Potassium-catalyzed steam gasification of petroleum coke for H2 production: Reactivity, selectivity and gas release
Introduction
With the increasing demand of petroleum and the development of deep processing technology of crude oil, the output of petroleum coke as a by-product from petroleum refinery has increased rapidly [1], [2], [3]. Thus, how to utilize petroleum coke (especially high-sulfur petroleum coke) in a reasonable, efficient and clean way becomes a subject worthy of being studied in depth. Due to its high calorific value and carbon content, petroleum coke can be used as feedstocks of gasifiers to produce syngases [4]. However, our previous studies [5], [6] found that the gasification activity of petroleum coke was much lower than that of coals or coal chars, which greatly restricted its applicability for feedstocks of gasifiers. Accordingly, how to improve its gasification activity becomes an urgent problem. It is well known that the gasification activity of carbon in carbonaceous materials (such as coals and coal chars) can be greatly enhanced by various alkali and alkaline earth metal compounds [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. Also, a rich array of publications has reported the enhanced production of H2 from the steam gasification of carbon catalyzed by potassium compounds [19], [20], [21], [22]. Consequently, the most cost-effective utilization of petroleum coke is to produce hydrogen, which is primarily used as synthesis and refining gases, from its catalytic steam gasification.
The catalytic gasification of coals and coal chars has long received the bulk of research attention because of its kinetic advantages of low-temperature operation and high efficient throughput [8], [9], [10], [19], [20], [21], [22], [23], [24], [25], [26]. Some interest has also been focused on improving hydrogen production from steam gasification catalyzed by various metal catalysts including alkali [14], [21], lime [27], iron-based compounds [28], and calcium–iron composites [22]. However, there are few reports on the H2 production from catalytic steam gasification of petroleum coke. Besides, the studies on the catalytic selectivity are surprisingly scarce. The work by Wigmans et al. [29] was an early investigation into the reaction selectivity. Recently, Wang et al. [20] and Sharma et al. [12] also discussed qualitatively the selectivity towards the formation of CO and CO2 in the catalytic steam gasification process. In this paper, a quantitative calculation method for the gasification selectivity towards CO and CO2 is proposed, and the potassium-catalyzed steam gasification (gasification reactivity, gasification selectivity and gas release) of petroleum coke for H2 production is further discussed.
Section snippets
Raw material and sample preparation
In this study, a petroleum coke from Jinshan Petrochemical Co. Ltd. of China was used as the raw materials. The proximate analysis showed that it contained 11.35% volatile matters, 0.31% ashes and 88.34% fixed carbons, on dry basis. The ultimate analysis showed that it consisted of 90.06% C, 3.53% H, 0.28% N, 4.34% S and 1.79% O (by difference), on dry basis. Potassium carbonate (K2CO3) was used as the catalyst for the steam gasification of petroleum coke.
The preparations for the samples of the
Theory on gasification selectivity towards the formation of CO and CO2
The main reactions occurring in the non-catalytic or catalytic steam gasification of carbon can be represented by the two following reactions:C + H20 → CO + H2, ΔH0 = 118.9 kJ/molCO + H20 → CO2 + H2, ΔH0 = −45.2 kJ/mol
In the case of catalytic gasification, the two reactions could be accelerated by active intermediates from metal catalyst. Presently, many literatures have reported some different viewpoints on active intermediates. For example, the proposed active intermediates for potassium catalyst includes
Gasification reactivity
Fig. 4 shows the gasification carbon conversion as a function of gasification time for the non-catalytic and catalytic steam gasification of petroleum coke at different temperatures. It could be seen that as the gasification temperature increased to 1000 °C, the non-catalytic gasification rate of petroleum coke was still very slow, suggesting that the industrial non-catalytic gasification of petroleum coke generally needed a temperature of at least higher than 1000 °C. In contrast, the catalytic
Conclusions
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In the catalytic steam gasification of petroleum coke, the catalyst could present some excellent performances: effectively lowering the gasification temperature, greatly enhancing the gasification reactivity of petroleum coke and the production of H2 (55.5–60.4%) with no virtual CH4 (below 0.1%), and effectively promoting the carbon–water reaction, the water–gas shift reaction and the steam reforming of methane. Petroleum coke could be feasibly used as raw materials for the catalytic steam
Acknowledgements
The work was supported by the Program for Changjiang Scholars and the Innovative Research Team in University (IRT0620). The authors thank the National Basic Research Program of China (2010CB227003-5), the State Natural Science Foundation of China (20876050) and Opening Fund of State Key Laboratory of Coal Combustion (fsklcc0911) for financial support.
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