Changes of total organic carbon and kinetics of ultrasonic-assisted coal water slurry electrolysis in NaOH system Xuzhong Gong a, ⁎, Ying Wu a , Zhi Wang a , Mingyong Wang a , Zhancheng Guo a,b a National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China b State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, China abstract article info Article history: Received 25 June 2013 Received in revised form 17 September 2013 Accepted 26 October 2013 Available online xxxx Keywords: Electrolysis Kinetics CWS TOC Ultrasonic Coal water slurry (CWS) electrolysis not only improved efficiency of water electrolysis for hydrogen, but also removed sulfur and mineral matters in coal. Fortunately, it may be a potential method which obtained directly organic compounds from coal. However, both the stability and mass transfer of coal particle were very poor during CWS electrolysis. As we known, ultrasonic wave can improve the stability for CWS and mass transfer strength of coal particle. In this paper, ultrasonic-assisted CWS electrolysis was carried out in NaOH solution. Results showed that the total organic carbon (TOC) concentration for CWS electrolysis increased. According to the results from kinetics study, it was not difficult to find that the chemical reaction is the controlling-step for CWS electrolysis. And the apparent activation energy (AAE) changed from 28.37 to 27.61 kJ mol -1 with ultrasonic addition. The slight change in the AAE suggested that the ultrasonic improved the mass transfer of coal particle only in electrolyte, and did not change reaction path. Additionally, TOC concentration decreased with the increase in mineral matter content, indicating that the mineral matters inhibited the organic structure electrolysis. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Coal mild oxidation can not only obtain essential information about structure, but also produce organic chemicals with high value [1,2]. H 2 O 2 [3–5], oxidative acid[6–9], and alkaline [10–12] were often used as oxidizing media since they could convert organic structure of coal into the valuable molecules under mild conditions, such as alcohols, acids, phenols, and ketones[13]. A number of oxidizing media were produced from water electrolysis on anode, including •OH 2 , and •OH [14], which could also degrade the organic chemicals (phenols) in waste water [15]. As a result, the chemical oxygen demand of waste water was reduced [16,17]. In 1979, Coughlin R.W. reported that CWS electrolysis resulted in the increase in efficiency for hydrogen production firstly [18]. Subsequently, many researches indicated that the sulfur and the mineral matters in coal were removed from electrolysis [19,20]. In general, the two reactions were involved in CWS electrolysis [21,22]: Atanode : CðsÞþ 2H 2 OðlÞ→CO 2 ðgÞþ 4H þ ðaqÞþ 4e - ð1Þ Atcathode : 2H þ ðaqÞþ 2e - →H 2 ðgÞ: ð2Þ In nature, CWS electrolysis on anode was also a way of the coal mild oxidation. CWS electrolysis on anode not only improved the efficiency of water electrolysis for hydrogen gas [18], but also purified coal [19]. Broadly, it may be a potential method to obtain organic compounds from coal directly. Due to the solid carbon skeleton structure, coal could not be oxidized completely from electrolysis, while forming a cer- tain number of organics, such as water soluble organic compounds (WSOCs) and water insoluble organic compounds (WIOCs). The organic chemicals were therefore obtained through separation and purification [23–26]. At present, H 2 O 2 was used as an oxidation medium owing to •OH from H 2 O 2 decomposition [27–30], so as to obtain WSOCs from biomass or coal oxidation under mild conditions. Moreover, metal ions (Fe 3+ /Fe 2+ ) in the oxidation–redox process catalyzed the H 2 O 2 decom- position [31]. For a given amount of H 2 O 2 , •OH concentration generated from H 2 O 2 decomposition decreased with the increase of reaction time, resulting in a decrease in the driving force of coal oxidation. By contrast, water electrolysis could continuously produce •OH, thus the overall oxidation ability would not reduce with time. It's worth mentioning that the concentration of the oxidizing medium was controlled effective- ly by electrolysis conditions, such as time, temperature, electrode materials, potential, electrolyte system, and so on. Thus the electrolysis could be easily adjustable [32]. However, both the stability of CWS and mass transfer of coal particle were very poor during CWS electrolysis. As we known, the ultrasonic cavitation could not only strengthen the mass transfer in liquid–solid, but also consolidate the stability of CWS [34,35]. In this paper, effects Fuel Processing Technology 119 (2014) 166–172 ⁎ Corresponding author at: No.1 ZhongGuanCun North Second Street, Beijing 100190, PR China. Tel./fax: +86 10 82544926/4818. E-mail address: xzgong@mail.ipe.ac.cn (X. Gong). 0378-3820/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fuproc.2013.10.029 Contents lists available at ScienceDirect Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc