(694d) Study of [Rmim][Al2Cl7] Using a Low AlCl3/[Rmim]Cl Molar Ratio As Electrolytes in Aluminum Electrolysis at 60 oc

Study
of [Rmim][Al₂Cl₇] using a low AlCl₃/[Rmim]Cl molar ratio as electrolytes in aluminum
electrolysis at 60 ^oC

WU Junshi¹, HAO Wenbin^2*,
MI Yongli¹

(¹Department of Chemical and Biological
Engineering, Hong Kong University of Science and Technology,
Clear Water Bay, Kowloon, Hong Kong;

²Department of Chemical Engineering, School
of Chemical Engineering and Technology, Xi'an Jiaotong
University, Xi¡¯an 710048, Shaanxi, China)

Hall-H¨¦roult
electrolytic aluminum process, as an industrial process, suffers high
energy-consuming and pollution problems due to its high operating temperature
(over 900 ^oC) and emissions of toxic and
harmful gases, such as CO and HF. Ionic liquids (ILs) could be feasible to solve
the abovementioned problems, because the electrolytic aluminum process using
ILs electrolytes can realize the electrolytic aluminum reactions at near room
temperature. Here, we report a study of electrolytic aluminum process using [Rmim][Al₂Cl₇] ILs electrolytes at 60 ^oC. The characteristics influences on the
morphology of electrolytic aluminum deposits were explored. Two kinds of
chloroaluminate ILs ([Emim][Al₂Cl₇]
and [Bmim][Al₂Cl₇]) were
prepared with a low AlCl₃/[Rmim]Cl molar
ratio (1.3:1) and used as the electrolytes for electrolytic aluminum reactions directly.
A three-electrode method was applied in the electrochemical characterization of
electrolytic aluminum process and copper foils were used to deposit aluminum.
Then, SEM was implemented to investigate the morphology of aluminum deposits.
It indicated that different side chain structures of ILs resulted in
variance of electrolytic
performance. As shown in Figure
1, the average grain size of deposited aluminium
crystallites in [Emim][Al₂Cl₇]
was larger than that in [Bmim][Al₂Cl₇].
Besides, it was proved that the aluminum deposition could occurred at a very
low AlCl₃/[Rmim]Cl molar ratio (1.3:1),
though the electrolytic performance might be degraded.

Key Words: Ionic Liquids (ILs); Low
Molar Ratio; Aluminum Electrolysis

Figure 1. Morphology of aluminium deposits in SEM images:
(a) pure copper base; (b) [Emim][Al₂Cl₇];
(c) [Bmim][Al₂Cl₇]