Conjoined reactor system

Details Conjoined reactor system Conjoined reactor system

2003-05-23

2004-10-05

Parsa, J. (Department: 1621)

Chemistry: fischer-tropsch processes; or purification or recover

Plural zones each having a fischer-tropsch reaction

C518S700000, C518S712000

Reexamination Certificate

active

06800664

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a process for the preparation of hydrocarbons from synthesis gas. More particularly, this invention relates to a gas-agitated multiphase reactor system with multiple reaction zones comprising gas-liquid or gas-liquid-solid mixtures that can maximize the production rate while allowing better control of the temperature distribution and better control of the liquid and solid phases in the reactors. Still more particularly, this invention relates to a method for operating a pair of linked gas-agitated slurry bed reactors such that the hydrodynamic behavior and reactor performance of such reactor system are improved compared to that of a conventional slurry bed reactor.
BACKGROUND
Natural gas, found in deposits in the earth, is an abundant energy resource. For example, natural gas commonly serves as a fuel for heating, cooking, and power generation, among other things. The process of obtaining natural gas from an earth formation typically includes drilling a well into the formation. Wells that provide natural gas are often remote from locations with a demand for the consumption of the natural gas.
Thus, natural gas is conventionally transported large distances from the wellhead to commercial destinations in pipelines. This transportation presents technological challenges due in part to the large volume occupied by a gas. Because the volume of an amount of gas is so much greater than the volume of the same number of gas molecules in a liquefied state, the process of transporting natural gas typically includes chilling and/or pressurizing the natural gas in order to liquefy it. However, this contributes to the final cost of the natural gas.
Further, naturally occurring sources of crude oil used for liquid fuels such as gasoline, jet fuel, kerosene, and diesel fuel have been decreasing and supplies are not expected to meet demand in the coming years. Fuels that are liquid under standard atmospheric conditions have the advantage that in addition to their value, they can be transported more easily in a pipeline than natural gas, since they do not require liquefaction.
Thus, for all of the above-described reasons, there has been interest in developing technologies for converting natural gas to more readily transportable liquid fuels, i.e. to fuels that are liquid at standard temperatures and pressures. One method for converting natural gas to liquid fuels involves two sequential chemical transformations. In the first transformation, natural gas or methane, the major chemical component of natural gas, is reacted with oxygen, or steam, or a combination of both to form synthesis gas, which is a combination of carbon monoxide gas and hydrogen gas. In the second transformation, known as the Fischer-Tropsch (FT) synthesis, carbon monoxide is reacted with hydrogen to form organic molecules containing carbon and hydrogen. Those molecules containing only carbon and hydrogen are known as hydrocarbons. Those molecules containing oxygen in addition to carbon and hydrogen are known as oxygenates. Hydrocarbons having carbons linked in a straight chain are known as aliphatic hydrocarbons and are particularly desirable as the basis of synthetic diesel fuel.
The Fischer-Tropsch process is commonly facilitated by a catalyst. Catalysts desirably have the function of increasing the rate of a reaction without being consumed by the reaction. Common catalysts for use in the Fischer-Tropsch process contain at least one metal from Groups 8, 9, or 10 of the Periodic Table (in the new IUPAC notation, which is used throughout the present specification). The molecules react to form hydrocarbons while confined on the surface of the catalyst. The hydrocarbon products then are desorbed from the catalyst and can be collected. H. Schulz (Applied Catalysis A: General 1999, 186, p. 3) gives an overview of trends in Fischer-Tropsch catalysis.
The catalyst may be contacted with synthesis gas in a variety of reaction zones that may include one or more reactors, either placed in series, in parallel or both. Common reactors include packed bed (also termed fixed bed) reactors and slurry bed reactors. Originally, the Fischer-Tropsch synthesis was carried out in packed bed reactors. These reactors have several drawbacks, such as temperature control, that can be overcome by gas-agitated slurry reactors or slurry bubble column reactors. Gas-agitated multiphase reactors comprising catalytic particles sometimes called “slurry reactors”, “slurry bed reactors” or “slurry bubble column reactors,” operate by suspending catalytic particles in liquid and feeding gas reactants into the bottom of the reactor through a gas distributor, which produces small gas bubbles. As the gas bubbles rise through the reactor, the reactants are absorbed into the liquid and diffuse to the catalyst where, depending on the catalyst system, they are typically converted to gaseous and liquid products. The gaseous products formed enter the gas bubbles and are collected at the top of the reactor. Liquid products are recovered from the suspending liquid by using different techniques like filtration, settling, hydrocyclones, magnetic techniques, etc. Some of the principal advantages of gas-agitated multiphase reactors or slurry bubble column reactors (SBCRs) for the exothermic Fischer-Tropsch synthesis are the very high heat transfer rates, and the ability to remove and add catalyst online. Sie and Krishna (Applied Catalysis A: General 1999, 186, p. 55) give a history of the development of various Fischer Tropsch reactors.
It is clear from the prior art that the performance of a SBCR is a combined result of reaction kinetics, heat and mass transfer, and multiphase hydrodynamics. Jackson, Torczynski, Shollenberger, O'Hern, and Adkins (Proc. Annual Int. Pittsburgh Coal Conf. 1996, 13
th
(Vol 2), p. 1226) showed experimental evidence of the increase of gas bold up with increase in the inlet superficial velocity in a SBCR for Fischer Tropsch synthesis. Krishna, DeSwart, Ellenberger,. Martina, and Maretto (AIChE J. 1997, 43(2), p. 311) measured experimentally the increase in gas holdup with an increase in the gas velocity and solids concentration in a slurry bubble column in churn turbulent regime. Letzel, Schouten, Krishna and van den Bleek (Chem. Eng. Sci 1999, 54, p. 2237) developed a simple model for gas holdup and mass transfer at high pressure in a slurry bubble column. Numerically, Sanyel, Vasquez, Roy, and Dudukovic (Chem. Eng. Sci. 1999, 54, p. 5071) and Pan, Dudukovic, and Chang (Chem. Eng. Sci. 1999, 54, p. 2481) showed examples of computational fluid dynamic modeling and optimization of a slurry bubble column reactor irrespective of the chemistry. Wu and Gidaspow, (Chem. Eng. Sci 2000, 55, p. 573) show examples of computational fluid dynamics simulations of hydrodynamics of Slurry Bubble Column processes.
Much previous work has been aimed at optimization of the slurry bubble column system for Fischer Tropsch and other chemistries. Stem et al. (Ind. Eng. Chem. Process Des. Dev. 1985 25, p. 1214) developed an axial dispersion model for describing the performance of gas agitated multiphase reactor used for Fiscber-Tropsch synthesis. Saxena (Cat. Rev.—Sci. Eng. 1995, 37, p. 227) gives a review of the detailed experimental findings and theoretical models for the design of a Fischer Tropsch SBCR.
Considerable patent literature examines optimization of Fischer Tropsch Slurry Bubble Column reactors (SBCRs). U.S. Pat. No. 5,252,613 presents a method for improving catalyst particle distribution by introducing a secondary suspending fluid. U.S. Pat. No. 5,348,982 discloses one mode of operation for an SBCR. U.S. Pat. No. 5,382,748 shows the use of a vertical downcomer to promote the uniform catalyst distribution. U.S. Pat. No. 5,961,933 and U.S. Pat. No. 6,060,524 disclose that optimal operation can be obtained by introduction of liquid recirculation. Despite the s

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