Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – Faujasite type
Reexamination Certificate
2001-08-31
2004-02-24
Elve, M. Alexandra (Department: 1725)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
Faujasite type
C502S064000, C502S065000, C502S068000, C502S073000
Reexamination Certificate
active
06696378
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to improvements in zeolitic fluid cracking catalysts (FCC) produced by an in situ reaction between an alkaline sodium silicate solution and microspheres composed of a mixture of two different forms of calcined kaolin clay, so-called “metakaolin” and “spinel”. The former is sometimes referred to as “reactive” calcined kaolin and the latter as “kaolin calcined through the characteristic exotherm”.
For many years a significant proportion of commercial FCC catalysts used throughout the world have been made by in situ synthesis from precursor microspheres containing kaolin that has been calcined at different severities prior to formation into microspheres by spray drying. Generally, these fluid cracking catalysts are microspheres composed of zeolite Y and matrix material, typically silica alumina. U.S. Pat. No. 4,493,902 to Brown et al., the teachings of which are incorporated herein by cross-reference, discloses fluid cracking catalysts comprising attrition-resistant, high zeolite content, catalytically active microspheres containing more than about 40%, preferably 50-70% by weight Y faujasite and methods for making such catalysts by crystallizing more than about 40% sodium Y zeolite in porous microspheres composed of a mixture of two different forms of chemically reactive calcined clay, namely, metakaolin (kaolin calcined to undergo a strong endothermic reaction associated with dehydroxylation) and kaolin clay calcined under conditions more severe that those used to convert kaolin to metakaolin, i.e., kaolin clay calcined to undergo the characteristic kaolin exothermic reaction, sometimes referred to as the spinel form of calcined kaolin. In preferred embodiments, the microspheres containing the two forms of calcined kaolin clay are immersed in an alkaline sodium silicate solution, which is heated, preferably until the maximum obtainable amount of Y faujasite is crystallized in the microspheres.
In the practice of the '902 technology, the porous microspheres in which the zeolite is crystallized are preferably prepared by forming an aqueous slurry of powdered raw (hydrated) kaolin clay (Al
2
O
3
:2SiO
2
:2H
2
O)) and powdered calcined kaolin clay that has undergone the exotherm together with a minor amount of sodium silicate which acts as fluidizing agent for the slurry that is charged to a spray dryer to form microspheres and then functions to provide physical integrity to the components of the spray dried microspheres. The spray dried microspheres containing a mixture of hydrated kaolin clay and kaolin calcined to undergo the exotherm are then calcined under controlled conditions, less severe than those required to cause kaolin to undergo the exotherm, in order to dehydrate the hydrated kaolin clay portion of the microspheres and to effect its conversion into metakaolin, this resulting in microspheres containing the desired mixture of metakaolin, kaolin calcined to undergo the exotherm and sodium silicate binder. In illustrative examples of the '902 patent, about equal weights of hydrated kaolin and spinel are present in the spray dryer feed and the resulting calcined microspheres contain somewhat more kaolin that has undergone the exotherm than metakaolin. The '902 patent teaches that the calcined microspheres comprise about 30-60% by weight metakaolin and about 40-70% by weight kaolin characterized through its characteristic exotherm. It is to be noted that no metakaolin is present in the spray dryer feed used in the preferred manufacturing process described in the '902 patent. A less preferred method described in the patent, involves spray drying a slurry containing a mixture of kaolin clay previously calcined to metakaolin and kaolin calcined to undergo the exotherm but without including any hydrated kaolin in the slurry, thus providing microspheres containing both metakaolin and kaolin calcined to undergo the exotherm directly, without calcining to convert hydrated kaolin to metakaolin. However, the patent teaches that less attrition zeolitized microspheres are produced by this approach.
In carrying out the invention described in the '902 patent, the microspheres composed of kaolin calcined to undergo the exotherm and metakaolin are reacted with a caustic enriched sodium silicate solution in the presence of a crystallization initiator (seeds) to convert silica and alumina in the microspheres into synthetic sodium faujasite (zeolite Y). The microspheres are separated form the sodium silicate mother liquor, ion-exchanged with rare earth, ammonium ions or both to form rare earth or various known stabilized forms of catalysts. The technology of the '902 patent provides means for achieving a desirable and unique combination of high zeolite content associated with high activity, good selectivity and thermal stability, as well as attrition-resistance.
The zeolite content of the crystallized microspheres is determined by X-ray diffraction from the zeolite, which is best performed on the sodium form crystallized microspheres. Conventional chemical analytical techniques are not deemed to be applicable to the determination of the zeolite content of materials in which the zeolite is crystallized in situ in a silica-alumina matrix, which cannot be readily physically or chemically isolated. In practice, it has been found that the apparent amount of zeolite crystallized from any given formulation using the '902 technology can vary, depending on the history of raw material, processing conditions and proportions and concentrations of reagents. The zeolite content (sodium form) of crystallized microspheres range from 40% to 72% in illustrative examples of the '902 patent. Commercial production and laboratory preparations typically result in the crystallization of a maximum of about 55-60% zeolite (sodium form). Since at least a substantial proportion of the zeolite grows in macropores of the precursor porous microspheres, it might be expected that simply increasing macroporosity of the precursor microspheres would result in the generation of higher levels of zeolite because more space would be available in which to grow zeolite crystals.
Surprisingly, merely providing more room for crystal growth by increasing macroporosity will not achieve this result.
The aforementioned technology has met widespread commercial success. Because of the availability of high zeolite content microspheres which are also attrition-resistant, custom designed catalysts are now available to oil refineries with specific performance goals, such as improved activity and/or selectivity without incurring costly mechanical redesigns. A significant portion of the FCC catalysts presently supplied to domestic and foreign oil refiners is based on this technology.
U.S. Pat. No. 5,023,220 to Dight et al. discloses an economically attractive method for increasing the zeolite content of high zeolite content kaolin derived microspheres obtained by reacting precursor microspheres composed of a mixture of metakaolin and kaolin calcined to undergo the exotherm with a sodium silicate solution to crystallize zeolite Y in situ in macropores of the precursor microspheres. The increase in zeolite content is associated with a desirable increase in catalytic activity and seems to improve selectivity. Improvements in activity and selectivity, specifically a reduction in coke and/or gas make are desirable. Reductions in coke or gas make or both serves the needs of refiners whose FCC units are limited by regenerator temperature, air blower and/or gas compressors.
The zeolite microspheres of the invention disclosed in Dight et al. are produced by novel processing, which is a modification of technology described in the '902 patent, and involves increasing the proportion of calcined kaolin in the form of metakaolin to kaolin calcined to undergo the exotherm in the porous precursor microspheres in which zeolite Y is crystallized while also increasing the macroporosity of the precursor microspheres. The increase in macroporosity is preferably achieved b
Barnes Robert E.
Gantt George E.
Gibson Clark W.
Stockwell David M.
Willis Mitchell J.
Elve M. Alexandra
Engelhard Corporation
Ildebrando Christina
Keller Raymond F.
LandOfFree
Fluid catalytic cracking catalyst manufacturing process does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fluid catalytic cracking catalyst manufacturing process, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fluid catalytic cracking catalyst manufacturing process will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3352733