Nickel catalyst in coupled plasma-catalytic system for tar removal

Abstract

Tar formation is a significant issue during biomass gasification. Catalytic removal of tars with the use of nickel catalyst allows to obtain high conversion rate but coke formation on catalysts surface lead to its deactivation. Toluene decomposition as a tar imitator was studied in gliding discharge plasma-catalytic system with the use of 5%, 10% and 15% by weight Ni and NiO catalyst on Al2O3 (α-Al2O3) and Peshiney (γ-Al2O3) carrier in gas composition similar to the gas after biomass pyrolysis. The optimal concentration of nickel was identified to be 10% by weight on Al2O3. It was stable in all studied initial toluene concentrations, discharge power while C7H8 conversion rate remained high – up to 82%. During the process, nickel catalysts were deactivated by sooth formation on the surface. On catalysts surface, toluene decomposition products were identified including benzyl alcohol and 3-hexen-2-one.

Toluene Decomposition in Plasma–Catalytic Systems with Nickel Catalysts on CaO-Al2O3 Carrier

“…In series B, more hydrogen radicals were present during the process, which could be used not only for the methanation reaction but also for the hydrogenation of toluene radical, resulting in lower C 7 H 8 conversion rates in the system with NiO/(CaO-Al 2 O 3 ). The amount of CH 4 produced in the plasma-catalytic system with the use of Ni/(CaO-Al 2 O 3 ) catalyst reached 600 ppm (Figure 1), which was significantly higher than that produced with NiO/(CaO-Al 2 O 3 )-70 ppm-or Ni/Al 2 O 3 -50 ppm [24]. The addition of CaO to the catalyst carrier resulted in an increased methane concentration in the outlet gas.…”

“…A higher methane concentration was observed in a gas composition with a higher hydrogen concentration (series B) because the reaction rate at the catalyst was higher. More H 2 in the initial gas lowered the toluene conversion in plasma-catalytic systems with NiO/(CaO-Al 2 O 3 ) and NiO/Al 2 O 3 [24] but increased in the system with the Ni/(CaO-Al 2 O 3 ) catalyst. In series B, more hydrogen radicals were present during the process, which could be used not only for the methanation reaction but also for the hydrogenation of toluene radical, resulting in lower C 7 H 8 conversion rates in the system with NiO/(CaO-Al 2 O 3 ).…”

“…The highest x C 7 H 8 was observed for the coupled system with the NiO/(CaO-Al 2 O 3 ) catalyst-85%. In the plasma-catalytic system with Ni/(CaO-Al 2 O 3 ) and NiO/Al 2 O 3 catalysts [24], the highest results were 77% and 82%, respectively. Without a catalyst, up to 68% of toluene was decomposed [21].…”

“…Catalysts NiO/Al2O3, NiO/(CaO-Al2O3), and Ni/(CaO-Al2O3) with 10 wt% active phase on Al2O3 and on the commercial catalysts support G-2117-7H/C (CaO-Al2O3), manufactured by INS Pulawy, Poland, had a specific surface area not exceeding 10 m 2 /g (Table 1). In previous studies, catalysts on the G-117 bed were successfully used and the optimal concentration of the active phase was identified to be 10 wt% [21][22][23][24]. Catalysts were prepared by the impregnation method using Ni(NO3)2•6H2O, which was deposited 1).…”

“…Reducing the amount of active phase on the catalyst's bed could result in less soot formation. It was found that a high toluene conversion rate could be achieved with 10% nickel on Al 2 O 3 , but soot formation remained a problem; therefore, further studies were needed [24]. The addition of trace amounts of calcium to a catalyst used for catalytic reforming resulted in an increase in its resistance and activity by reducing the formation of carbon deposits [21,[25][26][27].…”