Zeolites and molecular sieves and the use thereof

Details Zeolites and molecular sieves and the use thereof Zeolites and molecular sieves and the use thereof

2001-10-17

2004-10-26

Griffin, Walter D. (Department: 1764)

Catalyst, solid sorbent, or support therefor: product or process

Zeolite or clay, including gallium analogs

And additional al or si containing component

C502S064000, C502S066000, C502S071000, C502S077000, C502S078000

Reexamination Certificate

active

06809055

ABSTRACT:

This invention relates to zeolites and molecular sieves, and more particularly to the production of zeolites and molecular sieves and the use thereof.
Zeolites and molecular sieves are generally used in a wide variety of catalytic procedures. In general, zeolites and molecular sieves may be prepared by a procedure which involves forming the structure from a reaction mixture that includes silica and alumina, and often with an organic directing agent (often referred to as a “template”) such as, but not limiting to linear amines, linear diamines, and quaternary ammonium salts. As an example, such quaternary ammonium salt may be tetraethylammonium hydroxide. The organic directing agent can be removed from the resultant zeolite by a heat treatment process, often referred to as “calcincation”, at an elevated temperature. The acid form of the formed zeolite structure or molecular sieve is then produced by ion exchange, such as, but not limited to, ammonium exchange, followed by further calcination. In some processes, the ammonium exchange step occurs before the calcination, thereby simplifying the sequence of steps. In many cases, the (additional) heat treatment, also referred to as calcination, is executed subsequent to a forming step. In this forming or shaping step, the zeolite or molecular sieve is produced into a shape to allow use in for example fixed bed catalytic operation.
In the current art, it has been recognized that the state or characteristics of the zeolite or molecular sieve may be effected by the final heat treatment step. However, it has not been recognized that, in the heat treatment to remove the organic directing agent, the performance of the zeolite or molecular sieve is affected significantly by changing the state or characteristics of the zeolite or molecular sieve materials. Applicant has surprisingly found that controlled heat treatment or calcination to remove the organic directing agent and exposure of the zeolite or molecular sieve during this treatment to average temperatures no higher than 570° C. is desired to create acid sites of a specific nature and strength. These created acid sites, as can be measured by the temperature controlled desorption of ammonia performed in accordance with Example 3 (“TPD”), are surprisingly found to significantly enhance catalytic performance in reactions, such as, but not limited to, hydrocarbon conversion technologies, and environmental abatement technologies. Applicant has found that, contrary to what has been recognized by prior art findings, that the abundance of these sites, referred to as “strong acid sites” and measured by the temperature controlled desorption of ammonia performed in accordance with Example 3 (“TPD”), is beneficial in aromatics alkylation technologies, such as, but not limited to, the ethylation of benzene to form ethylbenzene. Applicant has also found, that in addition to the appearance of such acid sites, substantial restructuring of the zeolite or molecular sieve occurs, as can be characterized using porosity measurements, such as N2 physisorption and/or mercury porosimetry. According to the current understanding, Applicant believes that a combination of the above-mentioned characteristics of zeolites and molecular sieves is desirable in optimizing performance in catalytic applications, specifically in hydrocarbon conversion applications. The combination of the above-mentioned improved characteristic and enhanced catalytic performance is found to be characterized by the Acidity-Activity Index (AAI). The AAI, as used in the Specification and claims, the ratio of the total ammonia desorbed from the zeolite at a temperature above 300° C. to the total ammonia desorbed from the zeolite at a temperature below 300° C. as measured by the temperature controlled desorption performed in accordance with Example 3 (“TPD”).
Contrary to Applicants' findings, U.S. Pat. No. 5,258,570 teaches that the catalytic activity of zeolite beta can be approved by activating the formed zeolite by heating at elevated temperatures of from about 600° C. to 675° C. in order to reduce so-called “strong” acid sites. In accordance with U.S. Pat. No. 5,258,570, zeolite beta produced by conventional procedures is specifically treated to reduce acid sites to thereby increase catalyst activity.
In accordance with one aspect of the present invention, there is provided a zeolite or molecular sieve that has an increased number of so called “strong acid sites”, i.e. sites as measured by the temperature controlled desorption performed in accordance with Example 3 (“TPD”). More particularly, Applicant has found that by increasing the number of strong acid sites, there is provided a substantial increase in catalyst activity.
In yet another aspect of the present invention, there is provided a zeolite or molecular sieve that has an increased mesoporosity, i.e. pores of a size larger than 2 nm and smaller than 50 nm, in combination with an increased number of so called “strong acid sites”. More particularly, Applicant has found that by increasing both the mesoporosity of the zeolite of molecular sieve network and the number of so called “strong acid sites”, there is provided a substantial increase in catalyst activity.
Preferably, the zeolite or molecular sieve has pores which have an average pore diameter greater than 100 Angstroms.
In another embodiment, the zeolite or molecular sieve has a pore volume greater than 0.7 cm
3
/g.
In accordance with a preferred embodiment of the present invention, the zeolites or molecular sieve has an Acidity-Activity Index (AAI) of at least 1.0, preferably at least 1.2, and more preferably at least 1.4, and most preferably at least 1.6 wherein AAI, as used in the Specification and claims, is the ratio of the total ammonia desorbed from the zeolites or molecular sieve at a temperature above 300° C. to the total ammonia desorbed from the zeolites or molecular sieve at a temperature below 300° C. as measured by the temperature controlled desorption performed in accordance with Example 3 (“TPD”).
More particularly in a preferred embodiment, the zeolites or molecular sieve is one that contains silica and alumina in a silica to alumina molar ratio of 6:1 or higher or 15:1 or higher that is prepared by use of a templating or organic directing agent that includes an organic nitrogen compound. As representative but non-limiting examples of zeolites there may be mentioned: beta, TEA-mordenite, TEA-ZSM-12, MCM-22, MCM-36, MCM-39, MCM-41, MCM-48, PSH03, ZSM-5, TPA05, Breck 6, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48, SSZ-32, etc. A preferred zeolite is zeolite beta although the invention is not limited to the preferred zeolite.
In accordance with a further aspect of the present invention, Applicant has found that a zeolites or molecular sieve having an improved catalytic activity may be produced by increasing the strong acid sites thereof. In this respect, Applicant has found that during the procedures for producing zeolites and molecular sieves, and in particular the procedure for removing the organic nitrogen templating agent, the conditions employed therein should be controlled to preserve strong acid sites. In this respect, strong acid sites are maintained by employing process conditions which prevent loss of those sites that are proven to be beneficial in catalytic conversion applications and are be characterized by its AAI ratio. It is believed that those sites can be ascribed to be a specific kind of tetrahedral aluminum sites in the zeolites or molecular sieve structure.
In this respect, in removing the organic nitrogen templating agent (in general, at least 50% thereof is removed and in a preferred embodiment essentially all is removed), heating is controlled to prevent exposure to average temperatures that are above about 575° C. and preferably the heating is to an average temperature of no greater than 550° C. (in general, at least 50% thereof is removed and in a preferred embodiment essentially all is removed). Moreover, in a preferred embodiment, heating should be controlled so to in a controlled manner

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