Patent Grant
4316792
Hydroliquefaction of coal to valuable liquid products is currently of great interest. In one such process, coal dispersed in a suitable liquefaction solvent is hydroliquefied in an upflow expanded or ebullated hydroliquefaction catalyst bed. Such a process is described, for example, in U.S. Pat. No. 2,987,465. Applicant has found that such an upflow expanded or ebullated bed hydroliquefaction process has poor selectivity to liquid products, whereby there is an inefficient use of hydrogen and the production of light products, such as methane, ethane, propane, butane and light oils boiling below 400.degree. F. Such products contain a higher percentage of hydrogen than heavier distillates. In accordance with the present invention, applicant has provided a new and improved process and system for the hydroliquefaction of coal in an upflow expanded or ebullated catalyst bed which increases the selectivity to liquid products and thereby efficiently uses its hydrogen to provide a more economical process. In accordance with one aspect of the present invention, there is provided a process for the catalytic hydroliquefaction of coal by passing coal dispersed in a coal liquefaction or pasting solvent and hydrogen through at least one reactor which has at least two parallel upflow expanded catalyst beds, in separate streams, each stream having a cross-sectional flow area of no greater than 255 square inches, with the streams through each of the catalyst beds having a length and a gas and liquid superficial velocity to maintain an expanded bed and provide a Peclet Number of at least 3. If recycle is employed, the ratio of recycle to total feed (coal and liquefaction solvent) does not exceed 2:1, by volume. In accordance with another aspect of the present invention, there is provided a reaction system for the catalytic hydroliquefaction of coal which includes at least two upflow expanded or ebullated bed catalytic hydroliquefaction reaction zones in series, with each of the at least two reaction zones including at least two parallel expanded catalyst beds, each of the expanded catalyst beds providing for flow therethrough in a stream which has a cross-sectional flow area of no greater than 255 square inches and a flow length whereby the superficial velocities of gas and liquid therethrough maintain the expanded or ebullated catalyst bed and provides a Peclet Number of at least 3. The at least two parallel catalytic beds in each of the reaction zones are provided by the use of partitions in the reaction zones. Peclet Number is defined as follows: ##EQU1## wherein V.sub.L is liquid velocity, ft/hr. The cross-sectional flow area of the stream in each of the catalyst beds is no greater than 255 square inches, with the cross-sectional flow area generally being at least 10 square inches. In most cases, the cross-sectional flow area is at least 28 square inches. The selection of an optimum cross-sectional flow area will vary, and the selection of such an optimum cross-sectional flow area is deemed to be within the scope of those skilled in the art from the teachings herein. The other parameters included in the calculation of Peclet Number are reaction zone length and superficial gas and liquid velocities through the expanded catalyst beds. The velocity of gas and liquid through the beds must be at a value sufficient to maintain the ebullated or expanded catalyst bed state, and as a practical manner, such expansion is primarily related to the superficial liquid velocity. Thus, the reactor length and the superficial liquid and gas velocities are coordinated to provide a Peclet Number, as hereinabove described, as well as sufficient velocity to provide for the expanded or ebullated catalyst beds. In general the reaction zone lengths is in the order of from 20 to 130 feet, and most preferably in the order of from 40 to 90 feet, with the superficial liquid velocity generally being in the order of from 0.04 to 0.3 foot per second. The superficial gas velocity is generally in the order of from 0.04 to 1 foot per second. The selection of optimum values is deemed to be within the scope of those skilled in the art from the teachings herein. In accordance with the invention, recycle is limited, with the ratio of recycle to total feed (coal and liquefaction solvent) being no greater than 2:1. Although in some cases it may be possible to operate the process without any recycle; i.e., a recycle ratio of 0:1, in most cases, some recycle is required in order to maintain a sufficient liquid velocity for expanding the catalyst beds. As a result, in most cases, the recycle ratio is at least 0.2:1, with the recycle ratio generally not exceeding 1:1. In accordance with the preferred embodiment, all of such recycle is provided externally; i.e., no internal recycle, which thereby eliminates the necessity for an internal recycle pump as generally employed in the ebullated bed coal liquefaction process. It is to be understood, however, that it is possible within the scope of the invention to provide some internal recycle, provided that the recycle ratio (internal and/or external recycle) does not exceed 2:1. In accordance with the present invention by providing hydroliquefaction in a reactor having a plurality of parallel expanded catalyst beds it is possible to achieve efficient use of hydrogen in a reactor of a size suitable for commercial applications. Thus, for example, in accordance with the present invention, it is possible to employ a reactor having a total cross-sectional area in the order of at least 65 ft.sup.2, and up to 155 ft.sup.2 or greater, and to achieve improved hydrogen efficiency by providing for a plurality of separate parallel flow streams having the flow parameters, hereinabove described in separate parallel expanded beds in the reactor. The parallel flow through separate expanded beds in the reactor is achieved by providing appropriate partitions in the reactor which are designed and arranged to achieve cross-sectional flow areas as hereinabove described. The number of partitions and the number of parallel flow streams in part will be dependent upon the total cross-sectional area of the reactor in that there must be a sufficient number of partitions and resulting flow streams to provide parallel flow streams each of which has a cross-sectional flow area, as hereinabove described. In part, the total number of partitions and the resulting number of flow streams is dependent upon the desired cross-sectional flow area within the cross-sectional flow areas hereinabove described. The selection of partitions to provide a desired cross-sectional flow area is deemed to be within the scope of those skilled in the art from the teachings herein. The partitions for the reactor may take any one of a wide variety of forms, with a preferred form of partition being a vertical honeycomb type of structure. It is to be understood, however, that the partitions may provide for flow passages of other shapes; e.g., round, square, rectangular, etc. The selection of an optimum partition pattern is deemed to be within the scope of those skilled in the art from the teachings herein. In accordance with a preferred embodiment of the present invention, there are at least two catalytic hydroliquefaction zones of the type hereinabove described in series, and preferably at least three such zones in series. The additional hydroliquefaction zones are employed to provide the desired hydroliquefaction without an unacceptable increase in temperature; i.e., the exothermic heat of reaction is controlled by providing a series of reaction zones, rather than by providing large quantities of recycle. The selection of an optimum amount of reaction zones, in series, is deemed to be within the scope of those skilled in the art from the teachings herein. In most cases, it is not necessary to provide any more than 4 of such hydroliquefaction zones in series. In most cases, the number of hydroliquefaction zones in series is selected to limit the temperature increase of each of the zones to no greater than 150.degree. F., and preferably to no greater than 100.degree. F. The hydroliquefaction, as known in the art, is conducted at elevated temperatures and pressures. In general, the hydroliquefaction temperature is in the order of 650.degree. F., to 900.degree. F., and preferably from 750.degree. F. to 850.degree. F. The pressures are generally in the order of from 1800 to 3000 psig, and most generally in the order of from 2000 to 2700 psig. The selection of optimum temperatures and pressures are deemed to be within the scope of those skilled in the art from the teachings herein. Hydrogen is introduced into the hydroliquefaction zone in an amount, which when coordinated with the other processing conditions, provides an amount of hydrogen addition or absorption to provide the desired liquefied product. In addition, hydrogen is provided for effecting hydrodesulfurization and hydrodenitrification of the feedstock. In general, by proceeding in accordance with the present invention, it is possible to achieve a conversion of 90% or more of the MAF coal feed with hydrogen consumptions in the order of from 2 to 4 lbs. of hydrogen per 100 lbs. of coal. The hydroliquefaction is conducted with a catalyst suitable for liquefying the coal, and in addition, such catalyst should have desulfurization and denitrification activity. Such catalysts are generally known in the art; e.g., cobalt molybdate, nickel molybdate, tungsten-nickel sulfide, etc., and are generally supported on a suitable support such as alumina. The selection of a suitable catalyst is deemed to be within the scope of those skilled in the art from the teachings herein. The catalyst is maintained in the hydroliquefaction zone as an expanded or ebullated bed. As known in the art, such expanded or ebullated bed differs from a fluidized bed in that, in the expanded or ebullated bed, catalyst particles are not maintained in fluidized random motion. Such expanded or ebullated beds are known in the art, and as a result, no further details in this respect are deemed necessary for a complete understanding of the present invention. The coal, as known in the art, is dispersed in a suitable pasting or coal liquefaction solvent or oil for passage through the catalytic hydroliquefaction zone. Such pasting or liquefaction solvents are known in the art, and is preferably a solvent derived from the coal liquefaction product, although other pasting solvents or oils may also be employed for the hydroliquefaction. The selection of a particular pasting oil is well within the scope of those skilled in the art, and forms no part of the present invention. In general, as known in the art, the pasting solvent is provided in an amount to provide a pasting solvent to coal weight ratio in the order of those generally used in the art; e.g., from 1:1 to 20:1. The coal employed as a hydroliquefaction feed may be a bituminous coal, sub-bituminous coal or a lignitic coal. The selection of a suitable coal for producing a desired product forms no part of the present invention, and as a result no further details in this respect are deemed necessary for a complete understanding thereof.
The Government of the United States of America has rights in this invention pursuant to Contract No. EX-76-C-01-2514 awarded by the U.S. Energy Research & Development Administration.
| Number | Name | Date | Kind |
|---|---|---|---|
| 2359310 | Hemminger | Oct 1944 | |
| 3700584 | Johanson et al. | Oct 1972 | |
| 3769198 | Johanson et al. | Oct 1973 | |
| 4045329 | Johanson et al. | Aug 1977 |
