The present invention relates to a process for preparing polyoxymethylene dimethyl ethers, comprising the following steps: reaction of formaldehyde and methylal (OME.sub.1) in a reactor R1 to obtain a product mixture, distillative separation of the product mixture in a distillation unit D1 into a top stream which contains OME.sub.1, OME.sub.2, formaldehyde, methanol and water, and a bottom stream which contains OME.sub.≥3, mixing of the top stream drawn off from the distillation unit D1 with a methanol-containing stream, treatment of the mixture in a reactive distillation unit RD2 to form a top stream containing methylal and a water-containing bottom stream, introduction of the bottom stream drawn off from the distillation unit D1 into a distillation unit D3 and distillative separation of the polyoxymethylene dimethyl ethers.

Provided is a method with which an α-allylated cycloalkanone is obtained from a cyclic compound cycloalkanone used as a starting material. The method is a method for producing an α-allylated cycloalkanone represented by General Formula (III), and the method includes: a step 1: reacting a compound represented by General Formula (I) and alcohol having 1 or more and 4 or less of carbon atoms in the presence of a first acid catalyst and optionally a dehydrating agent; and a step 2: reacting a crude product obtained in the step 1 and a compound represented by General Formula (II) in the presence of a second acid catalyst to produce an α-allylated cycloalkanone represented by General Formula (III). The step 1 and the step 2 are consecutively performed. In the formulae above, the group -A.sup.1- (it should be noted that the front bond refers to a bond that binds to the carbon atom C.sup.1 and the back bond refers to a bond that binds to the carbon atom C.sup.2) is an alkylene group having 4 or more and 20 or less of carbon atoms that optionally contains a hetero atom and optionally has a substituent, and R.sup.4 is a hydrogen atom or an alkyl group having 1 or more and 4 or less of carbon atoms.

Provided is a method with which an α-allylated cycloalkanone is obtained from a cyclic compound cycloalkanone used as a starting material. The method is a method for producing an α-allylated cycloalkanone represented by General Formula (III), and the method includes: a step 1: reacting a compound represented by General Formula (I) and alcohol having 1 or more and 4 or less of carbon atoms in the presence of a first acid catalyst and optionally a dehydrating agent; and a step 2: reacting a crude product obtained in the step 1 and a compound represented by General Formula (II) in the presence of a second acid catalyst to produce an α-allylated cycloalkanone represented by General Formula (III). The step 1 and the step 2 are consecutively performed. In the formulae above, the group -A.sup.1- (it should be noted that the front bond refers to a bond that binds to the carbon atom C.sup.1 and the back bond refers to a bond that binds to the carbon atom C.sup.2) is an alkylene group having 4 or more and 20 or less of carbon atoms that optionally contains a hetero atom and optionally has a substituent, and R.sup.4 is a hydrogen atom or an alkyl group having 1 or more and 4 or less of carbon atoms.

A preparation method for polyoxymethylene dimethyl ether (DMMn, generally, n=3-8 or 2-8) and mixture thereof may include one or more of the following: mixture of aqueous formaldehyde solution and polyalcohol is heated and dehydrated under vacuum conditions to yield flowing polyoxymethylene containing low moisture, which is heated and gasified to obtain relatively pure gaseous formaldehyde, which is mixed with methylal, previous batch of low-boiling-point substances applied, macromolecules, etc. in presence of catalyst. Or, the method mainly includes: aqueous formaldehyde solution, polyalcohol, and previous batch of macromolecular mixture applied are heated under vacuum conditions to remove moisture so as to obtain anhydrous flowable polyoxymethylene etherate, which is mixed with methylal, previous batch of low-boiling-point substances applied, macromolecules, etc. in presence of catalyst.

A preparation method for polyoxymethylene dimethyl ether (DMMn, generally, n=3-8 or 2-8) and mixture thereof may include one or more of the following: mixture of aqueous formaldehyde solution and polyalcohol is heated and dehydrated under vacuum conditions to yield flowing polyoxymethylene containing low moisture, which is heated and gasified to obtain relatively pure gaseous formaldehyde, which is mixed with methylal, previous batch of low-boiling-point substances applied, macromolecules, etc. in presence of catalyst. Or, the method mainly includes: aqueous formaldehyde solution, polyalcohol, and previous batch of macromolecular mixture applied are heated under vacuum conditions to remove moisture so as to obtain anhydrous flowable polyoxymethylene etherate, which is mixed with methylal, previous batch of low-boiling-point substances applied, macromolecules, etc. in presence of catalyst.

A preparation method for polyoxymethylene dimethyl ether (DMMn, generally, n=3-8 or 2-8) and mixture thereof may include one or more of the following: mixture of aqueous formaldehyde solution and polyalcohol is heated and dehydrated under vacuum conditions to yield flowing polyoxymethylene containing low moisture, which is heated and gasified to obtain relatively pure gaseous formaldehyde, which is mixed with methylal, previous batch of low-boiling-point substances applied, macromolecules, etc. in presence of catalyst. Or, the method mainly includes: aqueous formaldehyde solution, polyalcohol, and previous batch of macromolecular mixture applied are heated under vacuum conditions to remove moisture so as to obtain anhydrous flowable polyoxymethylene etherate, which is mixed with methylal, previous batch of low-boiling-point substances applied, macromolecules, etc. in presence of catalyst.

A method for forming poly(dimethoxymethane) includes a step of separating a formaldehyde-containing blend into a first bottom stream and a first top stream. The first formaldehyde-containing blend includes methanol, formaldehyde, and water while the first bottom stream includes water. The first top stream includes dimethoxymethane that is produced from the reaction between methanol and formaldehyde. The first top stream is separated into a second bottom stream and a second top stream. The second bottom stream includes poly(dimethoxymethane) while the second top stream includes dimethoxymethane, methanol, and ethanol. The second top stream is separated into a third bottom stream and a third top stream. Third bottom stream includes methanol and ethanol while the third top stream includes dimethoxymethane. The third top steam can be recycled to form additional poly(dimethoxymethane). A system that implements the method is also provided.

A method for forming poly(dimethoxymethane) includes a step of separating a formaldehyde-containing blend into a first bottom stream and a first top stream. The first formaldehyde-containing blend includes methanol, formaldehyde, and water while the first bottom stream includes water. The first top stream includes dimethoxymethane that is produced from the reaction between methanol and formaldehyde. The first top stream is separated into a second bottom stream and a second top stream. The second bottom stream includes poly(dimethoxymethane) while the second top stream includes dimethoxymethane, methanol, and ethanol. The second top stream is separated into a third bottom stream and a third top stream. Third bottom stream includes methanol and ethanol while the third top stream includes dimethoxymethane. The third top steam can be recycled to form additional poly(dimethoxymethane). A system that implements the method is also provided.

A method for forming poly(dimethoxymethane) includes a step of separating a formaldehyde-containing blend into a first bottom stream and a first top stream. The first formaldehyde-containing blend includes methanol, formaldehyde, and water while the first bottom stream includes water. The first top stream includes dimethoxymethane that is produced from the reaction between methanol and formaldehyde. The first top stream is separated into a second bottom stream and a second top stream. The second bottom stream includes poly(dimethoxymethane) while the second top stream includes dimethoxymethane, methanol, and ethanol. The second top stream is separated into a third bottom stream and a third top stream. Third bottom stream includes methanol and ethanol while the third top stream includes dimethoxymethane. The third top steam can be recycled to form additional poly(dimethoxymethane). A system that implements the method is also provided.

The disclosure relates to a process for continuously producing polyoxymethylene dimethyl ethers at low temperature, pertains to the technical field of polyoxymethylene dimethyl ether preparation processes, and solves the technical problem of continuous production of polyoxymethylene dimethyl ether. A membrane separation element with precisely controlled pores in membrane is used to realize a direct separation of the feedstocks from the catalyst within the reactor, and effectively reduce the permeation resistance of the separation membrane tube. By oppositely switching the flowing direction of liquid reaction materials, the adhesion of the catalyst to the separation membrane tube is inhibited, and some particles stuck in separation membrane tube are removed, which ensures the continuous operation of the reaction process and allows a molecular sieve catalyst to exhibit its advantage of long catalytic life.