Effect of inorganic alkalis on interfacial tensions of novel betaine solutions against crude oil

- The unsaturated and branched alkyl chain can reduce the equilibrium IFTs.
- Alkali has little effect on the nmin values of all three betaine solutions.
- The stronger the alkali is, the obvious the synergism and antagonism are.
- Acidic fractions show the strongest ability of changing IFT and saturate has almost no effect.

The effects of inorganic alkalis on the dynamic interfacial tensions (IFTs) of three betaine surfactants with different structures against daqing crude oil and model oils containing crude oil fractions, such as saturate, aromatic, resin, asphaltene and acidic fractions, have been studied by spinning drop tensiometer. The influences of pH value (alkali concentration and types) have been investigated. On the basis of the experimental results, one can find that it is difficult to reach the ultralow IFT value for all betaine solutions because of the mismatching of the hydrophilic head and hydrophobic tail. The unsaturated and branched alkyl chain can enlarge the size of hydrophobic part and reduce the equilibrium IFTs. By adding alkali, the IFTs are controlled by the mixed adsorptions of the petroleum acids, produced soaps and betaine molecules. For betaines with small hydrophobic part, 18C and 22C, the mixed adsorption films are compact than those of pure betaine films, which results in the decrease of IFT. On the other hand, the petroleum acids and soaps adsorb competitively with betaine molecules, due to the tighter packing of 26C molecules at the interface, the equilibrium IFT values of 26C increase with an increase in pH value. The stronger the alkali is, the better the synergism or antagonism is. The effects of pH on the IFTs of betaine solutions against model oils containing crude oil fractions agree with those against crude oil. For all betaines, the order of the ability of affecting IFT is acidic fractions > resin > asphaltene > aromatic > saturate in general.