Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to conversion of coal to
various useful component parts thereof, principally gaseous
component parts and conversion of these gaseous components
into other distillates; more particularly, this invention
relates to the conversion of coal to desired conversion
products thereof such as hydrocarbons in liquid or gaseous
form by reacting coal with a particular reagent therefor, in
presence of water, steam and~or hydrogen, at a low to modera-
te temperature and at atmospheric pressure.
Still further, this invention relates to conversion
of coal to various preselected component cuts thereof, prin-
cipally gaseous component parts, by means of a specific
reagent, whereby coal, in the presence of this reagent
water, steam, and/or hydrogen, is converted into useful
breakdown materials thereof. These breakdown materials are
principally gaseous hydrocarbons which may be recycled to
obtain liquid distillates. Ultimately, at the high tempe-
ratures, coal in presence of the reagent and steam causes
production of some hydrogen. The residue of the coal
comprises ash and reagent from which the reagent may be
recovered and reusedO
It has become increasingly evident that liquid and
gaseous hydrocarbon sources such as petroleum and natural
gas are being depleted at such rapid rate that an intensive
effort is needed to meet anticipated future needs for obtain-
ing substitute energy, feedstock, or chemical starting
materials. One of the most readily available sources of
hydrocarbon materials is coal. Heretofore, there has been
no ready means, without extensive capital investment on
economically justifiable basis, to produce hydrocarbons
from coal. ~lthough various processes are known for
conversion of coal at hlgh temperatures, such as high tempe-
rature i.e. above 600C, high pressure e.g. above 25 atmosphe-
res coal gasification, there has been no readily available
lower temperature, low-pressure process which would readily
convert coal into its component hydrocarbons.
In considering the present invention, applicant
is aware of the following patents: U.S. Patent Nos. 1,904,586,
3,926,775, 3,933,475, 3,944,480, 3,960,513, 3,957,503, 4,018,572,
4,030,893, 4,057,422, and 4,078,917, 4,119,528, 4,155,717,
4,147,611, ~ 7,612.
It has now been found that when coal is treated
with a particwlar reagent, it can be converted in the presence
of this reagent and in the presence of steam to various hydro-
carbon fractions principally gaseous hydrocarbon fractions
of one to five carbon atoms (Cl to C5), e.g., methane, ethane,
ethene, etc.
Further, it has been found that when this conver-
sion is being carried out at different temperatures, i.e.,
using steam and coal at set steps, at elevated temperatures,
the proportion of the various hydrocarbons obtained from the
same coal can be changed. At lower temperatures volatile liquid
hydrocarbons will be produced. At higher temperatures, prin-
cipally gaseous hydrocarbons will be produced.
Still further, it has been found that various
coals, that is, lignites of various compositions and sub-
bit~minous coals show difLerent distillation points although
the production of the liquid and gaseous hydrocarbons will
still take place. Higher value (rank) coals give more liquid
hydrocarbon distillate than do lower value coals while other
process or reagent modifications allow the obtention of more
liquid distillates.
--2--
'
In general terms, it is believed that when the
alcoholic solution of KHS by itself (or with sulfur) is being
added to the coal, a reaction takes place as follows: KHS
+ S2 ~ 1/2 H2S ~ 1/2 K2S5. From the above it follows that
K~IS may be used without sulfur addition. However, sulfur tends
to stabilize KHS as a less hydrolyzed polysulfide. There is
some breakdown of KHS to K2S in the presence of water. This
breakdown is partial. Hence, in hydrogenating coal, both KHS
and K2S should be present in the reaction. When sulfur is
added less hydrolyzed and therefore a more water-stable poly-
sulfide is provided.
Although the above reaction is shown for KHS, NaHS
will also work, but appears to work best without elemental
sulfur addition.
It is also possible to use KHS or NaHS in dry state,
i.e., without alcohol addition. NaHS is obtainable as an
industrial bulk commodity, generally in a flake form with
about 30% by weight of water in the bulk form.
When the ~C2S and various polysulfide species thereof,
reacts with coal, it preferentially attacks the oxygen, sulfur
and nitrogen present in coal in a bound form to withdraw these
components of coal. As these components are forming in the
presence of steam or water, the bond scission of the various
coal constituent parts and abstraction of oxygen, nitrogen and
sulfur, allow the introduction of hydrogen and thus the forma-
tion of hydroaromatic, aromatic and shorter chain aliphatic
compounds.
It has been found that oxygen must be present in the
coal~ For this purpose, low quality coals, such as lignites,
are very suitable. As the quality of the coal increases, such
as in subituminous coal, the amount of oxygen in -these coals
decreases and consequently, the possibility for gaseous conver-
sion decreases thereby, and/or more liquid phase components are
produced. It has also been found that even su~-lignite coal and
peat can be converted according tothis method into various
hydrocarbon components.
In accordance with the invention, there is provided
a process for conversion of coal to gaseous hydrocar~ons and
volatile distillates comprising the steps of: reacting coal
or peat and a hydrosulfide or sulfide of an alkali metal or
mixtures thereof in presence of water and optionally sulfur up
to an amount such that up to a hydrogenated end product of
one or two carbon atoms is formed at a temperature between 50C
and up to 450C substantially at atmospheric pressure and
recovering volatile liquid distillates and hydrocarbon gases.
In order to illustrate the present invention, a
drawing has been enclosed herewith wherein:
the Figure shows the schematic reaction train of the
coal conversion and component recovery.
Turning now to the Figure, the reaction vessel 11 is
typically a retort or a similar device in which coal in a
finely ground stage is being fed. Typically, particle size of
_oal is up to 1/4 inch for lignite and can be more, as the
reaction is size independent. For sub~bituminous coal the
particle size can be up to 1/4 inch but is preferably about
1/32 of an inch. After the system has been first purged of
any oxygen by introducing inert gas such as hydrogen or
nitrogen, etc., K2S or KHS (or equivalent) in alkanol reagent
is introduced therein. The system is then closed and the
temperature is elevated to 65C at which temperature the
- 4 -
. ~
alkanol Erom the reagent is distilled. As the inert gas, i.e.,
nitrogen, or hydrogen, provide the agitation, the continuous
expulsion of water continues along with the expulsion of the
alkanol. Typically, the alkanol is methanol or ethanol,
- 4a -
although higher alcohols may be used such as alkanols up to
4 carbon atoms.
Once the desired operating temperature is reached
(after alkanol distillation - if used in the process) and
steam at an appropriate temperature is being introduced into
the sys-tem, the inert gas such as nitrogen, first used to
purge the system of oxygen, may no longer be needed. The
steam vessel 12 is provided with means for heating water in
the same or auxiliary heating may be supplied such as by
10 heating the line from the s-team generator 12 to reaction
vessel 11.
An appropriate means for monitoring or controlling
the reaction in the reaction vessel may also be provided such
as heating or cooling coils, temperature gauges, heat control
elements, stirring devices, etc. The reaction vessel may also
be externally heated.
The reaction products from the reaction vessel are
illtloduced into the conde..ser 13, which may be of a refluxing
type with the in and out water temperature adjusted to condense
20 the heavy fraction first coming over from the coal. The heavy
fraction may condense on the walls of the condenser device 13a
and then descend downwardly until received in the bottom collec-
tor 1~ from which these liquid products may be removed, recove-
red and analyzed from time to time.
From the bottom collector 14, the gaseous effluent
is then sent on to a second condenser 15 where the gaseous
products are further cooled and introduced into the scrubbers
16. In these scrubbers 16 appropriate scrubbing liquids are
kept so as to collect the desired product fraction in each of
30 the scrubber liquids. On an industrial scale, separation in a
distillation column may be more practical.
~6~
The nonsolubilized but scrubbed component, in its
yaseous form, in turn, is introduced into the next scrubber,
from which further components are separated (as will be further
explained herein). Although seven scrubbing stations have been
shown, the number depends on the gaseous fractions sought to be
recovered. Hence, the number of the scrubbing sections may be
increased or decreased. The final gaseous fraction is metered
by meter 17 and may be collected and treated such as by further
scrubbing and purification, i.e., distillation, or it may be
10 used directly.
~s it is well understood, inasmuch as the gaseous
fraction from the gasification of coals is a fairly narrow
fraction consisting in the major part o-f gaseous fractions
having from 1 to 6 carbon atoms or near liquids thereof,
fractionation may also be employed for recovery of the various
reaction products. Typical fractionation means are such as a
distillation tower and molecular sieve separation means. These
separation and distillation means are well known to those
skilled in the art and need not be illustrated.
For purposes of this invention, however, an embodiment
is shown which allows the separation of various fractions based
on the solubilities of the hydrocarbons having from 1 to 6
carbon atoms.
This process may be carried out continuously. Thus,
the separation function for the various reactants (such as the
alcohol based reagent) may be effected in such a manner that
the system may operate continuously with continuous introduction
of reagents, coal, and steam and continuous removal of product.
Under those conditions, inert gas purging may not be necessary.
From each of the scrubbers 16 the dissolved component may be
separated by conventional means and the liquid used therein
s~
separated therefrom.
Turning now to the solubilities which have been given
herein, typically, these are for the indicated gas at normal
room temperature defined as 72F. Inasmuch as the scrubbing
process can be operated at room temperature and at near atmos-
pheric pressure, the solubilities are intended to be for those
conditions. It is noted that higher pressures may also be
used such as in a distillation train so as to avoid any
excessively low temperatures. Again, when the pressure condi-
tions are changed, the recovery which may be effected at thechanging pressures is well understood by those skilled in the
distillation art.
Based on the well known solubility factors, such as
available from reference handbooks, these are listed for the
hydrocarbons recovered from the system. Solubilities of
Cl-C6 hydrocarbons are as follows:
Ethene is soluble in ether, slightly soluble in
alcohol, acetone and benzene and insoluble in water. Ethane is
soluble in benzene, slightly soluble in alcohol and acetone
and insoluble in water. Propane is soluble in water and in
alcohol, very soluble in ether and benzene and slightly soluble
in acetone. It is also very soluble in chloroform. Propene
is very soluble in water, in alcohol and in acetic acid.
Butane is very soluble in alcohol and ether and chloroform
and is soluble in water. Butene (1- & 2-) is very soluble in
alcohol and ether, is soluble in benzene and insoluble in water.
1- & 2-, and transpentene is miscible in alcohol and ether,
very soluble in dilute sulfuric acid, and soluble in benzene
but insoluble in water. Pentene is miscible in alcohol, ether,
acetone, benzene, chloroform and heptane slightly soluble in
water. ~exane is soluble in ether and chloroform and very
~,
soluble in alcohol and insoluble in water. Hexene (1-2,-,
trans,3-) are soluble in alcohol, ether, benzene, chloroform,
pet. ethers, and insoluble in water. Methane is soluble in
water, alcohol, ether, benzene, methanol and toluene and
slightly soluble in acetone.
The reagent such as the potassium hydrosulfide or
sodium hydrosulfide or a polysulfide thereof is reconstituted
such as in one of the reaction vessels when the scrubbing
li~uid therein is alkanolic KOH, or NaOH -to form either the
10 appropriate sulflde or hydrosulfide depending on the amount of
S to react with the hydroxide. Typically, at those conditions
the reagent will precipitate as a white precipitant, e.g., of
the formula K2S (hydrate) or Na2S (hydrate). In ethanol or
higher alkanols the only slightly soluble alkali metal sulfide
can be removed from the sys-tem by merely withdrawing the
precipitate from the scrubber.
The ash remaining in the reaction vessel 11 is
appropriately removed therefrom and worked up such as by dis-
solving the solubles therein and extracting, e.g., potassium
20 therefrom based on the differential solubility of calcium
hydroxide and potassium hydroxide, that is, extracting potassium
with calcium hydroxide precipitating calcium sulfate and remov-
ing potassium hydroxide. Sodium hydroxide is present in the
ash in lesser quantities and may be removed in the same or
different manner, as it is well known in the art. As sodium
is present in coal in considerably smaller proportions than
potassium, sodium may have to be augmented during the continuous
process if sodium based reagent is used. There is sufficient
amount of potassium present in coal. As it is evident from
30 the above, at lower temperatures, for lignite such as given
in the example ~to follow) the reaction provides a hydrocarbon
30 fraction which is in the C3-C6 hydrocarbon range with the
fraction having an average of C~ predominating. This fraction
is typically recovered up to 120C. At 220C, the methane
through butane fraction is being produced including the corres-
ponding double bond unsaturates. At 360 to 450C, typically
ethene and possibly some hydrogen is being produced. In order
to assure that no hydrogen sul~ide is being expelled, the
product stream is scrubbed in an alkali metal e~g, potassium
as sodium hydroxide al~canolic solution at saturated conditions.
The hydrogen sulfide reacts with the hydroxide to regenerate
the reagent i.e. K2S and Na2S and in presence of water regen-
erates KHS and NaHS. In the thus scrubbed gas stream, hydro-
gen sulfide is present in a very small amount e.g. less than
0.01%, by volume.
The above illustration of the process as well as the
invention herein is described by reference to the examples which
are not intended as a limitation of the invention, but rather
as an illustration of an embodiment thereof.
EXAMPLE 1
Fifty milliliters of a methanol solution of potassium
hydrosulfide, containing 0.37 grams of potassium hydrosulfide/
ml. were used as the base reagent. 71 grams of lignite were
used having a "dry ashless" content of 66% carbon, 3.97% hydro-
gen, 18.2% oxygen, and 0.9% nitrogen, by weight, plus a small
amount of volatiles. The raw lignite contained 33% water and
9/O dry ash. (The "as received" wet analysis was 6% ash). The
organic sulfur content of this lignite was 0. 69% and the pyrit-
ic sulfur content was unknown.
The run was made with lignite which had been dried
for 2 hours at 135C and with lignite which had not been dried.
The principal difference between the dry and wet lignite was
a production of very light hydrocarbon gases from the wet
lignite at temperatures below the boiling poin~ of water during
the period that the temperature was being elevated. Water from
" ~
the lignite provided the hydrogen for this production of hydro-
carbon distillate. In other respects, the reaction proceeds
the same.
Elemental sulfur was added to the lignite. It may also
also be added to the alcoholic KHS solution. The total amount
of sulfur present was 8.25 grams, which included the organic
sulfur content of the lignite.
The apparatus consists of a container and a conduit
for hydrogen or nitrogen as the flushing inert gases (see Fig-
ure herein). These inert gases may be fed directly or are fedthrough a steam generator via a steam line into the reaction
vessel 11. The steam line is heated to 140C and enters the
reaction vessel near the bottom of the vessel heated at that
temperature.
Means for measuring temperature are also provided.
Typically, the steam line enters through the center opening
for the flask. Initially, nitrogen or hydrogen provides the
agitation while the methanol of the reagent solution is being
distilled. Agitation may be effected by different means as
well, such as stirring. The presence of water in the raw
; lignite produces a methanol (or ethanol) soluble hydrocarbon
gas during this distillation.
This liquid hydrocarbon production is minimized when
dry lignite is used. The reaction vessel 11 may be of a suit-
able form, but as used in this experiment, it is a round
bottom flask, with appropriate introduction ports at the top
thereof.
Another introduction port is for the addition (and
removal) of lignite. The reagent is introduced through an
appropriate opening which ;s closed during the run.
A still further port leads to a vertical water cooled
condenser which empties into a round condensation flask 14
- 10
su
having an outlet port therefor and a port, at the bottom, for
removal of distillates.
Residual gases pass from the condensation flask
(vessel~ 14 into a second water-cooled condenser 15, conven-
iently above the same condensation flask 14.
The gases from the condensation flask, i.e., remain-
ing gases, are then passed through a series of scrubbers. The
scrubbers consist of at least the following: a) a water wash,
b) an ethanol (methanol) wash, c) a one mole solution of KOH
in 135 ml of methanol, d) a benzene wash, e) a one mole solu-
tion of KOH in two moles of water, f) sulfuric acid wash of
about 24% solution of a 98% H2SO4. As a back-fire preventer,
an empty scrubher may be used.
The remaining gases thereafter pass through a conduit
and are suitably collPcted by suitable collection means. A
chromatograph tube may be inserted before the gas test meter 17
(placed between the scrubbers and the collection means) so
that gas samples can be analyzed. A chromatograph tube may
also be inserted where desired, in the recovery train and the
gases or distillates analyzed.
A gas meter, on this line, calibrated in fractions
of a cubic foot, gives a cumulative total of cubic feet of
hydrocarbon gas recovered.
In conducting the process, the lignite (and the
sulfur it contains) is placed in the reaction vessel and heated
to 35-50C. 50 ml of reagent are added after flushing the
system with hydrogen or nitrogen to expel atmospheric oxygen.
The system is closed and the temperature elevated to 65C, at
which temperature the methanol component of the reagent is dis-
tilled. As mentioned before, the introduced hydrogen or nitro-
gen may provide sufficient agitation of the reagent-lignite
mixture. The reagent also contains water both as impurities
` ~6~34~
in the ingredients used to make the reagent and additional
water is formed as the reagent is formed. The water present in
the reagent and coal is distilled off at temperatures up to
135~C.
The distillate produced during the distillation of the
methanol (or ethanol) will contain methanol or ethanol soluble
hydrocarbon components including gases. Water is distilled
from the reaction mass, after most of the methanol has been re~
moved, it is mostly clear. This water may contain a small ~uan-
tity of amber colored liquid hydrocarbons (which increases with
coal rank). At a temperature from 135-190C, but typically at
135-190C, a small liquid hydrocarbon fraction will be produced
from the reaction mass, again this amount increases with the
rank of coal. This liquid hydrocarbon condenses within the
water cooled condenser 13, on the walls 13a of the condenser
as a solid or semi-solid.
After the water-methanol mixture has been distilled
from the reactant mass, optionally, the introduced hydrogen or
nitrogen can be turned off. At that point, i.e., at about 170-
190C steam alone is used to agitate the mix or a suitable
stirrer may be used. Steam is not introduced into the reaction
vessel until the methanol-water mixture has been distilled be-
cause the water-methanol mixture will hold the temperature at a
specific temperature range during this distillation.
After the introduction of the steam or the steam and
continuing hydrogen introduction, various lignites and sub-
bituminous coals, based on the inherent makeup of these, dis-
play different distillation points in the production of sizable
amounts of gaseous hydrocarbon.
It is suggested to discontinue the introduction of
hydrogen, when steam is injected into the reaction vessel, be-
cause an accurate test meter reading of the quantity (volume~ of
- 12 -
~l~6~
gas emitted from the apparatus cannot be made when hydrogen is
being introduced into the apparatus. However, appropriate means
such as a secol~d test meter on the hydroyen tank would give an
indication of the amount of hydrogen passing into the system
and this could be subtracted from the total reading of the
final test meter 17. It should be mentioned that some of the
hydrogen is utilized to hydrogenate -the coals and that quantity
of hydrogen cannot be measured by these means.
Generally, for low rank coal a sustained production of
hydrocarbon gases begins at the boiling point of the methanol
or ethanol and continues to increase as the reaction mass is
heated to approximately 280C. For higher rank coal, at these
low temperatures, i.e., up to about 280C little if any gas
production takes place. These gases are mostly taken up in
the scrubber system and very low reading is given on the gas
meter 17.
If the scrubber system is eliminated (and the initial
hydrogen sulfide production, from the reaction between the alka-
nolic reagent and the elemental and organic sulfur--the last
in the coal--is separately vented or measured or scrubbed with
a suitable aqueous reagent), the gas quantity can be measured.
As previously mentioned, depending on the particular
coal, the initial quantity of gas is low, e.g., from lignite at
temperatures below 280C about 0.025 to 0.05 cu. ft./50 grams
of gas is obtained from the wet coal.
Methane is generally given off first and it has the
greatest solubility in all of the scrubber system liquids as
compared to each of the other recovered hydrocarbons. Pentane,
hexane, hexene and pentene also have a considerable solubility
in -the scrubber liquids used in the system, except in water.
Hexenes and hexanes condense in the water cooled condenser and
are only gasified further as influenced by the partial pressure
- 13 -
` ~6~
of the other lighter gases passing over the liquid. A compon-
ent of the gas recovered and entering meter 17 is ethene.
Ethene has a limited solubility in the kerosene and little
solubility in the water and alcohol in the various scrubbing
stations 16. Ethene has a characteristic smell of unsaturated
hydrocarbon while the saturated hydrocarbon gases are odorless.
Solubility of unsaturated hydrocarbon gases in sulfuric acid
can be used to separate the saturated from the unsaturated hy-
drocarbons.
When the temperature reaches 335C, the initial 100
grams of wet lignite or sub-bituminous coal provide a more
rapid gas production in the Cl to C5 carbon atom range. The
yas produc-tion increases substantially when 360C is reached
and when the final temperature is between 380C and 450C a
very rapid gas production is encountered with some hydrogen
being produced. At a temperature of 360 to 380C carbonyl
sulfide is also produced and in sub-bituminous coal e.g. 4.7%
by weight of the total hydrocarbon gas may be carbonyl sulfide.
At the higher temperature, gases pass the scrubbers
and are registered on the flow meter. For exarnple, from 100
grams of wet sub-bituminous coal, after subtracting for hydro-
gen sulfide, generally up to 1.4 cubic feet of gas from ~7
grams of carbon (on dry basis) present in the sub-bituminous
coal can be obtained at the higher temperatures.
A standard temperature and pressure, about 3.7 moles
of gas containing 47 grams of carbon would indicate an average
carbon content of 2.25 for a product. Again, it should be noted
-that the products produced at different temperature levels con-
sist of different breakdown fractions.
Gas chromatographic analysis on Example 1 run, gives a
strong indication of two hydrogen atoms to each carbon atom in
the gases. The initial lignite contained one hydrogen atom for
- 14 -
~ ~6~
every 1.3~3 carbon atoms, or, for a direct comparison, 0.725
hydrogen atoms to each carbon atom. Gas chromatographic analy
sis did not indicate any substantial oxygen present and showed
that the collected gases were almost entirely hydrocarbon. The
hydrocarbon gases containing from 1 to 6 carbons in that frac-
tion are either gases or very volatile liquids.
The scrubbers do remove carbon dioxide as potassium
carbonate as a precipitate in the KO~-ethanol or -methanol
solution. Generally, a solution of one mole KOH in two moles
of water is used, and the alkanol can be added to this aqueous
solution of the alkali metal hydroxide.
EXAMPJ.E 2
25 grams of industrial grade sodium hydrosulfide
flakes were mixed with 100 grams of Maverick sub-bituminous
coal. Industrial grade Na~lS is in flake form and of varying
analysis and this particular sample contained approximately 30%
water. These flakes were placed on top of the coal in the re-
action vessel. The coal analysis was:
moisture 3.3%, ash 12.9%, sulfur 0.69%, carbon 70.2%
hydrogen 4.4%, nitrogen 1.13%, and oxygen 6.16% by weight.
The heating value for the coal is 12,656 BTU/lb.
The mixture was heated to 280C in a reaction vessel.
Steam was injected (1~0C steam) at the bottom of the reaction
vessel to provide agitation and supply hydrogen for the hydro-
genation of the coal. S-team was injected after a temperature of
of 175C was reached. I-t is believed that the hydrosulfide was
decomposed at least partially to the sulfide during this heat-
ing as a result of the water content in the reagent and coal.
Below 175C, a few clear drops of hydrocarbon dis-
tilled with the initially expelled water. The reagent bubbles
up at 175C apparently due to the formation of a lower hydrate
of sodium sulfide with the subsequent release of water.
- 15 -
At 2~0C the hy~r!o¢a~bon gas given off was produced
on a continuing basis and a flame could be sustained at the end
of the system in the glass tube. The gases were water washed
prior to burning. At 350C the run was terminated with about
half the coal reacted.
The liquid distillate, cooled and condensed in a water
cooled condenser was 15 ml and gave an analysis of 9.8% hydro-
gen, 87% carbon and 0067% sulfur and 0.07% nitrogen~ By chroma-
tographic analysis, the gases were principally ethene. Approxi-
mately 0.~3 cu. ft. of gas was produced.
Without being bound to any particular theory, in thepractice of this invention, it is believed that oxygen, sulfur
and nitrogen are rernoved from coal by a series of complex reac-
tions made poss:ible by sulfur compounds of potassium or equiva-
lently by the other alkali metal sulfur compounds, as will be
explained below. The reactions, via the water and hydrogen
sulfide molecules, provides hydrogen to react with coal at the
point where coal is being deoxygenated, desulfurized or de-
nitrogenated. Hence, for practice of this invention, it is
necessary that oxygen be present in coal but the benefit is
also gained when sulfur and nitrogen is present in coal in a
form such as an organic sulfur or organic nitrogen species.
Moreover, higher rank coal, such as bituminous coal, may not
as readily be converted to gaseous hydrocarbons although, as
explained below, it still may be done when the reaction scheme
is appropriately modified.
It has been found that coal with a carbon content
below about 70% was almost entirely gasified with no more than
5% being a solid and/or liquid distillate. A coal with about
75% carbon content gave a 10% liquid distillate, the rest was
gas. A coal with 82.5% carbon gave 33% liquid distillate, the
rest was gas. An anthracite coal of 92% carbon content gave
- 16 -
little gas and only about 2% li~uid-solid distillate. ~aen
sodium is used, instead of potassium, about the same amount of
liquid distillates are produced, but less gas.
For this reason, the present invention is concerned
preferably with lignite and sub-bituminous coal gasificationO
Further, this invention is applicable to sub-lignite and even
peat gasification, but economic factors do not render the pro-
cess as advantageous, due -to the lower carbon content in these
source materials per equivalent weight.
Although rubidium is equally active, for practical
reasons, potassium is the preferred hydrosulfide. Sodium is
also useful as sodium hydrosulfide and polysulfides do undergo
the necessary reactions. Cesium, rubidium, potassium and sod-
ium, hydrosulfides and polysulfides are useful but cesium
and rubidium are not cost advantageous. Lithium may also be
used, but is less effective than sodium. A mixture of rubid-
ium, potassium and sodium sulfides (generic), may be used with
greater effectiveness than any of the individual (generic)
sulfides. The term "generic" is intended to mean the series of
sulfides beginning with hydrosulfides to polysulfides. The
preferred ratio is 14% rubidiwn, 26% potassium and 60% sodium
sulfides (generic) by weight of the elemental metal. The ratio
ranges for the preceding mixture are 1:1.5-2.5 : 3.5-4.5,
respectively.
The amount of potassium hydrosulfide to coal is from
5 to 30 grams per 100 grams of coal with about 10 to 25 grams
being normally employed. Typically, about 18 grams of potas-
sium hydrosulfide per 100 grams of coal is used. ~Iowever, as
will be further explained herein, this reagent is reconstitut-
ed. If potassium in coal ash is converted to hydrosulfide noloss of potassium hydrosulfide is experienced, and the reagent
balance for the reaction, on batch or continuous basis, is very
favorable.
- 17 -
In general, it is emphasized that sufficient amounts
of sulfur, sulfide, hydrosulfide or polysulfide should be
present to take up the sulfur expelled from coal by oxygen
during deoxygenation thereby preventing the expelled sulfur
from dehydrogenating the coal at a temperature above 175C.
Also, the integrity of the various reagent species must be
preserved above 325C since a temperature increase above this
level will cause a slow de-hydrogenation of coal by alkali
metal hydroxide melt. As sulfur causes the formation of poly-
sulfides and the alkali polysulfide is less hydrolyzed withincreasing sulfur content thereof, the decomposition by steam
(or other water) of the hydrolysis product, i.e. the hydro-
sulfide is thereby prevented.
Consequently, the selection of the necessary amount
of reagent is fairly certain for each type of coal and can be
readily established for that coal based on the above broad
ranges for the reactants and ~he amounts of sulfur present in
coal.
In calculating sulfur in coal, only organic sulfur,
i.e., sulfur bound to carbon, is taken into consideration.
Nitrogen in coal is converted to ammonia and, for a large scale
operation, may be recovered as a valuable by-product.
Steam as shown above is ernployed at a temperature
at which the reaction is sought to be conducted, i.e, depend-
iny on the type of coal and the decomposition levels of coal
as well as the desired product. Steam also provides a source
of hydrogen apparently as H (apparently not from OH ). Appro-
priate steam generation at the selected temperature may be in
the generator 12 shown in the Figure. As a suitable arnount,
sufficient steam is used, e~g., to provide hydrogen for hydro-
genation of coal having a hydrocarbon end product from one totwo carbon atoms. If less hydrogenation is sought, less steam
is used.
- 18 -
~ .
s~
As the amount of sulfur content of the reagent is in~
creased, i.e., from sulfur in coal and added elemental sulfur,
the reaction temperature is lowered. For example, a reaction
temperature of 380C is lowere~ to 310C, when, as an illus-
tration, the sulfur balance is representative of a theoretical
compound K2S3 produced and maintained during reac-tion condi-
tions. A corollary of this phenomenon is that larger molecules
are produced, for example, pentane, i.e., isopentane and pen-
tane.
Further, rank of coal affects the distillate makeup,
the higher the rank of coal, the higher the proportion of
li~uid distillates under equivalent conditions, e.g., when
using the theoretical K2S3 compound at the same temperature
conditions.
Of course, as mentioned before, when the temperature
is varied, the produc-t composition changes. Moreover, as
illustrated above, when the amount of sulfur in the reagent
is changed, the product composition is also changed.
Thus, based on the above, one can vary temperature,
sulfur content, rank of coal, and use a recycle of alcohol ab-
sorbed distillates (as further explained herein) to obtain the
desired product cut. Within variation of a product cut, recycle
is contemplated of various other distillates in the recovery
train shown in the Figure 1 herein.
The above described variations are within the follow-
ing limits: temperature up to 425C but distillation starts at
40 to 50C, sulfur content in reagent (e.g., for potassium)
K2S but the sulfur content may go up to K2S5, ranX of coal is
desirably in the lignite to bituminous coal range. When applied
to anthracite, the results are less advantageous although a
distillate may be obtained at +380C and using a reagent such
as K2S~
-- 19 --
For sodium, the useful sulfur species are NaHS, and the
the Na2S to Na2S2 sulfides; NaHS is more stable than KHS with
respect to water in coal or steam and starts reacting to pro
duce a distillate at temperatures correspondingly lower (about
10 to 20C lower) from that of potassium, although in somewhat
lesser amounts -than potassium. Rubidium, while not price
advantageous, is at least as good and often even better than
potassium.
If the alcoholic distillate (including any hydro-
carbon components present) is recycled from separator 14 de-
picted in the Figure herein to the reaction vessel 11, the
product composition may also be varied. Moreover, the amount
of recycle may also be varied. Thus, up to about 280C, the
product composition can be forced towards a composition which
is a liquid distillate of a boiling point below about 180C.
At a reaction temperature up to about 310C paraffin distillates
are formed when employing the above-described alcohol recycle to
to the reaction vessel. As before, and in this recycle condi-
tion, water, i.e., steam at a temperature of about 135C and
higher must be present in order for the reaction to occur.
For the alcohol recycle, methanol is the preferred
al]~anol. As can be seen from this aspect of the recycling,
the alcoholic distillate provides for a further product modi-
fication employing the alcohol dissolved initial reaction pro-
ducts in the reaction vessel. As a result of this aspect, more
liquid distillates may be obtained.
When starting the process at about ar~bient conditions
(and raising the temperature), elemental sulfur is added to coal
or to the reagent to obtain the selected sulfur content for the
reagent. At these conditions ~2S formed in the system during
the reaction o~ the sulfur and the reagen-t is removed from the
gas stream and wash system to reconstitute the reagent. As the
- 20 -
~-, . .
temperature is being brought up, steam is not used, any hydro-
genation of coal that occurs i9 -from the water content in coal
or the reagent. At a~out 135C, steam may be added if light
distillates are desired. Typically, steam is added, however, at
about the temperature when a hydrate of the reagent starts re-
forming or reconstitutes itself to a lower hydrate thereof. For
potassium based reagent, steam addition temperature is selected
at about 170C.
As the precursor hydrates rearrange to lower hydrates
and give up water of hydration, copious amounts of steam are
liberated. Thus, that condition signals the point at which
steam may be safely introduced, provided the water of hydration
has left the reaction vessel.
The process can also be carried out continuously.
Generally, a particular temperature level is selected and coal
and reagent is introduced in the reaction zone, ashes withdrawn
and the reagent and alkali metal part of the reagent recovered
therefrom and the reagent reconstituted, e.g., with hydrogen
sulfide. The liquid and gaseous fractions are reco~ered typi-
cally in a distillation column or appropriate scrubbers includ-
ing the hydrogen sulfide. Consequently, a fully continuous pro-
cess with a reagent reconstitution - recycle is possible based
on the illustrations shown herein producing a desired cut of
product for the preselected temperature and other operating
conditions.
In outlining the complex stages by which the reactions
are believed to proceed, it must be remembered that the present
understanding is derived by inference as many reactions are
simultaneously taking place. Hence, the following explanation
is only offered in aid of understanding and not in any way to
espouse the correctness of a particular reaction or a theory
because this invention can be unders~ood and practiced without
reference to any theory.
- 21 -
If it were true that K2SO~ reacts with oxygen in coal,
at elevated temperatures, in a closed system, free of atmos-
pheric oxygen, to form K2SO4 directly, by the displacement of
all the coordinated sulfur of the pentasulfide ion by the oxy-
gen, then the reaction would stop when K2S05 has been converted
K2S ~,,.
Thus, K2S04 would be inert in the system unless it
were converted to carbon monoxide and K2S, by reduction with
carbon in coal. If, in fact, this were to happen, then a danger
would exist by the reaction of the potassium sulfides with the
carbon monoxide to form potassium carbonyl--a highly explosive
compound~ However, in accordance with the present process, it
is fairly clear that the analyzed gases, in the chromatography
conduits do no~ contain appreciable carbon monoxide or carbon
dioxide.
It is also known that sulfur, in elemental form, will
dehydrogenate coal at temperatures in excess of 175 C.
(Mazumdar et al., Fuel, Volume 41, pp. 121 et ~., (1962).
Further, air oxidation of potassium pentasulfide produces ele-
mental sulfur, potassium thiosulfate (K2S203) and potassiumtetrathionate (K2S406). (Letoffe et al., Journal Chimie Phys-
ique, Vol~ 71~ pp~ 427-430 (1974)o Potassium pentasulfide de-
composes into potassium tetrasulfide and sulfur at 300C--this
reaction is a slow reaction which progressively increases as
the temperatw-e is elevated above 300C.
Potassium sulfide will hold S molecules of water of
hydra-tion up to 150C,when it becomes the dihydrate; and the
dihydrate is decomposed, at 270C/ to a solid lower hydrate and
water and a still lower hydrate to 779C to 840C at which temp-
erature potassium sulfide decomposes to the disulfide and ele-
mental potassium. Elemental potassium is soluble in the solid
sulfide. The thiosulfate (K2S203) is decomposed above 200C to
- 22 -
3 . . .. ...
the sulfate plus the pentasulfide and the pentasulfide is, in
turn, decomposed to the tetrasulfide and sulfur at ~emperatures
beginning at 300C.
When the potassium hydrosulfide (in alkanol~ is used
as the reagent, the water content of the coal and the water
present in the solution of the potassium hydrosulfide react
to cause hydrolysis and then decomposition to hydrogen sulfide
and potassium hydroxide. Potassium hydroxide will react with
non-decomposed potassium hydrosulfide to form potassium sulfide
(in hydrated form) and water. Potassium pentasulfide (formed
by the reaction with the organic sulfur of the coal and the
added elemental sulfur) form potassium hydrosulfide as follows:
KHS + 2 S = 1/2 K2S5 ~ H2S-
For sodiwm the reaction is:
Na~S ~1 1/2 S = 1/2 ~a2S~ + 1/2 H2S.
No intermediate sulfur content polysulfides (defined as sul-
fides with 2 to 5 sulfur atoms) are formed in the reaction with
potassiwn and :insufficiency of sulfur will leave unreacted KHS.
,J
However, this reaction only occurs in alkaholic solutionsO For
sodium species only the tetrasulfide species is formed.
Potassium sulfides with a sulfur content less than
that of the pentasulfide are decomposed by oxygen to potassium.
In swnmary, as oxygen is removed as well as nitrogen
and organic sulfur, water or hydrogen sulfide (continually
produced by contact between water and the reagents) yield hydro-
gen to the coal at the point where coal has been deoxygenated,
desulfurized, or denitrogenated, nitrogen comes off principally
as ammonia' the sulfur comes off to form an alkali (e.g. potas-
sium) polysulfide and at lower temperatures forms a mercaptan
wi-th the alkanol solvent. Mercaptans are absorbed in alcohol
and in the KOH-alcohol solution.
- 23 -
~ .
The KOH in the methanol wash for the efluent gas
stream gives the alkanol insoluble thiosulfate. This overall
reaction proceeds through reduction of the hydrogen sulfide
gas to sulfur and water, with subsequent reaction of the sul-
fur with the KOH to form the potassium thiosulfate and -the
potassium sulfide as shown above. The potassium sulfide can
-then acquire additional sulfur from hydrogen sulfide to form
potassium polysulfide and are the reagents used in the reac-
tionO
In general, at different temperature levels, the coal
breakdown products have different compositional makeup. These
temperature levels can be selected for the desired composi-
tional makeup for the volatile distillates and gaseous frac-
tions suitable for a particular end use. For example, at a
temperature between 340C and 365C the following gas analysis
was obtained for a product gas obtained from a sub-bituminous
coal: methane 80.19%, ethane 9.12%; ethene 1~41~/o~ propane
2.67%, propene 1.41%, iso-butane 0.16%, n-butane 0.31%; hydro-
gen sulfide 0.001%; and carbonyl sulfide 4.72%; residue un-
identified gas components.
From the above, it is demonstrated that a readily
available source of hydrocarbons may be realized from coal by
a process carried out at low temperature, low pressure while
reconstituting the reagent, as part of the process.
- 24 -
