Note: Descriptions are shown in the official language in which they were submitted.
CA 02199435 2000-11-20
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This invention relates to a method of producing hydrogen
from a cellulose-containing biomass.
One known method for the production of hydrogen from wood
chips includes subjecting the wood chips to water gas shift
reactions in which the wood chips are converted into hydrogen and
carbon monoxide and the carbon monoxide in turn is converted into
hydrogen and carbon dioxide. Since the above reactions should be
performed at a high temperature of about 1,000°C, it is a general
practice to burn part of the wood chips to supply the heat for
the reactions. Thus, the Efficiency of the above method is not
satisfactory. Further, the above method is not applicable to a
wet cellulose-containing biomass.
The present invention has be<=_n made in view of the above
problems. In accordance wii~h one aspect of the present invention
there is provided a method of producing hydrogen from a
cellulose-containing biomass, comprising a method of producing
hydrogen from a cellulose-containing biomass, comprising forming
a liquid phase containing the biomass, water and a catalyst in a
reaction chamber such that an upper space is defined above the
liquid phase in the chamber, feeding an inert gas to said
reaction chamber to maintain the upper space at a pressure higher
than the saturated vapour pressure of water, heating the liquid
phase at a temperature of 250-374°~~ while maintaining the upper
space at a pressure higher than the saturated vapour pressure of
water, so that hydrogen is formed and collected in the upper
space, and discharging part of the collected hydrogen during
heating.
In another aspect, the present invention provides a method
of producing hydrogen from a cellulose-containing biomass,
comprising a method of p-~oducing hydrogen from a cellulose
containing biomass, comprising forming a liquid phase containing
the biomass, water and a cat=aly~;t in a first chamber of a
reaction zone having a gas-:Liquid separating membrane disposed to
partition the reaction zone into t:he first chamber and a second
chamber, heating the liquid phase i~o a temperature of 250-374°C,
feeding a pressurized inert gas to the second chamber to maintain
the first chamber at a pressure higher than the saturated vapour
CA 02199435 2000-11-20
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pressure of water during 1_he heating, so that the biomass is
decomposed to produce hydrogen which passes through the membrane
to the second chamber, and, during the feeding of the pressurized
inert gas, discharging part of the hydrogen from the second
chamber together with inert gas.
The present invention will be described in detail below
with reference to the accompanying drawings, in which:
Fig. 1 is a schematic illustration of one embodiment of an
apparatus useful for carrying oui; the method of the present
invention;
Fig. 2 is a vertical cross-sectional view diagrammatically
showing an embodiment of a :reactor for the apparatus of Fig. 1;
Fig. 3 is a sectional view diagrammatically showing a
tubular reactor useful for carrying out the method of the present
invention;
Fig. 4 is a sectional view taken on line IV-IV in Fig. 3;
and
Fig. 5 is a schematic illustr<~tion of another embodiment of
an apparatus useful for carrying out the method of the present
invention.
In accordance with one embodiment of the present invention,
cellulose-containing biomass is heat-treated in the presence of
water and a metal catalyst at a temperature of 250-374°C and a
pressure higher than the saturated vapor pressure of water.
The term "cellulose-cc>ntainin<~ biomass" used in the present
specification is intended to refer to various kinds of materials
containing cellulose. Examples of the cellulose-containing
biomass include wood, wood chips, wood powder, bark, baggasse,
bamboo, wastes of agricult:ura.L products, paper, peat, sewage,
soil, city wastes and other cellulose-containing waste materials.
The metal catalyst may be Fe, Ni, Co, Mo, W, Pt and Cu.
These metals may be used as various forms such as
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elemental metals, oxides and sulfides. A supported catalyst
containing a porous carrier and the above catalytic metal
supported thereon may also be suitably used. Illustrative of
suitable carriers are silica, alumina, silica-alumina,
zirconia, titania, zeolite, sepiolite, kieselguhr
(diatomacous earth) and clay. If desired, a co-catalyst such
as a hydroxide, a carbonate or a formate of an alkali metal
or an alkaline earth metal, e.g: sodium,, potassium, lithium
or magnesium, may be used in conjunction with the above metal
catalyst. The metal catalyst is generally used in an amount
of 0.01-10 parts by weight, preferably 0.1-1 part by weight,
per part by weight of the cellulose-containing biomass on the
dry basis.
Water is generally present in an amount of 2-100
parts by weight, preferably 4-10 parts by weight, per part by
weight of the cellulose-containing biomass on the dry basis.
The heat treatment is performed at a temperature of
250-374°C, preferably 300-370°C, at a pressure higher than the
saturated water vapor pressure at the heat treatment
temperature. The treatment time is generally 5-18O minutes:
If desired, an inert gas such as nitrogen, argon or helium
may be used to maintain the desired treatment pressure. An
organic solvent such as an alcohol, a ketone or a phenol
compound may be present in the reaction system
Referring now to Fig. 1, designated as 1 is a
reaction vessel having a lower part in which a metal catalyst
is packed. R feed containing biomass, water and, optionally,
a co-catalyst is fed to the reaction vessel 1 by a pump 2 to
form a liquid phase 3 within the reaction vessel l so that a
space 4 is defined above the liquid phase 3 and the packed
metal catalyst is immersed in the liquid phase 3. The
reaction vessel 1 is surrounded by a jacket 5 to which a
heating medium is fed to heat the liquid phase 3 by indirect
heat exchange therewith. A pressurized inert gas is fed
through a valve 6 to the upper space 4 to maintain the
pressure in the space 4 higher than the saturated vapor
pressure of water.
_ 4 _ ~'~9~4~3a
The biomass in the liquid phase 3 is decomposed to
form hydrogen which is collected in the upper space 4. The
hydrogen in the upper space. is continuously or intermittently
discharged for recovery through a valve 7 to maintain the
hydrogen partial pressure below a predetermined level. By
this expedient, the yield of methane by-product is minimized.
The pressure in the upper space 4 is monitored by a sensor 9
having an output coupled with the valve 6, so that the inert
gas is fed to the upper space 4 to maintain the upper space 4
at a pressure higher than a predetermined level. The liquid
phase 3 after the completion of the reaction is discharged
through a valve 8.
In Fig. 2, component parts similar to those in Fig.
1 are designated by the same reference numerals. Designated
as 1 is a reaction vessel surrounded by a heating jacket 5.
A packed bed of a metal catalyst is disposed in the reaction
vessel 1. In the embodiment shown in Fig. 2, the reaction
vessel 1 is vertically elongated to ensure a long residence
time of the biomass feed in the reaction vessel 1. However,
whilst a long residence time is desirable from the standpoint
of improved gasification rate, the yield of hydrogen has been
found to decrease as the residence time increases.
To cope with this problem, an inert gas is fed from
the bottom of the reaction vessel 1 so as to maintain an
upper space 4 above a liquid phase 3 at a pressure higher
than a predetermined level and to sweep hydrogen formed in
the liquid phase 3. Further, a plurality of funnel-like gas
flow control members 11-l3 having riser tubes 14-16 are
disposed to minimize the contact of the hydrogen formed in
the liquid phase 3 with the catalyst. Thus, the hydrogen
produced is swept by the inert gas and collected in the flow
control members 11-13. The collected hydrogen successively
ascends through the riser pipes 14-16 and is passed to the
upper space 4 with minimum contact with the catalyst bed. As
a consequence, a high yield of hydrogen is attained while
ensuring a high rate of gasification.
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Referring to Figs. 3 and 4, designated as 21 is a
tubular reactor surrounded by a jacket 25. A tubular
gas-liquid separating membrane 22 defining therewithin a
second chamber 23 is disposed in the reactor 21 to define an
annular first chamber 24 between them. A metal catalyst is
packed in the first chamber 24. A raw material feed
containing biomass, water and, optionally, a co-catalyst is
fed to the first chamber 24 and is contacted with the metal
catalyst. A heating medium is fed to the jacket 25 to heat
the liquid phase 3 by indirect heat exchange therewith.
A pressurized inert gas is fed to the second
chamber 23 to maintain the pressure within the first chamber
24 higher than the saturated vapor pressure of water. The
biomass in the first chamber 24 is decomposed to form
hydrogen which is diffused through the membrane 22 into the
second chamber 23. The hydrogen in the second chamber 23 is
discharged continuously or intermittently from the reactor
together with the inert gas.
The membrane 22 permits the passage of a gas
therethrough but prevents the passage of a liquid
therethrough. A membrane formed of a metal or a ceramic is
suitably used.
Since the above method uses a lower temperature
than that in the conventional method, solar energy can be
utilized to carry out the method according to the present
invention. Fig. 5 depicts a system flow chart for the
production of hydrogen from biomass using solar energy.
Designated as 30 is a reactor which may be similar
to that shown in Figs. 1-4. The reactor 30, in which a
packed bed of a catalyst is disposed, is surrounded by a
heating jacket 31 through which a heating medium is
recirculated. The heating medium is heated in a solar
concentrator 32 and is fed to a heat storage device 33
through a line 42. The medium in the device 33 is introduced
through a line 43 to the jacket 31 to heat the reactor 30 at
250-374°C by indirect heat exchange therewith. The heating
medium is discharged through a line 41 and recycled to the
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solar concentrator 32.
Biomass and make-up water are fed to a preparation
tank 35 to which a liquid recovered in a solid-liquid
separator 3 is also fed through a line 49. The mixture is
then introduced into heat exchangers 34a and 34b through a
line 46 and is fed through line 45 to the reactor 30.
An inert gas is also fed to the reactor 30 to
maintain the mixture fed through the line 45 so that the
decomposition of the biomass resulting in the formation of
hydrogen is performed at a pressure higher than the saturated
vapor pressure of water. The inert gas and the product gas
including hydrogen are discharged from the reactor through a
line 44a, introduced into the heat exchanger 34a to heat the
biomass feed, and then fed to a gas separator 38 where
hydrogen is isolated for recovery. The liquid phase in the
reactor 30 is introduced through a line 44b to the heat
exchanger 34b to heat the biomass feed and is then fed to a
solid-liquid separator 36, where it is separated into a solid
residue and the liquid which is recovered and recycled to the
preparation tank 35 as described previously.
The following examples will further illustrate the
present invention.
Example 1
A commercially available nickel catalyst (NI-3288
(trade name) manufactured by Engelhard Inc.) was used as the
metal catalyst. Prior to use, the nickel catalyst was ground
to 60-100 mesh (Tyler) and reduced with hydrogen gas. A
mixture of 5 g of cellulose (fine crystals, product of E.
Merck Inc.), 30 g of water, 2 g of the nickel catalyst and
0.5 g of sodium carbonate was charged in a reactor (inside
volume: 100 ml). The reactor was heated at 300°C. The
product gas was discharged at a rate of 2 liters per minute.
To maintain inside of the reactor at a pressure higher than
the saturated vapor pressure of water at 300°C, pressurized
nitrogen gas was fed to the reactor. The product gas was
cooled and measured for the amount thereof with a gas meter
_7_ ~~99435
and for the composition thereof with gas chromatography. The
yields of hydrogen, carbon dioxide and methane are shown in
Table 1. The production of carbon monoxide and hydrocarbons
having 2 or more carbon atoms was only trace. The
gasification rate was 83 ~ based on carbon.
Comparative Example 1
In the same manner as that in Example 1, a mixture
of 5 g of cellulose (fine crystals, product of E. Merck
Inc.), 30 g of water, 2 g of the nickel catalyst and 0.5 g of
sodium carbonate was charged in a reactor (inside volume: 100
ml). The reactor was pressurized with nitrogen gas to 3 MPa
so that the reaction pressure was the same as that in Example
1. The reactor was heated to 300°C and maintained at that
temperature for 30 minutes. Then, the reactor was cooled to
room temperature. The product gas was measured for the
amount thereof with a gas meter and for the composition
thereof with gas chromatography. The yields of hydrogen,
carbon dioxide and methane are shown in Table 1. The
production of carbon monoxide and hydrocarbons having 2 or
more carbon atoms was only trace. The gasification rate was
g0 ~ based on carbon.
Table 1
Yield of Gas (mmol)
H2 COZ CH4
Example 1 79.0 101.4 33.9
Comparative Example 1 16.2 74.8 52.8
As will be appreciated from the results shown
above, when the biomass decomposition is carried out without
removing produced HZ from the reaction zone, the yield of H2
is 16.2 mmol under the conditions where the gasification rate
is 80 $. In contrast, in the method according to the present
invention, the yield of Hz is 79.0 mmol under the conditions
providing a gasification rate of 83 ~.
