Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Removing only nonpolymerized or nonpolymerizable material...
Reexamination Certificate
1999-05-07
2001-09-18
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Removing only nonpolymerized or nonpolymerizable material...
C526S064000, C526S067000, C422S216000, C422S217000, C422S198000
Reexamination Certificate
active
06291603
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of providing filtration of solids from organic-based feed streams to chemical reactors. In another aspect, this invention relates to a method for providing flow distribution of organic-based feed streams to chemical reactors. More particularly, the invention relates to a method for filtering solids and providing liquid distribution for organic-based feed streams that are subsequently processed in chemical reactors having discrete solid element catalyst bed(s). In another aspect, the invention is directed toward distributing inlet air or vapors, particularly for fluidized bed reactors. A further aspect of the invention relates to a method for partially reacting polymer precursors in organic-based feed streams to chemical reactors to reduce fouling of the solid element catalyst bed(s).
2. Description of Related Art
Typically chemical reactor beds include discrete solid catalyst particles contained in one or more fixed beds. Often these beds are supported, or retained, at their inlet and/or outlet by materials which are inert to the reaction. These inert materials may trap all or some solid contaminants such as dirt, iron oxide, iron sulfide, asphaltenes, coke fines, catalyst fines, sediments or other entrained foreign particulate material in the reactor feed stream. The trapping of the contaminants is to prevent undesirable material from plugging, poisoning or otherwise deactivating the catalyst bed. The inert materials, or inerts, traditionally used are typically made of conventional ceramic materials in the form of pellets or spheres and typically must be resistant to crushing, high temperatures and/or high pressures. In addition, these materials may facilitate distribution of the feed stream across the catalyst bed in such a manner to reduce channeling through the catalyst bed.
To increase the efficiency of the inerts, graduated layers of inerts in different sizes and shapes along with perforated discs, or screen baskets, have been used to retard the surface of a catalyst bed from becoming plugged with contaminants such as dirt, iron oxide, iron sulfide, asphaltenes, coke fines, catalyst fines, sediments, or other entrained foreign particulate material. Skimming, or removal, of the top portion of the catalyst is required when the filtering capacity of the inerts is exhausted resulting in the catalyst itself being used as a filter. In addition to catalyst fouling by particulate matter in the organic-based stream, polymerization of polymer precursors, e.g., diolefins, found in the organic-based feed stream may also foul the catalyst. In particular, two mechanisms of polymerization, free radical polymerization and condensation-type polymerization, may cause catalyst bed fouling, gumming or plugging. The addition of antioxidants to control free radical polymerization has been found useful where the organic-based feed stream has encountered oxygen. Condensation polymerization of diolefins typically occurs after the organic-based feed is heated. Therefore, filtering prior to the organic-based feed stream entering the reactor may not be helpful to remove these foulants as the polymerization reactions generally take place in the reactors.
It is highly desirable to increase the efficiency of the inert bed filtration and to control the rate of reaction of the diolefins or other polymer precursors. Thus, the development of a method of filtration that increases the efficiency of the filtering of the contaminated feed stream may also reduce the volume of inerts required to protect the catalyst bed from solid deposition, as well as reduce the pressure drop associated with plugging. The method of the present invention for filtration and flow distribution for chemical reactors, when compared with previously proposed prior art methods, has the advantages of: providing more efficient filtering; increasing catalyst life; decreasing catalyst losses; and reducing the need to take the reactor off-line for maintenance when removal or replacement of the inert material or any catalyst that is plugged is required. These benefits may result in both capital and operating savings.
Disadvantages associated with current liquid distribution designs and methods in fixed bed chemical reactors may result in poor liquid distribution to the catalyst bed. Partial plugging of the catalyst bed with contaminants, or gumming by reactive diolefins or other polymer precursors, may also cause maldistribution. The maldistribution may result in channeling and corresponding bypassing of portions of the catalyst bed, reducing the catalyst efficiency. Usually, a maldistribution problem is evidenced by radial temperature differences. Therefore, the art has sought a flow distribution method that may spread the liquid more uniformly through the catalyst bed, provide efficient filtering and reduce fouling caused by undesired polymerization reactions.
Accordingly, prior to the development of the present invention, there has been no method for filtering and/or distributing organic-based feed streams to chemical reactors which: may capture a mixture of large and small contaminants without plugging or blinding; does not cause relatively large pressure drops across the filtering and/or distribution media; does not require excessive capital and operating costs; and does not cause process safety and environmental concerns arising from maintenance required shutdowns and start-ups. Therefore, the art has sought a method for extending the run life of catalyst beds by filtering and distributing organic-based feed streams to chemical reactors which: does not require excessive amounts of catalyst; does not require the use of relatively large amounts of inert material; does not cause relatively large pressure drops across the bed; does not require relatively large capacity circulation pumps or compressors; and does not cause process safety and environmental concerns arising from reactor shutdowns and start-ups.
SUMMARY OF INVENTION
In accordance with the invention, the foregoing advantages have been achieved through the present method of filtering and distributing an organic-based feed for chemical reactors. The present invention for removing contaminants from an organic-based feed stream may include the steps of providing a layer of reticulated ceramic material in a chemical reactor, the layer of reticulated ceramic material being in an amount sufficient to filter some or all of the contaminants from the organic-based feed stream; and passing the organic-based feed stream through the layer of reticulated ceramic material. The reticulated ceramic material may be made from any commercially available materials, for example, ZTA. The ZTA may have a product composition of ZrO
2
/Al
2
O
3
and is available from SELEE Corporation headquartered in Hendersonville, N.C. The organic-based feed stream may be an organic-based liquid, a vapor phase, or both, and the contaminants may include dirt, iron oxide, iron sulfide, asphaltenes, coke fines, catalyst fines, sediments or other entrained foreign particulate matter, or polymer precursors such as diolefins. The reticulated ceramic material should be provided in a layer in an amount sufficient to remove some or all of the contaminants from the organic-based feed stream. Another feature of the present invention for removing contaminants from a contaminated organic-based feed stream in a chemical reactor includes the steps of providing a layer of reticulated ceramic material in the chemical reactor and contacting the contaminated organic-based feed stream with the reticulated ceramic material to remove the contaminants from the contaminated organic-based feed stream. Another feature of the present invention may include the step of providing a decontaminated organic-based feed stream for further processing.
More particularly, the invention relates to a process for improving feed quality of organic-based feed streams to chemical reactors. Preferably, the chemical reactors use discrete solid element catalyst beds. The chem
Bracewell & Patterson L.L.P.
Choi Ling-Siu
Crystaphase International, Inc.
Wu David W.
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