Note: Descriptions are shown in the official language in which they were submitted.
80S451702 1 1 7 ~ ~ 3
9/~ 3
1 TREATMENT dF ORGANIC MATERIAL IN SUPERCRITICAL WATER
Background of the Invention
A number of alternate routes have been and are still being de-
veloped for converting organic feed materials such as coal and cellu-
losic materials including forest products, to liquid and gaseous
fuels. Among the approaches are pyrolysis, gasification with steam
and oxygen to form synthesis gas and liquefaction with hydrogen,
carbon monoxide or hydrogen donor solvents. Each of these approaches
have one or more drawbacks. In pyrolysis, there is a problem with
the feed ending up as char in certain instances. In steam-oxygen
gasification, high temperatures are necessary as for example 800 to
1000C and the process thus requires considerable high-temperature
heat. Liquefaction with hydrogen or carbon dioxide requires a
separate processing step to supply these materials in relatively large
quantities.
The prior art has also corlverted organic liquids to fuels by
reaction with water, as for example, by reforming petroleum fractions
catalytically to methane and carbon dioxide by a reaction with steam
at 20 to 40 atmospheres. This avoids the use of a high temperature
heat source and has met with some success where it is desirable to
convert organic liquids to gaseous products.
In a still more recent development, it has been suggested that
liquid or solid organic materials can be converted to high BTU gas
with little or no ~ormation of undesirable char or coke when the
organic material is reacted with water at a temperature at or above
the critical temperature of water and at or above the critical pressure
of water to achieve the critical density of water as for example set
forth in United States Patent 4,113,446.
In that patent, feed material was indicated to be converted to
gaseous products in an amount of about 8 to 10% after one hour in a
~
8045/702 i 1 7~ 8 3 ~L
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1 batch autoclave. In this prior gasification process, when a variety
of reforming catalysts were used, 20 to 25% of the feed carbon could
be gasified in relatively short times as for example 30 minutes. The
formation of char can easily be avoided and useful high BTU gas is
produced. However, as indicated in that patent, organic feeds were
not completely transformed to gaseous products having high fuel
value even after substantial periods of time at supercritical condi-
tions. Attempts to separate substantial organic liquid products with
methylene chloride resulted in recovery of only a small fraction,
often no more than 6%, of liquid products, see Reforming of Glucose
and Wood at The Critical Conditions of Wood, a paper presented at
Intersociety Conference on Environmental Systems July 11-14, 1977,
San Francisco, California, published by ASME, 1977. These results
indicated that organic products could not be separated on a commercial
scale.
Summary of the Invention
It has now been found that when organic materials are dispersed
in water and brought to supercritical conditions, the organic materials
are rapidly broken down and restructured to form organic materials
which have structures and properties which are different from those
of the feed materials. Only some of the restructured products
appear as gases such as CO, C02, H2, CH4, C2 while the major portion
of the products resulting are relatively volatile liquids. The gaseous
as well as the volatile organic liquid products can be relatively easily
separated from the water by reducing temperature and pressure below the
critical conditions of the reaction mixture and then carrying out con-
ventional separation steps.
It is an object of this invention to use the reaction of organic
materials wlth water in the region of the critical density of water to
reform the organic materials and obtain useful volatile organic liquid
materia1s.
It is a still further object of this invention to provide a method
of reacting toxic organic materials with water in the region of the
critical density of water to obtain non-toxic organic materials which
reaction can be carried out when the toxic materials are in sub-
8045/702
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1 stantially pure form or appear as trace or other amounts in other
materials such as river water, lake water or other mixtures to be
purified.
According to the invention, an organic material which can be
solid or liquid is treated by reacting in water to restructure the
organic material and form resulting organic material. The feed
organic material is admixed with water to form a reaction mixture
for a time period while maintaining the water in the region of its
critical density preferably by the use of a temperature at least as
high as about the critical temperature of water and a pressure at least
as high as about the critical pressure of water to form resulting
more volatile organic material than the feed organic material which
resulting material is selected from the group consisting essentially
of non-toxic organic materials where the original feed material was
toxic, and useful volatile organic liquids. The useful volatile
organic liquids are recovered in amounts of at least 25 weight per-
cent of the feed organic material.
Preferably, the organic material is a toxic material or a toxic
material in at least trace amounts in a mixture as for example river
water and the resulting product is a non-toxic material as for example
cleansed water containing lower molecular weight organic materials which
are non-toxic.
In another preferred process in accordance with this invention,
the original organic material is a solid or heavy liquid material and
the resulting products are lower molecular weight volatile organic
liquids which can be used as fuels or for other purposes.
Preferably, the process is carried out by bringing the reacting
temperature to at least 374C rapidly and preferably substantially instant-
aneously to avoid the formation of char. ~hen toxic materials are treated
by the process of this invention, the resulting products may be safely
discarded if no commercially useful products are formed.
The separation techniques for separating useful products from
the reaction mixture include distillation, flashing, decanting and
membrane separation.
It is a feature of this invention that the liquid products formed
8045/702
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1 can be hydrophilic and can have volatilities such that they will distill
off before water and thus be easily separated in distil1ation procedures.
The term "volatile" as used in this application with reference to
organic liquids means organic products which have a vapor pressure
no less than 1/10 that of water at any temperature in the range of
25C to 374C.
Description of Preferred Embodiments
In accordance with the invention, organic material is restructured
in water to form different organic materials which include Yolatile
organic liquids and in some cases, non-toxic organic materials which
may or may not be volatile liquids.
The process can be carried out in batch or continuous operations.
For example, the process can be carried out in an autoclave as
described in U.S. Patent 4,113,446. Continuous methods can be used
where a reaction slurry or liquid mixture of the reactants and water
is treated under heat and pressure. A feed mixture of organic material
to be treated is preferably brought to temperature of reaction as
for example at least 374 C, quickly, as by adding it in a continuous
stream to a flow of superheated water, heated for example to 600 to
900C, to quickly and substantially instantaneously bring the organic
material feed to temperature. The quick heating of the feed minimizes
or substantially eliminates char formation.
The reaction conditions are such that the organic material feed
is used in an amount up to about 25 weight percent of water and pref-
erably from about 5 to 10 weight percent of water. Low concentrationsmay be used, as for example fractional percentages, in reforming
toxic materials to non-toxic material as for example in the detoxi-
fication and purification of contaminated surface water or well water.
Catalysts can be used during the reaction to promote reforming
and hydrogenation of organic materials as well as to facilitate simple
breakdown of organic chains. Representative suitable catalysts include
nickel, molybdenum, cobalt, their oxides or sulfides, and noble metal
catalysts such as platinum, palladium or the like or mixtures thereof
either unsupported or supported on a base such as silica, alumina
mixtures thereof and the like.
8045/702
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1 The reaction often preferably is carried out at the critical
density of water which means that the temperature must be at least
the critical temperature and the pressure at least the critical pres-
sure of water. Parameters at the near critical condition of water
can also be used and should be considered the equivalent of exact
critical condition. Thus, as referred to herein, the terms "sub-
stantially at its critical density", "about its critical temperature"
and "about its critical pressure" refer to water in the near critical
region. The near critical region or the term "in the region of
the critical density of water" is encompassed by densities of from
0.2 to 0.7 grams per centimeter3. In this near critical region or
in the region of the critical density, pressures can be from 200 to
2500 atmospheres and temperatures can be from 374C to at least 450C.
A critical temperature range of 374C to 450C and a critical density
range of .3 to .55 grams per centimeter3 are preferred for use.
While the reactions can be carried out in batch operations over
long time periods of several hours, most efficient operation is achieved
by rapid reaction over time periods of no rnore than 15 minutes and
preferably from 1 to 10 minutes in flow-through, continuous reactors.
Toxic material which can be treated by reaction with water under
critical conditions include those on the EPA toxic chemical list of
toxic organic substances as for example:
Aldrin
Dieldrin
DDT
2,4,5-T and esters
2,4-diaminotoluene
Lindane
p-Aminobenzoic acid
Anthranilic acid
8045/702 1 J 7 ~ 8 3 ~
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1 Alfatoxin
Heptachlor
Malathion
Nitrosamines
When toxic chemicals are treated under critical conditions in
the process of this invention, restructuring of the toxic chemical
occurs to form non-toxic materials. As used in this application,
toxic materials are those recognized as hazardous by the U.S. Environ-
mental Protection Agency as for example those set out in EPA publi-
cation EPA-560/11-79-001 entitled Test Data Development Standards:
Chronic Health Effects Toxic Substances Control Act; Section 4.
The reaction mixture after reaction can then be discarded safely.
In some cases, the resulting materials can be removed as by biological
oxidation, activated carbon adsorption and the like before discarding
or reusing the remaining water. In other cases, the non-toxic prod-
ucts which result from reformation of the toxic organic starting
materials can be used for commercial purposes. For example, volatile
liquids formed can he used as fuels. It is found that since toxicity
is highly structure-specific, simple altering of one or more chemical
bonds in many organic toxic materials results in products which are
non-toxic and which can be safely disposed of.
The non-toxic starting materials which are to be reformed by the
process of this invention for use as fuels or for other commercial pur-
poses, can be a wide variety of staring materials. Solid organics
include coal or organic waste materials, cellulose, waxes, coal tars,
shale, wood products including trees, leaves, bark and the like.
Liquid organic materials including aryl or acyl hydrocarbons such as
petroleum fractions up to and including asphalt fractions, aromatic
hydrocarbons, sugars, black liquor from pulping of wood, green liquor
used to pulp, organic acids, alcohols, aldehydes, ketones, amines,
8045/702
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1 mixtures thereof and the like can be used.The reaction is preferably effected by continuously intimately
contacting the organic feed material with water. When employing solid
organic material such as coal or organic waste material, it is preferred
that the solid be in the form of small particles and the reaction be
conducted so that the organic particles in water are fed to the reactor
as a slurry. In order to promote intimate contact, the solid particles
can be smal1 and in the order of from submicron size to about 1 cm.
Larger particles can be emp1Oyed in some cases.
In a specific example of this invention, a flow reactor was used
with a one weight percent solution of glucose in water. At a flow
rate of about 10 ml per minute, the feed solution was heated rapidly
to supercritical conditions by pumping to 315 atmospheres and then
passing the mixture through a feed preheater, which was constructed
of 10 feet of 3/32 inch, inside diameter, stainless steel tubing im-
mersed in a molten lead bath at 380C. A residence time of less than
20 seconds was required to reach 374~C; within one minute, the feed
was brought to essentially the temperature of the lead bath.
Following preheat, the mixture was maintained at the supercritical
conditions of 315 atmospheres and 380~C for a residence time of about
7 to 11 minutes in a reactor consisting of a ten foot section of 5/16
inch, inside diameter, stainless steel tubing, which was also main-
tained at constant temperature by immersion in the molten lead bath.
The products were then passed through a water-cooled heat exchanger to
bring the resulting mixture to room temperature and then to a throttling
valve to bring the mixture to atmospheric pressure. Liquid and vapor
phases were separated and the flow rates of each of these phases was
measured. Samples of the vapor phase were analyzed by gas chroma-
tography and the liquid phase was analyzed for total carbon. The
results are shown in Tables 1 and 2.
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8045/702 1] 7 ~ 8 3 1
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1 At 380C with these short residence times as ;ndicated in
the Tables, 7 to 10% of the feed organic material was gasified
(Table 1, runs 1-7). This gas;fication is as much as had previously
been observed for a one-hour residence time in batch autoclave experi-
ments with glucose. The observation that a significant quantity of gas
can be obtained a~t a short residence time under supercritical conditions
is the indication of the occurrence of rapid breakdown and restruc-
turing of the feed organic material.
Attempts were made to extract the organic liquid products so
that they could be analyzed by a combination of gas chromatography,
liquid chromatography and mass spectrometry. In prior work, a
variety of solvents had been explored as extracting agents. Polar
solvents could not be used because they are water-soluble. Mebhylene
chloride was chosen because it is essentially immiscible with water
and volatile enough so that the extracted products could be concentrated
by evaporation of the solvent. In these prior tests, a 10 ml ali-
quot of aqueous product was extracted with 5 ml of methylene chloride.
After concentrating the extract to 0.1 ml, analysis of the concen-
trate could account for no more than 0.5 to 6 weight percent of the
carbon in the feed.
In an attempt to improve the extraction efficiency of liquid
products, separate 20 ml aliquots of the aqueous product were acidi-
fied with 7 ml of 0.9 molar sulfuric acid and made basic with 7 ml of
0.9 molar potassium hydroxide prior to extraction. Each aliquot was
extracted with three 10 ml portions of methylene chloride. The ex-
tracts were then air-dried at ambient temperature and the residue
weighed. The results, shown in columns 4 and 5 of Table 2, were con-
verted to percent by weight of feed material. The acidic extractions
resulted in a somewhat higher recovery of liquid products than the
basic extractions, but in both cases, the recovery efficiency was
8045/702 1 1 7 0 8 3 1
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1 1
1 extremely low (less than 10,0) .
To verify that the aqueous product actually contained sig-
nificantly more organic liquid products than that which was extracted
by methylene chloride, carbon analysis of feed and all products were
made for run 3. Total carbon analyses were made for feed and liquid
product and carbon content of the gaseous were calculated from
the composition of the vapor, as determined by gas chromatography.
The carbon content of the feed was found to be 0.42 weight percent,
whereas the liquid product contained 0.36 weight percent and the vapor
product 0.039 weight percent, for a total of 0.40 weight percent
carbon in the products. Thus, it was established that the liquid
products contained about 90% of the weight of the feed material,
no more than 10% of which could be recovered by methylene chloride
extraction.
T~e reaction mixture after 7 to 11 minutes of reacting, was
evaporated at ambient temperature. The fraction of organics
remaining after evaporation are shown in Table 2 column 6. Only 10
to 26% of the original carbon feed is accounted for in the residue.
A large fraction of organic liquid products are volatile,at least as
volatile as water, if not more so. Thus, the last column in Table 2
is the fraction of the carbon feed that was lost during evap~ration
of the water, i.e., frorn 63 to 74% of the carbon feed can be recovered
as volatile organic liquids. These materials are readily separable
from the aqueoùs product by distillation or sequential flashing or
in some cases by other conventional separation techniques at sub-
critical conditions. Moreover, these products are reformed products
of the original organic feed and can be useful as fuels in their
liquid or gaseous forms.
FIG. 1 illustrates a preferred flow diagram for a continuous
process of reforming solid organic material to form liquid fuels and
8045/702 1 ~ 7 ~ 8 3 ~
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1 chemicals as shown in FIG. 1 at 10. The supercritical water reformer
is noted at 2~ and is preferably sized as a tubular reactor with a flow
therethrough such that the material to be reformed spends only from
seconds to minutes under supercritical conditions to rapidly dissolve
and disperse the solid matter in the feed and rapidly break down high
molecular weight components into gases and volatile liquids such as
hydrogen, carbon monoxide, methane, carbon dioxide and other reformed
lower molecular weight volatile liquid organic compounds. Portions
of the products produced may be oxidized within the overall processing
scheme and utilized for internal energy requirements as in heating water
to supercritical conditions.
FIG. 1 shows a wood chip process where a feed of wood chips is
fed to a slurry tank 20 and suspended in water. Feed pump 19 pumps
the feed to a supercritical water reformer 21 which also receives super-
heated, supercritical water at high temperature so that the cold feedis instantly heated to supercritical conditions as previously described.
A heat exchanger 22 is positioned in the line from the reformer 21
so as to heat combustion air going to the furnace 11 which in turn heats
the water to supercritical conditions for use in the reformer 21.
The flow from the reformer 21, is brought to a subcritical flashing
unit 17 which removes gaseous products to a gas expander 16 and in
turn uses these gases in the heating process of the furnace 11. The
flashing unit 17 is maintained somewhat below the critical tempera-
ture of the aqueous solution, although the pressure may be above the
critical pressure of water. Typically, the temperat~re may be 300 to
350C in flashing unit 17. Organic liquids and water are taken through
a liquid expander 18 where liquids are passed to a steam stripper 12
and condenser 13 arrangement which takes off organic liquids for use
as fuel or chemicals. Off gases from the superheater 11 are passed
to a boiler 14 which acts to aid in the stripping occurring in the
stripper 12 while recycled water passes to water pump 15 for passage
8045/702
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1 to the water heater with some water passing to the feed slurry tank.
The feed can be mixed to the proper proportion in the feed slurry
tank bearing in mind the additional superheated water that will be
added in the reformer. No predrying of the feed is necessary. The
slurry can be pressurized and heated to supercritical conditions very
rapidly to avoid char formation. Heating can be obtained by mixing
the feed with the superheated, supercritical water at 600 to 900C
or by heating along the line leading from the slurry tank to the reformer.
In all cases, short residence times of up to 15 minutes are preferably
maintained in the supercritical water reactor.
FIG. 2 illustrates the processing of a slurry such as black
liquor from pulping which contains relatively high concentrations
of inorganic materials as well as organic materials. Black liquor
from the holding tank 31 is pumped through pump 32 to the super-
critical water reformer 33 which is maintained at near critical condi-
tions and causes rapid breakdown of organics. The reformer 33 passes
the reaction products to the heat exchanger 35 where heat is taken
off to heat water passing to the supercritical water superheater 41
which water is in turn used in the reformer. Combustion air is used
to heat the water in the superheater 41 along with combustible gases
and volatile organics obtained from a flash drum number 2 at 40 with
the oil phase from the flash drum passing to fuel storage. The feed
from the reformer 33 after passing through heat exchanger 35 is reduced
in pressure by a letdown valve 36 and then passed to flash drum number
1 at 38 whereupon an inorganic solution is removed through valve 42.
Flash drum number 1 at 38 is maintained at temperatures and pressures
below the critical conditions of water, where volatile organic material,
gaseous products, and steam can be collected overhead. These conditions
are typically in the range of 250 to 350C and 30 to 150 atmospheres.
The inorganic solution can be used to recover sodium and sulfur so as
8045/702
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1 to obtain an acceptable green liquor which is subsequently to be
mixed with wood feed. The temperature and pressure of the overhead
steam from flash drum number 1 are reduced further and fed to flash
drum number 2 at 40 through a heat exchanger 37. The conditions
in flash drum number 2 at 40 are typically ambient temperature to
200C and ambient pressure to 15 atmospheres. The aqueous phase con-
taining hydrophilic organics is taken from the flash drum number 2
passed through a booster 39 heat exchanger 37 and 35 and back to the
superheater 41. It is repressurized reheated and superheated before
recycled to the supercritical water heater 41,
While specific embodiments of the present invention have been
shown and generally described above, many variations are possible.
For example, the separation of the volatile liquid organics
formed during the reactions with water at the critical density can be
carried out under varying conditions. For example, steam stripping
at atmospheric pressure can be used to remove the volatile organic
liquids from the water in the reaction vessel after the reaction
or in a subsequent vessel in processing. Distillation in a distilla-
tion tower can be carried out at pressures ranging from atmospheric
to on the order of a 150 atmospheres to separate the liquid organic
products from the water. The volatile organics can be collected
in the vapor phase along with water to leave volatile organic residuals
in the liquid phase after the reaction as for example at temperatures
of from 250 to 350C at 30 to 150 atmospheres. This can be followed
by a distillation step in a distillation tower to separate the volatile
organic liquids from the water. Flashing can be used at temperatures
in the range oF 300 to 350C to take off gaseous products. Mem-
brane separation such as reverse osmosis can be used to separate
volatile organic liquids. The volatile organic liquids being highly
hydrophilic, require the separation step and are produced in sufficient
`8045/702 1 1 7Q83 1
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quantity to make separation feasible. Preferably, the volatile organic
liquids are produced in quantities at least as high as 25% but more
pref~rably at least as high as 50% of the original organic feed.
