Synthesis And Demulsification Performance Of N-carboxymethyl Chitosan Derived Crude Oil Demulsifier

With the application of secondary and tertiary recovery technologies in oil extraction,oil recovery rate increased,but the crude oil emulsification was aggravated and the contents of water and salts were elevated,making it increasingly difficult to break the emulsions.Therefore,it seems to be particularly necessary to develop a new type of high-efficiency demulsifier.Chitosan is abundant,widely available,environmentally friendly,and can be easily chemically modified.In this paper,chitosan was used as raw material,carboxyl group,quaternary ammonium salt and polyether group were introduced on its molecule,so that a series of methoxy polyethylene glycol grafted quaternized carboxymethyl chitosan were obtained.By changing the length of alkyl chain of quaternary ammonium salt,the hydrophilicity and hydrophobicity of the molecule was adjusted,so that a series of demulsifiers were synthesized and the demulsification performance of the demulsifiers was evaluated with the simulated crude oil emulsion with 50%water content.The details are as follows:Chitosan was reacted with glyoxylic acid and sodium borohydride to obtain N-carboxymethyl chitosan?CMC?,and then reacted with the quaternization reagents made in our own lab with a carbon chain length of 4,8,12 to get three kinds of quaternized carboxymethyl chitosans Q4CMC,Q8CMC and Q12CMC.Methoxy polyethylene glycol carboxylic methyl ester was synthesized from methoxy polyethylene glycol with the molecular weight of 1900 g/mol,and reacted with three different quaternized carboxymethyl chitosans by transesterification to obtain three kinds of methoxy polyethylene glycol grafted quaternized carboxymethyl chitosans Q₄CMC-MPEG-1900,Q₈CMC-MPEG-1900 and Q12CMC-MPEG-1900.The chemical structure of the products was characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance.The relationship between surface tension and concentration of three N-carboxymethyl chitosan derivatives was tested.The results showed that the surface tension of three substances rapidly decreased at low concentration.And with the increase of concentration,the decrease in surface tension became slower and then remained unchanged.And the surface activity of Q₄CMC-MPEG-1900,Q₈CMC-MPEG-1900,Q₁₂CMC-MPEG-1900increased in turn.The demulsificantion performance of three N-carboxymethyl chitosan derivatives was tested by bottle test.The results showed that the dehydration rate of Q₄CMC-MPEG-1900,Q₈CMC-MPEG-1900 and Q₁₂CMC-MPEG-1900 could reach 50.72%,61.33%and 71.91%respectively at the concentration of 250 mg/L.