CN106807387B - A kind of bifunctional catalyst and preparation method thereof for absorption enhancement hydrogen production by bio-oil steam reforming - Google Patents

Abstract

The bifunctional catalyst and preparation method thereof that the invention discloses a kind of for absorption enhancement hydrogen production by bio-oil steam reforming, the active component of the catalyst are Ni, auxiliary agent Co, CeO₂、MgO、K₂At least one of O, carrier ZrO₂Or Al₂O₃With the compound of CaO；Active component accounts for 5wt%~20wt% in the catalyst, auxiliary agent accounts for 1wt~15wt%, CaO accounts for 10wt%~60wt%.The preparation method of catalyst of the present invention is simple, compared with typical catalyst, the bifunctional catalyst is used for the steam reforming reaction of bio oil, the characteristics of promoting reaction balanced sequence using its absorption enhancement, the hydrogen that highest purity is greater than 95% can not only be obtained, the separation costs of High Purity Hydrogen are enormously simplified, while bio oil conversion ratio and hydrogen manufacturing yield can also be improved, there is broader prospects for commercial application.

Description

A bifunctional catalyst for absorbing and strengthening bio-oil steam reforming to produce hydrogen and the its preparation method

technical field

The invention belongs to the technical field of hydrogen production from bio-oil, and in particular relates to an absorption-enhanced bio-oil steam reforming bi-functional catalyst for hydrogen production and a preparation method thereof.

Background technique

As an efficient and clean secondary energy, hydrogen has attracted more and more attention and has been widely used in many industries. At present, most of the hydrogen production comes from fossil fuels, but the environmental pollution caused by the utilization of fossil fuels is almost irreversible. In addition, the current hydrogen production technology from water electrolysis is relatively mature, but the cost of hydrogen production is quite high, and the current electricity consumption per cubic meter of hydrogen production is 4.5 to 5.5 kW. Therefore, the use of renewable energy such as biomass to produce hydrogen has special significance for alleviating the increasingly tense energy supply and demand problems and environmental pollution problems, and is one of the most attractive and promising approaches.

At present, the use of biomass for hydrogen production includes biomass gasification for hydrogen production, biomass rapid pyrolysis liquefaction for indirect hydrogen production, biomass supercritical conversion for hydrogen production, microbial hydrogen production, and bio-oil steam reforming for hydrogen production. Among them, steam reforming of bio-oil for hydrogen production is considered to be one of the most economical routes to realize large-scale production of hydrogen from biomass, and its application prospects are very broad. However, the theoretical research and technological development of bio-oil steam reforming hydrogen production process is still in its infancy, especially the research on bio-oil steam reforming hydrogen production catalysts still has a lot of space for exploration.

At present, nickel-based catalysts and precious metal catalysts are the main catalysts suitable for hydrogen production by steam reforming of bio-oil. It can be said that they have good results in terms of hydrogen yield and hydrogen selectivity of bio-oil steam reforming. The highest hydrogen production yield is about 80%. However, due to the limitation of the thermodynamic equilibrium of the reforming reaction, it is very difficult to further improve the hydrogen yield. In particular, at the same time of hydrogen production, about 20% or more of CO ₂ is also produced. If an absorbent is used to remove CO ₂ in situ during the reaction, it can not only break the thermodynamic equilibrium, but also greatly improve the purity of hydrogen and simplify the subsequent separation process. It is a feasible method to directly physically mix absorbents such as calcium oxide, dolomite, etc. and reforming catalysts for the absorption-enhanced steam reforming of bio-oil for hydrogen production, but physical mixing is difficult to achieve uniformity at the microscopic scale, which is not conducive to the Mass and heat transfer of the reaction. In addition, the absorption-enhanced steam reforming process for hydrogen production requires continuous high-temperature calcination-absorption regeneration operations on the absorbent to obtain a stable high-purity hydrogen stream. The physical mixing of absorbent and catalyst is not conducive to the continuous absorbent regeneration process. This is because: (1) ordinary absorbents are easily sintered during high-temperature calcination-absorption regeneration operations, resulting in a rapid decline in their absorption performance; (2) the particle sizes of absorbents and catalysts are similar, so separation is difficult, and after repeated cycles Absorbents are not easy to update and replenish in a timely manner. In view of the above situation, the development of bifunctional catalysts with high activity and good stability, combining absorbent and reforming catalyst, is used to absorb and strengthen the hydrogen production process of bio-oil steam reforming, and improve the cycle stability of the reaction, which has important applications It can convert bio-oil into high-purity hydrogen in one step and obtain a stable hydrogen flow.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a bifunctional catalyst with high reaction activity, strong anti-coking ability and good stability, which is used for absorbing and strengthening the steam reforming of bio-oil for hydrogen production, and provides a preparation method for the catalyst.

The technical scheme adopted to solve the above-mentioned technical problems is: the active component of the catalyst is Ni, the auxiliary agent is at least one of Co, CeO ₂ , MgO and K ₂ O, and the carrier is ZrO ₂ or Al ₂ O ₃ and CaO. A composite; in the catalyst, the active components account for 5wt% to 20wt%, the auxiliary agent accounts for 1wt% to 15wt%, and the CaO accounts for 10wt% to 60wt%.

The above-mentioned auxiliary agent is any one of Co, CeO ₂ , MgO and K ₂ O.

3. The bifunctional catalyst for absorption-enhanced steam reforming of bio-oil for hydrogen production according to claim 1, wherein the compound of ZrO ₂ and CaO has an intermediate species CaZrO ₃ .

4. The bifunctional catalyst for hydrogen production by absorption-enhanced steam reforming of bio-oil according to claim 1, characterized in that: the compound of Al ₂ O ₃ and CaO has intermediate species Ca ₅ Al ₆ O ₁₄ .

5. The bifunctional catalyst for hydrogen production by absorption and enhanced steam reforming of bio-oil according to any one of claims 1 to 4, characterized in that: the active components in the catalyst account for 10wt% to 20wt%, the auxiliary The agent accounts for 5wt% to 10wt%, and the CaO accounts for 30wt% to 60wt%.

6. The bifunctional catalyst for absorbing and strengthening bio-oil steam reforming for hydrogen production according to claim 1, characterized in that: according to the mass percentage composition of the catalyst, soluble zirconium salt or aluminum nitrate or aluminum isopropoxide and cobalt The soluble nitrate of the agent is dissolved in deionized water, adding citric acid aqueous solution, reacting at room temperature for 2-4 hours, then adding calcium oxalate or soluble calcium salt aqueous solution, and reacting at 60-80 ° C until a gel is formed. After drying at 100-120 °C, calcining at 600-750 °C for 4-12 hours to obtain composite oxides; using the equal volume impregnation method, the composite oxides are immersed in a soluble nickel salt aqueous solution, and subjected to aging, drying and roasting. , hydrogen reduction, to obtain a bifunctional catalyst for absorbing and strengthening bio-oil steam reforming to produce hydrogen.

7. The bifunctional catalyst for absorbing and enhancing the steam reforming of bio-oil for hydrogen production according to claim 6, wherein the amount of the citric acid added is the molar amount of soluble zirconium salt or aluminum nitrate or aluminum isopropoxide 1 to 5 times.

8. The bifunctional catalyst for absorbing and strengthening bio-oil steam reforming for hydrogen production according to claim 6, characterized in that: after drying the gel at 100-120°C, calcining at 650°C for 6 hours to obtain a composite oxide.

Compared with the existing catalyst, the present invention has the following beneficial effects:

1. The present invention directly combines the absorbent and the reforming catalyst to prepare a bifunctional catalyst, which is used to absorb and strengthen the hydrogen production process of bio-oil steam reforming, which is beneficial to the mass transfer and heat transfer of the reaction, and can obtain a purity higher than More than 95% hydrogen.

2. The catalyst of the invention has strong anti-carbon deposition ability, good stability, the conversion rate of bio-oil reaches more than 90%, and the yield of hydrogen production reaches more than 85%. Hydrogen production.

Description of drawings

FIG. 1 is the XRD pattern of the 15wt% Ni/CeO ₂ -ZrO ₂ -CaO bifunctional catalyst prepared in Example 1. FIG.

Figure 2 is a graph showing the results of the 15wt% Ni/CeO ₂ -ZrO ₂ -CaO bifunctional catalyst prepared in Example 1 used for absorption-enhanced steam reforming of bio-oil at 550°C for hydrogen production over time.

Detailed ways

The present invention is further described in detail below with reference to the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

Example 1

Preparation of 15wt% Ni/CeO ₂ -ZrO ₂ -CaO Bifunctional Catalyst

2.4 g (7.5 mmol) ZrOCl ₂ .8H ₂ O and 3.25 g (7.5 mmol) Ce(NO ₃ ) ₃ .6H ₂ O were added to 200 mL of deionized water, and 100 mL containing 6 g (31.2 mmol) was added dropwise with stirring The aqueous solution of citric acid was added dropwise and stirred at room temperature for 2 hours; then 200 mL of aqueous solution containing 4.8 g (37.5 mmol) of calcium oxalate was added dropwise, and the reaction was carried out at 80 ° C after the dropwise addition until a gel was formed; The glue was dried at 110°C and then calcined in a muffle furnace at 650°C for 4 hours to obtain a composite oxide. The obtained composite oxide was immersed in an aqueous solution containing 3.3 g of nickel nitrate by an equal volume dipping method, aged at room temperature for 24 hours, dried at 110 °C for 6 hours, calcined at 600 °C for 6 hours, and then reduced at 400 °C for 4 hours in a hydrogen atmosphere to obtain Bifunctional catalyst 15wt% Ni/CeO ₂ -ZrO ₂ -CaO for absorption-enhanced steam reforming of bio-oil for hydrogen production. In the catalyst, calcium mainly exists in the form of CaO, and its content accounts for about 42wt%. In addition to forming a cerium zirconium solid solution (CZO) with CeO ₂ , ZrO ₂ also forms an intermediate species CaZrO ₃ with CaO (see Figure 1).

Comparative Example 1

2.4g ZrOCl ₂ ·8H ₂ O and 3.25g Ce(NO ₃ ) ₃ ·6H ₂ O were added to 200mL deionized water, and 100mL aqueous solution containing 6g citric acid was added dropwise under stirring conditions. The reaction was carried out at low temperature until a gel was formed; the gel was dried at 110° C. and then calcined in a muffle furnace at 650° C. for 4 hours to obtain a composite oxide. The obtained composite oxide was immersed in an aqueous solution containing 1.66 g of nickel nitrate by an equal volume impregnation method, aged at room temperature for 24 hours, dried at 110 °C for 6 hours, calcined at 600 °C for 6 hours, and then reduced at 400 °C for 4 hours in a hydrogen atmosphere to obtain Ni /CeO ₂ -ZrO ₂ catalyst. The prepared Ni/CeO ₂ -ZrO ₂ catalyst was directly used for hydrogen production by steam reforming of bio-oil.

Comparative Example 2

2.4g ZrOCl ₂ ·8H ₂ O and 3.25g Ce(NO ₃ ) ₃ ·6H ₂ O were added to 200mL deionized water, and 100mL aqueous solution containing 6g citric acid was added dropwise under stirring conditions. The reaction was carried out at low temperature until a gel was formed; the gel was dried at 110° C. and then calcined in a muffle furnace at 650° C. for 4 hours to obtain a composite oxide. The obtained composite oxide was immersed in an aqueous solution containing 1.66 g of nickel nitrate by an equal volume impregnation method, aged at room temperature for 24 hours, dried at 110 °C for 6 hours, calcined at 600 °C for 6 hours, and then reduced at 400 °C for 4 hours in a hydrogen atmosphere to obtain Ni /CeO ₂ -ZrO ₂ catalyst. 4.8 g of calcium oxalate was calcined at 650° C. for 6 hours to obtain a CaO absorbent. The prepared Ni/CeO ₂ -ZrO ₂ catalyst and CaO absorbent are mixed uniformly in a physical mixing manner, and used as a mixed catalyst for absorbing and strengthening bio-oil steam reforming to produce hydrogen.

Example 2

Preparation of 20wt% Ni/MgO-ZrO ₂ -CaO Bifunctional Catalyst

2.4 g (7.5 mmol) ZrOCl ₂ ·8H ₂ O and 1.2 g (8 mmol) Mg(NO ₃ ) ₃ were added to 200 mL of deionized water, and 100 mL of an aqueous solution containing 6 g (31.2 mmol) of citric acid was added dropwise with stirring, After the dropwise addition, the reaction was stirred at room temperature for 2 hours; 200 mL of an aqueous solution containing 4.6 g (28 mmol) of calcium nitrate was added dropwise, and the reaction was carried out at 80 °C after the dropwise addition until a gel was formed; the gel was dried at 110 °C The composite oxide was then calcined at 650° C. for 4 hours in a muffle furnace. The obtained composite oxide was immersed in an aqueous solution containing 2.8 g of nickel nitrate by an equal volume impregnation method, aged at room temperature for 24 hours, dried at 110 °C for 6 hours, calcined at 600 °C for 6 hours, and then reduced at 400 °C for 4 hours in a hydrogen atmosphere to obtain 20wt% Ni/MgO-ZrO ₂ -CaO bifunctional catalyst for hydrogen production by absorption and enhanced steam reforming of bio-oil, in which MgO accounts for 10wt%, calcium mainly exists in the form of CaO, and some CaO forms with ZrO ₂ The intermediate species is CaZrO ₃ , in which the CaO content accounts for about 46.5wt%.

Example 3

Preparation of 15wt% Ni/Co-Al ₂ O ₃ -CaO Bifunctional Catalyst

1.5 g (7.3 mmol) of aluminum isopropoxide and 0.58 g (2 mmol) of Co(NO ₃ ) ₂ ·6H ₂ O were added to 200 mL of deionized water, and 80 mL of a solution containing 3 g (15.6 mmol) of citric acid was added dropwise with stirring. After the dropwise addition, the reaction was stirred at room temperature for 2 hours; then 250 mL of an aqueous solution containing 7.2 g (56.25 mmol) of calcium oxalate was added dropwise. After drying at ℃, it was placed in a muffle furnace and calcined at 650 ℃ for 4 hours to obtain a composite oxide. The obtained composite oxide was immersed in an aqueous solution containing 3.2 g of nickel nitrate by an equal volume impregnation method, aged at room temperature for 24 hours, dried at 110°C, calcined at 600°C for 6 hours, and then reduced at 400°C for 4 hours in a hydrogen atmosphere to obtain 15wt% Ni/Co-Al ₂ O ₃ -CaO as a bifunctional catalyst for hydrogen production by absorption and enhanced steam reforming of bio-oil, in which Co accounts for 2.5wt%, calcium mainly exists in the form of CaO, and some CaO and Al ₂ O ₃ forms an intermediate species Ca ₅ Al ₆ O ₁₄ , in which the CaO content accounts for about 60wt%.

Example 4

Preparation of 10wt% Ni/K ₂ O-ZrO ₂ -CaO Bifunctional Catalyst

3.6 g (11.25 mmol) ZrOCl ₂ ·8H ₂ O and 0.2 g (2 mmol) K ₂ (NO ₃ ) ₃ were added to 200 mL of deionized water, and 100 mL of an aqueous solution containing 4 g (20.8 mmol) of citric acid was added dropwise with stirring After the dropwise addition, the reaction was stirred at room temperature for 2 hours; 200 mL of an aqueous solution containing 6.9 g (42 mmol) of calcium nitrate was added dropwise, and the reaction was carried out at 80 °C after the dropwise addition until a gel was formed; the gel was heated at 110 °C After drying, it was calcined in a muffle furnace at 650° C. for 4 hours to obtain a composite oxide. The obtained composite oxide was immersed in an aqueous solution containing 2 g of nickel nitrate by an equal volume impregnation method, aged at room temperature for 24 hours, dried at 110 °C for 6 hours, calcined at 600 °C for 6 hours, and then reduced at 400 °C for 4 hours in a hydrogen atmosphere to obtain The bifunctional catalyst for hydrogen production from steam reforming of bio-oil enhanced by absorption is 10wt% Ni/K ₂ O-ZrO ₂ -CaO, in which K ₂ O accounts for 3wt%, calcium mainly exists in the form of CaO, and some CaO and ZrO ₂ forms an intermediate species CaZrO ₃ , in which the CaO content is about 55 wt%.

In order to prove the beneficial effects of the present invention, the inventors used the bifunctional catalysts prepared in the above examples 1 to 4 to absorb and strengthen the hydrogen production reaction of bio-oil steam reforming respectively, and the catalyst prepared in the comparative example 1 was used for the traditional bio-oil water. Steam reforming hydrogen production reaction. The specific experiment is as follows: take 4.0g of the bifunctional catalyst or the catalyst prepared in Comparative Example 1 and put it into a quartz tube with a diameter of 12mm, heat it up to 400°C under _N2 atmosphere, first heat it for half an hour, turn off nitrogen, and then introduce hydrogen , reduced at 400 ° C for 2 hours, turned off hydrogen, and introduced a rice husk bio-oil aqueous solution with a flow rate of 0.05 mL/min and preheated to 200 ° C, the water-oil molar ratio was 8:1, and the reaction temperature of the catalyst bed was controlled At 500 ~ 650 ℃. The product after the atmospheric pressure reaction was analyzed online in real time by gas chromatography, and the results are shown in Figure 2 and Table 1. The dry gas composition of the product was _H2 , CO, _CO2 and _CH4 .

The concentration of hydrogen in the dry gas component is expressed as:

The yield of hydrogen is:

Table 1 Hydrogen yield and hydrogen concentration> 90% maintenance time of the hydrogen production reaction of the bio-oil steam reforming with enhanced absorption of the catalyst of the present invention

catalyst temperature(℃) hydrogen yield Duration of hydrogen concentration > 90% (min) Example 1 550 85% 18 Example 2 600 86% 25 Example 3 500 70% 35 Example 4 650 85% 30 Comparative Example 1 550 72% 0, the hydrogen concentration is stable at 68%

It can be seen from Figure 2 that the process is typically divided into three stages: in the first stage at the beginning of the reaction, due to the absorption of _CO2 by CaO, the reaction product is mainly hydrogen, and its concentration reaches more than 95%, _CO2 The concentration was maintained at a very low level and the duration of this phase was maintained for 18 minutes. After that, with the progress of the reaction, the absorption reaction gradually slowed down, the concentration of hydrogen decreased, and below 90%, the concentration of _CO2 increased. In the third stage, the absorption of the absorbent is saturated, and the concentration of hydrogen is maintained at about 70%. It can be seen from Table 1 that the bifunctional catalyst prepared by the present invention is used to absorb and strengthen the hydrogen production reaction of bio-oil steam reforming, and its hydrogen yield can reach about 86% at the highest, and high-purity hydrogen can be obtained during the reaction process, and gas products can be obtained. The duration of the medium hydrogen concentration > 90% is longer, which is far superior to the traditional process of hydrogen production by steam reforming of bio-oil.

In order to further prove the beneficial effects of the present invention, the inventors used the bifunctional catalysts prepared in Examples 1 to 4 and the mixed catalyst prepared in Comparative Example 2 for 10 cycles of absorbing and strengthening the hydrogen production reaction of bio-oil steam reforming. The experimental method is as follows: take 4.0g of bifunctional catalyst or mixed catalyst into a quartz tube with a diameter of 12mm, heat it up to 400°C under _N2 atmosphere, first heat it for half an hour, turn off nitrogen, and then pass in hydrogen, at 400°C Reduction was performed for 2 hours, hydrogen was turned off, and an aqueous solution of rice husk bio-oil with a flow rate of 0.05 mL/min and preheated to 200 °C was introduced, the water-oil molar ratio was 8:1, and the reaction temperature of the catalyst bed was controlled at 500-650 °C. °C. The reacted products were analyzed online in real time by gas chromatography. The feed was stopped after monitoring that the concentration of hydrogen in the outlet gas was less than 90%. The temperature was raised to 750°C to regenerate the absorption capacity of the material in preparation for obtaining high-purity hydrogen again. When it is detected online that no CO ₂ is released in the outlet gas, the temperature is lowered to 500-650 °C, and the rice husk bio-oil aqueous solution with a flow rate of 0.05 mL/min and preheated to 200 °C is introduced again to start the second cycle. This was repeated 10 times to evaluate the stability of the catalyst. The results are shown in Table 2.

Table 2 The time that the catalyst is continuously circulated for 10 times with a hydrogen concentration > 90%

It can be seen from Table 2 that the bifunctional catalyst prepared by the present invention has very excellent cyclic reaction performance for the reaction of absorbing and strengthening bio-oil steam reforming to produce hydrogen, with good repeatability and stable absorption performance. Obtaining high-purity hydrogen for a long time simplifies the subsequent separation process, reduces the production cost of hydrogen production, and has good application prospects.

Claims (6)

1. a kind of bifunctional catalyst for absorption enhancement hydrogen production by bio-oil steam reforming, it is characterised in that: the catalyst Active component be Ni, auxiliary agent Co, CeO₂、MgO、K₂At least one of O, carrier ZrO₂Or Al₂O₃With the compound of CaO, Wherein ZrO₂There are intermediate species CaZrO with the compound of CaO₃, Al₂O₃There are intermediate species Ca with the compound of CaO₅Al₆O₁₄； Active component accounts for wt % of 5 wt%~20 in the catalyst, auxiliary agent accounts for wt % of 1 wt~15, CaO accounts for 10 wt of wt %~60 %.

2. the bifunctional catalyst according to claim 1 for absorption enhancement hydrogen production by bio-oil steam reforming, special Sign is: the auxiliary agent is Co, CeO₂、MgO、K₂O any one.

3. the bifunctional catalyst according to claim 1 or 2 for absorption enhancement hydrogen production by bio-oil steam reforming, Be characterized in that: active component accounts for wt % of 10 wt%~20 in the catalyst, auxiliary agent accounts for wt % of 5 wt~10, CaO accounts for 30 wt The wt of %~60 %.

4. a kind of preparation of the bifunctional catalyst described in claim 1 for absorption enhancement hydrogen production by bio-oil steam reforming Method, it is characterised in that: according to the mass percentage composition of catalyst, by soluble zirconates or aluminum nitrate or aluminium isopropoxide with help The soluble nitrate of agent is dissolved in deionized water, and aqueous citric acid solution is added, and reacts at room temperature 2~4 hours, oxalic acid is then added Calcium or solubility calcium saline solution, react at 60~80 DEG C, until forming gel, the gel is dry at 100~120 DEG C Afterwards, it is roasted 4~12 hours in 600~750 DEG C, obtains composite oxides；Using equi-volume impregnating, composite oxides are impregnated In soluble nickel saline solution, through aging, drying, roasting, hydrogen reducing, obtain for absorption enhancement bio-oil steam weight The bifunctional catalyst of whole hydrogen manufacturing.

5. the preparation of the bifunctional catalyst according to claim 4 for absorption enhancement hydrogen production by bio-oil steam reforming Method, it is characterised in that: the additional amount of the citric acid is the 1~5 of soluble zirconates or aluminum nitrate or aluminium isopropoxide mole Times.

6. the preparation of the bifunctional catalyst according to claim 4 for absorption enhancement hydrogen production by bio-oil steam reforming Method, it is characterised in that: gel after drying, is roasted 6 hours in 650 DEG C at 100~120 DEG C, obtains composite oxides.