Molecular sieve abstract
Porous coke is impregnated with an organic compound which remains
in the pores thereby causing a reduction in the effective size of
the same. This results in molecular sieve coke capable of separating
different gases, particularly oxygen and nitrogen, and capable of
adsorbing smaller gas molecules more rapidly than larger gas molecules.
The organic compound has a boiling point of at least 200.degree.C
as measured at atmospheric pressure and of no more than 450.degree.C
as measured in vacuum.
Molecular sieve claims
What is claimed as new and desired to be protected by Letters Patent
is set forth in the appended claims:
1. A process for the production of a carbon-containing molecular
sieve capable of separating different gases, particularly oxygen
and nitrogen, and capable of adsorbing smaller gas molecules more
rapdily than larger gas molecules, said process consisting of impregnating
coke, having pores of a first size with a solution which includes
an organic substance and a solvent for said organic substance which
volatilizes more readily than said organic substance, said organic
substance having a boiling point of at least about 200.degree.C
at atmospheric pressure and at most about 450.degree.C at substantially
zero pressure being a member of the group consisting of the light
and heavy fuel oil fractions and hard paraffins derived from crude
oil and petroleum, the fractions derived from coal tar, phenanthrene,
anthracene, hexamethylbenzene, methylnaphthalene, diphenyl, dibenzl,
acenaphthene, 1234-tetrahydronaphthalene, stilbene, diphenylmethane,
triphenylmethane, maleic acid anhydride, paraffin oil, kerosene,
lubricating oil and pitch distillation residues; and permitting
said solvent to undergo evaporation under conditions such that said
organic substance remains in said pores thereby causing a reduction
of said first size to an effective second size between about 0.2
and about 0.6 millimicrons, said organic substance being left in
a non-coked condition.
2. A process as defined in claim 1 wherein said organic substance
has a boiling point of substantially 360.degree.C at most as measured
at substantially zero pressure.
3. A process as defined in claim 1 wherein the impregnating step
is carried out at a temperature in excess of room temperature.
4. A process as defined in claim 1 wherein said coke is particulate.
5. A process as defined in claim 4 wherein the coke particles
have a size between substantially 2 and 10 millimeters.
6. A process as defined in claim 1 wherein the impregnating step
is carried out for a period of substantially 10 to 60 minutes.
7. A process as defined in claim 1 wherein said organic substance
is a member of the group consisting of fuel oil, diphenyl, paraffin,
anthracene oil, phenanthrene, paraffin oil, pitch, lubricating oil
and maleic acid anhydride.
8. A process as defined in claim 1 wherein said solvent comprises
at least one member of the group consisting of petroleum ether,
ethylene chloride, methylene chloride, carbon tetrachloride, acetone,
benzene and cyclohexane.
Molecular sieve description
BACKGROUND OF THE INVENTION
The invention relates generally to molecular sieves or filters.
More particularly, the invention relates to carbon-containing molecular
sieves and to a process of making the same.
It is known that coke having a certain volume of pores is suitable
for adsorbing oxygen (O.sub.2) molecules preferentially to nitrogen
(N.sub.2) molecules, that is, such coke is able to effect a certain
separation of oxygen and nitrogen. The effective size or cross-section
of the pores for effecting such a separation lies in the approximate
range of 0.2 to 0.6 millimicrons. On the other hand, the pores in
conventional coke have substantially larger cross-sections than
this.
A manner of preparing molecular sieve coke which enables a gas
mixture such as, for example, air, to be separated into a gas containing
smaller gas molecules, for instance, oxygen, and a gas containing
larger gas molecules, for instance, nitrogen, is also already known.
Here, coke is heated to approximately 500 to 900.degree.C and a
stream of carbonaceous gas is passed through the coke. Carbon splits
off from the gas and is deposited in the effective pores of the
coke thereby reducing the cross-sections of these pores to the order
of 0.3 millimicrons.
While the process outlined above does cause a reduction in the
size of the pores, there are certain problems associated therewith.
Thus, this process requires painstaking temperature regulation.
Moreover, the product resulting from the treatment with the carbonaceous
gas must be cooled in an inert gas stream. Hence, the aforementioned
process is not only troublesome but is also relatively expensive.
SUMMARY OF THE INVENTION
It is, accordingly, a general object of the invention to provide
a novel molecular sieve and a novel process of making molecular
sieves.
More particularly, it is an object of the invention to provide
a novel carbon-containing molecular sieve and a novel process of
making the same.
Another object of the invention is to provide a process of making
a carbon-containing molecular sieve which is simple and economical
to perform.
A further object of the invention is to provide a carbon-containing
molecular sieve which is of lower cost than those known from the
art.
An additional object of the invention is to provide a carbon-containing
molecular sieve which possesses a very long life.
In accordance with the foregoing objects, and others which will
become readily apparent hereinafter, the invention sets forth a
process for the production of a carbon-containing molecular sieve
capable of separating different gases, particularly oxygen and nitrogen,
and capable of adsorbing smaller gas molecules more rapidly than,
or preferentially to, larger gas molecules. In brief, the novel
process comprises providing coke having pores of a first size and
effecting deposition of an organic substance in the pores so as
to cause a reduction in the aforementioned first size of the pores
to an effective second size. The novel carbon-containing molecular
sieve includes coke having pores of a first size and an organic
substance at least partially bounding these pores thereby effecting
a reduction of the first size thereof to an effective second size.
The effective size or diameter of the pores in which the organic
substance is deposited advantageously lies between 0.2 and 0.6 millimicrons.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has now been found that suitable molecular sieve coke for separating
gases, particularly oxygen and nitrogen, and which adsorbs smaller
gas molecules more rapidly than larger gas molecules, may be obtained
by impregnating coke with organic substances such as organic compounds
which advantageously have a boiling point between 200.degree. and
450.degree.C in the pressure range from atmospheric pressure to
vacuum, i.e. substantially zero pressure. This impregnation has
the result that the cross-sections of those pores in the porous
coke which are too large are reduced to the requisite dimensions
or diameter of approximately 0.2 to 0.6 millimicrons. Surprisingly,
the resulting openings or free cross-sections in the pore system
of the coke remain effective over a practically unlimited period
of time without, however, requiring coking or carbonization of the
substance which is responsible for the reduction in pore size as
was necessary heretofore. Consequently, molecular sieve coke is
produced wherein the openings or pores are partially or completely
bounded by an organic substance having a boiling point of about
200.degree. to 450.degree.C in the pressure range from atmospheric
pressure to vacuum, that is, wherein the pores are at least partially
lined with such organic substances or compounds.
It is pointed out here that it may be necessary to dry the coke
for an extended period of time after it has been impregnated with
the organic substance, i.e. the impregnating agent. There exists,
then, the danger that the impregnating agent will be vaporized during
the drying operation. Thus, the impregnating agent should have a
minimum boiling point of about 200.degree.C as measured at atmospheric
pressure. However, it is also possible to use higher boiling point
organic substances or compounds such as, for example, solid hydrocarbons,
as the impregnating agent in the process of the invention, which
organic substances may be dissolved in a solvent. Consequently,
the impregnating agent might have a boiling point as high as approximately
360.degree. to 450.degree.C as measured in vacuum. It will be understood
herein that the phrase "having a boiling point between 200.degree.
and 450.degree.C in the pressure range from atmospheric pressure
to vacuum", and similar phrases, are interpreted in the above
manner, namely, that the impregnating agent has a minimum boiling
point of about 200.degree.C at atmospheric pressure and a maximum
boiling point of about 450.degree.C in vacuum or at substantially
zero pressure. This corresponds approximately to a boiling range
of 200.degree. to 550.degree.C as measured at atmospheric pressure.
It is also pointed out that, although the impregnating agent may
have a boiling point between 200.degree. and 450.degree.C in the
pressure range from atmospheric pressure to vacuum, a boiling point
between 200.degree. and 360.degree.C in this pressure range has
been found to be quite satisfactory.
All carbonaceous or carbon-containing materials which neither melt
nor soften come into consideration as starting materials for the
coke to be impregnated or contacted with the organic substance or
compound. Thus, for example, oxidized bituminous coal, anthracite,
brown coal or lignite, peat, coconut shells and wood may be used
for this purpose. In addition, activated coke produced from the
aforementioned starting materials may be transformed into molecular
sieve coke using the impregnation according to the invention.
Carbonaceous or carbon-containing materials which are particularly
suitable for effecting a reduction in the pore size include hydrocarbon-containing
compounds and all of the aromatic or aliphatic hydrocarbons, as
well as substituted hydrocarbons, which can be distilled in the
temperature range of 200.degree. to 450.degree.C under atmospheric
pressure or under vacuum. For instance, the light or heavy fuel
oil fractions and hard paraffins derived from crude oil or petroleum,
either singly or in mixture with one another, are suitable for this
purpose. Other substances which are suitable for this purpose include
the fractions derived from coal tar, for example, anthracene oils,
as well as, for instance, phenanthrene, anthracene, hexamethylbenzene,
methylnaphthalene, diphenyl, dibenzyl, acenaphthene, 1234-tetrahydronaphthalene,
stilbene, diphenylmethane, triphenylmethane, maleic acid anhydride,
paraffin oil, kerosene and lubricating oil. In addition, distillation
residues such as, for example, soft pitch, may also suitably be
used.
The impregnation of the coke may be achieved by permitting the
impregnating substance or agent to flow through the coke at an elevated
temperature where the impregnating substance exists in vaporous
form or in gaseous form or in the form of an aerosol. The treating
temperature should, correspondingly, lie approximately in the range
of 250.degree. to 450.degree.C. In order to obtain a better distribution
of the impregnating agent, this manner of treating the coke is advantageously
performed using a stream of an inert gas such as, for instance,
nitrogen, which contains the impregnating agent. A treatment time
of about 10 to 60 minutes is usually sufficient to achieve the desired
reduction in pore size.
In accordance with another embodiment of the invention, it is possible
to perform the impregnation by soaking the coke with or immersing
the coke in an impregnating substance which is dissolved in a solvent.*
After the impregnation, the solvent is removed from or driven off
from the coke. Solvents which are suitable for dissolving the impregnating
substance include, for example, petroleum ether, ethylene chloride,
methylene chloride, carbon tetrachloride, acetone, benzene and cyclohexane.
In the treatment according to the invention, the solvent may be
distilled from the coke under atmospheric pressure or under vacuum.
If the coke is inadequately impregnated with a single treatment,
then the coke may be readily subjected to one or more additional
treatments in accordance with the invention until the desired reduction
in pore size has been achieved.
The coke to be impregnated may be in the form of particles having
a particle size of, for instance, 2 to 10 millimeters. The coke
may be brought to the desired particle size by pulverization. However,
it is also possible to subject shaped coke bodies to the process
of the invention instead of using coke which has been reduced to
a desired particle size by pulverization. For instance, spherical,
cylindrical, hollow cylindrical and egg-shaped coke bodies, as well
as larger coke briquettes which are pulverized to the desired particle
size, may be treated by the process of the invention. The coke to
be treated may be produced in several ways, two illustrative examples
of which are presented below:
1. Suitable coal, carbon, carbonaceous material and/or coke is
briquetted using 15 to 40% of a binding agent such as pitch, bitumen,
tar or tar oil. These briquettes are coked or carbonized at a temperature
of 600.degree. to 900.degree.C. The briquetting may be carried out
at normal or room temperature or may be carried out at elevated
temperature using a hand press, an extruder or a roll press.
2. Coal, carbon or carbonaceous material, if necessary, in mixture
with pitch, bitumen, tar or tar oil, is formed by pelletizing into
the shape of spheres having the desired size. The pellets are then
coked or carbonized.
As an example of one manner of accomplishing the impregnation according
to the invention, cold coke, for instance, may be immersed in solutions
of high boiling point hydrocarbons for a period of 10 to 60 minutes
or even longer. Thereafter, the coke is removed and excess solution
is permitted to drip off or drain or may be removed by centrifuging.
Subsequently, residual solvent is advantageously distilled off by
slightly heating the coke, for example, to a temperature of approximately
120.degree.C, while applying a vacuum. After removal of the solvent,
the thus-impregnated coke is advantageously dried at a temperature
in excess of about 100.degree.C for a period of approximately 1
to 3 hours or longer.
A quantity test may be performed for testing the quality of the
carbon-containing molecular sieve coke produced according to the
invention. Thus, a tube having a capacity of 1 liter is filled with
the impregnated coke. Air is passed through the tube from bottom
to top at atmospheric pressure and at a rate of 30 centimeters per
second for a period of two minutes. Subsequently, the adsorbed gas
is desorbed for a period of two minutes by means of a vacuum and
then analyzed.
Molecular sieve coke produced in accordance with the invention
and tested in this manner yielded gases having a composition of
35 volume % oxygen or more and 65 volume % nitrogen or less.
The following Examples illustrate the process according to the
invention. However, it is to be understood that these Examples are
merely illustrative in nature and are not intended to limit the
invention in any manner.
EXAMPLE 1
Coking coal particles, all having a particle size of less than
0.08 millimeters, were treated in a fluidized bed with air at a
temperature of 230.degree.C until an oxygen content of 12% by weight
was obtained. 77 parts by weight of the thus-treated coal was mixed
with 23 parts by weight of soft pitch (Kramer-Sarnow softening point
52.degree.-56.degree.C) at approximately 70.degree.C while adding
water. The mixture was then shaped in an extruder to the form of
cylindrical bodies having a diameter of 2 millimeters and degassed
in a rotating tubular oven from which air was excluded until a 3%
content of volatile components had been obtained. The temperature
in the oven was increased at an average of 10.degree.C per minute
until a final temperature of 700.degree.C had been reached. 150
parts by weight of the oxidized coke was then treated with a solution
containing 0.83 parts by weight of fuel oil in 50 parts by weight
of petroleum ether by immersion for a period of 15 minutes. Thereafter,
the excess solution was permitted to drain, the petroleum ether
removed at normal or room temperature under a vacuum of 15 torr
and the resulting product dried for 1 hour at 100.degree.C. The
quality test yielded the following gas composition: 51 volume %
oxygen and 49 volume % nitrogen.
EXAMPLE 2
Shaped coke derived from oxidized coking coal was produced in the
manner described in Example 1 and degassed to obtain a content of
volatile components of 3%. After cooling to a temperature of 260.degree.C
in a stream of nitrogen, 1 gram of diphenyl per Nm.sup.3 was added
to the nitrogen stream at 260.degree.C and the treatment continued
for 10 minutes while holding the temperature constant. The quality
test yielded the following gas composition: 46 volume % oxygen and
54 volume % nitrogen.
EXAMPLE 3
Coking coal particles, all having a particle size of less than
0.08 millimeters, were treated in a fluidized bed with air at a
temperature of 230.degree.C until an oxygen content of 12% by weight
was obtained. 83.75 parts by weight of the thus-treated coal was
pelletized with 15 parts by weight of hard pitch (Kramer-Sarnow
softening point 140.degree.C) and 5% solid substances of waste sulfite
liquor in 25 parts by weight of sprayed water. The resulting spherical,
shaped bodies, having a diameter between 3 and 4 millimeters, were
degassed in a rotating tubular oven from which air was excluded
until a 3% content of volatile components was obtained. The temperature
in the oven was increased at an average of 10.degree.C per minute
until a final temperature of 750.degree.C was reached. After cooling,
150 parts by weight of the oxidized coke was heated together with
a solution containing 2 parts by weight of heavy fuel oil in 80
parts by weight of methylene chloride for a period of 10 minutes
using a reflux condenser. After cooling, the excess solution was
filtered off, the remainder of the methylene chloride removed at
normal or room temperature in a vacuum of 50 torr and the resulting
product dried for 2 hours at 110.degree.C. The quality test yielded
the following gas composition: 41 volume % oxygen and 59 volume
% nitrogen.
EXAMPLE 4
75 parts by weight of ground charcoal, all of the particles of
which had a particle size of less than 0.1 millimeters, was mixed
with 25 parts by weight of soft pitch (Kramer-Sarnow softening point
52.degree. to 52.degree.C) while adding water. The mixture was then
shaped in an extruder to the form of cylindrical bodies having a
diameter of 2 millimeters and degassed in a rotating tubular oven
from which air was excluded until a 3% content of volatile components
was obtained. The temperature in the oven was increased at an average
of 10.degree.C per minute until a final temperature of 700.degree.C
had been reached. After cooling, 150 parts by weight of the shaped
charcoal coke was cooked or boiled together with a solution containing
1.6 parts by weight of hard paraffin in 50 parts by weight of cyclohexane
for a period of 30 minutes using a reflux condenser. After cooling,
the excess solution was filtered off and the residual solvent removed
by suction in a vacuum of 10 torr. The resulting product was subsequently
heated for 1 hour at 110.degree.C. The quality test yielded the
following gas composition: 46 volume % oxygen and 54 volume % nitrogen.
EXAMPLE 5
Anthracite coal having a particle size between 2 and 4 millimeters
was degassed in a rotating tubular oven from which air was excluded
until approximately a 1% content of volatile components had been
obtained. The temperature in the oven was increased at an average
of 10.degree.C per minute until a final temperature of 700.degree.C
had been reached. After cooling, 150 parts by weight of the anthracite
low-temperature coke was treated with a solution containing 0.6
parts by weight of anthracene oil in 60 parts by weight of benzene
by immersion for a period of 40 minutes. Thereafter, the excess
solution was filtered off and the resulting product dried for 1
hour at 130.degree.C. The quality test yielded the following gas
composition: 35 volume % oxygen and 65 volume % nitrogen.
EXAMPLE 6
Coconut shells were degassed in a rotating tubular oven from which
air was excluded until approximately a 1% content of volatile components
had been obtained. The temperature in the oven was increased at
an average of 10.degree.C per minute until a final temperature of
700.degree.C had been reached. After cooling, the coconut shell
coke was pulverized to a particle size of 2 to 4 millimeters and
150 parts by weight thereof treated with a solution containing 0.3
parts by weight of phenanthrene in 50 parts by weight of acetone
by immersion for a period of 15 minutes. Thereafter, the excess
solution was filtered off and the resulting product dried for 1
hour at 150.degree.C. The quality test yielded the following gas
composition: 39 volume % oxygen and 61 volume % nitrogen.
EXAMPLE 7
Coking coal particles, all having a particle size of less than
0.08 millimeters, were treated in a fluidized bed with air at a
temperature of 230.degree.C until an oxygen content of 12% by weight
was obtained. 77 parts by weight of the thus-treated coal was mixed
with 23 parts by weight of soft pitch (Kramer-Sarnow softening point
52.degree. to 56.degree.C) at 70.degree.C while adding water. The
mixture was then shaped in an extruder to the form of cylindrical
bodies having a diameter of 3 millimeters and degassed in a rotating
tubular oven from which air was excluded until approximatetely a
1% content of volatile components had been obtained. The temperature
in the oven was increased at an average of 10.degree.C per minute
until a final temperature of 800.degree.C had been reached. Thereafter,
an activation was performed in known manner through the introduction
of water vapor. After cooling, 150 parts by weight of the activated
coke was treated together with a solution containing 2 parts by
weight of paraffin oil in 80 parts by weight of ethylene chloride
by cooking or boiling with a reflux condenser for a period of 15
minutes. After cooling, the excess solution was filtered off, the
residual solvent distilled off at normal or room temperature in
a vacuum of 25 torr and the resulting product heated for 2 hours
at 120.degree.C. The quality test yielded the following gas composition:
52 volume % oxygen and 48 volume % nitrogen.
EXAMPLE 8
150 parts by weight of peak coke having a particle size of 1 to
3 millimeters was cooked or boiled for a period of 15 minutes together
with an aqueous solution of waste beechwood sulfite liquor (5% by
weight of dried substances) using a reflux condenser. The excess
solution was then filtered off and the resulting product dried and
subsequently heated at 400.degree.C for a period of 30 minutes under
nitrogen. Thereafter, the product was cooked or boiled for a period
of 15 minutes together with a solution containing 1 part by weight
of soft pitch, 1 part by weight of lubricating oil and 80 parts
by weight of benzene using a reflux condenser. The solution was
next filtered off and the product dried for 1 hour at 110.degree.C.
the quality test yielded the following gas composition: 35 volume
% oxygen and 65 volume % nitrogen.
EXAMPLE 9
Shaped coke derived from oxidized coking coal was produced in the
manner described in Example 1 and degassed to obtain a content of
volatile components of 3%. After cooling, 150 parts by weight of
the oxidized coke was treated with a solution containing 2.1 parts
by weight of maleic acid anhydride in 80 parts by weight of acetone
by immersion for a period of 20 minutes. Thereafter, the excess
solution was filtered off and the resulting product dried for 1
hour at 110.degree.C. The quality test yielded the following gas
composition: 35 volume % oxygen and 65 volume % nitrogen.
It will be appreciated that the invention has obviated the need
for coking or carbonizing the agent responsible for the reduction
in pore size as has been necessary heretofore.* On page 9 line
22 as indicated: An impregnating temperature from 10.degree. C
to the boiling point of the solvent is convenient. The impregnation
may be achieved with solutions having 0.2 - 50 % by weight of the
impregnating substance by contact for a period of 10 - 60 minutes.
It will be understood that each of the elements described above,
or two or more together, may also find a useful application in other
types of processes and uses differing from the types described above.
While the invention has been illustrated and described as embodied
in a molecular sieve and process for making the same, it is not
intended to be limited to the details shown, since various modifications
and structural changes may be made without departing in any way
from the spirit of the present invention.
Without further analysis, the foregoing will so fully reveal the
gist of the present invention that others can by applying current
knowledge readily adapt it for various applications without omitting
features that, from the standpoint of prior art, fairly constitute
essential characteristics of the generic or specific aspects of
this invention and, therefore, such adaptations should and are intended
to be comprehended within the meaning and range of equivalence of
the following claims. |