## 3 Results and Discussion  
Figure 3 shows the impurity or ash concentration after 24 h of continuous molten sulfur filtration. In total six experiments a 24 h were conducted for each of the three filter aids indicated by the numbers (1-6) in Figure 3. It can be seen that the results of both of the cellulose-based filter aids (FILTER-900 and FILTER-1100) are comparable to the results of the diatomaceous earth filter aid that is currently used in industrial production. The cellulose-based filter aid FILTER-1100 showed the best performance among all three different filter aids, especially if FILTER-900 and FILTER-1100 are compared with each other directly, and this is not surprising since the higher Dalton number of FILTER-1100 already indicates a finer mesh that would most likely result in better filtration results. For FILTER-1100, the unstirred filter aid resulted in slightly better results than the stirred one, while for FILTER-900, the results suggest the opposite trend. However, for FILTER-1100, particularly, it can be noted that the difference between the stirred and unstirred filter aid were negligible. Figure 4 shows that substituting the traditional diatomaceous earth filter aid with a new cellulose-based filter aid (FILTER-1100) can result in similar or even better filtration results. It is also noteworthy that the overall amount of utilized filter aid was reduced by one third from the former 75 kg per cycle (approximately) to the current 50 kg per cycle (approximately). The cellulose-based filter aid is less dense than the conventional diatomaceous earth filter aid, and this allows the formation of thicker pre-layers with appropriate pipes that promote the flow of liquid sulfur through these pre-layers. Moreover, the elasticity of the cellulose-based filter aid allows for more efficient filtration, even at lower specific consumption. These observations are supported by [PERSON] et al. and their previous experiments [24]. In the case of the cycle time, the performance of the filtration using cellulose-based FILTER-1100 for 72 h is comparable to using diatomaceous earth for 24 h. In other words, even after tripling the length of the filtration cycle, the amount of impurities in the molten sulfur is comparable. Only after 72 h does the impurity content raise to critical levels when FILTER-1100 is used, and, even then, a much smoother increase can be observed. The results thus indicate that the filtration cycle time can be increased from 24 h to 72 h if the diatomaceous earth filter aid is replaced with cellulose-based Filter-1100 while keeping the impurity level in the molten sulfur constant. It is noteworthy that if slightly cleaner sulfur is used, the filtration cycle time may be further increased. Each filtration cycle is followed by a cleaning operation. In fact, the cleaning operation is complicated when using diatomaceous earth. The pre-coat and solids must be removed  
Figure 4: The ash content (AC) according to the specific consumption and the cycle time. Figure 3: Molten sulfur impurity content using different filter aids (cellulose-based FILTER-900 and FILTER-1100 as well as a diatomaceous earth control) after 24 h of continuous operation. Experiments have been repeated six times (numbers 1–6) for each filter aid. from the filter leaves using wooden sticks, which if they are not carefully used, can damage the filter leaves. The large-scale experiments conducted for this study clearly showed that the cellulose-based filter aids can be removed much easier. In fact, in most cases, the filter aid and solids fell out automatically when opening the filters so that potential damage to the filter leaves can probably be largely mitigated if a cellulose-based filter material is used. This will most certainly have to be investigated in industrial application. We further strongly suggest considering the issue of disposing of the filter aid. It was already pointed out that [PERSON] et al.