The compositions of the inorganic elements in feedstocks were
analyzed with an X-ray fluorescence spectrometer (XRF, ZSX
Primus II, Rigaku, Japan). The molecular weight of the product was
measured by means of gel permeation chromatography (GPC, Agilent
1100 series, Agilent, USA). Two columns (Styragel HR 0.5 and
HR 1) connected in a series were used as a stationary phase, and
tetrahydrofuran was used as a solvent for the sample solution and
eluent