As a kind of excellent diesel-blending component, polyoxymethylene dimethyl ethers (PODEn) have received widespread attention. Herein, Al-SBA-15 molecular sieves with different Si/Al ratios and pore sizes were synthesized and used to investigate the catalytic performance for the synthesis of polyoxymethylene dimethyl ethers from methylal and trioxane. X-ray diffraction, N 2 adsorption−desorption, scanning electron microscopy, transmission electron microscopy, X-ray fluorescence, and 27 Al NMR were used to characterize the structures of obtained catalysts. Ammonia temperature-programmed desorption and pyridine adsorption were carried out to investigate the acid properties of the catalysts. Through comparison of the catalysts with different Al contents, it was found that the relatively weak acid was more suitable for the synthesis of PODEn than the relatively strong acid in the catalytic system of Al-SBA-15. On the Al-SBA-15(2)-150 catalyst, which has only a weak acid of 0.163 mmol/g, the highest TOX conversion rate and highest PODEn yield and selectivity were achieved, showing the best catalytic performance. It appears that the PODEn synthesis can be catalyzed by not only a Bronsted acid but also a Lewis acid. The catalysts with strong acid and/or with a large number of acids will cause the generation of significant amount of methyl formate byproduct. Through comparison of the catalysts with different pore sizes, it was found that a relative larger pore size of the catalyst was beneficial for the PODEn synthesis to a certain extent under the catalysts with strong acid and/or large acid amount, but on the catalyst that had only weak acid and a relatively lesser amount, the change of pore size had almost no effect on the yield and selectivity of PODEn products.
Sulfonic acid-functionalized mesoporous SBA-15 with different sulfur loading was synthesized and used to investigate the catalytic performance for PODEn synthesis.
Gasoline partially premixed combustion (PPC) has been reported as an advancing concept for high efficient and clean combustion, while there still remains some obstacles. In this study, polyoxymethylene dimethyl ethers (PODE), which has superior properties of high oxygen content, high cetane number and no CC bond, is employed as an additive to optimize the properties of gasoline and solve the problems faced in gasoline PPC. The effects of gasoline/PODE blends with PODE volume blending ratio of 0, 10% and 20% on combustion and emission have been investigated from low to high loads in a multi-cylinder heavy-duty diesel engine. The experimental results show that the soot emission can be maximally reduced by 79% and 94% at high load when fueling PODE 10 and PODE20, respectively. The NOx-soot trade off relationship can be dramatically improved without penalty of fuel economy by fueling gasoline/PODE blends. The raw NOx and soot emissions can meet Euro V standards at high load and Euro VI standards at medium load by fueling both PODE10 and PODE20. Furthermore, the pressure rise rate can be maximally reduced by 24% and 47% when fueling PODE10 and PODE20. At medium load, the combustion controllability and sensitivity can be improved by gasoline/PODE blends. At low load, the COV IMEP can be reduced to 2.7% by fueling PODE20 which means a stable combustion can be obtained. Furthermore, the combustion efficiency can be dramatically improved from 85.1% to 99.6% by fueling PODE20, which leads to lower HC and CO emissions. Overall, PODE shows great advantage in solving the obstacles faced in gasoline PPC.
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