Polyoxymethylene dimethyl ethers (PODEn) are kind of diesel fuel additives with features of environment friendly and high efficiency. PODEn were catalytically synthetized from methanol and formaldehyde by ZnCl2. In this work

the mechanism of the synthesis reaction was discussed

and the effects of preparation conditions

such as temperatures

time

usage of catalyst and reactant mass ratio were investigated. The comparison of different catalysts of ZnCl2

strong acid resin and ZnCl2 modified resin was carried out. The concentrations of the PODEn compounds and methanol were quantitatively analyzed using gas chromatography (GC)

and formaldehyde was also determined by chemical titration method. Sulfuric acid standard solution was used to titrate sodium hydroxide formed by reaction of formaldehyde and excessive sodium sulfite. To obtain accurate experimental data

all the experiments were conducted strictly using the following procedures: poly-formaldehyde was de-polymerized to form anhydrous formaldehyde-methanol mixture solution; reaction device was heated to reaction temperatures (80

95

105 and 115℃); different proportions [2:(3—4)] of the mixture solution obtained

and ZnCl2 were added into reaction vessel; then

the pressurized vessel was sealed quickly and fixed

and rotational speed of the reaction device was set for 20 r·min-1; this moment was considered as the starting time of reaction; sampling time was placed after reacting 60—360 min. Reaction mechanism of synthetising PODEn from methanol and formaldehyde catalyzed by ZnCl2 was proposed as follows: formaldehyde was polarized firstly in the presence of catalyst

the first intermediate obtained came from the reaction of formaldehyde polarized and methanol

then other intermediates and PODEn were produced from the reactions of the first intermediate and raw materials. The experimental results confirmed that ZnCl2 could be used as catalyst for synthesis of PODEn from methanol and formaldehyde. The yield and selectivity of PODE2—6 reached 19.90%

67.50%

respectively

when the better reaction conditions were used (mass ratio of methanol and formaldehyde 2:(3—4)

catalyst usage 3.0% (mass)

temperature 105℃ and reaction time 300 min). Content of the products was more than 10 percentage points higher for ZnCl2 modified resin catalyst which had higher catalytic activity than for ZnCl2 catalyst.