The first step, grass sample were pretreat with sodium hydroxide concentrations 0.5%, 1% and 2% w/v. A NaOH solution at a ratio of 1:10, solid: liquid, then autoclaved at 121 ℃, 15 psi for 60 min. The biomass was washed with tap water until the neutral pH and dried at 90 ℃ overnight. The second step, dried NaOH pretreated VG was mixed with sulfuric acid concentrations 0.5%, 1% and 2% w/v respectively. A solid to liquid ratio of 1 g dried NaOH pretreated VG: 10 ml of H2SO4 solution (สีฟ้าปรับปรุงมา) and heated in an autoclaved at 121 ℃, 15 psi for 60 min. then dried at 90 ℃ overnight.