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Investigation of potential of a bifunctional catalyst for the simultaneous esterification and transesterification of high free fatty acid feedstock
Author(s)
Maina, Linda
Date Issued
2021
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
There has been growing concern around the depletion of the world’s oil reserves as well as the
negative environmental impacts fossil fuels pose. Therefore, there has been a crucial demand
in the exploration of clean, sustainable, and alternative fuels/ fuel sources. Biodiesel, which
can be derived from edible plant oils, waste oils as well as animal fats has been regarded as a
clean, renewable and feasible substitute for diesel compression ignition engines without the
need for modification.
This study aimed to investigate the simultaneous esterification and transesterification of
various feedstocks using bi-functional catalysts. Four catalysts consisting of varying ratios of
CaO and Al2O3 were synthesised through co-precipitation in order to ensure their
bifunctionality where CaO provided basic sites and Al2O3 provided acidic sites. The four
catalysts (CaO: Al2O3 ratios of 80:20, 70:30, 60:40, and 50:50) were calcined at a temperature
of 600 °C. Catalysts were characterised using Brunauer Emmet Teller (BET), Scanning
Electron Microscope (SEM) and X-Ray diffraction (XRD). They exhibited adequate
morphological and catalytic characteristics where pore sizes were ≥209 Å, surface areas ≥11
m2/g and pore volumes ≥0.072 cm3/g.
Seven feedstock samples were used: 3 virgin oils (canola (VCO), sunflower (VSO) and palm
(VPO)), 4 non-edible oils (waste canola (WCO), waste sunflower (WSO), waste palm (WPO)
and neem oil (NO)). Free fatty acid contents ranged from 0.22 to 3.25%. Feedstocks were pretreated
through filtration, to eliminate solid particles and dehydrated to reduce moisture.
Thereafter, each feedstock underwent simultaneous esterification and transesterification using
the four catalysts. These experiments were carried out at temperature of 65 °C, agitation rate
of 1200 rpm, 2.5 wt% catalyst loading and a methanol to oil molar ratio of 12:1 at a reaction
time of 4 hours under reflux as the optimised conditions stipulated by (Zabeti et al., 2009).
The results showed that feedstocks with low FFA content required catalysts with less acidic
sites to produce the highest yield of biodiesel. In contrast, feedstock with a high FFA content
(>1 wt%) favoured a catalyst with a higher quantity of acidic sites. This was evident as VPO,
VCO and VSO, which had FFA contents of 0.67%, 0.33% and 0.22% respectively, performed
optimally through the use of 80% CaO:20%Al2O3 with yields of 97.85%, 98.95% and 95.6%
respectively. Neem oil, which had the highest FFA content of 3.25% achieved the highest yield
(97.63%) with the use of a catalyst with more acidic sites (60% CaO: 40%Al2O3). Therefore,
the relationship between FFA and acid site quantity was evident.
The effect of feedstock saturation on catalyst performance was also investigated. The highly
saturated feedstocks (WPO and NO) had a saturated fatty acid (SFA) content of 46.79 and
44.06%, respectively, where the highly unsaturated feedstocks (SO and WSO) had a
polyunsaturated fatty acid (PUFA) content of 67.8 and 64.0%, respectively. Monounsaturated
fatty acids (MUFA) were dominant in WCO and CO at values of 66.6 and 71.2%, respectively.
There were negligible differences in yields between PUFA, MUFA and SFA dominant
feedstocks. It was evident that the degree of unsaturation of the feedstock had no significant
effect on catalyst performance.
Transportation fuel characteristics of the biodiesel synthesised were also determined. These
included oxidation stability, density, kinematic viscosity, flash point, sulphur content, total acid
number (TAN) and water content in accordance with the ASTM reference test methods
(D4502, D 664, D 445, D 93, D 5453 and D 2709). Biodiesel density values ranged from 0.88
to 0.889 g/m3, viscosity from 0.4 to 30.4 cSt, flash point from 130 to 170 °C, sulphur content
from 0 to 334 ppm, TAN from 0.17 to 0.88 mgKOH/g and water content from 0.02 to 0.19
wt% The RANCIMAT procedure was also utilised for the measurement of induction time/
oxidation stability. The fuels adhered to the ASTM and EU restrictions with the exception to
neem oil biodiesel (NB100). This was attributed to the physio-chemical nature of the
corresponding feedstock used. Catalyst robustness was also investigated. It was found that all
four catalysts maintained excellent catalytic activity for up to 8 runs. Loss of catalytic activity
thereafter was attributed to loss of mass during the cleaning and drying process as well as
exposure to moisture and air. The current study provided evidence for the need to synthesise
tailor-made bifunctional catalysts with robust nature for the E and TE of low-cost feedstocks.
negative environmental impacts fossil fuels pose. Therefore, there has been a crucial demand
in the exploration of clean, sustainable, and alternative fuels/ fuel sources. Biodiesel, which
can be derived from edible plant oils, waste oils as well as animal fats has been regarded as a
clean, renewable and feasible substitute for diesel compression ignition engines without the
need for modification.
This study aimed to investigate the simultaneous esterification and transesterification of
various feedstocks using bi-functional catalysts. Four catalysts consisting of varying ratios of
CaO and Al2O3 were synthesised through co-precipitation in order to ensure their
bifunctionality where CaO provided basic sites and Al2O3 provided acidic sites. The four
catalysts (CaO: Al2O3 ratios of 80:20, 70:30, 60:40, and 50:50) were calcined at a temperature
of 600 °C. Catalysts were characterised using Brunauer Emmet Teller (BET), Scanning
Electron Microscope (SEM) and X-Ray diffraction (XRD). They exhibited adequate
morphological and catalytic characteristics where pore sizes were ≥209 Å, surface areas ≥11
m2/g and pore volumes ≥0.072 cm3/g.
Seven feedstock samples were used: 3 virgin oils (canola (VCO), sunflower (VSO) and palm
(VPO)), 4 non-edible oils (waste canola (WCO), waste sunflower (WSO), waste palm (WPO)
and neem oil (NO)). Free fatty acid contents ranged from 0.22 to 3.25%. Feedstocks were pretreated
through filtration, to eliminate solid particles and dehydrated to reduce moisture.
Thereafter, each feedstock underwent simultaneous esterification and transesterification using
the four catalysts. These experiments were carried out at temperature of 65 °C, agitation rate
of 1200 rpm, 2.5 wt% catalyst loading and a methanol to oil molar ratio of 12:1 at a reaction
time of 4 hours under reflux as the optimised conditions stipulated by (Zabeti et al., 2009).
The results showed that feedstocks with low FFA content required catalysts with less acidic
sites to produce the highest yield of biodiesel. In contrast, feedstock with a high FFA content
(>1 wt%) favoured a catalyst with a higher quantity of acidic sites. This was evident as VPO,
VCO and VSO, which had FFA contents of 0.67%, 0.33% and 0.22% respectively, performed
optimally through the use of 80% CaO:20%Al2O3 with yields of 97.85%, 98.95% and 95.6%
respectively. Neem oil, which had the highest FFA content of 3.25% achieved the highest yield
(97.63%) with the use of a catalyst with more acidic sites (60% CaO: 40%Al2O3). Therefore,
the relationship between FFA and acid site quantity was evident.
The effect of feedstock saturation on catalyst performance was also investigated. The highly
saturated feedstocks (WPO and NO) had a saturated fatty acid (SFA) content of 46.79 and
44.06%, respectively, where the highly unsaturated feedstocks (SO and WSO) had a
polyunsaturated fatty acid (PUFA) content of 67.8 and 64.0%, respectively. Monounsaturated
fatty acids (MUFA) were dominant in WCO and CO at values of 66.6 and 71.2%, respectively.
There were negligible differences in yields between PUFA, MUFA and SFA dominant
feedstocks. It was evident that the degree of unsaturation of the feedstock had no significant
effect on catalyst performance.
Transportation fuel characteristics of the biodiesel synthesised were also determined. These
included oxidation stability, density, kinematic viscosity, flash point, sulphur content, total acid
number (TAN) and water content in accordance with the ASTM reference test methods
(D4502, D 664, D 445, D 93, D 5453 and D 2709). Biodiesel density values ranged from 0.88
to 0.889 g/m3, viscosity from 0.4 to 30.4 cSt, flash point from 130 to 170 °C, sulphur content
from 0 to 334 ppm, TAN from 0.17 to 0.88 mgKOH/g and water content from 0.02 to 0.19
wt% The RANCIMAT procedure was also utilised for the measurement of induction time/
oxidation stability. The fuels adhered to the ASTM and EU restrictions with the exception to
neem oil biodiesel (NB100). This was attributed to the physio-chemical nature of the
corresponding feedstock used. Catalyst robustness was also investigated. It was found that all
four catalysts maintained excellent catalytic activity for up to 8 runs. Loss of catalytic activity
thereafter was attributed to loss of mass during the cleaning and drying process as well as
exposure to moisture and air. The current study provided evidence for the need to synthesise
tailor-made bifunctional catalysts with robust nature for the E and TE of low-cost feedstocks.
Additional information
Thesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2021
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