1. Factors affecting the effect of pour point depressant 

The pour point depressant molecule consists of two parts, namely long-chain alkyl group and polar group. The structural unit of long-chain alkyl group can be on the side chain, the main chain, or both. 

The factors affecting the pour point depressant effect of crude oil mainly include: 

① Long alkyl chain length and carbon number distribution 

② Content and polarity of polar groups 0 branching degree 

③ Molecular weight 

④ The form of pour point depressant in oil, etc

(1) Effects of long chain alkyl length and carbon number distribution 

The long-chain alkyl structural unit can be used as the crystal nucleus of wax crystallization in crude oil or eutectic precipitation with wax molecules. Generally speaking, the carbon number of long alkyl main chain or long alkyl side chain of pour point depressant should match the average carbon number within the most concentrated range of wax carbon number distribution in crude oil in order to have better pour point depressant effect. It is reported in the literature that the pour point depressant has good pour point depressant effect when the molecular structure and melting (crystallization) temperature range of pour point depressant are similar to those of crystalline hydrocarbons in crude oil and the temperature range of molten wax (wax precipitation). 

(2) Influence of polar group content and polar size 

The polar groups in pour point depressant molecules can be adsorbed on the surface of wax crystals to establish a certain energy barrier, change the crystallization habit of wax and prevent the crystal particles from approaching each other, so as to improve the low-temperature flow performance of crude oil. 

The content of polar group of pour point depressant is the factor affecting the crystallization performance of pour point depressant. 

When the content of polar groups in pour point depressant increases, the content of long-chain alkyl decreases relatively, so the crystallinity of pour point depressant decreases.

When the content of polar groups in pour point depressant increases, the content of long-chain alkyl decreases relatively, so the crystallinity of pour point depressant decreases. 

When the content of polar groups increases to a high level, the rigidity of the chain increases due to the obstacle of spatial arrangement, and the crystallization of pour point depressant is more difficult. 

If the crystallinity of pour point depressant is low, the ability of eutectic precipitation with wax molecules is reduced. However, if the crystallization ability of pour point depressant is too high, the polarity of pour point depressant will be relatively reduced, and the dispersion effect of pour point depressant on wax crystal will be reduced. 

Therefore, the content of polar group and long-chain alkyl group in pour point depressant should have an optimal ratio in order to obtain the best modification effect. 

The strong polarity or high surface activity of polar groups in the pour point depressant can increase the mutual exclusion between wax crystal particles and asphaltene particles. Therefore, the wax crystals combined with the pour point depressant are not easy to combine with each other to form large crystals, so as to improve their dispersion and anti deposition ability, 

Macroscopically, it shows good pour point reduction, viscosity reduction and shear resistance for crude oil, so as to improve the low-temperature fluidity of crude oil; However, if the activity is too high and the molecular polarity is too strong, the solubility of pour point depressant in crude oil will decrease, that is, the solubility in crude oil will become worse, which will also affect the effect of pour point depressant on pour point and viscosity reduction.

(3) Branching effect 

a. The degree of branching represents the number of branched chains in the polymer molecular structure 

b. The degree of branching can be evaluated by the ratio of average molecular size or intrinsic viscosity of branched polymers with the same molecular weight to linear polymers. The chain segments of branched molecules are more compact than linear molecules, so the higher the degree of branching, the smaller the above ratio. 

(4) Effect of molecular weight 

The greater the molecular weight of pour point depressant, the worse its solubility in oil. 

Generally speaking, it is better when the molecular weight range is 4000 ~ 10000, and the pour point reduction effect is not significant when the molecular weight is too low or too high. When the molecular weight distribution of pour point depressant is wide, the pour point depressant effect is the best, and there is an optimal molecular weight range of pour point depressant. 

(5) Effect of dosage 

The injection amount of pour point depressant is related to the content of wax, colloidal asphaltene in crude oil, and the dosage and effect are not linear. When the dosage reaches a certain critical value, the pour point depressant molecules co crystallize with most of the wax in crude oil or adsorb on the wax crystal surface to form a relatively stable crystal structure, and the modification effect of pour point depressant is close to its limit, Further increasing the dose will not significantly improve the treatment effect, but also increase the cost. As long as the dosage is enough to separate the wax crystals so that it is not easy to form a three-dimensional network structure. 

Summary of influencing factors: 

Because the content of paraffin and asphalt colloid in crude oil is different, and their molecular structure and size are different, they have strong selectivity for pour point depressant. 

The selection of pour point depressant for crude oil should be based on the wax content of crude oil, the distribution range of carbon atoms in wax molecules and the type of crude oil.