stream comprising essentially oxygenated contaminants and hydrocarbons and an essentially pure water bottoms stream. Optionally the overhead stream is burned to destroy the oxygenated contaminants and recover heat or is fractionated to recover the hydrocarbons. The contaminated hydrocarbon stream can also be cooled before the first compression step and water recovered.
In a specific embodiment the recycled absorbent to the absorption zone is cooled before entering into said absorption zone. Advantageously it is cooled to about 30° C. or lower, preferably to about 20° C. or lower.
The proportion of the oxygenated contaminants in the hydrocarbon stream comprising oxygenated contaminants and water can be up to 5 w %.
Advantageously the absorbent is selected from the group consisting of a polyol, amine, amide, nitrile, heterocyclic nitrogen containing compound, and mixtures thereof. Examples of polyol, amine, amide, nitrile, heterocyclic nitrogen containing compounds which can be used include ethylene glycol, diethylene glycol, triethylene glycol, ethanolamine, diethanolamine, triethylamine, hindered cyclic amines, acetonitrile, n-methylpyrrolidone, and dimethyl formamide, as well as mixtures of any two or more of these compounds. Olefins treated in accordance with this invention are particularly suitable for use as feedstock for making polyolefins.
Substantial amounts of water and oxygenated contaminants are removed from the hydrocarbon vapor stream by contacting the vapor stream with an effective amount of absorbent. It is preferred that the absorbent be a polyol, amine, amide, nitrile, and/or heterocyclic nitrogen containing compound. This type of absorbent is particularly desirable, since it will remove such hard to remove contaminants as dimethylether, acetaldehyde and water, yet it will not readily absorb olefins optionally present in the hydrocarbon stream. This means that oxygenated contaminants can be removed from an olefin stream with a very high efficiency.
To obtain a high degree of effectiveness, the absorbent material introduced into the absorption system should have little non-oxygenated hydrocarbon absorbing material, such as a diluent. For example, the absorbent material introduced into an absorber should contain at least about 75 wt % absorbent material that is effective in removing dimethylether and/or water from an olefin stream rich in ethylene and/or propylene. Desirably, the absorbent material should contain at least about 90 wt %, preferably at least about 95 wt %, more preferably at least about 98 wt absorbent. Examples of absorbents include at least one compound selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, ethanolamine, diethanolamine, triethylamine, hindered cyclic amines, acetonitrile, n-methylpyrrolidone, dimethyl formamide, and combinations thereof.
Conventional absorption systems can be used in this invention. In one embodiment, the absorption system uses packed columns, although plate absorption columns may also be used. In another embodiment, the absorption column has a liquid inlet located at a top portion of the absorption column. The absorbent liquid is evenly distributed across the top of the column. Desirably, an even distribution of the absorbent liquid is accomplished by using a distributor plate or spray nozzles. At the bottom of the absorption column is a gas inlet where the hydrocarbon stream, containing water and oxygenated contaminants, enters the absorption column. The vapor components move up the column countercurrent to the liquid absorbent moving down the column. This is known as countercurrent absorption. The packing or plates in the column provides a surface for intimate contact between the vapor and liquid components within the column. In a countercurrent absorption column, the concentration of soluble gasses in both the liquid and vapor phases is greatest at the bottom of the column, and lowest at the top of the column. The outlet for the liquid is at the bottom of the absorption column, typically below the gas inlet. The outlet for the gas phase lean in the gasses most soluble in the liquid absorbent is at the top of the absorption column, typically above the liquid inlet.
In a specific embodiment the stripping zone is a distillation column. The overhead stream of said distillation column of the stripping zone is cooled to produce an aqueous phase comprising oxygenated contaminants and a gaseous phase comprising hydrocarbons and oxygenated contaminants. A part of said aqueous phase is used as the reflux of the distillation column, the remaining part is optionally sent to the above cited water stripping column.
Advantageously the above gaseous phase is sent to a wash column fed with water to produce an overhead hydrocarbon stream comprising oxygenated contaminants and a bottoms aqueous stream comprising oxygenated contaminants. Advantageously the said bottoms of the wash column and the remaining part of the aqueous phase recovered by cooling the stripping column overhead in the stripping zone and not used as a reflux comprise an essential portion of the oxygenated contaminants to be removed. More precisely in case the contaminated hydrocarbon stream is compressed before entering the absorption zone a part of the oxygenated contaminants goes in the condensed water. The sum of,
the oxygenated contaminants in the said condensed water,
the oxygenated contaminants in the bottoms of the wash column,
the remaining part of the aqueous phase recovered by cooling the stripping column overhead in the stripping zone and not used as a reflux, comprise the essential portion of the oxygenated contaminants to be removed, advantageously more than 90 w %. Advantageously the overhead stream of the wash column comprises a very small portion of the oxygenated contaminants to be removed.
Optionally the said overhead of the wash column is recycled to the process which has produced the hydrocarbon stream comprising oxygenated contaminants and water to be purified. Optionally the aqueous bottoms stream is sent to the above cited water stripping column.
In an embodiment,
In an embodiment,
As regards the MTO process, such process is described in WO-2008-110526, WO-20084 10528, WO-2008-110530, WO-2009-016153, WO-2009-016154, WO-2009-016155, WO-2009-092779, WO-2009-092780, WO-2009-092781, the content of which is incorporated in the present application. The MTO process has also been described in US 2006 0235251, WO 2005 016856, US 2006 0063956, US 2006 0161035, U.S. Pat. No. 6,207,872, US 2005 0096214, U.S. Pat. No. 6,953,767 and U.S. Pat. No. 7,067,095, the content of which is incorporated in the present application.
The effluent produced by a MTO process which is an hydrocarbon stream comprising oxygenated contaminants and water can be purified with the process of the invention to get an ethylene/propylene stream having an acetaldehyde content of less than 5 ppm, often less than 3 ppm more often less than 2 ppm. Said stream can be purified with the process of the invention to get an ethylene/propylene stream having a DME content of less than 5 ppm, often less than 3 ppm more often less than 2 ppm.
| Number | Date | Country | Kind |
|---|---|---|---|
| 09180443.5 | Dec 2009 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/070279 | 12/20/2010 | WO | 00 | 10/8/2012 |
