Study On Synthesis And Refining Of Polyoxymethylene Dimethyl Ethers

Polyoxymethylene dimethyl ethers?DMM_n for short?has the general structure of CH₃O?CH₂O?_nCH₃?n?1?.DMM3-6 is known as a new type of diesel oil additive at home and abroad,which can improve the combustion efficiency and reduce the emission of pollutants.In addition,DMM_2-4 can be used as aromatic free green environmental protection solvent.Therefore,with the development focus more and more on environmental protection,the development of clean energy DMM_n products has been widely concerned by scholars at home and abroad.The synthesis of DMM_n was carried out in this study,choosing DMM and PF as the raw material and NKC-9 ion exchange resin as the catalyst.The selectivity of DMM_3-6,the selectivity of by-product,acid value,water and other factors were overall considered to optimize synthesis process.At the same time,the synthesis mechanism of DMM_n is explained and verified.In this paper,the separation and purification of DMM_n synthetic products were studied.The problems existing in the process of direct separation of DMM_n products are presented.Then the process of de-acid and de-formaldehyde purification by alkali washing extraction was studied.On the basis of the effect of deacidification,material loss and other factors,the alkali washing conditions were optimized.And the process conditions of distillation and separation of acid free and aldehyde free DMM_n products obtained by alkali washing were studied and analyzed in detail.In the end,the main problems in the process of separation of DMM_n which are formaldehyde polymerization,bottom polymerization and product decomposition were studied.A new process for separation and purification of DMM_3-8 from DMMn containing formaldehyde was proposed.The method can effectively solve above problems in the separation process of DMM_n containing aldehyde,what's more,the formaldehyde in the raw material can be completely recovered,and finally the DMM_3-8 product with the purity of more than 99%can be obtained.