The invention relates to a process for the preparation of a multimodal copolymer of ethylene and a comonomer which is 1-hexene and/or 1-butene in a series of polymerization reactors comprising at least a first polymerization reactor and a second polymerization reactor, the process comprising: a) feeding ethylene, hydrogen and catalyst components (1) and a first diluent (29) to the first polymerization reactor (A) to prepare a first suspension (3) of solid particles of a first ethylene polymer in a first suspension medium, wherein the first diluent (29) comprises branched heptane and is essentially free of the comonomer: b) feeding the first suspension (3) to a flash drum (E) for vaporizing a part of the first suspension medium to obtain a hydrogen-depleted suspension (4), c) feeding the hydrogen-depleted suspension (4), ethylene and comonomer (9) and a second diluent (24 & 34) to the second polymerization reactor (H) to prepare a second suspension (11) of solid particles of a second ethylene polymer in a second suspension medium, wherein the second diluent (24 & 34) comprises branched heptane and the comonomer dissolved in the second diluent, d) processing the second suspension (11) to obtain a dry effluent (15) of the solid particles of the second ethylene polymer and a liquid stream (23) comprising branched heptane, the comonomer, and low molecular weight hydrocarbon reaction products, e) feeding at least part (25) of the liquid stream (23) to an evaporation system (Q) for separating non-volatile, low-molecular-weight hydrocarbon reaction products and subsequently to a distillation column (R) for separating the comonomer from branched heptane to obtain 1) a branched heptane liquid stream (29) essentially free of the comonomer. 2) a vapor distillate (31) comprising the comonomer and branched heptane and 3) a liquid distillate (30) comprising branched heptane and the comonomer, f) feeding the liquid distillate stream (30) to the second polymerization reactor (B) to form at least part of the second diluent (34) and g) feeding the branched heptane liquid stream (29) to the first polymerization reactor as the first diluent.