3.4 Lifetime of H2SO4 with DESs
Based on the optimal reaction results at 281.2 K, ChCl-Pho (1:2) and ChCl-TsOH (1:1) were chosen to probe the effect of DESs on the recycling capability for the H2SO4. The recycling run of H2SO4/ChCl-Pho (1:2), H2SO4/ChCl-TsOH (1:1) and pure H2SO4 are shown in Figure 5(a), Figure 5(b) and Figure S2, respectively. From Figure 5(a), the RON and C8 components slightly increase initially and then decrease slowly. The C9+ components increase with the increased recycle times. The first 3 runs can be defined as catalytic activity strengthening stage. The RON and the C8 contents increase from 93.62 and 63.83% to 94.50 and 68.07%, respectively. In the initial strengthening stage, the acidity of catalyst is still high to promote the main reactions. The trace amount of side reactions products of H2O, esters and acid soluble oil (ASO) has a positive effect on C4 alkylation, which is the reason why the quality of alkylate is improved in first 3 times42. Nevertheless, the 4th-11th recycles step into the gradual deactivation stage. The C8 contents and RON decrease from 66.00% and 93.78 to 51.23% and 90.90, respectively. In this stage, the notorious side reactions products of H2O, esters and ASO gradually accumulate with the increase of recycle times and leads to the gradual decrease in the acid strength and the quality of the alkylate. After 11thruns, the catalyst tends to be inactive and the C9+ components dramatically increase from 36.77% to 53.55%.
The lifetime performance of H2SO4catalyst with ChCl-TsOH (1:1) additives is similar as that with ChCl-Pho (1:2) as additives. The first 2 recycle times is the stage of catalytic activity strengthening. After the 10 runs, the activity of catalyst dramatically decreases with RON down to 84.90 at 16 runs. The difference is the lifetime test with ChCl-TsOH (1:1) additives has a relatively stable high catalytic activity stage from 3th to 10th. In high catalytic activity stage, the performance of the catalyst remains stable, the RON and the C8 contents is still above 93.0 and 63.00%, respectively. In comparison to lifetime test of the pure H2SO4, however, the addition of ChCl-Pho (1:2) and ChCl-TsOH (1:1) do not improve the catalytic lifetime of H2SO4, although they show the effective catalytic performance,