Development of biolubricants from vegetable oils via chemical modification

Development of biolubricants from vegetable oils via chemical modification

Accepted Manuscript Title: Development of biolubricants from vegetable oils via chemical modification Author: Josiah McNutt Quan (Sophia) He PII: DOI:...

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Accepted Manuscript Title: Development of biolubricants from vegetable oils via chemical modification Author: Josiah McNutt Quan (Sophia) He PII: DOI: Reference:

S1226-086X(16)00070-8 http://dx.doi.org/doi:10.1016/j.jiec.2016.02.008 JIEC 2830

To appear in: Received date: Revised date: Accepted date:

23-11-2015 7-2-2016 12-2-2016

Please cite this article as: J. McNutt, Q.S. He, Development of biolubricants from vegetable oils via chemical modification, Journal of Industrial and Engineering Chemistry (2016), http://dx.doi.org/10.1016/j.jiec.2016.02.008 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Development of biolubricants from vegetable oils via chemical modification

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Josiah McNutt, Quan (Sophia) He*

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Department of Engineering, Faculty of Agriculture, Dalhousie University, Truro, Nova Scotia, Canada B2N 5E3

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Abstract

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In response to the increasing environmental pollution concern and depleting petroleum

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reserves, bio-based lubricants have received a great deal of interest as a substitute for mineral oil-

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based lubricants. Biolubricants have a number of advantages over mineral lubricants, including

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the high biodegradability, low toxicity, excellent lubrication performance, and minimal impact

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on human health/environment. This paper reviewed the most recent advancements in the

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synthesis of biolubricants from vegetable oils through chemical modification methods such as

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esterification /transesterification, estolide formation, and epoxidation of vegetable oils.

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Key words: biolubricant, vegetable oils, chemical modification, esterification, estolide,

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epoxidation, oxidative stability, viscosity

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Corresponding author: [email protected]

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1. Introduction With concern over global climate change and depleting petroleum reserves growing, the

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search for environmentally sustainable alternatives to current practices continues to intensify [1].

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One area of interest which could serve to reduce both reliance on petroleum and anthropogenic

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impact on the environment, is the use of vegetable oil-based lubricants in place of the commonly

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used petroleum-based lubricants. These products, known as “biolubricants”, carry several

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environmental, health, and performance benefits over current petroleum-based lubricants.

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It is estimated that 20% of the 5.2 million tons of lubricant consumed every year in

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Europe is released into the environment, and a kilogram of said mineral oil is capable of

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polluting a million litres of water [2]. Therefore, pollution caused by lubricants is far from

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insignificant. The petroleum-based lubricants can also contaminate soil directly, and pollute the

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air due to its volatility [3]. This pollution is hazardous to not only plants and animals inhabiting

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the contaminated areas, but potentially human residents as well [4]. Several studies have

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documented the harmful effects of petroleum based lubricants on human health. Chronic

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inhalation or dermal exposure to petroleum-based lubricants can have inflammatory effects on

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the respiratory system and location of contact, while also being carcinogenic [5-7]. These

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negative effects are even more severe in the used petroleum-based oils, as degradation leads to

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increased toxicity [8]. Many biolubricants however, are rapidly biodegradable and nontoxic, and

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therefore pose little or no risk to the environment or operators [4, 9, 10]. Biolubricants also boast

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several performance benefits, including better lubricity, higher flash point, lower volatility,

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higher viscosity indices, higher shear stability, lower compressibility, higher detergency, higher

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resistance to humidity, and higher dispersancy [4, 9, 11-16].

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Despite these advantages, biolubricants are still not widely used due to several major

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challenges and difficulties regarding its performance and production. Aside from issues

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regarding feedstock reliability and consistency as well as industry acceptance, biolubricants also

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have two main negative physical properties: poor low temperature performance, and low thermal

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oxidative stability [3, 9, 10, 12, 17, 18]. However, through appropriate chemical modification

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processes, these two properties can be improved to make biolubricants a feasible alternative to

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mineral lubricants for various applications. Much research has been done in previous years on

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the exploration of new feedstocks and modification methods, development of more efficient

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catalysts for modification of vegetable oils, and optimization of modification. However, there is

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need for a review paper on this topic. This paper aims to summarize the most current research

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focused on chemical modification methods and their respective advantages and disadvantages.

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The paper will also provide information on common feedstocks and the required properties of

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biolubricants, as well as the relevant testing methods. It is noteworthy that the focus is on the

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development of base oil for biolubricants from vegetable oils, therefore bio-based additive

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development is beyond the scope of this paper.

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The most commonly used feedstock for developing biolubricants are vegetable oils.

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Molecularly, vegetable oils are triglycerides, esters of glycerol and three straight chained fatty

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acids. The chain length of the fatty acids are usually in the range of C12-C24. The three fatty

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acids vary between feedstocks, and play an important role in determining the properties of the

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oil. The two main variables among fatty acids are the number of double bonds and the chain

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length. In general, a longer chain length results in a higher melting point and viscosity, and more

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double bonds correspond to lower melting points, decreased viscosity, and decreased thermo-

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oxidative stability [2]. Monounsaturated fatty acids, such as oleic and palmitoleic acid, have been

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found to have a good balance of low melting point, with good thermo-oxidative stability and

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viscosity [2, 3, 17]. It is for this reason feedstocks with high oleic or palmitoleic acid contents are

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generally preferred and sought after.

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Vegetable oil can be extracted from the over 350 different crops with oil-bearing seeds

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throughout the world [1, 19]. Popular feedstocks include palm, canola, soybean, sunflower,

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coconut, safflower, rapeseed, cottonseed, jatropha, karanja, castor, lesquerella, pennycress, and

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peanut oils, with many others being tested for potential use. While both edible and non-edible

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crops are currently being researched, non-edible crops are more desirable for several reasons.

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Non-edible vegetable oils are often derived from plants that are not in direct competition with

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cultivation of edible oil crops. For example, rubber seed oil, which is collected from rubber trees,

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cannot be used for edible purposes due to the presence of glycoside. However, the tree can grow

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in a wide range of pH values, meaning it could be produced on land that is largely unproductive

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[20]. Non-edible crop oils such as jatropha, linseed, karanja, neem, castor, coriander, cuphea,

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rice bran, milkweed, and many others have little to no impact on world food prices or

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production, as they can be grown on nutrient-deficient land and do not compete with existing

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agricultural resources [2, 19, 21]. However, harvesting, cultivation, and processing of these crops

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is often a challenge, as many of these crops had little incentive to be purposely produced until

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recently [21]. Genetic modification of oil-bearing crops is also a topic to consider when examining

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feedstocks. A majority of the genetic research in the field of lubricants involves the creation of

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high-oleic varieties of oil seed crops. As mentioned above, oleic acid is one of the most favorable

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fatty acids in biolubricant production due to its good balance of low temperature properties and

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high temperature thermo-oxidative stability. Sunflower, palm, camelina, rapeseed, and soybean

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all have genetically modified varieties which alter the composition of the seed oils [22-26].

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Another feedstock which is being investigated is waste cooking oil. One of the biggest

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barriers for biolubricant production is the high cost of feedstock, which can account for 70-80%

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of the total production cost [27]. Waste cooking oil is significantly cheaper than unused edible

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vegetable oils, and has therefore been examined as a possible alternative feedstock [27-30].

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Waste cooking oil is generally 30-60% cheaper than regular vegetable oil, which makes it a

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potentially promising candidate for profitable biolubricant production [27].

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3. Performance Requirements of Biolubricants The main function of a lubricant is to reduce the friction between contacting surfaces.

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Lubricants are used in a variety of industries such as agriculture, forestry, mining, automobile,

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and fishing, serving as engine oils, chainsaw oils, transmission oils, and hydraulic oils. With

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different applications, lubricants may have specifically required characteristics in terms of

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viscosity, chemical stability, fluidity, flammability, range of working temperature and water

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solubility. Currently, there are not a wide array of specifications for biolubricants, but generally

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the properties of biolubricants must be comparable to those of mineral oil based lubricants as

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regulated in USA or European standards. Table 1 shows some lubricant specifications, as well as

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some unmodified vegetable oil properties. One of the most popular sources for evaluation

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methods of lubricants is ASTM International, formerly known as the American Society for

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Testing and Materials. Their website contains over 1200 different testing methods relevant to

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lubricants, demonstrating how broad the use of lubricants is. Some of the most common ASTM

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tests include D97, D445, D2270, D2500, and D4172 which measure the most important

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properties such as pour point, viscosity, viscosity index, cloud point, and anti-wear

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characteristics, respectively [38-44].

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Herein Table 1. Lubricant requirements and unmodified vegetable oil properties.

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Most currently available vegetable oils cannot be used as lubricants directly due to poor

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low temperature performance and low oxidative and thermal stability. There are a number of

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methods to improve these undesired properties, such as genetic modification of fatty acid profile

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of vegetable oils, direct addition of antioxidants, viscosity modifiers, and pour point depressant

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to vegetable oils, emulsification of vegetable oils, and chemical modification of vegetable oils [3,

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9, 12]. Among these methods, chemical modification is the most promising one with great

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potential to improve chemical and broad temperature range stability. Chemical modification

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mainly revolves around modifying the acyl (C=O) and alkoxy (O-R) functional groups and

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double bonds present in the oil. As shown in Figure 1, one way is to rearrange the acyl moieties

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to form new triesters from triglyceride through esterification/ transesterification; the second way

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is to modify acyl group by the formation of estolides after the hydrolysis of triglyceride to give a

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variety of branched esters, and the third path is to modify double bonds by epoxidation and

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subsequent ring opening to give place to a versatile intermediate for the synthesis of different

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diesters. These three modification methods are comprehensively reviewed in the following

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sections, summarizing the most recent developments and advancements in this field.

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Herein Figure 1. Reaction pathways of the three main chemical modification methods. 4.1 Esterification/Transesterification

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Esterification and transesterification are commonly used to arrange acyl moieties in

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vegetable oils to form new esters with improved physical properties. Esterification or

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transesterification of vegetable oils to obtain lubricants is a multistep process. First, unmodified

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triglycerides are reacted with a short-chain alcohol (methanol) with a base catalyst to produce

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fatty acid methyl esters. The resulting methyl esters are then reacted with various types of

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alcohol, in the presence of an acidic or basic catalyst to yield triesters. This process is one of the

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most popular in the literature, due to the wide array of reactants that can be used, resulting in

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biolubricants with varying properties, thus broader applications. Generally, the transesterification

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of methyl esters leads to decreased pour points and increased thermo-oxidative stability, while

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maintaining the beneficial viscosity and lubricity characteristics of the base oils [20, 25, 37, 45,

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46]. The reaction of methyl esters (ME) and trimethylolpropane (TMP) with an alkaline or

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enzyme catalyst is the most common approach. Much work has been done in recent years to

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improve the efficiency of this process, and the properties of the lubricant, by examining different

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aspects of the reaction. Vegetable oil methyl esters, waste cooking oil, biodiesel, estolides, and

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ring opened products, can all be esterified or transesterified. This section will focus on vegetable

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oil methyl esters, waste cooking oil methyl esters, and biodiesel, as the esterification of estolides

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and ring opened products will be discussed in sections 4.2 and 4.3 respectively.

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Herein Table 2 Physical properties and reaction conditions of biolubricants derived from fatty acid methyl esters.

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Table 2 outlines the conversion of a number of methyl esters derived from vegetable oils

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to triesters. Jatropha oil has recently received significant attention as a feedstock for developing

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lubricants. Using sodium methoxide, the oxidative stability of the resulting TMP triesters has

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been improved significantly, and the degradation temperature was higher than 325°C as

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demonstrated in studies [37, 45]. Palm oil based triester was synthesized under the temperature

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range of 120-150 °C with sodium methoxide as catalyst for 45 minutes, and the pour point of

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obtained product was as low as -37°C [23]. Heterogeneous catalyst calcium methoxide [46] was

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also used to synthesize

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required compared to 45 min using homogenous catalyst [23]. Koh et al. attempted introducing a

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novel oscillatory flow reactor for the synthesis of palm biolubricant from palm methyl esters and

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trimethylolpropane. The final product had improved thermal and oxidative stability, a lower pour

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point, and comparable properties to other biolubricants, and the conversion time was less than

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half of other reported reaction times [47]. Biodiesel, another group of alternative feedstocks, is a

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mixture of fatty acid methyl/ethyl esters, which was studied to synthesize TMP-based triesters

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[48-50]. As shown in Table 2, the oxidative stabilities of the finished triesters were satisfactory.

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Similarly, studies have also been done using waste cooking oil (WCO) methyl esters to produce

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palm TMP triesters, and obviously a longer reaction time of 8 h was

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TMP triesters [27, 29, 30]. Waste cooking oil is a good source of methyl esters for making TMP

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triesters-based lubricants. The major drawback is an additional purification step required prior to

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performing esterification and/or transesterification reactions, due to the low quality of WCO

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compared to methyl esters derived from the virgin vegetable oils. The properties of the resulting

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TMP trimesters presented the satisfactory lubricating properties.

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Recently, improved metal-based heterogeneous catalysts (sulfated zirconia complexes

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[51] and Fe-Zn double-metal cyanide complexes [52]) as well as solid acid catalysts (Indion-130

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[53] and silica-sulfuric acid [54]) have been examined in order to improve efficiency by reducing

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waste. The recyclability of catalysts were evaluated in these studies.

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Enzymatic catalyst has advantages over chemical catalysts such as high selectivity and

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low reaction temperature required. The application of microfluidic reactor, an emerging novel

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continuous reactor was also explored in the chemical modification of vegetable oil for lubricant

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production. Enzymatic reactions performed in microchannel reactors represents an exciting and

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attractive field as the continuous packed bed microreactors are able to provide the extended

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lifetime of the bio-catalyst, simple enzyme reuse and relatively easy product recovery. Madarasz

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et al. found that the oleic fatty acid and isoamyl alcohol could be reacted with Novozym 435 as

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an enzymatic catalyst in an H-Cube™ microfluidic reactor continuously for 144h without any

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loss in catalytic from the enzyme [55]. Happe et al. created a novel microwave barrel reactor for

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the use in lipase catalyzed biolubricant synthesis, which reduced solvent use as well as energy

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consumption significantly [56]. Immobilized lipase was also tested in biolubricant syntheses

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[57]. Unfortunately, the properties of the products derived from the employment of enzymatic

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catalysts were not tested or not reported.

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Development of other alcohol esters rather than TMP triesters was exploited for

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biolubricant applications [20, 25, 32, 51, 52]. Research has also been done on how the type of

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alcohol used impacts the physical properties of the lubricant. Table 3 summarizes the effect of

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different

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trimethylolpropane (TMP) on lubricant properties of rapeseed derived biolubricants in a study

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done by Gryglewicz et al. [25]. It was observed that using 2-EP led to an ester product with a

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better low temperature property, the pour point of -31.3 °C compared to the products resulting

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from employing NPG and TMP. In addition, transesterification of FAME with NPG and TMP

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required a longer reaction time.

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Here in Table 3: Physical properties of rapeseed esters using various alcohols.

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4.2 Estolide Formation Estolides are formed by the bonding of a fatty acid’s carboxylic acid functionality to the

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double bond of another fatty acid [12]. Fatty acids are usually obtained from the base triglyceride

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through hydrolysis, and the resulting fatty acids react in the presence of hydrogen ions to

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produce estolides. Lubricants based on estolides can provide improved lubricity, improved

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oxidation stability, and decreased pour points [58-60]. Another benefit of estolides is the reaction

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temperatures in which they are produced are reasonably low (<100°C), and therefore require less

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energy.

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Estolides can be formed from a variety of different base oils. Franco’s group has been

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dedicated to the synthesis and property characterization of lubricants from vegetable oils. They

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synthesized a variety of very high viscosity estolides from high-oleic sunflower oil, olive pomace

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acid oil, oleic acid, and ricinoleic acid [58, 59, 60, 61]. They also examined the difference the

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choice of catalyst had on the physically properties of the estolides, finding that sulfuric acid

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provided higher viscosities than perchloric acid or p-Toluensulphonic acid, but also increased the

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frictional coefficient leading to increased wear [58, 59]. The results are summarized in Table 4.

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The formation of estolides from pennycress, composed mostly of erucic and linoleic acid, by

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Cermak’s team yielded biolubricant with remarkably high viscosities [62]. Cermak et al. [64]

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also synthesized estolides from lesquerella and castor fatty acid esters with differing degrees of

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saturation, and multiple capping fatty acids. The study found that the estolides with the best low

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temperature performance were those formed with oleic acid or 2-ethylhexanoic acid as a capping

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material, and that saturation of the estolide resulted in higher pour and cloud points. Formation

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of estolides from esters was also economically beneficial, as it required no catalyst or solvent.

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Herein Table 4: Physcial properties and reaction conditions of assorted estolides

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Unmodified estolides are not always used on their own; often they are mixed with

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vegetable oils, esterified, or modified in some other way to further enhance their properties [59,

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63, 64, 65]. Cermak et al. also conducted research on the esterification of estolides, which are

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presented in Table 5. Petroselinic acid found in coriander was combined with various capping

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fatty acids, and the resulting estolide was then esterified with 2-ethylhexyl alcohol, to yield

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estolide 2-EH esters. These petroselinic based estolide esters were found to be comparable to

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their oleic based counterparts, possessing good low temperature properties, and viscosities [66].

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In a separate study, estolides derived from oleic acid were esterified using a variety of linear and

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branched alcohols to evaluate the effect it had on physical properties. Esterification with

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branched alcohols yielded significant improvements in the low temperature properties of

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currently available commercial products, and as expected the longer the chain length, the higher

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the viscosity [65]. Esterification of estolides derived from pennycress was also performed. This

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esterification improved the low temperature properties, and had much better viscosity properties

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than any other estolide esters synthesized [62]. Another method of altering estolides, is by sulfur

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modification. Biresaw et al. created a sulfur modified castor 2-EH ester estolide, by first

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synthesizing an estolide from castor 2-EH esters and capping lauric acid, and then reacting the

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resultant estolide with butanethiol in a photochemical reactor. The sulfur modified castor 2-EH

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ester estolide showed a much improved oxidative stability over the unmodified estolide, and a

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decreased viscosity index [63].

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Herein Table 5: Physical properties of assorted estolide esters

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4.3 Epoxidation, Ring Opening and Acetylation

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Epoxidation involves the removal of double bonds between two carbons via an atom of

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oxygen, which results in an epoxide functional group, a three atom ring composed of two carbon

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atoms and an oxygen atom. This reaction usually involves a base olefinic material, reacted with

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hydrogen peroxide, in the presence of formic or acetic acid, and sometimes involving the use of

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various enzymatic or heterogeneous catalysts, such as Amberlite IR-120H, sulfuric acid,

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sulfated-SnO2 catalyst, Novozym 435, or peracetic acid

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vegetable oils generally results in increased oxidative stability, better acidity value, increased

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adsorption to metal surfaces which results in better lubricity, increased viscosity, decreased

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viscosity index, and increased pour point [26, 31, 36, 67-70, 74]. Some physical characteristics

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and reaction conditions of the epoxidation of vegetable oils and their derived fatty acids are

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shown in Table 6. As can be seen, this modification is generally favorable due to the low

[31, 36, 67-73]. Epoxidation of

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temperature required for the reaction, however the pour points of the products are unsatisfactory

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for many applications.

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and their derived fatty acids

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As the epoxidized vegetable oil still has poor low temperature properties, it is essential to

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further modify it. The epoxidized product is often subjected to a combination of oxirane ring-

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opening, esterification, and/or acetylation. After the vegetable oil is epoxidized, the first

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modification step performed is oxirane ring opening, then esterification, or a reaction that does

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both simultaneously. Because the ring opening and esterification reactions of the epoxidized

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vegetable oils can be performed with an array of alcohols and other materials, the resulting ring

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opened products and esters can have differing beneficial properties. This process is sometimes

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followed by the acetylation of the produced ester. Numerous studies have shown that ring

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opening, esterification and/or acetylation result in improved viscosity index, better low

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temperature flow properties, increased thermal and oxidative stability, lower coefficients of

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friction, and better lubricity characteristics [28, 35, 70, 75, 76, 78-86]. Table 7 summarizes the

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properties of some of these modified epoxidized vegetable oils as well as modification

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conditions.

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Herein Table 7: Physical properties and reaction conditions of various modified epoxidized

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vegetable oils.

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Much attention has been given in recent years to further improving the efficiency and

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properties of the products of epoxidation of vegetable oils, ring opening reactions, esterification,

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and acetylation of the epoxidized vegetable oils. This is being done by finding new catalysts,

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improving existing processes, and experimenting with new feedstocks. For example, Sammaiah

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et al. employed a mineral acid, H2SO4, to accelerate the epoxidation of Jatropha oil, and the

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product yield was 96% [36]. H2SO4 was also widely used in the modification of epoxidized

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vegetable oils such as soybeans [80], mustard oil [83] and oleic acid [84]. However, the mineral

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acid catalyst is generally not favorable due to the potential corrosion to reactor vessels as well as

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waste stream handling problems. Dr. Dalai’s group has conducted considerable research on

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developing advanced catalysts for modifying canola oil to high quality biolubricants. Early work

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used acidic ion exchange resin catalyst in the epoxidation of canola oil with hydrogen peroxide

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[72]. Recently, a number of high performance catalysts were developed and applied in the

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synthesis of canola oil-based lubricants. For example, Somidi et al. found that sulfated-SnO2

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catalyst provided very good catalytic activity and had a 100% conversion rate of canola oil to

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epoxidized canola oil within 6 h, and the induction time of the resulting epoxidized canola oil

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was 60 h [68]. Catalyst Amberlite IR - 120H [75, 76] was also tested and evaluated in

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epoxidation of canola oil or canola biodiesel. Sharma et al. found that epoxidation followed by

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simultaneous ring opening and esterification of canola oil and canola biodiesel made viable

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biolubricants. Modified canola biodiesel had good low temperature properties, viscosity, anti-

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wear properties, and oxidative stability, making it a promising candidate for use in general

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automotive applications. Modified canola oil was highly viscous, and worked extremely well at

325

high temperatures which gave it a promising outlook for use in heavy machinery. In the study on

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the ring opening and esterification of epoxidized canola oil, another novel sulfated Ti-SBA-15

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catalyst demonstrated higher activity, selectivity, stability, and reusability than the commonly

328

used catalysts such as Amberlyst-15, IRA-200 and IRA-400 [81]. In the research carried out by

329

Ahn et al. magnesium stearate was an efficient catalyst for solvent-free ring opening of

330

epoxidized methyl oleate, and had a superior efficiency when compared to many other catalysts.

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This process increased the viscosity, and was also less wasteful than most other processes, as it

332

was solvent free [78].

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Along with improved catalysts, alternative basestocks have also been studied.

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Sankaranarayanan and Srinivasan experimented with ricinoleic derivatives, as opposed to the

335

more popular oleic derivatives, and found that they were highly tunable and showed promise as

336

for a range of industrial lubricants [89]. The study performed by Salih et al. found that longer

337

midchain esters were good for low temperature operability and anti-wear properties, but resulted

338

in worse thermal stability than shorter midchain esters [35]. Kamalakar et al. observed that

339

epoxidized thumba oil could be used as aviation grade lubricant, while esterification of the epoxy

340

oil derivatives were suitable for hydraulic and metal working applications [32]. Hashem et al.

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produced epoxidized castor, linseed, sunflower, and jatropha oil and then esterified them with

342

oleic acid, which produced several promising lubricants [87]. Li and Wang epoxidized waste

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cooking oil, formed methyl esters, and subsequently esterified those methyl esters with branched

344

alcohols, resulting in increased viscosity index and improved pour points [28]. Aside from improved catalysts or feedstocks, research has also been done on modifying

346

the traditional conversion methods. Hwang and Erhan found that epoxidized soybean oil reacted

347

with Guerbet alcohols gave ring opened products which were either transesterified or not

348

depending on the amount of alcohol used. The ring opened products which were simultaneously

349

transesterified had lower pour points and viscosities, and higher viscosity indices [80]. Lee et al.

350

experimented with the amidation of epoxidized vegetable oil derivatives, and successfully

351

formulated cross-linking products, but gave no information on the physical properties of these

352

materials [90].

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345

353 4.4 Other Efforts

an

354

Various other methods that do not fall into the above categories have been examined, but

356

also offer promising advancements in the study of biolubricants. One of these methods is

357

hydrogenation. Ting and Chen found that various mineral oils can be replaced by blends of

358

hydrogenated, epoxidized, and unmodified soybean oil in different ratios [91]. Shomchoam and

359

Yoosuk hydrogenated palm oil using Pd/γ-Al2O3 as a catalyst, and found the partial

360

hydrogenation improved the oxidative and thermal stability of the oil, while leaving other

361

properties such as viscosity, viscosity index, and low temperature properties relatively

362

unchanged [92]. Lee et al. hydrogenated soybean oils and observed that the more it was

363

hydrogenated, the higher its viscosity became. They also experimented with hydrogenation with

364

various catalysts, such as Ni/SiO2, Ra-N, and Pt/C catalysts and observed that 5 % Pt/C catalyst

365

gave the highest degree of reduction [93]. Nohaira et al. used palladium to catalyze the

366

hydrogenation of sunflower oil ethyl esters with ethanol as a solvent, and found that the addition

367

of lead to the palladium catalyst, and adding amines to the reaction medium, improved the

368

selectivity of the catalyst [94].

Ac ce p

te

d

M

355

369

Examination and production of new feedstocks has also been studied. Eller et al.

370

extracted decanoic acid, which is good for estolide formation, from cuphea seed oil using

371

subcritical water without any catalyst in a continuous flow tubular reactor. They propose the

372

method could be used for the extraction of various fatty acids from triglyceride-based fats and

373

oils [95]. Arad et al. examined the properties of a sulfated polysaccharide from porphyridium sp.,

Page 12 of 33

a red microalga. The polysaccharide biolubricant showed promise as a medical lubricant for use

375

in artificial joints, as well as various other applications. The viscosity was found to be stable over

376

a wide range of temperatures, pH values, and salinities, and its wear scar and coefficient of

377

friction were significantly lower than the currently used lubricant [96]. Liu et al. modified a

378

high-oleic camelina variety by adding the EaDAcT gene from Euonymus alatus so that it would

379

produce more sn-3 acetyl triacylglycerols, which have reduced viscosity, improved cold

380

temperature properties, and increased oxidative stability compared to most vegetable oils [24].

cr

ip t

374

Several more novel methods of modifying vegetable oils have also been proposed. Wang

382

et al. formulated microemulsions from vegetable oil (continuous phase), ionic liquid (IL) 1-

383

butyl-3-methyl-imidazolium tetrafluoroborate (polar phase), TritonX-100 (surfactant), and 1-

384

butanol (cosurfactant), which had excellent viscosity and frictional wear properties [97]. Doll

385

and Sharma emulsified epoxidized vegetable oils and vegetable oil derivatives, and found that

386

even 1% emulsification of the vegetable oil can undo the negative effects of epoxidation on the

387

coefficient of friction, and improve frictional properties [98]. Biswas et al. heat-bodied and

388

microwave-irradiated soybean oil and found that while both increased viscosity, decreased pour

389

point, and increased oxidative stability, microwave-irradiation improved all these qualities more

390

than heat-bodying did. However, microwave-irradiation hindered the lubricity properties of the

391

soybean oil [99]. Biresaw and Bantchev produced phosphonate derivatives of methyl oleate via a

392

radical chain reaction with varying alkoxy groups. The resulting phosphonates had increased

393

viscosities, as well as improved oxidative stability, low temperature properties, and deceased

394

coefficients of friction and wear scar [100].

396

an

M

d

te

Ac ce p

395

us

381

5: Conclusions

397

Chemical modification of vegetable oils is a promising option for producing biolubricants

398

from vegetable oils. These methods have been found to significantly increase the physical

399

properties of the base vegetable oils, and produce biolubricants that meet or exceed

400

requirements. Esterification/transesterification of vegetable oils improves their low temperature

401

properties and increases their stability, but generally requires crops rich in oleic acid, and the

402

process requires relatively high reaction temperatures and negative pressure. Estolide formation

403

provides improved lubricity, oxidative stability, and low temperature properties and generally

404

requires lower reaction temperatures. It can also make use of a variety of fatty acids, producing a

Page 13 of 33

wide array of lubricants with dramatically different properties, and the resulting estolides can be

406

esterified to further improve low temperature properties and stability. However, the initial

407

estolide formation reaction often requires the use of capping fatty acids, which are an expensive

408

reactant. Epoxidation improves the lubricity characteristics and stability of the vegetable oil, and

409

has relatively low reaction temperatures due to the exothermic nature of the reaction, but

410

significantly increases the pour point and decreased the viscosity index. Subsequent ring

411

opening, esterification, and/or acetylation of the epoxidized vegetable oils can provide a final

412

product with good lubricity, stability, low temperature properties, and viscosity index, while

413

requires two or three additional reactions after the epoxidation reaction which is economically

414

unfavorable.

us

cr

ip t

405

Despite much progress being made in technical knowledge, large-scale production of

416

biolubricants using the methods described in this paper has not been performed. The production

417

and use of biolubricants still faces many challenges that must be overcome before large-scale

418

production is viable. Homogeneity of the feedstock is a major issue which can lead to

419

inconsistency in the final biolubricant. While not as much of an issue in small-scale labs tests,

420

variation in oil content during large-scale manufacturing could lead to unsatisfactory properties.

421

Similarly, the reliability and price of current feedstocks can fluctuate significantly, making

422

production of biolubricants economically risky. In terms of reaction processes, mineral acid

423

catalysts and multiple steps are generally involved, decreasing the economic and environmental

424

viabilities. Another issue is lack of acceptance by many machine manufacturers and operators,

425

which makes large-scale production pointless.

Ac ce p

te

d

M

an

415

426

Focus moving forward should be on continually improving the cost-effectiveness of

427

production methods. Developing cheaper feedstocks, higher performance catalysts, and

428

optimized reaction processes will be necessary in furthering the study of biolubricants, as

429

incentivizing the switch from mineral to vegetable based oils through economic benefits will be

430

essential to attract support from industry partners. More thorough testing of the use of vegetable

431

oils in the place of mineral oils will also be needed in order to convince manufacturers and

432

operators of vegetable oils’ merits. These efforts will lead to a wide use of biolubricants in the

433

future, offering enormous benefits including excellent biodegradability, reduced the reliance on

434

petroleum, less negative impact to human health and minimum harm to the environment.

435

Page 14 of 33

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581

Page 20 of 33

668

List of Figures:

669

Figure 1. Reaction pathways of the three main chemical modification methods.

670

M

an

us

cr

ip t

671

Figure 1. Reaction pathways of the three chemical modification methods. Red, green and blue solid arrows represent the pathway of esterification/transesterification, estolide formation, and epoxidation/ring opening respectively.

te

674 675 676 677 678

Ac ce p

673

d

672

Page 21 of 33

us

cr

ip t

678

an

679 680

te

d

M

Three chemical modifications: red, green and blue solid arrows represent the pathway of esterification/transesterification, estolide formation, and epoxidation/ring opening respectively.

Ac ce p

681 682 683 684

Page 22 of 33

Table

List of Figures: Table 1: Lubricant requirements and unmodified vegetable oil properties Table 2: Physical properties and reaction conditions of lubricants derived from faccty acid methyl esters

ip t

Table 3: Physical properties of rapeseed esters using various alcohols

cr

Table 5: Physical properties of assorted estolide esters Table 4: Physical properties and reaction conditions of assorted estolides

us

Table 6: Physical properties and reaction conditions of the epoxidation of vegetable oils and their derived fatty acids

an

Table 7: Physical properties and reaction conditions of various modified epoxidized vegetable oils. Table 1. Lubricant requirements and unmodified vegetable oil properties Viscosity Index >90 >90 >198 >216 102 97 132 103 140 174 139

28.86 40.05 31.78 44.88 220.6 45.60 35.4 24.8 40.6 52.4 119.8 40.0

7.55 8.65 19.72 10.07 7.9 5.5 8.7 10.2 14.7 9.3

246 206 220 180 205 169 169 186 125 226

Pour Point (°C) -6 -6 -6 -6 -21 -18 -48 -54 -36

Flash Point (°C) 204 220 226 246 195 200 244 205 228 210

Oxidative stability (min) 1670.26 931.16 -

Coefficient of Friction 0.117 -

Wear Scar (mm) 0.549 -

-

-

-

Ref. [27] [27] [27] [27, 31] [13] [13] [31] [4] [32] [33] [34] [33]

-9 -12 -27.00 -12.00 -6 21 -13 -5 -21 -21

325 252 228 204 250 240 186 325 318 -

7.5 28.27 5 -

0.101 0.073 0.045 0.054

0.601 0.585 0.857 0.769

[15] [15] [31] [31] [35] [35] [36] [4] [4] [37] [16] [16]

M

Viscosity 100°C (cSt) >4.1 >4.1 >4.1 >4.1 10 31 13.9 19.6 15.9 24.7 31.2

te

d

Viscosity 40°C (cSt) >28.8 >41.4 >61.4 >90.0 95 461 150.04 105 216 120 175 310

Ac ce p

Lubricant Requirement ISO VG32 ISO VG46 ISO VG68 ISO VG100 Paraffin VG95 Paraffin VG460 R150 SAE20W40 AG100 75W-90 75W-140 80W-140 Vegetable Oil Soybean Sunflower Passion Fruit Moringa Castor Rapeseed Jatropha Coconut Rice bran Palm Lesquerella Pennycress

1 Page 23 of 33

Product

Catalyst

Viscosity 40°C (cSt)

Viscosity 100°C (cSt)

Viscosity Index

Pour Point (°C)

Oxidative/ Thermal Stability

Yield (%)

Ref.

8.71

180

-6

-

>80

[37]

9.37

183

-6

325°C Degradati on temp

-

[45]

9.2 – 10

183 – 200

(-37) – (-9)

-

-

[23]

9.0

176

-2

355°C Degradati on temp

94.6

[46]

us

Reactants

Reaction Conditions

cr

ip t

Table 2. Physical properties and reaction conditions of lubricants derived from faccty acid methyl esters

TMP triesters

Sodium methoxide

150°C, 10mbar, 3h

43.90

Jatropha ME and TMP

TMP triesters

Sodium methoxide

150°C, 55 min

42.57

High oleic palm ME and TMP

TMP triesters

Sodium methoxide

120 – 150°C, 0.3 mbar, 45 min

Palm ME and TMP

TMP triesters

Sodium methoxide

140°C, 25mbar, 25 min, oscillatory flow reactor at 1.5 Hz with 20 mm amplitude

Palm ME and TMP

TMP triesters

Calcium methoxide

180°C, 50 mbar, 8h

-

-

-

-

-

92.38

[47]

Canola biodiesel ME and TMP Castor biodiesel and TMP

TMP triester

Sodium methoxide

110°C, 1 mbar, 5h

40.5

7.8

204

-66

induction time: 0.74h

90.9

[49]

Dibutyltin dilaurate

170°C, 0.01 bar

287.2

26.13

119

-27

89.7

[50]

Castor biodiesel and TMP

TMP triester

120°C, 0.01 bar

20.94

4.467

127

-

-

[50]

Castor biodiesel and TMP

TMP triester

Amberlyst 15 ionic exchange resin Sodium methoxide

RPVOT: 43 min (Butylated hydroxytol uene added) -

120°C, 0.01 bar

11.28

3.100

141

-

-

[50]

WCO ME and TMP

TMP triester

KOH

128°C, 200 Pa, 1.5h

38.60

8.44

204

-8

RPVOT: 150 min (Butylated hydroxytol uene added) FP: 240°C

85.7

[27]

M

d

47.1

te

Ac ce p

TMP triester

45.5 – 50.7

an

Jatropha and TMP

2 Soybean oil and various alcohols

n-alcoholesters

Sulfated zirconia catalysts

140°C, 4h

10.3 – 432.7

3.0 – 34.4

45 – 195

-

-

>80 Page 24 of 33[51]

FA-n-octyl esters

Fe-Zn double-metal cyanide (DMC) complexes

170°C, 8h

7.93

2.74

226

-3

23 min (RBOT)

Pentaerythrit ol and oleic acid

pentaerythritol tetraoleate ester

ion exchange resin, Indion‐130

110°C, 6h toluene solvent

63.08

12.00

190

-24

-

Valeric acid TMP

Valeric acid TMP ester

silica– sulphuric acid

70°C molar ratio of 3:1, toluene

9.5

2.5

80

Rubber ME and NPG/TMP/P E

NPG/TMP/ PE triesters

pToluensulpho nic acid

135 – 140°C, until theoretical reaction complete

23.1 – 62.6

5.9 – 12.6

206 – 222

Rapeseed ME and NPG/TMP/P E

NPG/TMP/ PE triesters

C Antarctica lipase

150, 200, 50h

7.8 – 38.2

2.7 – 8.4

Thumba ME, xylene and NPG/TMP/P E

NPG/TMP/ PE triesters

pToluensulpho nic acid

135-140°C, until complete

20.65 – 60.26

ip t

Sunflower oil and octanol

us

cr

-75

M

209 – 220

-

[53]

-

[54]

10 – 15 min (RBOT) FP: 266308°C

94.5 – 96.5

[20]

(-31.3) – (-18)

Δv : 90.1147.1 ΔAc: 2.97.7

98

[25]

(-12) – (-3)

10-15 min (RBOT) FP: 270318°C

89 – 95

[32]

Ac ce p

te

d

5.45 – 11.89

[52]

(-15) – (-3)

an

205 – 224

-

98

Note: RPVOT represents rotating pressure vessel oxidation test; RBOT denotes Rotary Bomb Oxidation Test; RSSOT denots Rapid Small Scale Oxidation Test; and FP represnts flash point.

3 Page 25 of 33

Table 3. Physical properties of rapeseed esters using various alcohols

7.8 17.4 38.2 35.1

Viscosity Pour Point Index (°C) 224 209 205 207

-31.3 -19.5 -18.0 -19.1

∆v (%)

∆Ac

ip t

2-EH NPG TMP None (original oil)

Viscosity 100°C (cSt) 2.7 4.7 8.4 7.9

147.1 136.5 90.1 145.7

cr

Alcohol used

Viscosity 40°C (cSt)

7.7 6.0 2.9 7.5

Ac ce p

te

d

M

an

us

Note: Δv denotes change in viscosity at 40°C after 12L/h of air bubbles were passed through the lubricant for 24h at 100°C. ΔAc represents denotes change in acid number at 40°C after 12L/h of air bubbles were passed through the lubricant for 24h at 100°C.

4 Page 26 of 33

Table 4. Physcial properties and reaction conditions of assorted estolides Viscosity 100°C (cSt) 17.2 – 42.7

Viscosity Index 153 – 185

100°C, 3-24h

271.8 – 518.6

33.5 – 60.2

168 – 188

Pour Point (°C) -

Oxidative/ Thermal stability -

Yield (%) -

Ref. [58]

-

-

[58]

-

-

-

[60]

-

-

-

-

[61]

51.26 – 232.62

-

-

-

-

[61]

494.4 – 497.1

42.2 – 75.3

134 – 163

(-15) – (-6)

-

-

[62]

51.4

9.9

183

<-54

RPVOT 16 min

73

[63]

56.0

10.6

144

<-54

RPVOT 224 min

96

[63]

37.0 – 45.7

7.9 – 9.1

187 – 196

(-12) – 6

-

-

[64]

200°C , 20 Pa, 24h

35.4 – 51.1

7.8 – 10.1

189 – 200

(-54) – 3

-

-

[64]

-

200°C , 20 Pa, 24h

43.6 – 68.3

8.7 – 12.2

178 – 186

(-36) – 6

-

[64]

-

200°C , 20 Pa, 24h

29.0 – 70.6

6.5 – 11.8

164 – 196

(<-54) – 23

RBOT: 403 min with 3.5% of an Lubrizol oxidative stability package RBOT: 159 min with 3.5% of an Lubrizol oxidative stability package

-

[64]

Olive oil

Estolide

Catalyst H2SO4,HClO4, or pToluensulphonic acid H2SO4

Sunflower oil

Estolide

H2SO4

50°C, 3-24h

278.8 – 430.8

50.1 – 35.3

Oleic acid

Estolide

H2SO4,HClO4, or pToluensulphonic acid

50-100°C depending on catalyst

75.61 – 415.59

9.51 – 17.02

Ricinoleic acid

Estolide

H2SO4,HClO4, or pToluensulphonic acid

50-100°C depending on catalyst

581.56 – 6712.98

Pennycress FA

FFA estolide

HClO4

60°C, 7.5-10.9 kPa, 24h

Castor 2-EH ester and lauric acid

Estolide

tin (II) 2ethylhexanoate

130°C , 12-18 Pa, 24h

Castor 2-EH ester estolide and butanethiol

Estolide

-

Saturated lesquerella FA ester and capping FA Unsaturated lesquerella FA ester and capping FA Saturated castor FA ester and capping FA

Saturated estolide

-

Unsaturated estolide

-

Saturated estolide

Unsaturated castor FA ester and capping FA

Unsaturated estolide

an

M

d

Ac ce p

(-28) – (18)°C, photochemical reactor, 3h 200°C , 20 Pa, 24h

-

cr

Products Estolide

-

us

Reactants Sunflower oil

ip t

Viscosity 40°C (cSt) 102.4 – 425.3

te

Reaction Conditions 50-100°C depending on catalyst, 3-24h

5 Page 27 of 33

Table 5: Physical properties of assorted estolide esters Viscosity 40°C (cSt) 55.2 – 108.9

Viscosity 100°C (cSt) 10.2 – 15.3

62.5 – 209.3

11.1 – 24.9

149 – 192

53.7 – 92

9.1 – 14.6

151 – 165

BF3

60-80°C, until 99% complete

Estolide ester

HClO4

Estolide: 60°C, 7.5-10.9 kPa, 24h Ester: additional 3-4 h after 2-EH added

Castor 2-EH ester estolide and butanethiol Pennycress estolide and 2-EH, capped with various FA

Sulfide modified estolide

-

(-28)-(-18)°C, photochemical reactor, 3h

56.0

Estolide ester

BF3

80°C, 7.5-10.9 kPa, 8h,

116.3 – 245.8

Oxidative/ Thermal Stability -

(-39) – (-24) (-33) – (-12)

10.6

Ref.

-

-

[65]

RPVOT: 16273 min depending on how much Lubrizol® 7652 additive RPVOT: 224 min

65 – 76

[66]

144

<-54

96

[63]

169 – 183

(-24) – (-12)

-

-

[62]

[65]

Ac ce p

te

d

18.2 – 33.6

Yield (%) -

cr

Estolide ester

Pour Point (°C) (-33) – (-9)

us

Catalyst BF3

an

Products Estolide ester

M

Reactants Oleic acid estolide and linear alcohols Oleic acid estolide and branched alcohols Coriander FA and 2EH, capped with various FA

Viscosity Index 163 – 184

ip t

Reaction Conditions 60-80°C, until 99% complete

6 Page 28 of 33

Table 6: Physical properties and reaction conditions of the epoxidation of vegetable oils and their derived fatty acids

Catalyst

Thumba oil, formic acid, and H2O2

Epoxidized thumba oil

-

Passion fruit oil, formic acid, and H2O2

Epoxidized passion fruit oil

Moringa oil, formic acid, and H2O2

-

Reaction Conditions 4°C, 2h

Viscosity Index 45.44

Pour Point (°C) 0

Oxidative/ Thermal Stability FP: 113.11°C

128

-3

-

Yield (%) -

Ref. [35]

RBOT: 20 min

-

[32]

-

RSSOT: 16.89 min

-

[31]

-

-

RSSOT: 24.57 min

-

[31]

18.2

139

0

RBOT: 20 min FP: 288°C

96

[36]

114

19

141

9

Ox induction time: 60h

-

-

-

9

Therm stab: 319°C

-

[75]

-

-

-

0

Therm stab: 160°C

-

[75]

ip t

Products Epoxidized oleic acid

Viscosity 100°C (cSt) -

an

Reactants Oleic acid, formic acid, and H2O2

Viscosity 40°C (cSt) -

185.65

-

Epoxidized moringa oil

-

30°C, 3h

80.37

Jatropha oil, formic acid, and H2O2

Epoxidized jatropha oil

H2SO4

10°C for 2h while H2O2 added, then 60°C until complete

146.5

Canola oil, acetic acid, and H2O2

Epoxidized canola oil

SulfatedSnO2 Catalyst

70°C, 6.5h

Canola oil, acetic acid, H2O2

Epoxidized canola oil

Amberlite IR −120H

65°C, 8h

Canola biodiesel, acetic acid, H2O2 Canola oil, acetic acid, and H2O2

Epoxidized biodiesel

Amberlite IR −120H

65°C, 8h

Epoxidized canola oil

Amberlite IR −120H

65°C, 8h

151

-

-

10

Therm stab: 320°C

-

[76]

Methyl oleate, formic acid, and H2O2

Epoxidized methyl oleate

-

-

8.0

2.5

151

0

Ox onset temp: 189.75°C

97

[77]

Methyl linoleate, formic acid, and H2O2 Methyl linolenate, formic acid and H2O2

Epoxidized methyl linoleate

-

-

14.3

3.5

132

-1.5

Ox onset temp: 180.3°C

95

[77]

Epoxidized methyl linolenate

-

-

308

19.3

63

-7.5

Ox onset temp: 131.2°C

85

[77]

d

te

Ac ce p

us

cr

22.7

M

216.9

-

5-10°C, before adding H2O2 and heating to 60°C for 7h 30°C, 3h

-

-

[68]

7 Page 29 of 33

Table 7: Physical properties and reaction conditions of various modified epoxidized vegetable oils. Viscosity 40°C (cSt) -

Viscosity 100°C (cSt) -

Viscosity Index 105 – 159

Pour Point (°C) (-35) – (-5)

Oxidative/ Thermal Stability -

-

670

-

-9

8.3 – 10.3

Ref. [83]

Ox induct time: 56.1h

100

[81]

(-36) – (-27)

-

-

[80]

86 – 113

-18

-

-

[80]

-

71.21 – 232.15

(-43.25) – (20.11)

FP: 123.09305.08°C

-

[35]

-

-

85.32 – 183.15

(-44.17) – (21.14)

FP: 123.38256.34°C

-

[35]

-

-

95 – 215

(-28) – (-11)

-

[84]

-

-

153

-51

Onset temp: 77156°C FP: 113233 Ox stab: 180.94°C

-

[79]

0

670

-

-9

-

[75]

130°C, 15h

116

19

-

-18

Ox stab: 56.1h Therm stab: 309°C Ox stab: 76.3h therm stab: 194 °C

-

[75]

100°C, 15h

251.7

-

-

-5

Epoxidized canola oil ester

sulfated Ti-SBA15

130°C, 5h

Epoxidized soybean oil and Guerbet alcohols (1) Epoxidized soybean oil and Guerbet alcohols (2) Epoxidized oleic acid, and fatty acids

Transesterified, ring opened product

H2SO4

120°C, 20h, 0.61 mol alcohol

59.6 – 74.5

Ring opened product

H2SO4

110°C, 20h, 0.47 mol alcohol

195.6 – 23.4

9-Hydroxy-10acyloxyoctadecan oic acid

p-Toluensulphonic acid and toluene

9-Hydroxy-10acyloxyoctadeca noic acid, octanol, and hexanes Epoxidized oleic acid, various alcohols

Octyl 9-hydroxy10acyloxyoctadecan oate

-

Oleic acid added over 1.5h at 7080°C, then heated to 90100°C for 3h 60°C, 10h

Alkyl 9-alkyloxy10hydroxyoctadecan oate

H2SO4

60°C, 20-22h

Monoepoxide linoleic acid, oleic acid

9(12)-hydroxy10(13)-oleoxy12(9)octadecanoic acid

p-Toluensulphonic acid

Epoxidized canola oil, acetic anhydride

Diacetylated ring opened product

Amberlyst-15

70-80°C, while oleic acid added over 1.5h, then heated to 90110°C for 3-6h 130°C, 15h

Epoxidized canola biodiesel, acetic anhydride

Diacetylated ring opened product

Amberlyst-15

Epoxidized canola oil and nbutanol

Ring opened product

Amberlyst-15

Ac ce p

te

d

M

-

cr

Catalyst H2SO4, H3NSO3, or CH4O3S

16.4 – 20.9

an

Products Epoxidized mustard oil ester

ip t

Yield (%) 92-95

Reactants Epoxidized mustard oil, 2-EH Epoxidized canola oil and acetic anhydride

96 – 135

us

Reaction Conditions 120°C, until complete

Therm stab: 355 °C

-

[76]

8 Page 30 of 33

Ring opened product

Amberlyst-15

100°C, 15h

190.5

-

-

-8

Therm stab: 361°C

-

[76]

Epoxidized canola oil and 2EH

Ring opened product

Amberlyst-15

100°C, 15h

85.5

-

-

-15

Therm stab: 405°C

-

[76]

Epoxidized castor oil, oleic acid, and xylene

Polyoleate ester

p-Toluensulphonic acid

150°C, 4-5h

95.15

16.53

189

<-36

-

[87]

Epoxidized linseed oil, oleic acid, and xylene

Polyoleate ester

p-Toluensulphonic acid

150°C, 4-5h

102.88

16.84

-

[87]

Epoxidized sunflower oil, oleic acid, and xylene

Polyoleate ester

p-Toluensulphonic acid

150°C, 4-5h

-

[87]

Epoxidized fatty acid waste cooking oil methyl esters, methanol, and isooctanol Epoxidized fatty acid waste cooking oi methyl esters, methanol, and isotridecanol Epoxidized fatty acid waste cooking oi methyl esters, methanol, and isooctadecanol Ring opened epoxidized soybean oil (1) and acetic anhydride Ring opened epoxidized soybean oil (2) and acetic anhydride

Epoxidized branched ester

CaO

90-140°C

FP(open/cl ose): 227/198 °C Ox stab: 272 min Therm stab: 325°C FP(open/cl ose): 238/209 °C Ox stab: 181min Therm stab: 330°C FP(open/cl ose): 153/72 °C Ox stab: 278 min Therm stab: 290°C RPVOT: 127.4 min PDSC: 79.2 min

-

[28]

cr

ip t

Epoxidized canola oil and amyl alcohol

-15

an

us

179

8.78

180

-9

15.9

3.4

157

-15

Ac ce p

te

d

M

44.79

Epoxidized branched ester

CaO

90-140°C

24.7

5.1

142

-20

RPVOT: 92.9 min PDSC: 50.4 min

-

[28]

Epoxidized branched ester

CaO

90-140°C

43.4

7.4

135

-24

RPVOT: 69.8 min PDSC: 35 min

-

[28]

Acetylated, transesterified, ring opened product

Pyridine

80°C, 2h, nitrogen atmosphere

35.6 – 41.5

6.5 – 7.5

137 – 149

(-42) – (-27)

-

-

[80]

Acetylated, ring opened product

Pyridine

80°C, 2h, nitrogen atmosphere

74.3 – 103.4

11.7 – 14.6

136 – 152

(-27) – (-33)

-

-

[80]

9 Page 31 of 33

Pyridine

50°C, 5h

34.634 – 46.154

6.473 – 14.925

127 – 171

(-20) – (-60)

Onset temp: 176.29188.5 °C

66 – 88

[88]

Pyridine

4°C, 2h

-

-

93.37 – 185.36

(-45.34) – (23.41)

FP: 135.12211.29°C

-

[35]

Acylated karanja oil

dimethylaminopyr idine

140-150°C, 7-9h

-

36.5 – 63.7

111 – 128

-

[86]

ip t

Triester derived from 9,10hydroxyacyloxystearic acid methyl esters Octyl 9lauroyloxy-10acyloxyoctadecan oate

FP: 228288°C

te

d

M

an

us

cr

-

Ac ce p

9,10-hydroxyacyloxystearic acid methyl esters, CCl4 and acylchlorides Octyl 9hydroxy-10acyloxyoctadeca noate, CCl4, and lauroyl chloride Epoxidized karanja oil, alkanoic anhydride, and xylene

10 Page 32 of 33

Figure

List of Figures:

d

M

an

us

cr

ip t

Figure 1. Reaction pathways of the three main chemical modification methods.

Ac ce p

te

Figure 1. Reaction pathways of the three chemical modification methods. Red, green and blue solid arrows represent the pathway of esterification/transesterification, estolide formation, and epoxidation/ring opening respectively.

Page 33 of 33