Present RD Progress

Some vegetable oils such as SBO, linseed oil and rapeseed oil have a high degree of unsaturation, depending on the amount of linoleic and linolenic acid derivatives. As a result, the thermo-oxidative stability of these oils is poor and leads to polymerization, resulting in gummy and resinous products at elevated temperatures. Their use as lubricants without reduction of unsaturation can cause deposit formation, corrosive action, and damage with relatively short useful service life. One of the several ways to reduce unsaturation is to partially hydrogenate [89, 97] these vegetable oils to improve their service lives without affecting the freezing points to a large extent. Epoxidation [98-101] is another convenient method to improve the poor thermo-oxidative stability caused by the presence of unsaturated double bonds in vegetable oils.

Additionally, neat vegetable oils also pose some problems when subjected to extended use in internal combustion engine. These problems are attributed to high viscosity, low volatility and polyunsaturated character of neat vegetable oils, which could be substantially reduced, by subjecting chemical modifications at the carboxyl group in triacylglycerol molecule of vegetable oils. Transeste-rification [95, 102, 103] is one of the common ways to chemically break the molecule of the raw vegetable oils into their methyl or ethyl esters with glycerol as a by-product. Transesterification reactions of the partially hydrogenated and cyclized ester vegetable oils are important because these reactions yield monoesters of vegetable oils with better thermal stability and lower freezing points than the vegetable oils as such [104-106]. The glycerol obtained as a by-product, commands as much market value or more than the monohydric alcohols used for transesterification. Therefore, transesterification leads to value addition without much cost escalation.

The most efficient method to improve the lubricating properties of vegetable oils is to combine both reactions at double bond and carboxyl position of to modify the triacylglycerol molecules in vegetable oils. Erhan and co-workers [70] have chemically modified SBO to produce SBO-based lubricants with good oxidative stability and low pour point. They [78, 91, 99] performed the reaction of epoxi-dized SBO with various alcohols in the presence of an acid as a catalyst to give a ring-opened intermediate product with the structure of-CH(OR1)CH(OH)—where the R group is different alkyl group. Then they esterified the hydroxyl groups by acid anhydride. Based on different alkyl group, they found that pour point decreased and these changes significantly increased the performance of lubricant material. Later on, the same group [70] also reported a simple one-step synthesis of potentially useful acyl derivatives of SBO. These derivatives were prepared using epoxidized SBO and various common acid anhydrides. The process retained the vegetable oil structure while it allowed for removal of polyunsaturation in the fatty acid chain. The lubricants formulated with these chemically modified SBO derivatives exhibited superior low-temperature flow properties, improved thermo-oxidative stability, and better tribological properties [69].

Also Kodali at Cargill central research [107] has introduced the family of asymmetric diester compounds from renewable raw materials. He claimed that these lubricants are non-toxic, biodegradable, cost-effective and environmentally friendly that exhibit excellent lubrication properties such as low viscosity, high flashpoint and high oxidative stability.

Recently, Erhan and co-workers [108] reported the synthesis and evaluation of a series of diesters derived from oleic acid in three-step reactions which include esterification of oleic acid, epoxidation of double bond and ring-opening esterifi-cation. The achieved diesters have one ester group at the end of the chain and another one in the middle of the chain. It was discovered that low-temperature properties of these diesters were improved with the increasing chain length of both esters. Decreasing chain length of the mid-chain ester had a positive influence on the oxidation stability. The other effort of this group was to prepare oleochemicals from commercially available methyl oleate and common organic acids; and determine their lubricant properties [69]. These branched oleochemicals are characterized as 9(10)-hydroxy-10(9)-ester derivatives of methyl oleate. These derivatives showed improved low-temperature properties, over olefinic oleochemicals, as determined by pour point and cloud point measurements.

In the similar process, Salimon and Salih [109] have reported several diesters compounds, synthesized from commercially available oleic acid and common fatty acids. The key step in the three-step synthesis of oleochemical diesters entails a ring-opening of epoxidized oleic acid with different fatty acids (octanoic, nona-noic, lauric, myristic, palmatic, stearic and behenic acids) using p-toluenesulfonic acid (PTSA) as catalyst. All of these produced compounds are solid except 9(10)-hydroxy-10(9)-(octanoyloxy) stearic acid and 9(10)-hydroxy-10(9)-(nonanoyloxy) stearic acid. The esterification reaction of these compounds with octanol was further carried out in the presence of 10 mol-% H2SO4 giving diester compounds. This study described a systematic approach to improve the low-temperature pour property of oleic acid derivative. The presence of long chains alkyl group in the middle of the molecule has strong influence on the pour point property by disrupting the stacking process and results in improved low-temperature behavior. Therefore it is plausible to use the prepared products as biolubricant base stock oil. Also this group [110] has published another similar paper that synthesized the same procedure but using 2-ethyl hexanol in final esterification. They found out that one of the products, the behenic ester of 2-ethylhexyl hydroxy stearate showed pour point, flash point and viscosity indices of -53, 161°C and 215 cp, respectively, which was favorable properties in the synthesis of a bio-based lubrication base fluid. Overall, the data indicated that most of these synthesized derivative compounds had significant potential as lubricant base oil.

Erhan and co-workers [111-113] also reported the preparation of branched-chain ethers from oleic acid in three-step synthesis. First esterification of Oleic acid followed by epoxidation of double bond and then ring-opening step by an alcohol in acidic medium. Low-temperature performance has been studied for different derivatives [111, 112]. Further studies such as oxidation stability and lubricate behavior have been performed [113]. The same group also studied the oxidative stability of synthesized epoxidized methyl oleate (EMO), epoxidized methyl linoleate (EMLO) and epoxidized methyl linolenate (EMLEN), as well as that of a commercial epoxidized SBO, and epoxidized 2-ethylhexyl soyate [114]. They found that under some conditions, epoxy fatty methyl esters epoxides showed increased stability and friction reducing properties which enable them to outperform their methyl ester analogs, and therefore have significant potential to be used as a fuel additive or lubricating fluid.

Because of the development of a suitable molecule of lubricant via chemical synthetic pathway alone will be expensive and a lengthy process, Erhan and co-workers [115] applied molecular modeling of desired compounds and subsequent computation of their minimum energy profile, steric environment and electron charge density distribution, prior to actual synthesis, can shed valuable information on their physicochemical properties. They claimed that based on such information, chemical synthesis can be focused only on the promising molecules. Calculations based on equilibrium geometries were optimized using AM1 semiempirical molecular orbital models. They observed that ring-opening of the triacylglycerol epoxy group and subsequent derivatization of the epoxy carbons can improve the oxidation and low-temperature stability of these synthetic lubricant base oils.

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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