A method is disclosed of purifying a recycled or renewable organic material, wherein the recycled or renewable organic material includes more than 1 ppm silicon as silicon compounds. Exemplary steps include (a) providing the recycled or renewable organic material; (b) heat treating the recycled or renewable organic material to form a heat treated recycled or renewable organic material, wherein the at least part of silicon compounds present in the recycled or renewable organic material are converted to volatile silicon compounds, and (c) evaporating volatile silicon compounds from the heat treated recycled or renewable organic material to obtain recycled or renewable organic material fraction containing less silicon than the recycled or renewable organic material provided in step (a).