Potassium-salt-catalyzed tar reduction during pyrolysis oil gasification

The gasification of pinewood pyrolysis oil with potassium hydroxide dissolved was investigated, using a potassium salt loaded char as catalyst, to screen if this would result in a lower tar yield in the product stream. Experiments were performed at 700 °C, after which the product stream was thoroughly condensed and the gas stream was analyzed. The results show a significant tar reduction for a fixed potassium-loaded char bed at a gas hourly space velocity (GC1HSV) of 237 h–1. If the GC1HSV is reduced, the reduction in tar increases. A reduction of a factor of 10 was observed when the feed was also loaded with 5 wt % KOH. Based on the principle that the potassium ion catalyzes the cracking of tars into char or gas, it is proposed that this formed char is easily and fully gasifiable, leading to a feasible, continuous low-tar pyrolysis oil gasification process. The results show promise of deep tar removal under more severe conditions, resulting in a much smaller tar removal step afterward. This process would fit well into the concept where lignocellulose residues are first locally pyrolyzed to pyrolysis oil, after which they will be collected and gasified at a low temperature, of ∼700 °C, on a large scale.