Lignin sulfonyl betaine surfactant for oil field and preparation method thereof

The invention discloses a preparation method of a lignin sulfonyl betaine surfactant for an oil field and belongs to the field of surfactants. The surfactant takes lignin as a raw material; and the lignin is oxidized and sulfonated to generate oxidized and sulfonated lignin, and the oxidized and sulfonated lignin is subjected to an alkylation reaction to synthesize lignin sulfonyl betaine which is an amphoteric surfactant. The raw material disclosed by the invention is a byproduct of industries including papermaking and the like; reaction conditions are moderate and pollution is not generated; the prepared surfactant has relatively good surface activity and can be used in tertiary oil recovery as an alkali-free oil displacement agent; when the surfactant is singly used, the surfactant can form ultralow interfacial tension smaller than 10 mN/m with Daqing crude oil, Xinjiang crude oil and Northern China crude oil; and the surfactant is the sulfonyl-containing lignin amphoteric betaine surfactant which can be applied to the oil field, is novel and efficient and is low in cost.