화학공학소재연구정보센터
Chemical Engineering Science, Vol.134, 758-766, 2015
Kinetics of synthesis of polyoxymethylene dimethyl ethers from paraformaldehyde and dimethoxymethane catalyzed by ion-exchange resin
Polyoxymethylene dimethyl ethers (CH3-O-(CH2O)-CH3, PODEn, n > 1) are new concerned environmental benign alternative components for diesel fuels. This work aimed to investigate the kinetics of synthesis of PODEn from paraformaldehyde and dimethoxymethane catalyzed by ion-exchange resin NKC-9. Experiments were conducted in a designed space, namely reaction temperatures (60, 70, and 80 degrees C) vs. reaction times (2, 5, 10, 20, 30, 60, and 90 min), in a batch stirred autoclave. The transient molecular size distribution of PODEn compounds from paraformaldehyde and methylal followed Schulz-Flory distribution model. In this system, the concentration of formaldehyde in the homogenous solution (C-F) was nearly constant. The sequential reversible reactions to produce PODE were verified to follow a second-order kinetics for propagation and a first-order kinetics for depolymerization. The rate constants of propagation (k(p)) and depolymerization (k(d)) and the reaction equilibrium constant K-n were the same for the series of PODEn synthesis reactions. Respecting to 5 wt% dosage of NKC-9 resin catalyst, the pre-exponential factors A(p) for propagation and A(d) for depolymerization were 1.84 x 10(7) L mol(-1) min(-1) and 536 x 10(6) min(-1), respectively. The activation energy E-p (39.52 kJ mol(-1)) for propagation was lower than E-d (52.01 kJ mol(-1)) for depolymerization, validating that the reversible reactions of producing PODEn. compounds were exothermic. (C) 2015 Elsevier Ltd. All rights reserved.