The Thermodynamic Research Of Wax Precipitation In Crude Oils

When crude oils are transported at low temperature, the plug of pipeline caused by waxprecipitation influences the transportation and production of crude oils. At present, manyphysical and chemical methods are used to solve this problem. Adding Chemical pour pointdepressants (PPD) to the oils have been applied extensively because of its simple operation,low investment and non-after treatments. As a result, it is important to study the effects ofpour point depressants (PPD) on wax precipitation from oil. Due to the complexity of thecrude oil, the research works mainly focus on the precipitated wax from the simulation oil.This work involves both experiments and thermodynamic models. Specific details are asfollows:(1) The amount of wax precipitated at different temperatures is measured by the highspeed centrifuge which can separate precipitated wax from oil under specific temperature;(2) The carbon number distributions and composition of simulation oil, PPDconcentration, and the oil with PPD are measured by gas chromatography.(3) The WAT are measured by differential scanning calorimetry (DSC);A series of experimental data can be obtained through the above methods, and then thedata are used for the model input data.(4) The modified regular solution thermodynamic theories and modified thermodynamicsolid-liquid equilibrium model are used to calculate wax appearance temperature (WAT),theamount of wax precipitation and distributions of carbon number with and without the PPDadded.The influence of PPD concentration on WAT and the amount of wax precipitation atdifferent temperatures as well as the wax contents on PPD are measured in this work.According to the experiments, the results indicate that: the WAT of oil decreased when PPDis added, and the value of WAT slow down the incensement when the PPD is eontinuinglyadded; the amount of wax precipitation at different temperatures are all decreased when PPDis added; Along with the increase of wax content, the sensitivity of PPD get worse; Thecarbon number distributions curves of precipitated wax show double peaks(it is similar withthe distributions of the original wax, but the percentage of every carbon number isdifferent); PPD restrains the deposition of hydrocarbon of small carbon number in thesimulation oil, and promotes the deposition of hydrocarbon of large carbon number. In the model confirmation aspect, the simulation results and experiment data are in agood agreement when the experiment is carried out without PPD. On the other hand, whenPPD is added, the model is modified by the eutectic theory, and the simulation results showsgreat consistency with the experiment data of high-wax oils.