A project dissertation submitted to the Universiti Teknologi PETRONAS Chemical Engineering Program in partial fulfillment of the requirement for. Its molecular structure in crude oil is said to be undetermined, making it difficult to study asphaltene precipitation, which has long been problematic for the oil and gas industry. Examining past studies, the effects of oil composition and titrant type were analyzed to be able to further explain this topic.
Based on a study on the effect of bulk temperature on the precipitation of asphaltenes, the Automatic Flocculation Titration which refers to the Heithaus test method becomes the main equipment and concept that will be used to carry out the study in this project. The results from the test method require the determination of the Hildebrand solubility parameters related to the relationship between the solubility of asphaltenes and precipitation; high solubility of asphaltenes, low chance of precipitation. She has been supportive from the beginning of the project to the final presentation of the report.
Mona often came together to the lab to teach me about the procedures to be performed and even to solve problems together, despite her busy schedule. Without them I could not be as passionate as I am until the end of the project.
INTRODUCTION
- Background
- Flocculation/Precipitation
- Problem Statement
- Research Objectives
- Scope of Study
- Oil composition
- Titrant type
Anderson (1999) applied the flocculation-onset-titration method to estimate the precipitation and stability of asphaltenes in crude oil. This mathematical modeling has been used in predicting the precipitation and solubility of asphaltenes for different crude oils under different operating conditions. In the study of asphaltene precipitation, the mechanism of asphaltene flocculation and precipitation has been mentioned in numerous studies.
The existing studies on asphaltene precipitation are not unanimous in their conclusions about the mechanism of asphaltene precipitation. Based on the background studies and the defined problems, two parameters are believed to be instrumental in the asphalt precipitation studies. The study of the oil composition is carried out by changing the type of crude oil used in accordance with the different titrants used.
Based on the defined objectives, the research on the two parameters has been limited and defined to characterize the oil composition and titrant type. The research will analyze the relationship between the carbon number of commonly used n-alkanes and the precipitation behavior of asphaltenes.
LITERATURE REVIEW
- Automated Flocculation Titrimeter
- Effect of oil composition
- Effect of tirant type
- Summary
FR, which stands for flocculation ratio, is the fraction of the volume of solvent to the total volume of solvent-titrant mixture at the starting point of flocculation. This can be explained by an increasing number of asphaltenes that precipitate, indicating a higher proportion of asphaltenes. The change in molecular structures of asphaltenes can lead to phase changes and solid formation.
Some simple calculations are stated using SARA fractions to understand the stability of asphaltenes. The injection of titrant to induce precipitation is said to vary depending on the type of solvent. According to Arciniegas & Babadagli, as the solvent carbon number decreases, the hair size increases.
Compared to propane and butane, n-heptane is more solvent due to its lower viscosity reduction and is therefore slower to precipitate asphaltenes and resins. The scope to represent oil composition can be represented by fractal composition of saturates, aromatics, resins and asphaltenes.
METHODOLOGY
- Equipment
- Experimental Design
- Crude Oil & Titrant Properties
- Experimental Procedures
- Preparation of Sample
- Preparation of AFT (Automated Flocculation
- Test run with AFT
- Cleaning
- SARA Analysis
- Asphaltenes separation
- Maltenes Analysis
- Result Analysis Method
- Gantt Chart & Milestones
Based on the studies done earlier, the composition of the crude oil and the type of titrant will be manipulated in the experimental work. Within the first 7 weeks, the focus is on getting the result by manipulating the crude oil and solvent used. Three types of crude oil are selected to be investigated and represent three different types of crude oil.
Crude oil samples in a 30 ml vial are weighed accordingly using electronic balance weighing machine from Shimadzu (AX120). The sample inlet and outlet tubing should be purged by allowing the toluene to circulate for several minutes. The sample vials are kept in an oven for 12 hours at a maximum of 60 degrees Celsius before being used again to ensure evaporation of the water and toluene.
The three different crude oils must be measured using high performance liquid chromatography and gravimetry. A weighing container with filter paper is kept in an oven at more than 100 degrees Celsius for 15 minutes. Crude oil is heated to a boiling point of approximately 97 degrees Celsius and allowed to boil for 30 minutes.
The cooled crude oil is poured into the weighing container with filter paper placed in the filter flask. 10 ml, 5 ml and 5 ml of N-heptane are added to the crude oil to allow the asphaltenes to flocculate. The weighing pan is then placed in an oven for 15 minutes at more than 100 degrees Celsius.
Standards are injected into columns and the area under the refractive index curve is calculated for the calibration curve graph. Resin solution is placed in a glass flask to allow evaporation using a rotary evaporator. The parameters of both Heithaus and Hildebrand are calculated from the raw data of the AFT result.
RESULTS AND DISCUSSION
SARA Fractions
From the figure, Arab Light appears to contain the highest amount of resins compared to other crude oils at 22.43 wt%. It has been proven that Wafra Ratawi contains the largest amount of asphaltene fractions, which is supported by the analysis of crude analysis in any crude oil. For saturates, Pyrenese has been roughly analyzed to contain more saturates compared to Ratawi and Arab Light.
Heithaus Parameters Analysis
- Pa parameter
- Po parameter
- P Parameter
In the aspect of different crude oil, Pa is higher for Pyrenees, followed by Arabian Light and Ratawi in general. However, even with large differences in the composition of asphaltenes, Pa values for Ratawi and Arabian Light are vague. The effect of resins may explain the similar behavior of Pa values for Ratawi and Arabic Light.
This explains on the same concept with Pa values where the contribution of asphaltene fractions to solvency properties of asphaltenes in oil is not reliable. Likewise, the carbon number effect of titrant does not show constant tendency to the precipitate. Figures 4.10 and 4.11 above clearly show the effect of saturates causing low solvency properties of asphaltenes, but isooctane shows contradictory behaviour.
Having a larger amount of aromatics for Arabian Light does not help to increase the dispersion forces for asphaltenes, therefore Po parameters show typical values compared to others. Similar to Po parameter, increasing amount of asphaltenes does not give decreasing trend of P values. The overall stability parameters are generally higher at Arab Light with the second most asphaltene fractions for hexane and heptane conditions.
Referring to resin fractions, he explains the behavior of P values that are higher in Arabic light.
Hildebrand’s Solubility Parameter
- δ oil
- δ as
Figures 4.17 and 4.18 above show that δoil is highest in the Pyrenees, followed by Wafra Ratawi and Arab Light. This is reasonable because it proves a study on the effect of asphaltene composition on precipitation. As for titrant, increasing number of carbon atoms of titrant does not lead to increase in δoil.
Referring to the effect of resin fractions against δoil, δoil is lowest at Arab Light despite having the highest resin content followed by Wafra Ratawi and Pyrenese. This behavior may be caused by other factors taken into account in the calculation of δoil. Based on Figures 4.19 and 4.20 above, a high amount of saturates does not reflect the high solubility of the system, which contradicts the Heithaus Parameter Analysis.
For the Hildebrand solubility parameter, the consideration of titrant used, solvent solubility and the flocculation ratio create more detailed interaction between different aspects. The oil itself may not be so solvent-like, which may not directly affect the precipitation behavior of the asphaltenes. The two figures 4.21 and 4.22 show the δas relation with regard to asphaltenes and resin fractions and different titrants.
The higher the solubility of asphaltenes, the better the interaction with other components causing less chance of precipitation. Resins and asphaltenes may not have a strong influence on the solubility state of the asphaltenes in relation to the system. The trend similar to δ oil, δas in the saturated and aromatic fractions show a linear relationship, which is the opposite of the Heithaus Parameter Analysis.
CONCLUSION AND RECOMMENDATION
Conclusion
Recommendation
