In the present study, the synthesis process of methylal, as a diesel fuel improver, by acetalization of methanol and formaldehyde is introduced using p-toluenesulfonic acid (PTSA) as an efficient catalyst. The catalytic behavior of PTSA is compared to sulfuric acid and cationic exchange resin of Amberlite IR-120, and also in the presence of PTSA, the two responses of methylal production capacity and synthesis rate in a batch process were optimized using statistical modelling of extreme vertices mixture design of experiments results by Minitab software and based on three variables of methanol, formalin and PTSA catalyst proportions. Statistical analysis of the results showed that predicted values for the two responses be in good agreement with experimental values. The results showed that the high production rate mainly was affected by the increasing of catalyst proportion in the mixture and the amount of methanol and formalin and also their stoichiometric ratio determine the production capacity of process. The optimized experimental conditions for the synthesis of methylal by the highest production capacity and rate were achieved from the mixture formulation contained 56.23 wt.% methanol, 37.91 wt.% formalin solution (35.1 wt.%), and 5.86 wt.% of PTSA catalyst, with production capacity of 43.8 mL methylal per 100 mL of initial reactant mixture, production rate of 27.35 mL/h, and experimental relative error of 2.7% and 7.4%, respectively. This study has shown that mixture experimental design could efficiently be applied for the modeling of catalytic process of DMM, and it is an economical way of obtaining the maximum amount of information with the fewest number of experiments. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.