• Poor low temperature fluidity and higher pour point:

The presence of long chain and saturated fatty acids of vegetable oils makes them crystallize at higher temperatures than mineral oils. Higher melting point of vegetable oils is also for the same reason. Highly saturated fatty acids containing vegetable oils such as coconut and palm oils show higher pour point. The presence of double bonds in the monounsaturated and polyunsaturated fatty acids forms a kink structure due to which they crystallize at a lower temperature than saturated fatty acids [8].

• Hydrolytic Stability:

Vegetable oils are highly susceptible to hydrolysis in the presence of water to produce corrosive acidic breakdown products as compared to mineral-based oils. The carboxylic acids formed by hydrolysis may corrode metal bearings, affect seals and shorten life [2]

• Poor resistance to foaming:

Presence of foam reduces the lubrication properties of a lubricant. Vegetable oils produce higher foam than mineral-based oils.

• Limited resistance to oxidation in storage:

The presence of mono-unsaturation and poly-unsaturation promotes the autooxidation of vegetable oils during storage. Another cause for auto-oxidation is the presence of beta proton in the triglyceride structure. The electron shift in the beta carbons weakens the C-O bonds and breaks off the ester bond to form carboxylic acids. Refined vegetable oils are devoid of natural antioxidants that are present in unrefined oils which make the former more susceptible to oxidation [12, 13].

• Tendency to clog the filter:

The high viscosity of vegetable oils and oxidized vegetable oils due to the presence of polymerized products cause the clogging of filters.

• Poor thermal stability compared to mineral and synthetic oils:

Vegetable oils undergo oxidation at higher temperatures. In general, vegetable oils can be used up to a maximum temperature of 120°C.

• Narrow range of viscosities:

One of the biggest limitations of vegetable oils as potential lubricants is their narrow range of available viscosities.

11.1.3 Application of Vegetable Oils

The use of vegetable oils is encouraged in applications where recycling is not easy or the usage is a complete loss one. The examples include the following:

• Chain bar and saw frame oils

• Concrete mold release oils

• Outboard two-stroke engine oils

• Chain and conveyor lubricants

• Corrosion preventive oils

• Wire rope lubricants

• Hydraulic fluids

• Compressor oils

• Milking machine lubes

• Gear and transmission lubes

• Metal working Fluids

• Machine tool lubricants

• Truck centralized system lubricants

• Lubricants for agricultural equipment

• Lubricants for sewage treatment plants, water weir plants and lock gate mechanisms

• Lubricants for food machinery

• Lubricants for snow mobiles and sky run maintenance equipment

• Railway wheel tread lubricants

The current major areas of applications where biodegradable lubricants have been put to real use:

• Boating two-stroke lubricants: Due to stringent rules in Western Europe and in the US, mineral-based boating two-stroke lubricants have been replaced with vegetable ester-based lubricants. Ethylhexyl esters of partially hydrogenated rice bran oil and karanja oil are good candidates for such applications [14].

• Forestry and Chain saw lubricants: Chain bar and saw frame oils have been completely replaced by vegetable-based oils such as rapeseed and sunflower oils containing formulation primarily in Europe, US, Canada and Australia. It provided improved lubrication at much lower application rates and also increased the life of saw blades. The use of this fluid has eliminated respiratory and skin problems in operators attributed to the petroleum products [14].

• Concrete mould release fluids: The use of biodegradable fluids for concrete mould release fluids has started. About 15% of the total lubricant application for this purpose has been already replaced by biodegradable lubricants [14].

• Hydraulic system oils: Hydraulic systems involved in agriculture, forestry, off highway construction, waterways, open cast mining, quarrying etc., can cause significant pollution to the environment during leakage. At present the highly visible areas where their use is well advanced in certain countries are fluids for hydraulic system on canals and waterways, agriculture tractors, other farm equipments and off highway construction equipment, particularly in the European Unions, US and Japan. The share of rapidly biodegradable hydraulic oils increased from 5% in 1998 to more than 50% by 2003 [14].

• Manufacturing industries: Since 1996 Germany has taken the initiative to use biodegradable lubricants in manufacturing industries. Another major industry built a diesel engine which uses only ester-based cutting fluids, hydraulic fluids, gear oils etc.

The areas for possible applications of biodegradable lubricants in the near future are turbine oils for hydro electric plants metalworking fluids, engine oils and Rail Curve Grease.

The possible potential applications for various vegetable oils are given in Table 11.1 [15].

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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