Vapor-phase diethyl oxalate pretreatment of wood chips: Part 1. Energy savings and improved pulps

Diethyl oxalate (DEO) was injected into a digester containing wood chips (pine, spruce, or aspen) preheated to 130-140 degrees C and held for 30 min at the same temperature. When mechanical pulps were produced from these pretreated chips, savings in electrical refiner energy could be achieved. For southern yellow pine (Pinus taeda), the electrical refiner energy required to produce pulps with Canadian standard freeness (CSF) of 100 ml was 3855% less than for an untreated control. Energy savings were also observed for aspen (Populus spp.) and spruce (Picea spp.). DEO-treated pine handsheets showed a 26% improvement in tear index compared with a control at 100 ml CSF. Under the pretreatment conditions described, DEO rapidly vaporizes, reacts with water already present in the chip, and forms an oxalic acid (OA) solution. Reported handsheet properties and energy savings for pine chips treated with a solution of OA are similar to DEO-treated handsheets. It can be concluded that the effect of DEO treatment is due to reactions catalyzed by OA.