CHANCELLOR COLLEGE BIODIESEL RESEARCH-Biodiesel Properties

Measurement of Physical and Chemical Properties

Viscosity Measurements

Dynamic viscosity measurement were carried out at Lever Brothers plc. laboratories in Blantyre. The viscometer used was a Brookfield Synchroro Viscometer. Measurements, for all oils and esters, and also for mineral diesel [Petroda], were taken at three different temperatures, 20^oC, 40^oC and 70^oC. The measurements at 70^oC were carried out as this is the approximate temperature of a fuel as it enters the combustion chamber in an engine. From the measurements taken, values of kinematic viscosity could then be found.

Density

Density measurements were carried out using a pyconometer.

Acid Value

The acid value was found using the techinique descibed by Cocks and van Rede (1966).

Free Glycerol

To determine the level of free glycerol, a weighed amount of oil or ester was placed into a beaker, and diluted to approximately 50ml with water. Five to seven drops of bromothymol blue indicator were added to the solution, which was then acidified using 0.2M sulphuric acid solution to give a definite green colour. The solution was then neutrolised by titration with 0.05M sodium hydroxide solution.

Miscibility

The miscibility of the oil or ester was considered by mixing volumes of the oil or ester with diesel, in the range of 0% to 100% of the oil or the ester. The mixtures were shaken vigorously and then left to allow any layers to separate out. A visial observation of two layers was described as an immiscible mixture.

Results

Vegetable oils

The measured physical properties of the vegetable oils are shown in table 1. The values for diesel measured using the same techniques, are included for comparison, as are the ASTM standards for biodiesel

 

Oil	Kinematic Viscosity at 20oC (x10-6m2s-1)	Kinematic Viscosity at 40oC (x10-6m2s-1)	Kinematic viscosity at 70oC (x10-6m2s-1)	Density (kgm-3)	Acid value (mgKOH/g)	Glycerol (wt%)	Miscible
Castor	961	268	61.9	993	0.022	4.12	Between 70% and 100% oil
Cotton seed	85.0	43.7	23.2	951	7.073	18.40	0-100% oil
Groundnut	91.8	41.4	27.6	942	3.185	5.43	0-100% oil
Moringa oil	53.7	39.1	21.7	919	22.754	11.47	insufficient oil
Rubber seed	44.0	39.9	33.0	920	10.814	4.00	insufficient oil
Soya bean	74.1	35.8	30.7	950	0.669	5.50	0-100% oil
Sunflower	78.9	45.6	24.7	953	2.124	7.64	0-100% oil
Petroda Diesel	22.8	12.3	8.53	879	4.17x10-4	0.70	-
ASTM Standard	-	1.9-6.0	-	-	0.8 max	0.02 max	-

Table 1.

Methyl Esters

The physical and chemical properties of the methyl esters produced are shown in Table 2. Again these values are accompanied with those for Petroda and the ASTM Standard.

 

Methyl Ester	Kinematic Viscosity at 20oC (x10-6m2s-1)	Kinematic Viscosity at 40oC (x10-6m2s-1)	Kinematic Viscosity at 70oC (x10-6m2s-1)	Density (kgm-3)	Acid Value (mgKOH/g)	Glycerol  (wt%)
Castor	40.6	19.4	15.8	956	6.24x10-3	80.39
Cotton seed	25.0	23.1	16.1	921	2.04x10-3	3.44
Groungnut	22.0	15.4	7.16	908	7.20x10-4	1.03
Moringa	22.4	13.3	11.1	903	2.13x10-3	0.81
Rubber seed	23.9	21.7	19.8	891	6.29x10-3	21.91
Soya bean	18.8	11.1	6.56	915	1.56x10-3	8.69
Sunflower	18.9	13.2	8.80	909	3.07x10-3	4.46
petroda Diesel	22.8	12.3	8.53	879	6.24x10-3	0.7
ASTM standard	-	1.9-6.0	-	-	0.8 max	0.02 max

Table 2.

Discussion

Viscosity Measurements : The viscosity of the proposed biodiesel is important when considering the spray characteristics of the fuel within the engine, since the change in spray can greatly alter the combustion properties of the mixture. From the results obtained it can be seen that the esterification of vegetable oils produced a marked decrease in values of viscosity measured, and it was found that in general, the measured viscosities of methyl esters were approximately equal to the value measured for diesel over the range of temperatures considered. This would give an indication that the methyl esters, especially those of groundnut, soye bean and sunflower, are suitable as a possible diesel substitute. It should be noted however that all the values quoted from the ASTM standards, and further work needs to be carried out to determine the reasons for this - it is possibly due to an excess of glycerol remaining in the ester - and to look at the possible methods of reducing the viscosity to a suitable level.

Acid Values : The acid value of the oils or the esters gives an indication of the quantity of fatty acids present in the sample. The acid values obtained for vegetable oils reflect the high fatty acid content of the oils, and it can be seen that all the oils, apart from castor and soya bean have values exceeding those given by ASTM. The effect of esterification is to reduce the level of fatty acids greatly, and it was found that all methyl esters had acid values very much less than the ASTM levels.

Glycerol : The glycerol level in the oil or ester is important as it can affect the running of an engine in a negative way [Meyer 1993]. It can be seen from the results given that the glycerol levels in all oils and esters tested were above the maximum values qouted by the ASTM, which would indicate that none of them are suitable for use in engines. However, the levels found in the esters were very high due to the glycerol being a by-product of the esterification process. The glycerol is usually removed by washing, but the results show that an improved washing system needs to be found in order to produce glycerol levels in line with the ASTM.

Miscibility : Since the use of oil/diesel blends is quite common, it is important to consider the mixing properties of the oils and the esters with mineral diesel fuel. Unifortunately the range the test was restricted by the limited volumes of some of the oils. However all of the oils tested, apart from castor, were found to be fully miscible which would indicate that they could be suitable for diesel blending.

Conclussion

From the the discussion of the processes and the results obtained, it can be seen that there are currently several options available in Malawi in terms of fuel production from locally available vegetable sources. Of the oils investigated, there were none that matched the required ASTM standards. These oils could therefore not be used as a sole component of a fuel, although there is always a possibility of blending with diesel to produce a compound fuel.
The methyl esters however fulfil the ASTM standard for acid value. The values of viscosity measured were close to those of the standard, but this could be reduced by blending the esters with diesel to reduce the viscosity to the required level. The reason for excess glycerol has already been discussed and it is hoped in future to be able to reduce the value to acceptable levels by suitable processing of the ester. The methyl esters of the oils show a great deal of promise, however, as a locally produced fuel in Malawi. It is accepted that several of the source oils have importance as food, and it is suggested that any future work be concentrated on moringa and and rubber seed methyl esters.