TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: Portion(s) of synthesis gas effluent is converted to methanol containing effluent and liquid water-rich by-product (P2). Portion(s) of methanol containing effluent is converted to dimethylether containing effluent and liquid water-rich by-product (P3). The by-products (P2,P3) form portion of primary liquid water-rich by-product (P1). Methanol is converted to dimethylether over a catalyst (C1), to yield dimethylether product stream containing methanol, alcohol, dimethylether and water. A base is added to the dimethylether product stream, and stream is separated into a vaporous dimethylether-rich stream and a liquid water-containing stream as liquid water-rich by-product (P3). The water-containing stream comprises 5 wt.% or less of methanol based on the total weight of water and methanol. Portion of water-rich by-product (P2,P3) is recycled as cooling medium. The recycled liquid water-rich by-product contains 1 wt.% or more, preferably 3 wt.% or more, more preferably 5 wt.% or more of oxygenates based on total recycled liquid water-rich by-product. Sulfur compounds, carbon dioxide and other impurities are separated from the shifted gas to obtain a purified synthesis gas. Oxygen-comprising gas and carbonaceous feedstock are fed to burner firing into combustion chamber (6) at the upper end of the reactor vessel and a quench chamber (7) at the lower end of the reactor vessel fluidly connected by a combustion chamber outlet opening. The cooling is performed by injecting the liquid water-containing cooling medium as a spray into the synthesis gas. The synthesis gas flows through a dip tube (9) fluidly connected to the outlet opening of the combustion chamber and partly submerged in a water bath. The inner walls of the dip tube are cooled by a stream of a liquid comprising the liquid water-containing cooling medium which flows downwardly and along the inner wall of the dip tube. The liquid water-containing cooling medium has temperature less than bubble point temperature of water by 50 degrees C or less. Portion of synthesis gas is subjected to water shift reaction, and remaining gas is combined with the shifted synthesis gas to obtain a combined synthesis gas effluent having modified hydrogen to carbon monoxide molar ratio as feedstock for oxygenate synthesis.