Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Phosphorus or compound containing same
Reexamination Certificate
2001-11-30
2003-12-09
Harlan, Robert (Department: 1713)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Phosphorus or compound containing same
C423S305000, C423S328100, C423S705000, C423S708000
Reexamination Certificate
active
06660682
ABSTRACT:
RELATED APPLICATION DATA
None
1. Field of the Invention
The present invention relates to a method of synthesizing a molecular sieve. In particular, the invention is directed to a method for synthesizing a molecular sieve, especially a silicoaluminophosphate molecular sieve, and to its formulation into a catalyst composition useful in a process for producing olefin(s), preferably ethylene and/or propylene, from a feedstock, preferably an oxygenate containing feedstock.
2. Background of the Invention
Olefins are traditionally produced from petroleum feedstock by catalytic or steam cracking processes. These cracking processes, especially steam cracking, produce light olefin(s) such as ethylene and/or propylene from a variety of hydrocarbon feedstock. Ethylene and propylene are important commodity petrochemicals useful in a variety of processes for making plastics and other chemical compounds. Ethylene is used to make various polyethylene plastics, and in making other chemicals such as vinyl chloride, ethylene oxide, ethylbenzene and alcohol. Propylene is used to make various polypropylene plastics, and in making other chemicals such as acrylonitrile and propylene oxide.
The petrochemical industry has known for some time that oxygenates, especially alcohols, are convertible into light olefin(s). There are numerous technologies available for producing oxygenates including fermentation or reaction of synthesis gas derived from natural gas, petroleum liquids, carbonaceous materials including coal, recycled plastics, municipal waste or any other organic material. Generally, the production of synthesis gas involves a combustion reaction of natural gas, mostly methane, and an oxygen source into hydrogen, carbon monoxide and/or carbon dioxide. Syngas production processes are well known, and include conventional steam reforming, autothermal reforming, or a combination thereof.
Methanol, the preferred alcohol for light olefin production, is typically synthesized from the catalytic reaction of hydrogen, carbon monoxide and/or carbon dioxide in a methanol reactor in the presence of a heterogeneous catalyst. For example, in one synthesis process methanol is produced using a copper/zinc oxide catalyst in a water-cooled tubular methanol reactor. The preferred methanol conversion process is generally referred to as a methanol-to-olefin(s) process, where methanol is converted to primarily ethylene and/or propylene in the presence of a molecular sieve.
Molecular sieves are porous solids having pores of different sizes such as zeolites or zeolite-type molecular sieves, carbons and oxides. There are amorphous and crystalline molecular sieves. Molecular sieves include natural, mineral molecular sieves, or chemically formed, synthetic molecular sieves that are typically crystalline materials containing silica, and optionally alumina. The most commercially useful molecular sieves for the petroleum and petrochemical industries are known as zeolites. A zeolite is an aluminosilicate having an open framework structure that usually carries negative charges. This negative charge within portions of the framework is a result of an Al
3+
replacing a Si
4+
. Cations counter-balance these negative charges preserving the electroneutrality of the framework, and these cations are exchangeable with other cations and/or protons. Synthetic molecular sieves, particularly zeolites, are typically synthesized by mixing sources of alumina and silica in a strongly basic aqueous media, often in the presence of a structure directing agent or templating agent. The structure of the molecular sieve formed is determined in part by solubility of the various sources, silica-to-alumina ratio, nature of the cation, synthesis temperature, order of addition, type of templating agent, and the like.
A zeolite is typically formed from comer sharing the oxygen atoms of [SiO
4
] and [AlO
4
] tetrahedra or octahedra. Zeolites in general have a one-, two- or three- dimensional crystalline pore structure having uniformly sized pores of molecular dimensions that selectively adsorb molecules that can enter the pores, and exclude those molecules that are too large. The pore size, pore shape, interstitial spacing or channels, composition, crystal morphology and structure are a few characteristics of molecular sieves that determine their use in various hydrocarbon adsorption and conversion processes.
There are many different types of zeolites well known to convert a feedstock, especially oxygenate containing feedstock, into one or more olefin(s). For example, U.S. Pat. No. 5,367,100 describes the use of a well known zeolite, ZSM-5, to convert methanol into olefin(s); U.S. Pat. No. 4,062,905 discusses the conversion of methanol and other oxygenates to ethylene and propylene using crystalline aluminosilicate zeolites, for example Zeolite T, ZK5, erionite and chabazite; and U.S. Pat. No. 4,079,095 describes the use of ZSM-34 to convert methanol to hydrocarbon products such as ethylene and propylene.
Crystalline aluminophosphates, ALPO
4
, formed from corner sharing [AlO
2
] and [PO
2
] tetrahedra linked by shared oxygen atoms are described in U.S. Pat. No. 4,310,440 to produce light olefin(s) from an alcohol. Metal containing aluminophosphate molecular sieves, MeAPO's and ElAPO's, have been also described to convert alcohols into olefin(s). MeAPO's have a [MeO
2
], [AlO
2
] and [PO
2
] tetrahedra microporous structure, where Me is a metal source having one or more of the divalent elements Co, Fe, Mg, Mn and Zn, and trivalent Fe from the Periodic Table of Elements. ElAPO's have an [ElO
2
], [AlO
2
] and [PO
2
] tetrahedra microporous structure, where El is a metal source having one or more of the elements As, B, Be, Ga, Ge, Li, Ti and Zr. MeAPO's and ElAPO's are typically synthesized by the hydrothermal crystallization of a reaction mixture of a metal source, an aluminum source, a phosphorous source and a templating agent. The preparation of MeAPO's and ElAPO's are found in U.S. Pat. Nos. 4,310,440, 4,500,651, 4,554,143, 4,567,029, 4,752,651, 4,853,197, 4,873,390 and 5,191,141.
One of the most useful molecular sieves for converting methanol to olefin(s) are those ELAPO's or MeAPO's where the metal source is silicon, often a fumed, colloidal or precipitated silica. These molecular sieves are known as silicoaluminophosphate molecular sieves. Silicoaluminophosphate (SAPO) molecular sieves contain a three-dimensional microporous crystalline framework structure of [SiO
2
], [AlO
2
] and [PO
2
] comer sharing tetrahedral units. SAPO synthesis is described in U.S. Pat. No. 4,440,871, which is herein fully incorporated by reference. SAPO is generally synthesized by the hydrothermal crystallization of a reaction mixture of silicon-, aluminum- and phosphorus-sources and at least one templating agent. Synthesis of a SAPO molecular sieve, its formulation into a SAPO catalyst, and its use in converting a hydrocarbon feedstock into olefin(s), particularly where the feedstock is methanol, is shown in U.S. Pat. Nos. 4,499,327, 4,677,242, 4,677,243, 4,873,390, 5,095,163, 5,714,662 and 6,166,282, all of which are herein fully incorporated by reference.
Templating agents are used in the synthesis of molecular sieves, particularly SAPO molecular sieves, as a crystal structure-directing agent or affecting agent. Furthermore, templating agents are typically nitrogen containing organic bases such as quaternary ammonium salts or hydroxides. Typically, because templating agents are also used to control the pH during the synthesis of molecular sieves, the quaternary ammonium hydroxide is often used instead of the less expensive quaternary ammonium salt. Additionally, the quantity of the templating agent used is often dictated by the pH of the reaction mixture in which the molecular sieve forms. Templating agents are typically used in excess, relative to its incorporation in the crystalline
Cao Guang
Shah Matu J.
Exxon Mobil Chemical Patents Inc.
Harlan Robert
Sher Jaimes
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