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Biodegradability of Cationic Surfactants

Ⅰ. Biodegradability of cationic surfactants

Since cationic surfactants have strong bactericidal properties and are easily adsorbed on suspended solids, it is difficult to distinguish whether they are degraded. This determines that the research on cationic surfactants is more difficult than anionic and non-ionic. Researchers studied the degradation of 21 linear cationic surfactants under aerobic conditions by using the oxygen consumption measurement method, bromophenol blue colorimetry method, and dissolved organic carbon method. The results show that: alkyl trimethyl ammonium chloride Alkyl benzyl dimethyl ammonium chloride is easily biodegradable, while dialkyl dimethyl ammonium chloride and alkyl pyridine chloride are slightly less degradable.

When studying the biodegradation of alkyl polyoxyethylene benzyl ammonium chloride, the biodegradability of the hydrocarbon chain, polyoxyethylene chain, and benzene ring was also investigated. The results showed that the hydrocarbon chain and polyoxyethylene chain were partially degraded, and the benzene ring was also degradable.

Generally, the main component of softener, double-long-chain quaternary ammonium salt, will be replaced by a large amount of double-long-chain ester quaternary ammonium salt. In EQ, there are two carbons between the ester bond and the nitrogen atom. The cleavage of the ester bond produces fatty acids and quaternary ammonium diols or triols with greater water solubility. These degradation products are low in toxicity to fish and can be quickly metabolized. Such cationic surfactants are called "cleavable surfactants," which are super soft in the true sense.

Ⅱ. The main classification and structural formula of common cationic surfactants

Common natural cationic surfactants are mostly organic nitrogen-containing compound derivatives and anchor salt cationic surfactants. Organic nitrogen-containing compound cationic surfactants are mainly divided into ammonium salts and quaternary ammonium salts. Ammoniums (organic primary, secondary and tertiary ammonium) do not have a positive charge, but they can be combined with protons to be positively charged.

Ammonium salt is a weakly basic salt, which only has surface activity under acidic conditions, and easily releases ammonium under alkaline conditions, and loses surface activity. The quaternary ammonium compound has a positive charge and can dissociate positively charged active surface ions in acidic and alkaline solutions.

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