GB2310865A - Pyrolysis of wet cellulose containing biomass to produce hydrogen - Google Patents

Description

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 1,0000C, 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 cellulosecontaining biomass.

The present invention has been made in view of the above problems. In accordance with one aspect of the present invention there is provided a method of producing hydrogen from a cellulose-containing biomass, comprising the steps of: (a) providing a liquid phase containing said biomass, water and a catalyst in a reaction chamber such that an upper space is defined above said liquid phase in said chamber; (b) heating said liquid phase at a temperature of 250-3740C while maintaining said upper space at a pressure higher than the saturated vapor pressure of water, so that hydrogen is formed and collected in said upper space; and (c) discharging part of said collected hydrogen during step (b).

In another aspect, the present invention provides a method of producing hydrogen from a cellulose-containing biomass, comprising the steps of: (a) providing a reaction zone having a gas-liquid separating membrane disposed to partition said reaction zone into a first chamber and a second chamber; (b) forming a liquid phase containing said biomass, water and a catalyst in said first chamber; (c) heating said liquid phase at a temperature of 250-374 C; (d) feeding a pressurized inert gas to said second chamber to maintain said first chamber at a pressure higher than the saturated vapor pressure of water during step (c), so that said biomass is decomposed to produce hydrogen which passes through said membrane to said second chamber; and (e) discharging part of said hydrogen from said second chamber together with said inert gas during step (d).

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 out 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 illustration 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 250-3740C and a pressure higher than the saturated vapor pressure of water.

The term "cellulose-containing 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 agricultural 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 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 250-3740C, preferably 300-370 C, at a pressure higher than the saturated water vapor pressure at the heat treatment temperature. The treatment time is generally 5-180 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. A 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 1 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.

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 11-13 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.

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 250-3740C by indirect heat exchange therewith. The heating medium is discharged through a line 41 and recycled to the 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 3000C. 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 3000C, pressurized nitrogen gas was fed to the reactor. The product gas was cooled and 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 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 3000C 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 80 g based on carbon.

Table 1 Yield of Gas (mmol) H2 CO2 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 H2 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 H2 is 79.0 mmol under the conditions providing a gasification rate of 83 %.

Claims (9)

WHAT IS CLAIMED IS:

1. A method of producing hydrogen from a cellulosecontaining biomass, comprising the steps of: (a) forming a liquid phase containing said biomass, water and a catalyst in a reaction chamber such that an upper space is defined above said liquid phase in said chamber; (b) heating said liquid phase at a temperature of 250-3740C while maintaining said upper space at a pressure higher than the saturated vapor pressure of water, so that hydrogen is formed and collected in said upper space; and (c) discharging part of said collected hydrogen during step (b).

2. A method as claimed in claim 1, further comprising feeding an inert gas to said reaction chamber to maintain said upper space at a pressure higher than the saturated vapor pressure of water.

3. A method as claimed in claim 2, wherein said inert gas is directly fed to said upper space.

4. A method as claimed in claim 2, wherein said inert gas is fed to a bottom portion of said liquid phase.

5. A method as claimed in claim 1, step (b) includes heating a heating medium with solar energy and feeding said heated heating medium to said reaction chamber for heating said liquid phase by indirect heat exchange therewith.

6. A method of producing hydrogen from a cellulosecontaining biomass, comprising the steps of: (a) providing a reaction zone having a gas-liquid separating membrane disposed to partition said reaction zone into a first chamber and a second chamber; (b) forming a liquid phase containing said biomass, water and a catalyst in said first chamber; (c) heating said liquid phase at a temperature of 250-374 C; (d) feeding a pressurized inert gas to said second chamber to maintain said first chamber at a pressure higher than the saturated vapor pressure of water during step (c) so that said biomass is decomposed to produce hydrogen which passes through said membrane to said second chamber; and (e) discharging part of said hydrogen from said second chamber together with said inert gas during step (d).

7 A method as claimed in claim 6, wherein said reaction zone is a tubular reactor and said membrane is a tubular membrane defining therewith said second chamber, said tubular membrane being coaxially disposed in said tubular reactor to define said first chamber between said membrane and said tubular reactor.

8. A method as claimed in claim 7, step (c) includes heating a heating medium with solar energy and feeding said heated heating medium to said reactor for heating said liquid phase by indirect heat exchange therewith.

9. A method of producing hydrogen from a cellulosecontaining biomass, such as herein described with reference to the accompanying drawings.