Elsevier

Catalysis Communications

Volume 39, 5 September 2013, Pages 106-114
Catalysis Communications

Short Communication
Hydrogen production from wood vinegar of camellia oleifera shell by Ni/M/γ-Al2O3 catalyst

https://doi.org/10.1016/j.catcom.2013.04.024Get rights and content

Highlights

  • Wood vinegar, the upper light liquid of bio-oil, was chosen to produce H2.

  • Ni-Cr/Fe-Al2O3 shows excellent catalytic activity and anti-sintering function.

  • The active sites (metals of Fe and Ni) promote the acetic acid to produce H2.

  • Phenolic compounds took demethylation or demethoxyation reaction to form phenol.

Abstract

Hydrogen production from wood vinegar was investigated by catalytic reforming with Ni/M/γ-Al2O3 (M = Co, Cr, Fe) as the catalysts. The maximal H2 yield rate and concentration were 22.03 mg/g sample and 64.33% respectively. And the selectivity sequence for hydrogen is Fe, Cr, Co. After catalytic reforming, the content of the compounds was decreased from 16% to 6%. Especially, the content of the acetic acid was decreased from 5.599% to 1.859%, while the content of the phenol was increased from 0.998% to 1.904% due to the demethylation or the demethoxyation of the phenolic compounds. The characteristic analysis showed that the metals of Fe and Ni were the active centers. The amount of carbon deposit was decreased from 5.53% to 2.66%. The distribution of carbon was also shifted to the lower temperature area.

Introduction

Recently, the technologies have been explored for bio-oil to produce fuel to alleviate energy crisis and environmental pollution [1]. However, bio-oils are low-quality fuels due to their higher oxygen content that is up to 60% in weight [2]. Other challenges with pyrolysis oils are that they are acidic, have a high water content (25 to 50 wt.%), and constitute an emulsion that will phase-separate when being stored and bio-oil derived transportation fuels require expensive upgrading techniques [3]. At present, it is not suitable to utilize bio-oil as the fuel directly. Therefore, some researchers had separated the pyrolysis oil and used the heavy oil at the bottom of the container (with water content (2–5%)) for the boiler fuel or mixed the heavy oil with diesel for the transportation fuel. However, the light liquid at the upper part of the crude bio-oil container can hardly be used. In this paper, we chose the wood vinegar (component of the upper light oil), as the feedstock for producing hydrogen by catalytic steam reforming with Ni/M/γ-Al2O3 as the catalysts.

Moreover, due to the complexity of pyrolysis oil composition, many researchers choose model compounds such as acetic acid, ethanol, etc. instead of pyrolysis oil for investigating the characteristics of hydrogen production from pyrolysis oil [4], but the physical and chemical properties of pyrolysis oil are quite different from the model compounds. Therefore, we just use the wood vinegar as the feedstock in the study. Moreover, there are some researchers investigating hydrogen production from aqueous fraction of biomass pyrolysis oil by catalytic steam reforming in fluidized bed and the H2 yield rate researches 0.1056 g/g organics, which confirms it is a promising method to produce hydrogen from the pyrolysis oil [5]. Besides, due to the smaller viscosity and the existence of some aromatic compounds, wood vinegar would not tend to be polymerized that results in clogging the feedstock inlet and sticking on the inner surface of the transportation pipeline.

In China, the planting area of camellia oleifera is around 3.5 × 1011 m2 and the annual yield is 5.6 million tons. The shell of camellia oleifera is the by-product of tea oil processing, which could reach the percentage of 50%–60% of the total fresh weight. The yield of wood vinegar (including water) is 30% of the shell dry weight during the pyrolysis process. The resource of the shell of camellia oleifera is rich in China. However, the technology for utilizing the camellia oleifera shell has not been developed yet, and the discarded shell would cause serious pollution to the atmosphere, the water and the ecological environment. It is an urgent task to utilize camellia oleifera shell. Therefore, we chose camellia oleifera shell as the feedstock for pyrolysis.

It was investigated that the nickel-based catalysts could help to realize higher hydrogen yield for steam reforming of both the model compounds and the aqueous fraction of pyrolysis oil. For instance, Vagia et al. [6] reported that calcium aluminates supported nickel and noble metal catalysts had played a positive role on steam reforming of pyrolysis oil components to get hydrogen, moreover, Co, Cr, and Fe are usually used in the catalyst as the active materials. Kaddouri et al. demonstrated that oxides of cobalt supported Al2O3 catalyst had a high catalytic activity for ethanol steam reforming [7]. The Co–P–B catalyst also showed higher efficiency for hydrogen production. The enhanced activity can be attributed to: the large active surface area, the amorphous short range structure, and the synergic effects caused by B and P atoms in the catalyst [8]. Bangala et al. [9] indicated that Cr reduced the encapsulation of nickel by inactive carbon filaments, and by the way of forming an alloy with Ni, geometrically rearranged the Ni crystal plane and altered the electronic properties of the Ni atoms. Xu et al. [10] found that Fe/γ-Al2O3 could fully convert biomass pyrolysis volatile into gaseous products, such as H2, CH4, CO, etc.

Therefore, in this study, we added the active materials of Co, Cr and Fe to the catalyst Ni/γ-Al2O in order to enhance the activity and reduce the carbon deposit in the research.

Section snippets

Wood vinegar feedstock

The pyrolysis oil was produced by pyrolyzing the camellia oleifera shell at the pyrolysis box at 500 °C for 3 h. Wood vinegar is the light liquid at the upper part of the pyrolysis oil container. It appears as a dark brown liquid with a strong pungent smell. The composition of wood vinegar used in the experiment was detected by GC–MS. And the result is shown in Table 1. The main component of wood vinegar is acetic acid, which tends to be catalytically cracked into H2. The phenolic compound is the

The experiments of wood vinegar non-catalytic steam reforming

Initially, the reactor was filled with 50 g of silica sands for non-catalytic tests. The flow rate of feedstock was 2.19 g/min. As soon as the desired reaction temperature was reached, the wood vinegar was introduced into the reactor and the experiment began with nitrogen as the carrier inert gas at a flow rate of 50 cm3/min. As shown in Table 2, due to the reaction, the wood vinegar was converted into CO, H2, CO2, H2O, CH4 and hydrocarbons [12], the main gaseous products from wood vinegar steam

Conclusions

  • (1)

    Wood vinegar was the lighter liquid in the upper part of the crude bio-oil container. It was chosen to produce H2 rich producer gas (including CO, CH4, C2H4, etc.) by catalytic reforming at lower temperature.

  • (2)

    The experiments of wood vinegar catalytic reforming showed that except Co, Fe and Cr could effectively enhance the H2 selectivity of Ni-based catalyst due to the enhancement in dispersion of nickel and the alleviation in carbon deposition. The best result was obtained for Ni/Fe/γ-Al2O3

Acknowledgments

The research work was funded by the Science and Technology Planning Project of Guangdong Province, PR China (2009B050600008 and 2010A030200013).

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