NOVELTY - A cellulosic biomass solid (2) containing chlorine and phosphorus is introduced into base solution (4). Obtained base-washed cellulosic biomass solid (16) is introduced into aqueous solution (24). Gas and/or organic solvent (34) is introduced through obtained water-washed cellulosic biomass solid to produce pretreated cellulosic biomass solid and separated aqueous effluent (32). The separated aqueous effluent is recycled to produce portion(s) of aqueous solution. Portion(s) of treated cellulosic biomass solid is transferred to digestion and/or reaction zone (50).    USE - Selective removal of chlorine and phosphorus from cellulosic biomass solid used for producing industrial chemical and transportation fuel for propulsion engine and internal combustion engine of transportation vehicle.    ADVANTAGE - Chlorine and phosphorus are removed from cellulosic biomass solid by effective method with high selectivity and reduced usage of water.    DETAILED DESCRIPTION - A cellulosic biomass solid containing chlorine and phosphorus is provided and introduced into base solution having pH of more than 9 at 0-60 degrees C in contact zone (10) to produce base-washed cellulosic biomass solid and basic water effluent (6). The content of basic water effluent is 3-0.5 pts. wt. relative to about 1 pt. wt. cellulosic biomass solid (dry basis). The base-washed cellulosic biomass solid is introduced into aqueous solution having pH of 8 or less in contact zone (20) to produce water-washed cellulosic biomass solid having reduced content of chlorine and phosphorus compared to the cellulosic biomass solid. A gas and/or organic solvent is introduced through water-washed cellulosic biomass solid in contact zone (30) to produce pretreated cellulosic biomass solid with reduced water content compared to water-washed cellulosic biomass solids and separated aqueous effluent. The separated aqueous effluent is recycled to contact zone (20) to produce portion(s) of aqueous solution. Portion(s) of treated cellulosic biomass solid is transferred to digestion and/or reaction zone. Thus, chlorine and phosphorus are selectively removed (100) from cellulosic biomass solid.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view explaining the selective removal of chlorine and phosphorus from cellulosic biomass solid.    Cellulosic biomass solid (2)    Base solution (4)    Basic water effluent (6)    Contact zones (10,20,30)    Base-washed cellulosic biomass solid (16)    Aqueous solution (24)    Water-washed cellulosic biomass solid (26)    Separated aqueous effluent (32)    Gas and organic solvent (34)    Digestion/reaction zone (50)    Hydrogen (54)    Intermediate oxygenated product stream (56)    Selective removal of chlorine and phosphorus from cellulosic biomass solid (100)