Note: Descriptions are shown in the official language in which they were submitted.
~ 1 ~4382
1 B~CKGRO~T~D OF T~ V~N~IO~
2 The present mvention relates to an iT~ro~ed process for the
3 pyrolysis of carbonous materials, such as coal, to produce
~ liquid and gaseous products, by the use of iron and/or zinc
soluble salts prior to pyrolysis.
6 Coal, once the leading source of energy in the
7 United States, is beginning to play a more important role
8 in the nation's energy future The primary xeason for the
9 growing importance of coal is the r pid depletion o~ known
petroleum and natural ~as reserves. These known reserves
11 ~re being depleted at a rate considerably faster than the
12 rate of discovering new reserves. As the era of petroleum
13 qrowth draws to a close, the world's commerical energy
14 mix will have to change. Transition energy sources will be
needed as a bridge between petroleum and the potentially
16 unlimited ener~y sources of the future; such sources
17 being, for example, solar power and nuclear fusion. Owing
18 to their great abundance, coal and oil shale are perceived
19 as the keystones of such a bridge. Consequently, much
work is presently in progress to provide economical ways
21 of converting these resources to valuable liquid and
22 gaseous products. Coal liquefaction and pyrolysis pro-
23 cesses in which coal, with or without a diluent, is sub-
24 jected to elevated temperatures and pressures to convert
solid coal to normally liquid hydrocarbonaceous products,
26 are well known.
27 Pyrolysis of coal to yield li~uids and char is
28 an area of technology which has the potential of leading
29 the way to a successful national synfuels program. The
major limitation~ of present coal pyrolysis technolo~y
31 are the l~w quality of simple pyrolysis liquids combi~ed
32 with hiah sulur content. Even when a coal in relatively
3~ low sulfur content is employed to reduce the need for
34 hydrotreating, the product is generally low in yield and
has stability problems.
36 By the practice of the present invention,
37 pyrolysis in the presence of hvdrogen is advantageously
3 ~ ~
combined, under certain conditions, to give increased yields and
more stable liquid products than those aquired by use of pyrolysis
processes conventionally known.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is pro-
vided a process for converting carbonGus materials selected from
the group consisting of subbituminous coal, oil-shale, lignite
and peat, to liquid and gaseous products, said process comprising:
(a) impregnating the carbonous material with one or more water
solu~le salts of a metal selected from the group consisting of
iron and zinc; (b~ treating the impregnated material in such a way
as to precipitate, into the structure of the material, the metal
of the soluble salt as its oxide or in a form which can be readily
converted to its oxide by decomposition; and (c) pyrolyzing the
treated impregnated material in the presence of hydrogen, at a
temperature from about 400C to about 700C, and at gas residence
times of less than about 30 seconds and solids residence times of
from about 5 to 100 minutes.
In preferred embodiments of the present invention sub-
bituminous coal or oil-shale is impregnated with iron sulfate,
treated with sodium carbonate, and pyrolyzed at a temperature of
about 550C.
DETAILED DESCRIPTION OF THE INVENTION
. . . _
Any type of coal or oil shale may be treated according
to the present invention, although for coal it is preferred to
treat only the lower rank coals such as, subbituminous coal,
lignite, and peat; of course, other similar solid carbonous ma-
terials may also be employed. Such coals usually have the follow-
ing character: carbon content ranging from about 55 to 88 wt. %,
hydrogen content ranging from about 3.8 to 6.2 wt. %, oxygen
content ranging from about 2.6 to 33 wt. ~ (M~F basis), and a H/C
ratio from about 0.3 to 1.1. In addition, oil shales, particularly
those with high aromatic content, can be treated in accordance
with the present invention.
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1 It is preferred that the carbonous material have
2 as high a surface area as possible; althouyh, it is not
3 economically justifiable to pulveri~e it to a very fine
4 powder. Consequently, it is desirable to expose as much
of the material's surface area as possible without losing
6 material as dust or fines or as the economics of grinding
7 or process e~uipment may dictate. Generally, for purposes
8 of this invention, the material will be ground to a finely
9 divided state and will contain a majority of particles
less than about 4 mesh, U.S. Sieve Size. The coal may be
11 dried by conventional drying techni~ues, for example,
12 heatinq to a temperature of about 100C to 110C.
13 The carbonous material, after grindin~, is im-
14 pregnated with a water soluble salt of a metal selected
from the gr~up consisting of iron and zin~ by forming a
16 slurry of coal and salt solution. Non-limiting examples
17 o' water soluble salts suitable for use herein include iron
18 chloride, iron sulfate, iron nitrate, zinc chloride and
19 zinc sulfate. More preferred is iron sulfate.
The salt solution is prepared bY dissolving
21 enough of the salt in water to result in at least a O.OlM
22 sol~tion. Preferably a O.lM solution is employed. It is
23 desirable to di solve the salt in enouqh polar solvent, pre-
24 ferably water so as to have about the same weight of~ter as the
weight of cæbonous material. The salt solution and car~onous
26 material are slurried at a temperature from about room
27 temperature (20C) to about the boiling point of the
28 solution- Generallv about 1 ~art of salt solution
29 by weight is employed for each part of carbonous material
by weiqht.
31 After the carbonous material has been slurried
32 with the salt solution for an effective amount of time,
33 it is treated in such a way as to precipitate, into the
34 structure of the carbonous material, the metal of the
soluble salt employed, in a well dispersed form as its
36 oxide or in a form which can be readily converted to the
37 oxide by decomposition~ Ef'ective amount of time, as used
38 in this context, means at least that amount of time needed
J ~ 3 ~ ~
to ensure substantially total impregnation of the salt solution
into the structure of the carbonous material. This amount of time
is primarily dependent on the moisture content of the carbonous
material. For example, impregnation of dry coal is achieved in
a matter of minutes whereas impregnation of wet coal may require
about 24 hours owing to transfer problems of the salt into the
wet coal structure.
After the carbonous material is impregnated with the water
soluble salt, it is treated in such a way as to cause precipita-
tion, into the structure of the carbonous material, of the metalof the soluble salt used for impregnation. The precipitated metal
will most likely be in a well dispersed form, preferably as its
oxide, or in a form which can be readily converted to its oxide by
decomposition. Non-limiting examples of such methods which can be
employed herein, to cause precipitation, include: (a) raising the
pH of the slurry to an effective pH to cause precipitation of the
metal as a hydroxide or hydrated oxide; (b) introducing an anion
into the slurry in form of another soluble salt which will produce
the oxide of the metal or which will produce a form which can
readily be converted to its oxide by decomposition, for example
at the pyrolysis conditions employed herein.
Non~limiting examples of cations of which this other anion
producing soluble salt is comprised include sodillm, ammonium and
potassium. Considerations which should be kept in mind when
choosing such other salt as well as any other agent used to cause
precipitation: (a) not adversely affect the pyrolysis products
or their evolution and recovery, (b) be economically feasible, and
(c) be non-toxic.
If the method used for precipitating the metal of the
impre~nating salt employed herein is to raise the pH, an appro-
priate base is introduced into the slurry. Non-limiting examples
of bases suitable for being employed h~rein include ammonia, a
caustic solution, and an organic base. The pH to which the
impregnated carbonous
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l material slurry would ha~e to be raised to affect precipi-
2 tation would vary depending upon tne solubility product of
3 the salts employe~. General~y a p~ in excess of about ll
4 will precipitate most salts.
If the method used to precipitate the metal of
6 the impregnating salt employed is to introduce an anion
7 into the slurry, the anion chosen is one which will pro-
8 d~ce an insoluble form of the metal of the soluble salt
9 ~mployed herein for ~ regnating. Such an insoluble fo~m should be
one w~ich is its oxi~è already or one w~ich can be readily decomposed,
11 under the pyrolysis conditions employed herein, -to its
12 oxide. Non-limiting examples of anions suitable for such
13 purposes include carbonates, bicarbonates, hydroxides,
14 etc.
After treatin~, so as to precipitate the metal
16 in a well-dispersed form, it is preferred to dry the treated
17 carbonous material. Any conventional drying means may be
18 employed.
l9 The treated and preferably dried carbonous
material is then subiected to pyrolysis at tem~eratures from
21 about 400C to about 700C, preferably from about 450C to
22 600C. The pyrolysis is per~ormed in the presence of
23 hvdrogen, generally at hydro~en pressures from about 500
24 to 2500 psi. Any excess hvdrogen, of course, will be
recyc7edO Furthermore, the pyrolysis is performed at re-
26 latively short gas and long solids residence times. That
~7 is, the gas residence time should be less than about 30
28 seconds, preferably less than lO seconds and the solids
29 residence times should be from about 5 to lO0 minutes, pre-
ferably from about 10 to 30 minutes. By choosing the
31 proper residence time, substantially maximum conversion
32 of carbonous material to liauids and gases are achieved
33 and undesirable secondary reactions are minimized. Such
34 undesirable secondary reactions include irreversible con-
densation reactions of molecules which will lead to char.
36 Non-limiting examples of reactors suitable for
37 use herein include fixed and fluid bed. The primary con-
38 straint on the reactor employed is to mini~ize contact
z
with the solid phase with hydrogen at reaction temperatures.
The following examples serve to more fully describe the
manner of practicing the above-described invention, as well as to
set forth the best modes contemplated for carrying out various
aspects of the invention. It is undexstood that these examples in
no way serve to limit the true scope of this invention, but rather,
are presented for illustrative purposes.
EXAMPLE 1
200g of Rawhide subbituminous coal was washed with 1.0
HCl solutions until no calcium appeared in the wash. This also
improved the wetability of the coal. The coal was then washed
with distilled water until the wash was neutral. The washed coal
was then dried in a vacuum oven at 105C for thre~ hours after
which it was treated with an equal weight of a 10% by weight solu-
tion of zinc chloride. An equal weight, bas~d on the weight of
dry coal, of a 10~ by weight solution of sodium carbonate was
added. The mixture was allowed to stand overnight at room tempera-
ture after which it was dried in a vacuum oven at 105C for three
hours.
150g of this dried and treated coal was pyrolyzed in a
fixed bed type reactor, by heating it at a rate of 6C/min. to
600C and holding it at about that temperature for 20 minutes,
The fixed bed was an annular configuration having the dimensions
of 4" ID x 4 1/2" OD x 6'` deep, and had a hydrogen flow rate of 2
standard cu. ft~min.
The total liquid product collected was 39.3 wt. ~ of the
dry coal.
Comparative Examp~e A
The procedure of Example 1 was followed except the coal
was not treated with salt solutions~ After pyrolysis the untreated
coal produced a liquid product of 30.2 wt. % based on the weight of
the dry coal.
These examples illustrate the advantages of employing the
present invention to obtain maximum amounts of liquid product from
coal by pyrolysis.
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J 1 6~382
1 EXAMPLE 2
2 The procedure of Example 1 above was followed
3 except ferrous a~onium sulfate was substituted for zi~c
4 chloride and 1% by weight solution of sodium carbonate was
employed to precipitate ferrous hydro~ide into the coal
6 structure. The iron cuntent Oc the impregnating s~lution
7 was 0.14 wt. ~.
8 Pyrolysis was carried out by heating the
9 sample, unaer 400 psi hydrogen pressure, to 300C
rapidly then utilizin~ a heating rate of 100C/30 min.,
11 to 500C.
12 The total conversion of dry coal to volatile
13 tliquid and qas) products was 52.8 wt. ~.
14 Comparative Example B
The procedure of Example 2 above was followed
16 except the coal was not treated with the salt solutions
17 before pyrolysis. After pyrolysis, it was found that
18 43.0 wt. ~ based on the weiqht of the dry coal, had been
19 converted to volatile products.
