Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Halogenous component
Reexamination Certificate
2000-09-21
2001-12-04
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Halogenous component
C095S273000, C706S032000, C208S004000, C208S005000, C208S006000, C208S022000, C208S044000, C423S24000R, C423S005000
Reexamination Certificate
active
06325986
ABSTRACT:
TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION
This invention relates in general to processing asphalt, and particularly to a method for reducing hydrogen chloride emissions from an asphalt air-blowing process. More particularly, this invention relates to a method for reducing hydrogen chloride emissions from air-blowing an asphalt modified with ferric chloride or ferrous chloride, by adding a chemical modifier to the liquid seal of a knockout tank used in the process. The method has industrial applicability, e.g., in air-blowing asphalt for use as a roofing asphalt.
BACKGROUND OF THE INVENTION
Although most asphalts are used for paving, some asphalts are used for other applications such as roofing. Not all available asphalts are naturally suitable for roofing applications. Asphalts for roofing are air-blown to raise the softening point of the asphalt and to meet other specifications. One way to utilize more asphalt feedstocks for roofing is to add a ferric chloride or ferrous chloride catalyst to the asphalt before the air-blowing process. The ferric chloride or ferrous chloride improves asphalt properties such as penetration at a targeted softening point and accelerates the air-blowing process to reduce processing time.
Unfortunately, hydrogen chloride emissions are generated when an asphalt modified with ferric chloride or ferrous chloride is air-blown. When the asphalt is modified with ferric chloride, the reduction of ferric chloride to ferrous chloride during the air-blowing process generates hydrogen chloride emissions. When ferric chloride is added as an aqueous solution to the asphalt, hydrogen chloride emissions are also generated from free hydrochloric acid present in the aqueous solution. More emphasis is being put on regulating the levels of hydrogen chloride emissions to reduce air pollution, and this trend will increase with time. If the regulated emission levels are not achieved, the asphalt production with ferric chloride or ferrous chloride will be restricted. Current methods for reducing hydrogen chloride emissions from an asphalt air-blowing process do not exist.
The patent literature does not suggest a suitable solution to the problem of hydrogen chloride emissions. U.S. Pat. No. 2,506,283 to Smith et al. discloses the use of ferric chloride as a catalyst during an asphalt air-blowing process, and the addition of calcium oxide or calcium hydroxide to the air-blown asphalt in a separate mixing operation after the air-blowing process is completed.
The purpose of the Smith et al. patent is to prevent the formation of scum on the surface of the asphalt, not to reduce hydrogen chloride emissions. There is no suggestion to add a chemical modifier to the knockout tank after the air-blowing but before the fume stream from the air-blowing process is emitted to the atmosphere.
U.S. Pat. No. 5,611,910 to Marzari et al. discloses a method for reducing SO
x
emissions from an asphalt air-blowing process by adding an emission reducing additive to the asphalt prior to air-blowing or early in the process. The additive comprises: (a) at least one compound selected from metal hydroxides, metal oxides, metal carbonates and metal bicarbonates, where the metal is selected from calcium, sodium, potassium and magnesium; and (b) at least one compound selected from metal hydroxides, metal oxides, metal carbonates and metal bicarbonates, where the metal is selected from zinc, copper and aluminum.
The Marzari et al. patent does not disclose the use of ferric chloride or ferrous chloride, or the resulting problem of hydrogen chloride emissions. There is no discussion of a method for reducing hydrogen chloride emissions, and in particular, there is no suggestion to add a chemical modifier to the liquid seal of a knockout tank to reduce hydrogen chloride emissions. Accordingly, it would be desirable to provide a method for reducing hydrogen chloride emissions from air-blowing an asphalt modified with ferric chloride.
SUMMARY OF THE INVENTION
The present invention relates to a method for reducing hydrogen chloride emissions from an asphalt air-blowing process. In the method, an asphalt is subjected to an air-blowing process where air is bubbled through hot asphalt to raise the softening point of the asphalt. The fumes from the air-blowing process are bubbled through a liquid seal in a knockout tank before going to an incinerator and finally being emitted to the atmosphere. The knockout tank normally operates to condense oil in the fume stream, and the liquid seal is composed of this oil, as well as some of the water evolved in the air-blowing process. When using ferric chloride or ferrous chloride as a catalyst in the air-blowing process, the fume stream contains significant levels of hydrogen chloride. In this invention, a chemical modifier is added to the process oil and water seal in the knockout tank prior to the start of the process in order to reduce the amount of hydrogen chloride in the emitted fume stream by at least 25% by weight compared to the same process without the addition of the chemical modifier. The method has the advantage that it does not significantly affect the benefits from the addition of the ferric chloride or ferrous chloride.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION
This invention relates to a method for reducing hydrogen chloride emissions from air-blowing an asphalt modified with ferric chloride and/or ferrous chloride, by adding a chemical modifier to the process oil and water seal in the knockout tank prior to the start of the process.
The asphalt raw material to be air-blown can be either a naturally occurring asphalt or a manufactured asphalt produced by refining petroleum. It can include straight-run fractional-derived asphalts, cracked asphalts, asphalts derived from processing such as asphalt oxidizing, propane deasphalting, steam distilling, chemically modifying, and the like. The asphalt can be either modified or unmodified. Blends of different kinds of asphalt can also be air-blown.
The asphalt raw material is loaded into an apparatus suitable for air-blowing the asphalt, such as a converter. The asphalt is usually loaded at a temperature ranging from about 175° C. to about 230° C. The air-blowing process involves passing air or another oxygen-containing gas through the asphalt in the converter. A mixture of an oxygen-containing gas with an inert gas such as nitrogen or helium can also be used.
The reaction produced by the air-blowing is exothermic and raises the temperature of the asphalt. The temperature of the asphalt during the air-blowing process usually ranges from about 200° C. to about 270° C. The maximum temperature is usually controlled by a water-cooled jacket or other means.
The air-blowing process increases the usefulness of the asphalt by raising the softening point from a typical starting point below about 40° C. to a final softening point of at least about 80° C. The processing time can take from about 1 hour to about 18 hours to reach the desired softening point. The processing time is dependent on the process temperature, the air flow rate, the characteristics of the asphalt, and the specifications of the desired product.
As discussed above, ferric chloride and/or ferrous chloride can be added by blending it into the asphalt prior to the air-blowing process, or by adding it to the asphalt in the converter early in the process, usually within about the first hour. The addition of ferric chloride and/or ferrous chloride increases the rate of the air-blowing process compared to the same process without the addition of ferric chloride and/or ferrous chloride. The ferric chloride usually increases the rate by at least about 20%, while the ferrous chloride usually increases the rate by at least about 35%. The addition of ferric chloride and/or ferrous chloride also usually has other beneficial effects, such as increased final penetr
Marzari Jorge A.
Picman Timothy T.
Poterek Katherine E.
Griffin Steven P.
Inger H. Eckert, James D. Dottavio
Medina Maribel
Owens Corning Fiberglas Technology Inc.
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