Improved oxidative stability of biodiesel via alternative processing methods using cottonseed oil

Figures & data

Figure 1. Chemical structures of glycerol and two naturally occurring antioxidants found in cottonseed oil: α-tocopherol and gossypol.

Figure 2. Laboratory set-up and process diagram.

Note: Cell homogeniser, temperature probe, hot plate, with Erlenmeyer reactor for transesterification. Washing and drying operations with waste streams indicated.

Table 1. Free and total glycerol in batch processes compared to limits specified in ASTM D6751 and EN 14214, and residual glycerides.

Processing method	Batch number	Monoglyceride (mass %)	Diglyceride (mass %)	Triglyceride (mass %)	Free glycerol (mass %)	Bound glycerol (mass %)	Total glycerol (mass %)
ASTM D6751 maximum limits					0.020		0.240
EN 14214 maximum limits					0.020		0.250
Mixed oil process	1	0.024	0.480	0.800	0.003	0.161	0.164
	2	0.025	0.184	0.081	0.002	0.042	0.045
	3	0.026	0.180	0.057	0.002	0.039	0.041
Separate oil process	1	0.024	0.152	0.142	0.001	0.044	0.045
	2	0.022	0.155	0.101	0.002	0.039	0.041
	3	0.025	0.195	0.129	0.003	0.049	0.052
Reduced WCO glycerine process	1	0.024	0.702	1.553	0.002	0.273	0.275
	2	0.025	0.188	0.120	0.002	0.049	0.049
	3	0.025	0.599	1.204	0.002	0.221	0.223
WCOME extraction process	1	0.025	0.183	0.135	0.001	0.048	0.049
	2	0.025	0.187	0.157	0.002	0.051	0.053
	3	0.025	0.196	0.176	0.002	0.054	0.056

Table 2. Acid values of batch processes compared to limits specified in ASTM D6751 and EN 14214.

Processing method	Process batch number	Acid value average (mg KOH/g ME)	Standard deviation (mg KOH/g ME)
ASTM D6751 maximum limit		0.50
EN 14214 maximum limit		0.50
Mixed oil process	1	0.02	0.01
	2	0.04	0.01
	3	0.08	0.01
Separate oil process	1	0.07	0.00
	2	0.01	0.00
	3	0.03	0.00
Reduced WCO glycerine process	1	0.08	0.01
	2	0.02	0.02
	3	0.02	0.01
WCOME extraction process	1	0.06	0.02
	2	0.05	0.03
	3	0.05	0.00

Table 3. Moisture content of batch processes compared to limits specified in ASTM D6751 and EN 14214.

Processing method	Process batch number	Moisture content average (ppm)	Standard deviation (ppm)
ASTM D6751 maximum limit		500
EN 14214 maximum limit		500
Mixed oil process	1	356	9
	2	395	11
	3	443	7
Separate oil process	1	323	6
	2	301	12
	3	370	2
Reduced WCO glycerine process	1	325	4
	2	291	2
	3	436	6
WCOME extraction process	1	309	7
	2	327	5
	3	502	1

Table 4. Kinematic viscosity of batch processes compared to limits specified in ASTM D6751 and EN 14214.

Processing method	Process batch number	Kinematic viscosity average (mm^2/s @ 40C)	Standard deviation (mm^2/s @ 40 C)
ASTM D6751 min–max		1.9–6.0
EN 14214 min–max		3.5–5.0
Mixed oil process	1	4.66	0.00
	2	4.57	0.01
	3	4.57	0.01
Separate oil process	1	4.47	0.00
	2	4.50	0.00
	3	4.49	0.00
Reduced WCO glycerine process	1	4.68	0.01
	2	4.46	0.00
	3	4.66	0.01
WCOME extraction process	1	4.41	0.00
	2	4.46	0.00
	3	4.43	0.00

Figure 3. Cloud point comparison.

Note: Cloud point of twelve process batches compared with three batches of CSOME and three batches of WCOME, indicating strong influence of WCO properties.

Figure 4. Pour point comparison.

Note: Pour point of twelve process batches compared with three batches of CSOME and three batches of WCOME, indicating strong influence of WCO properties.

Table 5. Average induction period for raw oils: CSO, WCO, and 4:1 WCO:CSO blend with oil means and standard deviations.

Raw oil source	Induction period average (h)	Oil mean (h)	Standard deviation (h)
Cottonseed oil (CSO)	29.08
	24.95	28.52	3.33
	31.53
Waste cooking oil (WCO)	0.42
	0.43	0.43	0.01
	0.43
4:1 WCO:CSO blend	20.06
	19.80	19.93	0.13
	19.93

Table 6. Average induction period for process batches and process means compared to the IP limits specified in ASTM D6751 and EN 14214, with process standard deviations.

Processing method	Induction period average (h)	Process mean (h)	Process standard deviation (h)
ASTM D6751 minimum		3.0
EN 14214 minimum		6.0
Mixed oil process	0.76
	0.65	0.64^a	0.12
	0.52
Separate oil process	1.40
	1.11	1.14^a	0.25
	0.91
Reduced WCO glycerine process	2.01
	1.56	1.74^b	0.24
	1.65
WCOME extraction process	1.92
	1.80	1.95^b	0.17
	2.13

^a,b Means that do not significantly differ have the same letter (a,b).

Table 7. Peroxide values of batch process averages, process means and process standard deviations.

Processing method	Peroxide value average (meq peroxide/kg)	Process mean (meq peroxide/kg)	Standard deviation (meq peroxide/kg)
Mixed oil process	10.6
	11.0	10.7^a	0.31
	10.4
Separate oil process	11.3
	10.4	10.7^a	0.49
	10.5
Reduced WCO glycerine process	10.2
	10.6	10.5^a	0.23
	10.6
WCOME extraction process	10.4
	10.8	10.5^a	0.31
	10.2

^a Means that do not significantly differ have the same letter (a).