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Use of surfactants for crude oil-in-water emulsions demulsification
Author(s)
Ngoupeyou, Edith Laure Yonguep
Date Issued
2020
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
Enhanced oil recovery (EOR), known as tertiary crude oil recovery, is an important technique
applied by the petroleum industries to improve crude oil recovery. Over 30 to 60% of the
original oil in place (OOIP) is improved by this technique as compared to primary and
secondary techniques. However, the EOR technique results in the formation of stable waterin-
oil and oil-in-water emulsions. Emulsions are undesirable in the petroleum industry as
these add to the overall production cost and also to the loss of valuable amounts of crude oil.
It is therefore essential for economic and environmental reasons to demulsify these
emulsions in order to separate the oil from water. Chemical demulsification (use of
demulsifiers to separate oil from water) is the most commonly practiced method to treat
these emulsions. Nevertheless, no studies have been reported on the use of response
surface methodology (RSM) to optimize the demulsification efficiency of crude oil-in-water
emulsions resulting from the EOR technique.
This study aims to investigate the effectiveness of two demulsifiers, namely cetyl
trimethylammonium bromide (CTAB), and trimethyl-tetradecyl ammonium chloride (TTAC)
on the demulsification efficiency of crude oil-in-water emulsions resulting from EOR
techniques using response surface methodology (RSM). In order to achieve this aim,
synthetic oil-in-water emulsions containing various oil to water ratios (15:85, 25:75, 35:65
and 45:55) were simulated with diesel as the oil phase. The emulsion stability index (ESI) of
the simulated oil-in-water emulsions was investigated based on the emulsifier concentration,
homogenization speed, brine salinity and oil to water ratio. The result showed that an
increase in the homogenization speed and surfactant concentration helped to achieve better
ESI. It was also observed that high brine salinity led to poor emulsion stability for this case
study. In addition, the oil to water ratio did not have much influence on the emulsions’
stability index as long as the homogenization speed was as high as 24000 rpm. In this study,
2% surfactant concentration, 24000 rpm homogenization speed and 1000 ppm NaCl were
the optimal conditions to formulate the emulsions. At this condition, the ESI of 15:85, 25:75,
35:65 and 45:55 was found to be 99.3, 92.5, 91.2, and 90% respectively.
Central composite design (CCD) and response surface methodology (RSM) was used to
design and optimize the settling time, demulsifier concentration and the oil to water ratio on
the demulsification efficiency of CTAB and TTAC. The results showed that the settling time,
demulsifiers concentration, oil to water ratio as well as the interaction between the
demulsifiers concentration and oil to water ratio had significantly impacted the response
(demulsification efficiency) because of their p-values < 0.0001.
The quadratic model obtained was proven to be significant with the F-value of 16.03 and
16.63 for CTAB and TTAC demulsifiers respectively. The coefficient of determination (R2)
was found to be 0.944 and 0.863 for CTAB and TTAC demulsifiers respectively. These high
values validated the accuracy of the model. The results revealed that a maximum
demulsification efficiency of 82.6% and 80% was achieved by adding 850 ppm of CTAB and
TTAC demulsifier and settling for 10 h with 15 and 25% diesel in water (D/W) emulsions
respectively. These were proven to be the optimum conditions for maximum oil recovery for
this case study.
It was also found that ageing the emulsion could greatly influence the performance of the
demulsifier. This study showed ageing of the emulsions decreased the demulsification
efficiency of CTAB from 86.66 for fresh emulsions to 50% after ageing the emulsions for 60
days.
applied by the petroleum industries to improve crude oil recovery. Over 30 to 60% of the
original oil in place (OOIP) is improved by this technique as compared to primary and
secondary techniques. However, the EOR technique results in the formation of stable waterin-
oil and oil-in-water emulsions. Emulsions are undesirable in the petroleum industry as
these add to the overall production cost and also to the loss of valuable amounts of crude oil.
It is therefore essential for economic and environmental reasons to demulsify these
emulsions in order to separate the oil from water. Chemical demulsification (use of
demulsifiers to separate oil from water) is the most commonly practiced method to treat
these emulsions. Nevertheless, no studies have been reported on the use of response
surface methodology (RSM) to optimize the demulsification efficiency of crude oil-in-water
emulsions resulting from the EOR technique.
This study aims to investigate the effectiveness of two demulsifiers, namely cetyl
trimethylammonium bromide (CTAB), and trimethyl-tetradecyl ammonium chloride (TTAC)
on the demulsification efficiency of crude oil-in-water emulsions resulting from EOR
techniques using response surface methodology (RSM). In order to achieve this aim,
synthetic oil-in-water emulsions containing various oil to water ratios (15:85, 25:75, 35:65
and 45:55) were simulated with diesel as the oil phase. The emulsion stability index (ESI) of
the simulated oil-in-water emulsions was investigated based on the emulsifier concentration,
homogenization speed, brine salinity and oil to water ratio. The result showed that an
increase in the homogenization speed and surfactant concentration helped to achieve better
ESI. It was also observed that high brine salinity led to poor emulsion stability for this case
study. In addition, the oil to water ratio did not have much influence on the emulsions’
stability index as long as the homogenization speed was as high as 24000 rpm. In this study,
2% surfactant concentration, 24000 rpm homogenization speed and 1000 ppm NaCl were
the optimal conditions to formulate the emulsions. At this condition, the ESI of 15:85, 25:75,
35:65 and 45:55 was found to be 99.3, 92.5, 91.2, and 90% respectively.
Central composite design (CCD) and response surface methodology (RSM) was used to
design and optimize the settling time, demulsifier concentration and the oil to water ratio on
the demulsification efficiency of CTAB and TTAC. The results showed that the settling time,
demulsifiers concentration, oil to water ratio as well as the interaction between the
demulsifiers concentration and oil to water ratio had significantly impacted the response
(demulsification efficiency) because of their p-values < 0.0001.
The quadratic model obtained was proven to be significant with the F-value of 16.03 and
16.63 for CTAB and TTAC demulsifiers respectively. The coefficient of determination (R2)
was found to be 0.944 and 0.863 for CTAB and TTAC demulsifiers respectively. These high
values validated the accuracy of the model. The results revealed that a maximum
demulsification efficiency of 82.6% and 80% was achieved by adding 850 ppm of CTAB and
TTAC demulsifier and settling for 10 h with 15 and 25% diesel in water (D/W) emulsions
respectively. These were proven to be the optimum conditions for maximum oil recovery for
this case study.
It was also found that ageing the emulsion could greatly influence the performance of the
demulsifier. This study showed ageing of the emulsions decreased the demulsification
efficiency of CTAB from 86.66 for fresh emulsions to 50% after ageing the emulsions for 60
days.
Additional information
Thesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2020
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