Method for coproducing nanometer calcium carbonate by purifying methane

The invention provides a method capable of enabling methane content to reach the standards of fuel gas for vehicles after methane is purified, and obtaining high added-value nanometer calcium carbonate in a purification process. The method comprises the following steps: firstly digesting quick lime, then filtering so as to obtain lime milk fine thick liquid, adding to a storage tank of a carbonization device, and adding a dispersing agent; feeding methane into membrane reactors, carrying out carbonization reaction and online monitoring, when the pH value is less than 7, ending reaction, wherein the membrane reactor a and the membrane reactor B in the process respectively represent a purification stage and a carbonization stage so as to ensure that a completely carbonized calcium carbonate product is obtained while the methane is completely purified; centrifuging calcium carbonate emulsion obtained after reaction so as to obtain calcium carbonate filter cakes, drying and crushing, thus obtaining the nanometer calcium carbonate. The novel membrane reactors in the method are used for purifying the methane so as to obtain high-purity biomethane and simultaneously obtaining the nanometer calcium carbonate with the excellent performance.