WO2001037974A1

WO2001037974A1 - Removal of volatile aluminum alkyls from gas streams

Info

Publication number: WO2001037974A1
Application number: PCT/US2000/031380
Authority: WO
Inventors: Steven R. Alferi
Original assignee: Albemarle Corporation
Priority date: 1999-11-22
Filing date: 2000-11-15
Publication date: 2001-05-31

Abstract

A gas stream containing volatile aluminum alkyl is contacted with a liquid phase comprised of one or more non-volatile alkyl aluminum compounds. This removes the volatile aluminum alkyl from the gas stream and converts the aluminum alkyl into an industrially useful form, e.g., into a mixed aluminum alkyl useful as an alkylation catalyst. The purified gas stream can then be flared without production of visually perceptible amounts of aluminum containing particulates.

Description

REMOVAL OF VOLATILE ALUMINUM ALKYLS FROM GAS STREAMS

In various chemical processing operations, gaseous waste or vent streams are produced which contain one or more volatile alkyl aluminum compounds, such as methyl aluminum sesquichloride, trimethyl aluminum, methyl aluminum dichloride, or dimethyl aluminum chloride, or mixture of two or more such compounds In practice, such streams have been flared so as to burn the volatile alkyl aluminum component(s) and thereby prevent their dissemination into the environment However the combustion process produces aluminum oxides of little or no commercial value

It would be advantageous if a new way could be found to effectively purge such volatile alkyl aluminum compounds from gaseous waste or vent streams It would be particularly advantageous if the purged alkyl aluminum compound(s) could be of recovered in an industrially useful form, and thereby minimize waste and improve plant economics at the same time This invention makes it possible to achieve one or both of these advantages, depending upon the nature of the operations being conducted on site

Provided by this invention is a process that effectively removes of at least one volatile alkyl aluminum compound from a gas stream which contains at least one volatile alkyl aluminum compound. The process comprises contacting such gas stream with a liquid phase comprised of one or more non-volatile alkyl aluminum compounds Typically such gas stream is passed into the liquid phase of the non-volatile alkyl aluminum compound(s) to scrub out the volatile alkyl aluminum compound(s) from the gas stream, which can then be flared or subjected to other processing or use, if desired. The temperature of the liquid phase of the non-volatile alkyl aluminum compound(s) when conducting the process of this invention is typically in the range of 20 to 120°C, and preferably in the range of 40 to 90 °C, to purge volatile alkyl aluminum compound(s) from the gas stream

For convenience, the volatile alkyl aluminum compound or compounds are sometimes referred to hereinafter as "volatile aluminum alkyl(s)", and the non-volatile alkyl aluminum compound or compounds are often referred to hereinafter as "non-volatile aluminum alkyl(s)" Aluminum trialkyls such as triethylaluminum and tri-n-propylaluminum are sufficiently nonvolatile to serve as the purging non-volatile aluminum alkyl(s) Also useful as the non-volatile aluminum alkyl(s) are dialkylaluminum compounds such as one or more dialkylaluminum halides, hydroxides, alkoxides, or phenoxides in which each alkyl group has at least 2 and preferably at least 4 carbon atoms and in which the dialkylaluminum compound has a volatility no greater than that of triethylaluminum, and preferably no greater than that of tri-n-butylaluminum The most preferred non-volatile aluminum alkyl(s) are aluminum trialkyls wherein each alkyl group contains at least about 4 carbon atoms. The available evidence indicates that under the conditions of the process a virtually instantaneous redistribution reaction takes place in the liquid phase whereby methyl groups of the volatile aluminum alkyl(s) exchange with higher alkyl groups of the non-volatile aluminum alkyl(s). Thus as the reaction proceeds, the overall composition of the alkyl aluminum compounds in the liquid phase changes. For example as methyl groups exchange with, say, butyl groups to form mixed methyl-butyl aluminum alkyls, the volatility of the overall mixture at a given temperature will increase.

Thus, when using aluminum trialkyls as the initial purging alkyl aluminum compounds, the process should be conducted such that the number of moles of the volatile aluminum alkyl(s) removed from the gas stream does not exceed about twice the number of moles of the initial nonvolatile aluminum alkyl(s) used. Preferably, the number of moles of the volatile aluminum alkyl(s) removed from the gas stream should not be more than about one-half the number of moles of the initial non-volatile aluminum alkyl(s) used. If a dialkylaluminum compound is being used as the non- volatile aluminum alkyl(s), a proportionately larger amount should be used, e.g., typically the number of moles of the volatile aluminum alkyl(s) removed from the gas stream should not exceed the number of moles of the initial non- volatile dialkylaluminum compound(s) used.

In preferred embodiments of this invention, the composition of the liquid phase maintained in contact with the gas stream is such that if the purged gas stream leaving such liquid phase is flared to the atmosphere, no visually-perceptible quantity of aluminum-containing particulates can be seen by the naked eye. Normally, air-oxidation of aluminum alkyls will form paniculate alumina.

It is also preferred periodically or, slowly but continuously, to replace the purging liquid phase with fresh liquid phase of non-volatile aluminum alkyl(s) in order to ensure that the level of aluminum component(s), if any, in the purged gas stream is continuously kept to a minimum.

The process can utilize various types of equipment for effecting the contact between the gas stream which contains the volatile aluminum alkyl(s) and the liquid phase which contains the non-volatile aluminum alkyl(s). For example, use can be made of a gas-liquid contacting column, a bubbling pot equipped with a sparger, or any other apparatus that ensures direct and thorough contact between the gas phase and the liquid phase under the temperature conditions used. Once the system has been calibrated, the volume of the liquid can be used as a guide as to when to replace or replenish the scrubbing fluid with fresh scrubbing fluid. Typically the gas streams will contain up to about 0 50 pound of volatile aluminum alkyl(s) per cubic foot, but as long as the scrubbing fluid contains a sufficient amount of the non-volatile aluminum alkyl(s), there is no upper limit on the amount of volatile aluminum alkyl(s) in the gas stream being treated Nor is there any lower limit, either Although the initial or fresh charge of non-volatile aluminum alkyl(s) is preferably one or more aluminum trialkyls, the initial charge or fresh charge can be a dialkyl aluminum compound or even an alkyl aluminum sesquihalide of sufficient non-volatility, such as a dialkyl aluminum chloride, dialkyl aluminum hydride, dialkyl aluminum alkoxide, or alkyl aluminum sesquihalide in which each alkyl group contains at least 2 carbon atoms and preferably at least 4 carbon atoms Also useful are aluminum trialkyls in which one of the alkyl groups is a methyl group and the other two alkyl groups each contain at least 2 and preferably at least 4 carbon atoms Dimeric or oligomeric alkyl aluminum compounds such as tetraethylaluminoxane, (C₂H₅)₂AJ-O-A](C₂H₅)₂, tetrapropylaluminoxane,(C H₇)₂Al-O-Al(C₃H₇)₂, and tetrabutylaluminoxane,(C₄H₉)₂AJ-O-Al(C₄H₉)₂ can also be used as the non-volatile aluminum alkyl(s). If used without an inert solvent, the non- volatile aluminum alkyl(s) should of course be in the liquid state at the temperature being used in the scrubbing apparatus. On the other hand, liquid or solid non-volatile aluminum alkyl(s) can be used if dissolved in a suitably non-volatile, inert liquid solvent, such as a liquid paraffinic hydrocarbon, liquid cycloparaffinic hydrocarbon, liquid aromatic hydrocarbon containing only aromatic unsaturation, or a mixture of any of these. If a solution is used, it should contain at least 5 wt% of the non-volatile aluminum alkyl(s)

As one example of the process, a vent stream containing methyl aluminum sesquichloride is passed through tri-n-butylaluminum at 38 °C (ca. 100°F) at atmospheric pressure The resulting gas stream was virtually free of volatile aluminum alkyl(s). The mixture of methyl-butyl aluminum compounds formed in the process was successfully used as catalyst in the orthoalkylation of aniline with ethylene, and of ortho-toluidine with ethylene

Similarly, a vent stream composed of trimethyl aluminum is passed into the bottom of a 20- foot tall packed column containing an initial liquid phase composed of 100% of tri-n-butyl aluminum maintained at about 38 °C (ca 100°F) at atmospheric pressure The trimethyl aluminum is effectively scrubbed from the vent stream

Claims

CLAIMS:

1. A process for removal of at least one volatile alkyl aluminum compound from a gas stream containing in the gaseous state at least one volatile alkyl aluminum compound, which process comprises contacting said gas stream with a liquid phase comprising one or more nonvolatile alkyl aluminum compounds at a temperature in the range of 20 to 120°C, to purge volatile alkyl aluminum compound from said gas stream.

2. A process of Claim 1 wherein said one or more non-volatile alkyl aluminum compounds initially consist(s) essentially of at least one alkyl aluminum compound containing at least 2 alkyl groups each of which contains at least about 3 carbon atoms.

3. A process of Claim 1 wherein said one or more non-volatile alkyl aluminum compounds initially consist(s) essentially of at least one alkyl aluminum compound containing at least 2 alkyl groups each of which contains at least about 4 carbon atoms.

4. A process of Claim 1 wherein said one or more non-volatile alkyl aluminum compounds initially consist(s) essentially of at least one alkyl aluminum compound containing at least 3 alkyl groups each of which contains at least about 2 carbon atoms.

5. A process of Claim 1 wherein said one or more non-volatile alkyl aluminum compounds initially consist(s) essentially of at least one alkyl aluminum compound containing at least 3 alkyl groups each of which contains at least about 3 carbon atoms.

6. A process of Claim 1 wherein said one or more non-volatile alkyl aluminum compounds initially consist(s) essentially of at least one alkyl aluminum compound containing at least 3 alkyl groups each of which contains at least about 4 carbon atoms.

7. A process of Claim 1 wherein said one or more non-volatile alkyl aluminum compounds initially consist(s) essentially of at least one aluminum trialkyl in which each alkyl group is other than methyl, and wherein the process is conducted such that the number of moles of the volatile aluminum alkyl(s) removed from said gas stream does not exceed about twice the number of moles of said at least one aluminum trialkyl initially being contacted with said gas stream.

8. A process of Claim 1 wherein said one or more non-volatile alkyl aluminum compounds initially consist(s) essentially of at least one aluminum trialkyl in which each alkyl group is other than methyl, and wherein the process is conducted such that the number of moles of volatile aluminum alkyl(s) removed from the gas stream is not more than about one-half the number of moles of said at least one aluminum trialkyl initially being contacted with said gas stream.

9. A process of Claim 1 wherein the composition of said liquid phase is maintained such that the purged gas stream leaving said liquid phase if flared to the atmosphere produces no visually-perceptible amount of aluminum-containing particulates.

10. A process of any of Claims 1-9 wherein said gas stream that is being contacted with said liquid phase contains methyl aluminum sesquichloride, trimethyl aluminum, methyl aluminum dichloride, or dimethyl aluminum chloride, or a mixture of any two or more of the foregoing.