JP2002346388A - Catalyst for manufacturing synthetic gas and method for converting biomass to synthetic gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reducing the formation of tar or forming no tar at all in manufacturing synthetic gas by the gasification of biomass. SOLUTION: A catalyst for manufacturing the synthetic gas from biomass is obtained by supporting rhodium, ruthenium, palladium or platinum on the surface of a cerium oxide carrier as a catalytic metal. The method for converting the biomass to the synthetic gas using this catalyst is also disclosed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a catalyst for producing synthesis gas from biomass and a method for converting biomass to synthesis gas using the catalyst.

[0002]

2. Description of the Related Art Heretofore, biomass has been used as combustion fuel for power generation or treated as waste. Gasification of biomass to synthesis gas has many advantages from an environmental protection point of view. That is, the synthesis gas is CO +
Since it is a gas containing H ₂ , it is possible to reduce the emission of CO ₂ into the atmosphere by converting it to a clean fuel.
For example, clean diesel fuel and dimethyl ether are promising superclean fuels that can be efficiently produced from syngas (T. Shikad
al., Stud. Surf. Sci. Catal. 119, 1998, 515).

[0003] Therefore, the only interest in this field is:
Developing more efficient processes for gasification of biomass to synthesis gas (I. Narvaez et al., In
d. Eng. Chem. Res. 35, 1996, 2110; D. Xianwen et al., E
nergy Fuels 14, 2000, 552; ID Bari et al., Energy Fue
ls 14, 2000, 889; P. Vriesman et al., Fuel 79, 2000, 137
1; CD Blasi et al., Energy Fuels 11, 1997, 1109). The most serious problem in this process is that tar is formed even at very high reaction temperatures (MA Caballero et al., Ind. Eng. Chem. Res. 39, 200
0, 1143).

In order to be energy efficient and reduce production costs and CO ₂ emissions, the process should be operated at lower temperatures. However, it is known that when the reaction is carried out at a low temperature, the yield of synthesis gas decreases and the production of tar increases. (DN Bangala et al., Ind.
Eng. Chem. Res. 36, 1997, 4184). Therefore, gasification of biomass using a catalyst is one of the most promising methods for suppressing tar production at low temperatures.
(L. Garcia et al., Energy Fuels 13, 1999, 851; L. Garcia
Et al., Ind. Eng. Chem. Res. 37, 1998, 3812).

[0005] The thermal decomposition and gasification of biomass using a catalyst has already been studied (J. Arauzo et al.,
Ind. Eng. Chem. Res. 36, 1997, 67; A. Olivares et al.,
Ind.Eng. Chem. Res. 36, 1997, 5220; J. Arauzo et al., E
nergy Fuels 8, 1994, 1192). However, it has been shown that when a catalyst is used, deposits due to carbon accumulation on the catalyst surface can hinder access to the catalyst pores and rapidly deactivate the catalyst (EG Baker et al.). , Ind. Eng. Ch
em. Res. 26, 1987, 1335). The production of synthesis gas by the catalytic gasification reaction of biomass is usually performed at a high temperature of 800 ° C. or more. At this time, as described above, tar production on the catalyst surface deteriorates the catalytic activity. Also, at lower temperatures, the production of tar also tends to increase, and it has been difficult to gasify at low temperatures. Therefore, in the gasification of biomass using a catalyst, it is very important to completely convert carbon into gas.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the production of tar at a low temperature in the production of synthesis gas by biomass gasification. Or to provide a method in which no tar is formed.

[0007]

Means for Solving the Problems The present inventors have used cellulose as a model compound of biomass and studied the effects of various supports and metal-supported catalysts in the reaction for gasifying the cellulose. As a result, when a catalyst prepared by using cerium oxide as a carrier and supporting a small amount of a noble metal such as rhodium on its surface is used, no tar is produced even at low temperatures, and cellulose is synthesized at a high conversion rate. Found to convert to gas.

Further, the present inventors have found that a fluidized bed reactor is very effective in a synthesis gas production technique by an internal supply type reforming reaction of natural gas, and carbon deposition is particularly likely to occur. It has been found that, even under high pressure conditions, carbon deposition is significantly suppressed by using a fluidized bed reactor. This technique was applied to biomass where tar is likely to be produced, and by using a very excellent catalyst and fluidized bed reactor, it was possible to achieve a carbon conversion of 100% even at low temperatures.

That is, the present invention provides (1) rhodium, ruthenium as a catalyst metal on a surface of a cerium oxide carrier;
Catalyst for producing synthesis gas from biomass supporting palladium or platinum, (2) the catalyst according to (1), (3) the catalyst according to (1) or (2), wherein the catalyst metal is rhodium A method of converting biomass into a synthesis gas using the method described in (4) or (3), wherein the reaction temperature is 4
(5) The method according to (3) or (4), wherein the reaction is carried out using a fluidized bed reactor, (6) the method according to (3) to (5). The above object is attained by the method according to any one of the above, wherein the reaction is carried out by bringing the catalyst into direct contact with the cellulose.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The catalyst of the present invention is a catalyst in which cerium oxide (CeO ₂ ) is used as a carrier and a metal is supported on the surface thereof. Metals to be supported are rhodium, ruthenium, palladium and platinum, preferably rhodium and ruthenium, and particularly preferably rhodium. The catalyst is
According to a conventional impregnation method, it can be prepared using an acetone solution of the above-mentioned metal acetylacetonato complex. In the present specification, the “metal-supported catalyst” is, as described above,
It means a catalyst in which a noble metal such as rhodium is supported on a carrier such as cerium oxide.

[0011] The temperature of the method of the present invention is from 400 ° C to 100 ° C.
0 ° C, preferably 500 ° C to 900 ° C, more preferably 550 ° C to 800 ° C.

In the present invention, "biomass" is a renewable energy source that is available in large quantities and means an unused portion or waste of agricultural, forestry and fishery products. For example,
Rice straw, wood, sugarcane scum and the like. In the present invention, “synthesis gas” means a gas containing carbon monoxide and hydrogen, and as long as it reacts as CO + H ₂ ,
CO ₂ , CH ₄ , C ₂ H _{6 and the} like may be included. The synthesis gas is used as a raw material for chemical industry such as methanol synthesis and oxo method.

The reaction vessel for carrying out the present invention is preferably a fluidized bed reactor, but is not limited thereto. Fluidized bed reactors offer high heat transfer rates and can maintain isothermal operation, making them very useful in gas production by a combination of combustion and reforming (U. Olsbye et al., Stud. Surf.
Sci. Catal. 81, 1994, 303).

[0014] The following examples illustrate the present invention and are not to be construed as limiting the scope of the claims.

[0015]

EXAMPLES Examples 1 to 4 Investigations on the gasification of cellulose into synthesis gas were conducted using a fluidized bed reactor supplied in batches and various catalysts. All gasification reactions described below were performed on pure cellulose (C: 1850 μmol; H ₂ : 1543 μmo).
l; O ₂ : 772 μmol; purchased from Merck) 5
Performed with 0 mg. The reaction was carried out at atmospheric pressure and at a reaction temperature of 5
It is performed at 50 ° C., and the flow conditions are air 60 cm ³ / min, A
r50 cm ³ / min, W / F = 1.8 gh / mol [W / F
Means the contact time, where W is the catalyst mass (g) and F is the flow rate (mol / h)], the height of the fluidized bed is 2 cm, and the residence time of volatiles is 0.7 seconds.

Gasification Reaction Using Fluidized Bed Reactor: FIG. 1 schematically shows an experimental system using a fluidized bed reactor supplied in batch. The reactor (made of quartz) 2 has a height of 72 cm and a diameter of 9 mm.
And is composed of a fluidized bed portion. Another quartz tube 8 having a diameter of 4 mm was inserted from the feeder 4 into the catalyst layer 6. Desired amount of cellulose powder (250-350μ)
m) was set in the feeder 4 and supplied through a tube. Using Ar gas as a carrier, the cellulose powder was sent to the fluidized bed. Air (or oxygen) was introduced as a gasifying agent from the bottom of the reactor 2 through a dispersion plate (made of quartz) 10. The reactor 2 was heated to 550 ° C. in the electric furnace 12, and the temperature was continuously monitored by the temperature controller using the thermocouple 14. FIG. 2 is a schematic view of a fluidized bed portion in a gasification reaction using a fluidized bed reactor. The cellulose reacts by interacting with the catalyst surface.

The generated gas flows out of the reaction system, passes through a sintered metal filter 16 for removing solid particles, and passes through an ice bath trap 20 provided between the outlet of the reactor and a gas sampling port 18 for GC analysis. This ice bath trap 20
As a result, water in the effluent gas is removed for gas chromatography (hereinafter also referred to as “GC”) analysis. The final gas mixture is collected in gas bag 22.

Gas analysis: The gas sampled at the sampling port 18 and the gas collected in the gas bag 22 were analyzed by GC. CO, with respect to the amount of CO _2, CH ₄ and higher hydrocarbons were measured by FID-GC.
This FID-GC uses a stainless steel column filled with a gas chroma pack 54, and uses CO and CO ₂
Equipped with a methanation reactor. The amount of hydrogen was measured by TCD-GC, and this TCD-GC used a stainless steel column filled with molecular sieve 13X.

Preparation of catalyst: The catalyst used in the experiment was Ce
This is a catalyst in which rhodium (Example 1), ruthenium (Example 2), palladium (Example 3) and platinum (Example 4) are supported on O ₂ . These catalysts can be prepared by a conventional impregnation method using an acetone solution of a metal acetylacetonate complex, and the obtained catalyst was sized to an appropriate size and used in experiments. The amount of metal carried on the catalyst was 1.2 × 10 ⁻⁴ mol / g (catalyst). Before each experiment, the catalyst prepared as described above was flowed at a flow rate of 4
Heated to 500 ° C. for 30 minutes under H ₂ at 0 cm ³ / min.

Results of gasification reaction: 550 ° C. using various supports and metal-supported catalysts using the above-mentioned fluidized bed reactor.
Was carried out (air was used as a gasifying agent). Cellulose 50 mg, each catalyst 0.5
g used. No catalyst, only carrier (CeO ₂ , MgO,
Experiments were performed on TiO ₂ , ZrO ₂ , Al ₂ O ₃ , and SiO ₂ ), the prepared metal-supported catalysts (Examples 1 to 5), and a commercially available steam reforming catalyst G-91 (TOYO CCI). The composition of the G-91 catalyst was Ni
14% by mass, 65 to 70% by mass of Al ₂ O ₃ , CaO 10
１４14% by mass and K ₂ O 1.4-1.8% by mass.
Table 1 shows the obtained results. Based on the results obtained from the analysis of the gas collected in the gas bag, the total amount of gas products was calculated and summarized in Table 1.

[0021]

[Table 1]

When a Rh / CeO ₂ catalyst is used, G-9
More CO and H ₂ were produced than with 1. On the other hand, when G-91 was used, a large amount of CH ₄ was produced, whereas when Rh / CeO ₂ was used, C ₄ was produced.
H ₄ formation was small.

Next, FIGS. 3 and 4 show the generation rates of various gases with respect to time in the gasification reaction using the Rh / CeO ₂ catalyst and G-91. After introducing the cellulose into the catalyst layer, the gaseous products CO, H ₂ , CO ₂ , CH
₄ and H ₂ O formed. Even after the production of CO, H ₂ and CH ₄ was completed, the production of CO ₂ was still observed.

FIG. 5 shows various carriers, the metal-supporting contact of the present invention.
CO and H for medium and G-91 _TwoShow the amount of
I have. Among the carriers that do not carry metal, only Ce
O_TwoShowed slightly higher activity than the other carrier materials.

As shown in Table 1, when no catalyst is used,
The carbon conversion of the gasification reaction of cellulose at 550 ° C. is 5
Only 3%. Here, the carbon conversion is calculated according to the following formula: carbon conversion (%) = (CO amount + CO ₂ amount + CH ₄ amount) / (total C amount in cellulose) × 100 [CO amount in the formula, The units of the amount of CO _{2, the} amount of CH _{4 and the} amount of total C in cellulose are μmol.] The remaining carbon corresponds to tar and coke. Tar formation is a disadvantage of non-catalytic gasification of biomass at low temperatures. Low carbon conversion could also be improved by using the support alone. CeO ₂ , MgO, ZrO ₂
And when TiO ₂ was used, the carbon conversion was almost the same, but when CeO ₂ was used, more CO and H ₂ were produced than other carriers (see FIG. 5). Al ₂ O ₃ and Si
In O ₂ , coke deposition was very serious.

From Table 1 and FIG. 5, it can be seen that the formation of CO and H ₂ is dramatically promoted by the loading of the metal on the support. Among the CeO ₂ metal-supported catalysts, Rh / CeO ₂ showed the most excellent catalytic ability. The effect of the metal on the amount of CO and H ₂ produced in the gasification reaction is as follows: Rh >>Ru> Pt ≒ Pd From these results, in the gasification reaction of cellulose,
CeO ₂ was found to be the best carrier, and the Rh / CeO ₂ catalyst was also an excellent catalyst. As a result, it was found that the carbon component could be converted to gas at a conversion rate of 100%.

The following scheme 1 shows a model diagram of the gasification reaction of cellulose.

Embedded image

CO and H ₂ can be obtained by the route (d) in Scheme 1.
And route (e). Tar is a substance rich in carbon and poor in hydrogen, and is formed by thermal decomposition of the pathway (b) of this reaction. Path (a) and path (c) are combustion reactions. In the gasification reaction of cellulose, when no catalyst was used, the conversion of carbon to gas was low, and the main product was tar. In this case, the gaseous product mainly contains CO ₂ , CO and H ₂ (H ₂
/CO=0.6) is hardly contained (see Table 1).
Therefore, in this case, it is estimated that the route (a) and the route (b) mainly proceed, and it is considered that the generation of the synthesis gas proceeds via the route (d) via the tar.

On the other hand, when CeO ₂ is used, the carbon conversion rate becomes higher, and the production of synthesis gas (particularly, H ₂ ) is promoted. These trends suggest that CeO ₂ promotes pathways (c) and (d).

Further, Rh / CeO_TwoWith a catalyst, charcoal
The conversion rate reaches 100%,_TwoHigh / CO ratio
More syngas was produced. From these results, Rh is
CeO _TwoPromotes pathways (d) and (e) more significantly than
It is suggested that Furthermore, Rh / CeO_TwoUsing a catalyst
If the tar is completely removed,
It is considered that the reaction (e) proceeds more easily.

In the model diagram of the gasification reaction of cellulose using the above catalyst (Scheme 1), it is considered that the catalyst directly acts on the tar reaction. in this case,
Contact between the cellulose and the catalyst surface is very important. Thus, as shown in the upper right (B) of FIG. 1, an experiment using a Rh / CeO ₂ catalyst in the secondary layer was performed to clarify the importance of direct contact (A) between cellulose and the catalyst.
In the case of (B), first, cellulose is supplied to the primary layer, noncatalytic gasification occurs in the primary layer, and the generated gas comes into contact with the secondary layer. Table 1 also shows the results of this experiment. In the reaction using this secondary layer (indirect contact), the production of CH ₄ and CO ₂ increased remarkably, and the production of CO and H ₂ simultaneously decreased. Tar is generated in the primary layer where the non-catalytic reaction proceeds, and the contribution of the combustion reaction in the route (a) and the route (c) increases. Further, the methane generation reaction of CO and H ₂ using the catalyst causes It is believed that CH ₄ is formed. This experiment demonstrates that direct contact of the cellulose with the catalyst promotes the desired reaction. Further, the catalyst of the present invention could be used 20 times without deactivation.

At present, further studies are being made on the life of the catalyst in the gasification reaction using a continuous flow system. The gasification reaction in the method of the present invention is performed using a batch reactor. Further, the method of the present invention can improve the carbon conversion rate and increase the amounts of CO and H ₂ in the synthesis gas, but still generate a large amount of CO ₂ . Therefore, it is necessary to carry out further studies in the future and establish a method capable of performing a reaction using a continuous flow reactor for gasification of biomass and minimizing the generation of CO _2. .

[0033]

According to the method of the present invention, CeO_TwoMetal loading
By using a catalyst, a low temperature of 800 ° C. or less (for example, 5
Cell using air (or oxygen) even at 50 ° C)
It is possible to carry out a gasification reaction of loin. Note that this
Excellent properties include direct contact between cellulose and catalyst,
And the reforming of tar on the catalyst surface
It is thought to be awakened. That is, according to the method of the present invention,
CO and H from cellulose and air (or oxygen) _TwoGo
CO and H_TwoVolume can be increased, and
The remaining tar is CO_TwoAnd on the catalyst surface
No tar is deposited. In the present invention, the reaction is carried out at a low temperature.
Can be used for syngas production from biomass.
Energy efficiency can be dramatically improved.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a gasification reaction system for cellulose using a fluidized bed reactor.

FIG. 2 is a schematic view of a fluidized bed portion in a gasification reaction of cellulose using a fluidized bed reactor.

FIG. 3 is a diagram showing generation of various gases with respect to time in a gasification reaction of cellulose using Rh / CeO ₂ .

FIG. 4 is a diagram showing generation of various gases with respect to time in gasification of cellulose using G-91.

FIG. 5 is a diagram showing the catalytic ability of various catalysts in a gasification reaction of cellulose.

[Description of Signs] 2 ... Reactor 4 ... Feeder 6 ... Catalyst layer 8 ... Quartz tube 10 ... Dispersion plate 12 ... Electric furnace 14 ... Thermocouple 16 ...・ Filter 18 ・ ・ ・ Sampling port 20 ・ ・ ・ Ice bath trap 22 ・ ・ ・ Gas bag

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Asadura Mohamad 3-236-202, Shin-Matsudo, Matsudo, Chiba Prefecture Person Kaoru Fujimoto 6-18-1-1031 Minamioi, Shinagawa-ku, Tokyo 4G069 AA02 AA08 BB04A BB04B BC43A BC43B BC70A BC70B BC71A BC71B BC72A BC72B BC75A BC75B CC40 DA08 EA02Y FA01 FA02 FB14

Claims (6)

[Claims] 1. A catalyst for producing synthesis gas from biomass, wherein rhodium, ruthenium, palladium or platinum is supported as a catalyst metal on the surface of a cerium oxide carrier. 2. The catalyst according to claim 1, wherein the catalyst metal is rhodium. 3. Using the catalyst according to claim 1 or 2,
A method for converting biomass to synthesis gas. 4. The method according to claim 3, wherein the reaction temperature is from 400 ° C. to 1000 ° C. 5. The method according to claim 3 or 4, wherein
A method in which a reaction is performed using a fluidized bed reactor. 6. The method according to claim 3, wherein the catalyst is brought into direct contact with the biomass to carry out the reaction.