Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Fluidized bed
Reexamination Certificate
2000-02-16
2001-04-17
Padmanabhan, Sreeni (Department: 1621)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Fluidized bed
C422S224000, C422S227000, C518S700000
Reexamination Certificate
active
06217830
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods of separating Fischer-Tropsch catalysts from the liquid product (wax) of a Fischer-Tropsch slurry bubble column (SBC) reactor.
BACKGROUND OF THE INVENTION
The conversion of synthesis gas—a mixture of hydrogen, carbon monoxide and other gases such as carbon dioxide and methane—into hydrocarbons has been of interest for more than fifty years. This conversion is frequently referred to as the Fischer-Tropsch (F-T) synthesis in honor of the pioneering work of Franz Fischer and Hans Tropsch in the early 1920's (C. Satterfield,
Heterogeneous Catalysis in Industrial Practice
, p. 432-442 (2d Ed. 1991)).
All large-scale F-T reactors built to date have utilized either fixed-bed or fluidized-bed reactors (See, e.g., G. Stiegel,
PETC Review
, p. 14-23 (Fall 1991);
Fischer
-
Tropsch Synthesis—The SASOL high
-
efficiency synfuels process
, Sasol Technology (Pty) Ltd., South Africa). However, a good deal of research and development in the United States, the United Kingdom, and Germany has been devoted to a different reactor concept known as the slurry bubble column (SBC) reactor. (See, e.g., H. Kolbel and M. Ralek,
Catal. Rev
.-
Sci. Eng.,
21, 225 (1980)).
Slurry bubble column reactors have distinct advantages over fixed and fluidized bed reactors. Some of these advantages are generic, e.g., a very close approach to isothermal operation, simple construction leading to low capital cost, and the ability to continuously withdraw and add catalyst in order to maintain a constant level of catalyst activity in the reactor. A major advantage that is specific to F-T chemistry, and related reactions such as alcohol synthesis, is the ability of SBC reactors to operate with a feed gas that contains a high ratio of carbon monoxide to hydrogen. Such CO/H
2
ratios are characteristic of modern, thermally-efficient coal gasifiers. The use of a SBC reactor in conjunction with a thermally-efficient coal gasifier can lead to a significant reduction in the cost of producing hydrocarbon liquids from coal, and in the overall thermal efficiency of the coal-to-liquids process, relative to current commercial technology.
An important and difficult problem which must be overcome before SBC reactors can be widely used is separating the small catalyst particles in the viscous slurry from the liquid hydrocarbon product. This separation is essential to the commercial implementation of F-T technology based on slurry bubble column reactors for several reasons. First, the liquid product from F-T synthesis must undergo further processing in catalytic reactors. The presence of catalyst particles in the liquid interferes with subsequent processing steps such as hydrocracking and distillation. Second, the portion of the catalyst slurry that is withdrawn for either regeneration or disposal should be as concentrated as possible in order to minimize the amount of valuable hydrocarbon liquid that must be processed during catalyst regeneration or disposal.
P. Zhou,
Status Review of Fischer
-
Tropsch Slurry Reactor Catalyst/Wax Separation Techniques
, Burns and Roe Service Corp. (February 1991) recently reviewed previous work on F-T slurry catalyst/wax separation, including techniques such as vacuum distillation, thermal cracking of vacuum bottoms, sedimentation, filtration, various forms of centrifugation, high-gradient magnetic separation (HGMS), solvent-assisted catalyst/wax separation and chemical methods. The review concludes that no single technology is entirely satisfactory, and recommends certain “hybrid” approaches. Accordingly, there is a continued need for new methods and apparatus for the separation SBC reactor slurry into F-T catalyst and the hydrocarbon product.
SUMMARY OF THE INVENTION
A first aspect of the present invention is a method of separating Fischer-Tropsch catalyst particles from the output slurry of a Fischer-Tropsch bubble column reactor, the slurry comprising Fischer-Tropsch catalyst particles and liquid hydrocarbon product (those skilled in the art will understand that not all of the liquid in the slurry is net product). The method comprises contacting a compressed hydrocarbon solvent (e.g., a supercritical hydrocarbon solvent, or liquid hydrocarbon solvent which may be at near supercritical conditions) with the output slurry at a temperature and pressure where the liquid hydrocarbon product is soluble in the solvent. This contacting step forms a concentrated slurry phase containing the catalyst particles, and an enriched solvent phase containing liquid hydrocarbon product. The contacting step is then followed by the step of separating the concentrated slurry from the enriched solvent.
Also disclosed is an apparatus for making a hydrocarbon product by a Fischer-Tropsch reaction. The apparatus comprises a Fischer-Tropsch slurry bubble column reactor; a slurry output line connected to the slurry bubble column reactor; a compressed hydrocarbon solvent supply; a contactor connected to the slurry output line and the compressed hydrocarbon solvent supply for contacting compressed hydrocarbon solvent with the output slurry to form a concentrated slurry phase containing the catalyst and an enriched solvent phase containing liquid hydrocarbon product; and a separator connected to the contactor for separating the concentrated slurry from said enriched solvent. In one embodiment, the separator and the contactor are a continuous countercurrent contactor.
As will be explained in greater detail below, an advantage of the present invention is the potential to meet all of the requirements of the separation with a single technology, rather than with a hybrid approach of two different technologies.
Another advantage of the present invention is that it may be practiced with relatively simple apparatus that can be readily assembled from known equipment in a new combination.
Another advantage of the present invention is the capacity for very simple, continuous operation without cyclic operations such as backflushing of filters.
Still another advantage of the present invention is the capacity to fractionate the recovered hydrocarbon product and selectively recycle a lower-molecular-weight cut in order to control the viscosity of the slurry in the SBR reactor.
It is noteworthy that in the recent comprehensive review of F-T slurry catalyst/wax separation techniques (P. Zhou,
Status Review of Fischer
-
Tropsch Slurry Reactor Catalyst/Way Separation Techniques,
Burns and Roe Service Corp. (Februaryu 1991)), the use of supercritical extraction is neither described nor suggested. Rather, this review proposes hybrids of multiple techniques.
The foregoing and other objects and aspects of the present invention are explained in detail in the Figures herein and the specification set forth hereinbelow.
REFERENCES:
patent: 4162965 (1979-07-01), Clapper
patent: 4605678 (1986-08-01), Brennan et al.
patent: 5332552 (1994-07-01), Chang
patent: 5348982 (1994-09-01), Herbolzheimer et al.
Schehl, R.R., Rose® Process Solves the LaPorte Catalyst/Wax Separation Problem (5051-238A), 1992.
Zhou, PhZ., Status Review of Fischer-Tropsch Slurry Reactor Catalyst/Wax Separation Techniques,Burns&Roe Services Corp.(1991).
Eisenbach, W.O., et al., Supercritical Fluid Extraction of Oil Sands and Residues from Oil and Coal Hydrogenation,Chemical Engineering at Supercritical Fluid Conditions, vol. 20, pp. 419-433 (1983).
Stutzer, D., et al., Separatin of Finely Dispersed Solids from Low-Volatile Viscous Media by Gas Extraction,Chemical Engineering at Supercritical Fluid Conditions, vol. 21, pp. 435-443 (1983).
Kolbel, H., et al., The Fischer-Tropsch Synthesis in the Liquid Phase,Catal. Rev.-Sci. Enc., vol. 21, pp. 225-274 (1980).
McGee, K., A Better Bottom Line from the Bottom of the Barrel,Rose Supercritical Fluid Technology(1992).
Kilpatrick Peter K.
Roberts George W.
Myers Bigel & Sibley & Sajovec
North Carolina State University
Padmanabhan Sreeni
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