Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2000-08-11
2003-01-07
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S202000, C502S208000, C502S232000, C502S302000, C502S341000, C502S351000, C502S355000, C501S127000, C423S275000, C423S600000, C423S625000, C423S628000, C423S629000
Reexamination Certificate
active
06503867
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to quasi-crystalline boehmites containing additives.
2. Description of the Prior Art
Alumina, alpha-monohydrates or boehmites and their dehydrated and or sintered forms are some of the most extensively used aluminum oxide-hydroxides materials. Some of the major commercial applications, for example, ceramics, abrasive materials, fire-retardants, adsorbents, catalysts fillers in composites, and so on, involve one or more forms of these materials. Also, a substantial portion of commercial boehmite aluminas is used in catalytic applications such as refinery catalysts, catalyst for hydroprocessing hydrocarbon feeds, reforming catalysts, pollution control catalysts, cracking catalysts. The term “hydroprocessing” in this context encompasses all processes in which a hydrocarbon feed is reacted with hydrogen at elevated temperature and elevated pressure. These processes include hydrodesulphurisation, hydrodenitrogenation, hydrodemetallisation, hydrodearomatisation, hydro-isomerisation, hydrodewaxing, hydrocracking, and hydrocracking under mild pressure conditions, which is commonly referred to as mild hydrocracking. This type of alumina is also used as a catalyst for specific chemical processes such as ethylene-oxide production and methanol synthesis. Relatively more recent commercial uses of boehmite types of aluminas or modified forms thereof involve the transformation of environmentally unfriendly chemical components such as chlorofluorohydrocarbons (CFCs) and other undesirable pollutants. Boehmite alumina types are further used as catalytic material in the combustion of gas turbines for reducing nitrogen oxide.
The main reason for the successful extensive and diversified use of these materials in such variety of commercial uses is their flexibility, which enables them to be tailor-made into products with a very wide range of physical-chemical and mechanical properties.
Some of the main properties which determine the suitability of commercial applications involving gas-solid phase interactions such as catalysts and adsorbents are pore volume, pore size distribution, pore texture, specific density, surface areas, density and type of active center, basicity and acidity, crushing strength, abrasion properties, thermal and hydrothermal aging (sintering), and long-term stability.
By and large, the desired properties of the alumina product can be obtained by selecting and carefully controlling certain parameters. These usually involve: raw materials, impurities, precipitation or conversion process conditions, aging conditions and subsequent thermal treatments (calcination/steaming), and mechanical treatments.
Nevertheless, in spite of this wide and diversified range of existing know-how, this technology is still under development and presents unlimited scientific and technological challenges to both the manufacturers and the end-users for further development of such alumina-based materials.
The term boehmite is used in the industry to describe alumina hydrates which exhibit XRD patterns close to that of aluminum oxide-hydroxide [AlO(OH)], naturally occurring boehmite or diaspore. Further, the general term boehmite tends to be used to describe a wide range of alumina hydrates which contain different amounts of water of hydration, have different surface areas, pore volumes, and specific densities, and exhibit different thermal characteristics upon thermal treatment. Yet although their XRD patterns exhibit the characteristic boehmite [AlO(OH)] peaks, their widths usually vary and they can also shift location. The sharpness of the XRD peaks and their locations have been used to indicate the degree of crystallinity, crystal size, and amount of imperfections.
Broadly, there are two categories of boehmite aluminas. Category I, in general, contains boehmites which have been synthesized and/or aged at temperatures close to 100° C., most of the time under ambient atmospheric pressure. In the present specification, this type of boehmite is referred to as quasi-crystalline boehmite. The second category of boehmites consists of so-called micro-crystalline boehmites.
In the state of the art, category I boehmites, i.e. quasi-crystalline boehmites, are referred to interchangeably as: pseudo-boehmites, gelatinous boehmites or quasi-crystalline boehmites (QCBs). Usually, these QCB aluminas have very high surface areas, large pores and pore volumes, and lower specific densities than micro-crystalline boehmites. They disperse easily in water of acids, have smaller crystal sizes than micro-crystalline boehmites, and contain a larger number of water molecules of hydration. The extent of hydration of the QCB can have a wide range of values, for example from about 1.4 up, and about 2 moles of water per mole of AlO, usually intercalated orderly or otherwise between the octahedral layers.
The DTG (differential thermographimetry) curves of the water release from the QCB materials as a function of temperature show that the major peak appears at much lower temperatures compared to that of the much more crystalline boehmites. The XRD patterns of QCBs show quite broad peaks, and their half-widths are indicative of the crystal size as well as the degree of crystal perfection.
The broadening of the widths at half-maximum intensities varies substantially and for the QCBs typically can be from about 2°-6° to 2&thgr;. Further, as the amount of water intercalated in the QCB crystals is increased, the main (020) XRD reflection moves to lower 2&thgr; values corresponding to greater d-spacings. Some typical, commercially available QCB's are: Condea Pural®, Catapal® and Versale® products.
The category II boehmites consist of micro-crystalline boehmites (MCBs), which are distinguished from the QCBs by their high degree of crystallinity, relatively large crystal sizes, very low surface areas, and high densities. Unlike the QCBs, the MCBs show XRD patterns with higher peak intensities and very narrow half-peak line widths. This is due to the relatively small number of intercalated water molecules, large crystal sizes, higher degree of crystallization of the bulk material, and smaller amount of crystal imperfections present. Typically, the number of intercalated molecules of water can vary from about 1 up to about 1.4 per mole of AlO. The main XRD reflection peaks (020) at half-length of maximum intensity have widths from about 1.5 down to about 0.1 degree 2-theta (2&thgr;). For the purpose of this specification we define quasi-crystalline boehmites as having 020 peak widths at half-length of the maximum intensity of 1.5 or greater than 1.5°. Boehmites having a (020) peak width at half-length of maximum intensity smaller than 2 are considered micro-crystalline boehmites.
A typical commercially available MCB product is Condea's P-200® grade of alumina. Overall, the basic, characteristic differences between the QCB and MCB types of boehmites involve variations in the following: 3-dimensional lattice order, sizes of the crystallites, amount of water intercalated between the octahedral layers, and degree of crystal imperfections.
As for the commercial preparation of these boehmite aluminas, QCBs are most commonly manufactured via processes involving:
Neutralization of aluminum salts by alkalines, acidification of aluminate salts, hydrolysis of aluminum alkoxides, reaction of aluminum metal (amalgamated) with water, and rehydration of amorphous rho-alumina obtained by calcining gibbsite. The MCB types of boehmite aluminas in general are commercially produced by hydrothermal processes using temperatures usually above 150° C. and autogeneous pressures. These processes usually involve hydrolysis of aluminum salts to form gelatinous aluminas, which are subsequently hydrothermally aged in an autoclave at elevated temperatures and pressures. This type of process is described in U.S. Pat. No. 3,357,791. There are several variations on this basic process involving different starting aluminum sources, additions of acids or salts dur
Jones William
O'Connor Paul
Pearson Gregory
Stamires Dennis
Akzo Nobel N.V.
Bell Mark L.
Hailey Patricia L.
Morris Louis A.
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