The invention is directed to a process to prepare a gas mixture of hydrogen and carbon monoxide from an ash containing carbonaceous feedstock. The process involves a partial oxidation obtaining liquid ash and a gas mixture comprising hydrogen, carbon monoxide and solids. The liquid ash is separated from the gas mixture and the temperature of the gas mixture is reduced in the absence of the separated ash. The gas mixture is passed through a vertically positioned diptube wherein water is added to the gas mixture flowing through the diptube to obtain a gas/water mixture. The liquid is separated from the gas/water mixture. The gas thus obtained is passed together with an amount of liquid water through a venturi mixer and scrubbed.