3.2 | HCl Catalyst Results
The selectivity and conversion values obtained from semi-batch experiments in various feed modes using 5% HCl catalyst are given in Table 2. In general, conversion and selectivity are lower at 5% acid concentration. All selectivity values are below 91% from 0.81 and the average value is around 0.87±0.028. It is understood that the average conversion is around 26% ±0.035%. The selectivity tends to remain almost constant and conversions increasing are being observed over time.
An increase of approximately 15% in conversion between each hour, regardless of acid concentration is noticeable (Table 2). When the acid concentration increases from 5% to 15%, conversions increase by more than 60%. When the acid concentration increases from 15% to 25%, it is encountered that the increase in conversion is about 20%. Selectivity values between the modes do not show very obvious relationships because the acetone concentration in the medium varies with the feeding modes, and many series and parallel reactions in the reaction medium depend on this acetone concentra-tion. When it is looked at the data, which 25% acid concentration is used, it is seen that the selectivity is 91% for continues feeding mode (360-0) and 88% for batch mode (1-359). Interestingly, the selectivity values for ‘60-30’ feeding mode (similar to the other acid conc.) are lower than the other feeding modes, while the others showed almost similar selectivity.
Again, generally the highest conversion and selectivity are observed in cases where the acid concentrations are 25%, as can be seen from Table 2. Although, 54% conversion and 95% selectivity are peak values, the selectivity shows an average value of 0.92 ±0.02. In the case of using 15% acid concentration, the values of selectivity (94%) belong to the 5th and 6th hours of ‘45-15’ feeding mode are close to the values when using 25% acid concentration. Selectivity value is 89% at 15% acid concentration in 180-180 feeding mode. Also ‘90-30’ feeding mode shows similar performance. The ‘45 -15’ mode is therefore used as the basis for conducting further trials. As can be seen from the tables, in many trials, the impurities actually occur during the first 4th hour, after which they either fall or remain almost constant.
The higher selectivity values at the 15% acid concentration in the ‘45-15’ feeding mode (the need for low acid usage) led to the progression through this mode as previously mentioned. Afterwards, studies were conducted in over ratios (3.5/1, 5/1) in ‘45-15’ feeding mode. The effect of co-catalyst usage was also investigated in batch and semi-batch systems. The results are given in Table 2.
In the case where 25% HCl and the co-catalyst are used, 97% selectivity was attained at 6th hours. Although, the conver-sions in the 3.5/1 and 5/1 mole ratios are higher than stochiometric ratio ‘45-15’ feeding mode, the selectivity’s are lower. In these experiments, no co-catalyst was used, and if used, it is estimated that it would provide a 20 percent increase in returns and improvements in selectivity would be observed. Again, in the case of batch stochiometric run was carried out with co-catalyst, the conversion increased from 49% to 60% and the selectivity increased from 85% to 91%.
By-products form undesired colors as mentioned before. Lighter color obtained with semi-batch system. Parameters are same for both experiments except semi-batch was applied with 45-15 feeding mode.