Catalyst – solid sorbent – or support therefor: product or process – Solid sorbent – Aluminum containing
Reexamination Certificate
2000-04-03
2004-11-02
Langel, Wayne A. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Solid sorbent
Aluminum containing
C502S504000, C502S517000
Reexamination Certificate
active
06812189
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to zinc titanate-containing compositions used to remove reduced sulfur gases such as H
2
S, COS, and CS
2
from gas streams. More specifically, it relates to those zinc titanate-containing compositions that, aside from their chemical reactivity toward reduced sulfur gases, also have she physical attributes of toughness and attrition resistance.
2. Background of the Invention
Reduced sulfur gases are present in many industrial processes. For example, reduced sulfur gases are found in flue gas, coal gas and fuel gas streams. They are also found in industrial product gas streams such as olefin-containing gas streams which are a component of petroleum refining operations. These gases are often removed from such gas streams by vise of various metal oxides that have the ability to capture a reduced sulfur-containing gas component from such gas streams. In order to capture such a gas from certain industrial processes (such as packed-bed, fluidized-bed or moving-bed reactors) the metal oxide, reduced sulfur gas sorbent materials must be used in forms which are mechanically strong and resistant to attrition. Otherwise, problems such as pressure drops through a process reactor unit, particulate matter elutriation and/or clogging of valves or other mechanical components will take place.
Moreover, almost all industrial processes that deal with reduced sulfur gases also are confronted with the problem of desorbing these gases from the metal oxide sorbent material so that said sorbent material can be used over and over again in order to obtain its maximum economic benefit. Other problems associated with the presence of reduced sulfur gases (such as H
2
S, COS and CS
2
) in gas streams such as fuel gases, flue gases and waste gases arise from the fact that reduced sulfur gases are corrosive toward ferrous metals. They are especially corrosive toward steel turbine blades. Therefore, the presence of reduced sulfur gases in those hot fuel cases used to power turbines results in their severe corrosion. Oxidation of hot fuel gases also serves to oxidize any reduced sulfur gases contained therein. The resulting sulfur oxide gases (e.g., SO
2
and SO
3
which are commonly referred to as “SOX
x
” gases) also are highly corrosive toward ferrous metals. Moreover, upon release to the atmosphere, SO
x
gases form so-called “acid-rain.” Therefore, the concentration of reduced sulfur gases contained in those hot fuel gases introduced into power producing equipment such as turbines and fuel cells must be brought to very low concentrations, e.g., a is few parts per million (ppm), before they are combusted in equipment of this kind.
Next, it should be noted that, in the case of sulfur oxide sorbents—as opposed to the reduced sulfur sorbents that form the subject matter of this patent disclosure—the subject sulfur oxide is normally usually captured in an oxidizing atmosphere such as those extant in the catalyst regenerator of a FCC unit. This is done through use of various metal oxide particles having an affinity for a given sulfur oxide-containing gas. These particles are often entrained in a “fluidized” process. For example, sulfur oxide (e.g., SO
2
or SO
3
) sorption is often carried out through use of fluidized microspheroidal magnesium-containing particles that can withstand the hot (e.g., 1350° F.) oxidizing conditions present in the catalyst regenerator units of those fluid catalytic conversion (“FCC”) processes used to refine petroleum. Conversely, release of such sorbed sulfur-containing gases usually occurs in the reducing environment of a FCC reactor. The sulfur component of such gases is released as hydrogen sulfide H
2
S. This released H
2
S gas is readily captured downstream of the reactor and normally does not create an environmental hazard.
Again, however, the processes of the present patent disclosure are different from such So, sorption processes in that applicant's compositions are specifically designed to capture chemically reduced forms of sulfur (e.g., those in H
2
S, COS and CS
2
) rather than chemically oxidized forms of sulfur (e.g., those in SO
2
and S
3
O). Thus, applicant's capture of reduced sulfur gases must take place under chemical reduction conditions, rather than under chemical oxidizing conditions.
Many different zinc—containing compounds have been used in both fixed bed and fluid bed systems in order to remove one or more species of reduced sulfur gases from various industrial gas streams (e.g., fuel gases, such as those derived from the gasification of coal, flue or waste gases and/or industrial product gases such as those that contaminate olefin-type gases). Such zinc—containing compounds have included zinc oxide, zinc titanate and zinc aluminate. Zinc oxide, for example, has been used as a sorbent for selectively removing hydrogen sulfide gas. H
2
S, from certain industrial gas streams. This metal oxide is normally used by placing it in contact with a hydrogen sulfide-containing gas stream at elevated temperatures. Zinc oxide, in and of itself, has not, however, proven to be a particularly effective hydrogen sulfide sorbent for many industrial applications. For example, its hydrogen sulfide sorption ability is relatively limited, especially at lower temperatures. It also suffers from the drawback of not being easily regenerated. This drawback follows from the relatively high thermodynamic stability of the zinc sulfide product of zinc oxide-hydrogen sulfide reactions. Zinc oxide also lacks the qualities of hardness, toughness and/or attrition resistance that are needed for many industrial applications.
Regeneration of the zinc sulfide product of zinc oxide-hydrogen sulfide reactions requires subsequent oxidation of the sulfur component of the zinc sulfide reaction product. This must be done at relatively high temperatures (e.g., 900° F. to 1500° F.). Unfortunately, the relatively high temperatures needed to oxidize zinc sulfide back to zinc oxide also tend to degrade the already inherently low mechanical strength and/or toughness of these zinc oxide-based materials. Consequently, zinc oxide sorbents tend to quickly disintegrate hen they are repeatedly used and regenerated.
Therefore, in order for zinc oxide-containing compounds to be effectively used in the harsh environments where they are needed (e.g., in the high temperature/high velocity particle impact environments of fluid, fixed or bubbling bed processes), they must be combined with other tougher and more attrition resistant metal oxide components in order to produce overall zinc oxide/metal oxide compositions having the requisite mechanical strength, hardness, durability, toughness and attrition resistance that they will need to function as reduced sulfur gas sorbents.
Generally speaking, this has been accomplished by mixing certain prescribed proportions of a relatively soft zinc oxide component with certain prescribed portions of another, relatively harder, tougher, metal oxide component in the same particle. The most effective and widely used metal oxide used for this hardening/toughening purpose has been unreacted alumina (Al
2
O
3
). Such use of alumina as a catalyst support for zinc oxide sorbents follows from the unusually high degree of hardness this material imparts to such compositions—as well as from the excellent binding capabilities of many forms of so-called “gelling” or “sol” alumina forms. Examples of such aluminas are the various grades of VISTA CATAPAL and CONDEA DISPERSAL aluminas. Such aluminas have been used in producing relatively harder, tougher and more attrition resistant extrudate, granule, microsphere, powder, particle, pellet, bead, etc. forms of zinc oxide/unreacted alumina compositions.
Many of the above-noted improvements in the sorption, regeneration and physical attributes of zinc oxide-containing compositions are taught in the patent literature. For example, U.S. Pat. No. 4,088,736 (“the '736 patent”) discloses a reduced sulfur sorbent comprised of homogenous mixtures of zinc o
Gupta Raghubir P.
Turk Brian S.
Vierheilig Albert A.
Langel Wayne A.
Research Triangle Institute
LandOfFree
Attrition resistant, zinc titanate-containing, reduced... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Attrition resistant, zinc titanate-containing, reduced..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Attrition resistant, zinc titanate-containing, reduced... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3352075