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Vegetable Oils, Animal Fats, Carbohydrates and Polyols

1.1 Introduction

This chapter describes polyols in detail, including diols, the chemical components of which are obtained from sources other than crude oil.

The polyols are used in the manufacture of commercial polymers and polyurethanes, for example.

Among the major natural chemicals from which polyols can be derived are:

• Vegetable oils
• Fish oils
• Animal fats
• Carbohydrates

For industrial purposes vegetable oils and carbohydrates are the most approachable sources of chemicals. Work on polyols derived from animal fats can be found in the patent literature [1].

Those products are, quite rightly, described as green products because they originate from natural sources, the production of which humans can control almost at will. They are renewable because, in contrast to crude oil, they originate from non-depletable sources. Their availability is not the monopoly of some countries which possess vast amounts of oil reserves. Agricultural products require the right weather conditions to grow as well as an area large enough for them to be cultivated on.

The first detailed studies on the use of vegetable oils and animal fats in polyurethane technology date back to the late fifties and early sixties.

Among the reasons given for utilizing polyols from natural sources were:

• Since a favorable price differential exists for castor oil over most polyesters, information concerning the properties of various castor urethane foams should be useful to manufacturers and consumers of expanded foams [2].
• Dimer acids are commercially available and are produced by the polymerization of polyunsaturated fatty acids derived from soybean, cottonseed, and linseed oils. Less expensive polyols should result from the condensation of ethylene oxide with dimer acid [3, 4].
• The properties of the castor oil-based foams (PU) are comparable to those of foams obtained from more costly polyols [5].
• A large potential market exists for polyols from natural sources in the rapidly expanding urethane foam industry [6].

In general, the price of oil (Figure 1.1) used to produce the components of polyether and polyester polyols is determined by speculation largely founded on the production policies of the OPEC cartel.

Unfortunately, the pricing of basic carbohydrates or bean oils generally is not much different from that of crude oil.

Soybean oil futures are traded at the Chicago Futures Market, where the price of soybean oil is still lower than that of petroleum (Figure 1.2).

This means that, triglycerides, even if considered renewable sources of chemicals, are subject to speculative pricing the same way crude oil is. However, the difference is that their production is not restricted to only a few countries. Bean oil, or carbohydrate cartels, will be difficult to establish and organize on a global scale. This trading approach does not exclude speculative price hikes similar to those of crude oil.

Figure 1.1 Crude oil (petroleum) price chart (1barrel of crude ~ 140 kg) [7].

Figure 1.2 Soybean oil price variation compared to that of crude oil in USD/ton [7].

Polyols based on renewable raw materials, such as fatty acid triglycerides, sugar, sorbitol, glycerol and dimer fatty alcohols, are already used in diverse ways as raw materials in the preparation of polymer chemicals.

It is claimed that soybean-oil-based polyols cost less than the petroleum polyols they replace, because they require considerably less energy to produce; can be used in a broad range of polyurethane applications; and produce polyurethane products with equivalent or better physical characteristics [8].

In any event, polyols manufactured from petrochemical sources constitute the majority of the polyols, polyesters as well as polyethers used in industry.

Another source of polyols has emerged from the co-polymerization of CO2 and epoxides [9].

1.2 Sustainability

During the last few years, the term sustainability has been mentioned repeatedly in published articles, speeches, presentations as well as in company reports, to say the least. This was not the case when fluorocarbons, for example, were widely used as blowing agents in the polyurethanes industry. Many decades have elapsed since their deleterious effect on the ozone layer was discovered.

The negative effect of CO2 on the atmosphere and the migration of bisphenol A from polycarbonate utilized in feeding bottles are additional examples which indicate that the consequences of chemicals are spotted only after a type of specific damage has already been inflicated on the environment, the economy, human health, etc.

According to the Cambridge Dictionary, the verb "to sustain" has the following meanings:

• To allow something to continue for a period of time; (The economy looks set to sustain its growth into next year.)
• To keep alive; (Many planets are unable to sustain human or plant life.)
• To experience; (The company has sustained heavy losses this year.)
• To support emotionally.

A succinct but detailed definition of the name derived from the verb "to sustain," i.e., sustainability is given in Wikipedia. Accordingly, "Sustainability is the process of maintaining change in a balanced fashion, in which the exploitation of resources, the direction of investments, the orientation of technological development and institutional change are all in harmony and enhance both current and future potential to meet human needs and aspirations."

Not long ago, the course of the polyurethanes industry was sluggish. Sustainablility studies carried out by some multinationals pointed to the closure of old isocyanate plants. A few months later, the state of the economy changed. The polyurethanes market picked up and the same plants, instead of being shut, were upgraded. Ironically, a short time later, the same companies showed poor earnings because the market did not follow the predicted growth trend. But this is not the exception.

The biobased chemicals market has recently seen the collapse of bio-succinic acid producer BioAmber, despite the numerous reorganizations aimed at reviving the sales of the company. A year before the company was shut, BioAmber was planning a seven-fold increase of its production capacity. According to their management, the business plan the company put forward to its creditors was sustainable.

Succinic acid is a dicarboxylic acid widely used in the manufacture of polyester polyols. The manufacturing process from natural sources proves to be expensive, even if the science involved is brilliant. Therefore, the profit margins generated to sustain its production must be high. BioAmber's capacity was 30 Ktpa, but the returns did not justify the operation of the company.

Whereas the applications of succinic acid in the polymers industry are well known, the production of polyols from natural sources has only recently gained momentum. Their successful inclusion in current technologies will show whether their use is sustainable. There is no need to use a polyol produced from palm or rapeseed oil in a polyurethane formulation if its contribution to the properties of the end product does not offer any economic or qualitative appeal to the consumer.

There is no doubt that the final outlet of all industrial and agricultural products are aimed at the direct or indirect consumption by humans. The higher the production rates, the more energy will be required by the production processes. A simple mathematical model will certainly prove that sustainabilty as well as cyclic economy will be convincigly achieved and implemented, at least, when the growth of the world population will be controllable. But this is a very difficult target to attain.

1.3 Polyols from Vegetable Oils

Vegetable oils have been known to mankind since prehistoric times. Humans have used fats and oils for food, healing and other ends. Over the years, the extraction of oils from agricultural products has been elaborated.

Nowadays, for some polymerization purposes, many vegetable oil molecules must be chemically transformed in order to include hydroxyl groups in their structure.

For instance, soybean oil does not contain any hydroxyl groups but has an average of 4.6 double bonds per triglyceride molecule. The unsaturation of the vegetable oil molecule can accommodate hydroxyl groups. However, many reactions for preparing polyols from vegetable oils are not very selective.

By-products are created during the transformation. Furthermore, many conventional methods of preparing polyols from vegetable oils do not produce polyols having a significant content of hydroxyl groups, and the available methods do not produce products having a desirable viscosity. Greases or waxes often result as a consequence of such chemical transformations.

1.3.1 Polyols from Triglycerides

Chemically, vegetable oils are defined as triglycerides (also called glyceryl trialkanoates) because they are esters of glycerol and fatty acids (Figure 1.3).

The structures in Figure 1.4 put the glyceride definition in a broader context.

Figure 1.3 Products resulting from the hydrolysis of triglycerides.

Figure 1.4 The definition of glycerides reflects the number...