Medium oil for slurry-bed reaction process and process of producing dimethyl ether

332232n232 32(a) A medium oil wherein a main component is a hydrocarbon, and the number of paraffinic carbon atoms is 70% or more with respect to a total number of carbon atoms, (b) a medium oil wherein a main component is a polybutene, (c) a medium oil wherein a main component is a mixture of hydrocarbons of the formula (1): CH-C(CH)-[-CH-C(CH)-]-CH-R (1) wherein R is -CH(CH)or -C(CH)═CH, and n is 1 to 10, (d) a medium oil wherein a main component is a hydrocarbon prepared by a Fischer-Tropsch synthesis, or (e) a medium oil wherein a main component is a branched paraffinic hydrocarbon prepared by hydrogenolysis of a hydrocarbon prepared by a Fischer-Tropsch synthesis, and a process of producing dimethyl ether using the medium oil, are disclosed.