I have synthesized a heterogeneous catalyst using waste eggshell followed by sulfonation treatment in order to perform simultaneous esterification and transesterification of rice bran oil. According to my observations, the effect of sulfuric acid concentration on the particle size is little confusing and not much has been found in the literature either. So, can anyone describe why does the particle size decrease with increase in the concentration of sulfonation? However, the EDS analysis reveals that overall S/c and O/C ratios are high for 5 wt% sample than 7 wt% sample, that is why I am using 5 wt% sample, but I am unable to find a reason and justification for the decreasing particle size of the 7 wt% sample.