Synthesis, and molecular interaction study of poly (BA-co-SMA-co-MA) as pour point depressants for improving malaysia crude oil flowability / Ibrahim Ismail Ali Elganidi

Faculty of Chemical and Process Engineering Technology

Thesis (Doctor of Philosophy) -- Universiti Malaysia Pahang – 2024

Includes bibliographical references

The flow of crude oil gets impeded due to the precipitation of wax on the inner wall of pipelines when the temperature drops below the wax appearance temperature (WAT). Polymeric pour point depressants (PPDs) are an effective method to enhance the flowability of waxy crude oil. In this thesis, a PPD of poly(behenyl acrylate-co-stearyl methacrylate-co-maleic anhydride) (BA-co-SMA-co-MA) was synthesised. The novel PPD was optimised using the OFAT technique, considering key parameters: monomer ratio, reaction time (4–12 hours), initiator concentration (0.5–2.5 wt%), and reaction temperature (60–120 °C). The most contributing factors were further optimized using central composite design software (CCD) to develop a polynomial regression model for predicting the maximum polymerisation yield. Besides, viscosity measurement, pour point, and cold finger apparatus were employed to evaluate the efficiency of the synthesised PPD. Lastly, molecular dynamics (MD) simulation was used to understand the molecular level interaction between wax and PPD, analysed through radial distribution function (RDF) values, which described the structure of PPD in wax crystals. The chemical structure of poly(BA-co-SMA-co-MA) has been successfully identified through FTIR and NMR. Also, from the thermal stability characterisation, the results showed that all prepared PPDs had a slightly high degradation temperature, which reflected excellent thermal stability and could be employed as a potential material for PPD additives. Furthermore, GPC results concluded that the degrees of polymerisation of the polymer are very suitable and have the optimum applicability as PPDs of crude oil. The optimum conditions for obtaining the highest yield were an 8.1 h reaction time, 102 °C reaction temperature, 1.57 wt% initiator concentration, and a monomer ratio of 1:1:1 (BA: SMA: MA), with a yield of 93.75%. Also, the regression model analysis (ANOVA) showed an R2 value of 0.9696, implying that the model can explain 96.96% of the data variation. Using the optimal conditions, the highest average yield value obtained is 93.20%. Consequently, the results indicate that this model is reliable and can predict the yield response. The rheological results show a significant viscosity reduction of crude oil at a shear rate of 100 rpm and after the addition of 1500 ppm polymer concentration at 5 °C by 75.33%, from 33.25 mPa.s to 8.2 mPa.s. The cold finger experiment demonstrated that after poly(BA-co-SMA-co-MA) was used as a wax inhibitor at a concentration of 1500 ppm, the maximum efficiency of paraffin inhibition of 45.6% was achieved at 200 rpm and 5 °C. Besides, the best performance in depressing the pour point by 14 °C was observed at a concentration of 1500 ppm, which can change the growth characteristics of wax crystals and delay the aggregation of wax and resin, thus effectively improving the flowability of crude oil. Also, from these results can conclude that the synthesised polymer can alter the wax crystals’ morphology, prevents agglomeration in general, and can act as an efficient flow improver. From the MD simulation result, the RDF value in the pure wax system (n-icosane-n-icosane) is 2.75 Å which shifted to 3.25 Å after using (BA-co-SMA-co-MA). The RDF value shift may indicate that the dissolution of wax molecules in wax inhibitors occurs through the breaking of H57 •••H60 bonding. As a result, poly(BA-co-SMA-co-MA) weakens the van der Waals interaction, lowering the interaction between wax molecules and modifying crystal morphology. As a consequence, the presence of this wax inhibitor reduces the ability of wax molecules to coalesce, making adherence to wax surfaces less desirable