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Advanced Oil Crop Biorefineries
By Abbas Kazmi
The Royal Society of ChemistryCopyright © 2012 Royal Society of Chemistry
All rights reserved.
ABBAS KAZMI, BIRGIT KAMM, SÖREN HENKE, LUDWIG THEUVSEN AND RAINER HÖFER
1.1 Green Chemistry and the Biorefinery
The principles of green chemistry are now having a real impact on industry and key players such as P&G are now providing greener alternatives that could have a global impact. One such example targets the alkyd resins which provide robust, high-gloss coatings at relatively low prices for a variety of applications including architectural finishes, industrial metal and construction equipment. However, these coatings require hazardous solvents to solubilise the organic polymers, which has led to novel greener resins developed by P&G in association with Cook Composites & Polymers, USA. The novel resins are produced from the esterification of sucrose with fatty acids, both of which are renewable resources that are readily available. Furthermore the process requires significantly less VOC content and therefore is much greener.
Biodiesel is now a well-established industry, although it has had turbulent times, and is based on renewable resources such as plant oils; however, the transesterification process could be made more green. An alternative method for manufacturing biodiesel, called the 'Mcgyan Process', has been developed by SarTec Corporation and is based on a fixed-bed, flow-through reactor. The fixed-bed zirconia catalyst, which is continuously used, results in no catalyst waste, unlike the conventional acid/base catalyst systems. The novel process not only improves efficiency but also has a positive impact on the economics to the extent that a large-scale 3 million gallon per year facility is to be constructed.
The future biorefinery needs to be based on existing supply chains and product streams. Biorefinery processes need to remove inefficiencies and wastes from existing processes. This is the only way biorefinery concepts will penetrate conventional markets. The plant oil industry is a great example of this as the oils are mainly used for human consumption (126 million tons); however, a considerable amount is used for chemical (15 million tons) and fuel applications (8 million tons). European vegetable oils are used in the oleochemical industry; however, the majority of oils are imported such as soya, palm and castor oil.
The oleochemical industry uses the key components of plant oils to produce chemicals for various applications such as cosmetics, paints, lubricants, biofuels, plastics, soaps and pharmaceuticals. Using fatty acids, glycerine or fatty acid methyl esters a number of important derivatives such as esters, sulfates, ethoxylates and other chemical functionalities can be produced.
In the surfactant market the crude oil derived alkyl benzene sulfonate has the largest market share; however, greener alternatives such as alcohol ether sulfates, alcohol sulfates and alcohol ethoxylates are significantly growing in the market. With pressure from governments and NGOs the paint industry is looking to reduce VOC emissions by using greener resins such as those derived from soya and sunflower oils. Long-chain fatty acids can also be used as biolubricants; however, the estimated volume of such products in the EU is 127 000 tons as of 2006, out of a 5 million ton lubricant market, mainly due to the high cost of biolubricants.
The polymer industry is also currently based on crude oil and with stricter regulations the industry is shifting towards greener alternatives. A host of polymers can be made from plant oils, for example alkyd resins can be made from condensation polymerisation of polyols, organic acids and fatty acids. Furthermore, smaller building blocks based on plant oils can be used in conventional polymers to improve properties such as elasticity, flexibility, strength and hydrophobicity. For example, oleic acid can be used as a building block to produce important products such as linoleum, polyamides, polyurethanes, polyamido amines and non-nylon polyamides. However, with many of these products the properties and pricing are inferior to crude-oil derived polymers, therefore further research is required.
Additional opportunities exist when cross-metathesis reactions are employed with fatty acids and a number of polymers can be produced such as polyesters, polyethers and polyolefins. It has been shown by Rybak and Meier that the cross-metathesis of fatty acid methyl esters with methyl acrylate with only 0.5 mol% of catalyst can be successfully achieved. Furthermore it was shown that oleyl alcohol can be cross-metathesised with methyl acrylate successfully to produce 11-hydroxy-2-undecanoic acid methyl ester and 2-undecanoic acid methyl ester. The former ester is commonly used to make polymers and the latter is used for detergent applications.
Although there is a well-established market for plant oils in the speciality chemicals industry, the biodiesel industry has rapidly grown through government subsidies and high prices of mineral diesel. Therefore a well-defined stream of products from plant oils exists currently and the biorefinery concept can add value to these processes by utilising the by-products such as straw, meal and glycerol.
Wheat straw, rapeseed straw and sunflower stalks are commonly left on the field to replenish the soil or are used as low-grade animal feeds. Although there are environmentally friendly uses of these materials, they do not significantly contribute economically to farming operations. In attempting to increase revenue, the green chemistry approach is the best as it ensures that any additional processing will not harm the environment with a low carbon footprint. A good example of this is the use of supercritical CO2 extraction technology, which uses compressed CO2 to extract valuable chemicals from straws. Wheat straws have a waxy surface and the key components of this wax can be selectively extracted with very high efficiencies. A suitable marketable product from biomass that is of a value that can cover the capital cost requirements is yet to be identified. A number of secondary metabolites that have significant potential include cetearyl alcohol, benzoic acid and fumaric acid, which have applications in the personal care, food and chemical industries. In oilseed crops significant quantities of phenolics, falavanoids and sinapine are found, which can all be used as natural antioxidants. These components can easily be extracted from the oilseed cake by using conventional solvents such as methanol, acetone, water and ethyl acetate from the oilseed cake. However, after extraction of such chemicals and proteins the value of the remaining material decreases as it is no longer viable for animal feed. On the other hand it is a legal requirement to remove glucosinolates from rape meal due to their toxicity. Glucosinolates are an important group of chemicals which can easily be broken down by enzymes to produce isothiocyanates, which have good pesticidal properties. Furthermore, low concentrations of glucosinolates in human diets can offer anti-inflammatory, anti-microbial and chemo-preventive effects.
After extracting key secondary metabolites from biomass, the bulk material still contains a rich resource, which can be further utilised to add value to the process. The main components of straw are cellulose, hemicellulose and lignin, all of which have important uses. Cellulosic material can be enzymatically converted to sugars, which can be used as building blocks for a number of commodity chemicals such as succinic acid. The presence of lignin in fermentation broths can reduce the efficiency of enzymes, therefore separation of this component via the organosolv process is becoming common practice. The sugars can be converted to commodity chemicals such as glycerol, aspartic acid, levulinic acid and citric acid. These chemicals are currently derived from crude oil economically and for bioderived alternatives to penetrate the market they must be cost effective.
Such biochemical processes can be energy intensive and the enzymes tend to be very expensive. Furthermore, the processes developed to date do not take into account the lignin that is produced as a by-product. Indeed the lignin could be used to provide heat and power to the process; however, other value-added products can also be made to improve the economic viability. Pyrolysis of ligno-cellulosic materials has been well known for many years and recent developments in this technology may offer a more efficient method of producing fuels and chemicals. Microwave pyrolysis is an energy-efficient method of converting biomass into various products at low temperature. The three forms of products for any biomass are char, oil and gas with the respective ratios being specific to the feedstock and processing conditions. The pyrolysis oil contains a cocktail of chemicals which can be used directly in a variety of applications or can be derivatised to form high-value speciality chemicals. With the addition of certain metal oxides, salts or acids the final composition of the bio-oil can be controlled, for example when MgCl2 is added with biomass, the resulting biooil mainly contains furfural, an important commodity chemical.
1.2 The Biorefinery Concept
Dedicated to Michael Kamm, Founder of biorefinery.de GmbH.
Sustainable economical growth requires safe supply of raw materials for industrial production. Today's most frequently used industrial raw material is petroleum, which is neither sustainable nor environmentally friendly. While the economy of energy can be based on various alternative raw materials, such as wind, sun, water, biomass, as well as nuclear fission and fusion, the economy of substances is fundamentally dependent on biomass, in particular the biomass of plants. The development of biorefineries represents the key for access to an integrated production of food, feed, chemicals, materials, goods and fuels of the future.
Nature is a permanently renewing production chain for chemicals, materials, fuels, cosmetics and pharmaceuticals. Many of the current biobased products are results of a direct physical or chemical treatment and processing of biomass, such as cellulose, starch, oil, protein, lignin and terpene. On one hand one has to mention that with the help of biotechnological processes and methods, chemicals can be produced such as ethanol, butanol, aceton, lactic acid and itaconic acid as well as amino acids, e.g. glutaminic acid, lysine and tryptophan. On the other hand, currently only 6 billion tons of the yearly produced bio-mass, 1.7–2.0 × 1011 tons, is used, and only 3 to 3.5% of this amount is used in the non-food area, such as chemistry.
The basic reaction of biomass photosynthesis is according to:
[MATHEMATICAL EXPRESSION OMITTED]
Industrial utilisation of raw materials for the energetic and material-demanding industry from agriculture and forestry is still at an early stage.
The majority of biological raw materials are produced in agriculture, in forestry and by microbial systems. The forest can provide excellent raw materials for the paper and cardboard industry, the construction industry and the chemical industry. Field fruits represent an organically chemical pool, from which fuels, chemicals and chemical products as well as biomaterials are produced (Figure 1.1). Waste biomass and biomass of nature and landscape cultivation are valuable organic reservoirs of raw material and must be used in accordance with their organic composition. During the development of biorefinery systems the term 'waste biomass' will become obsolete in the medium term. Due to low cost, plentiful supply and amenability to biotechnology, carbohydrates appear likely to be the dominant source of feedstocks for biocommodity processing. Starch-rich and cellulosic materials each have important advantages in this context. Corn is by far the dominant feedstock for biological production of commodity products today. Advantages over cellulosic materials include much larger ultimate supply, lower purchase cost, lower anticipated transfer cost and lower inputs of chemicals and energy required for production. Recently the goal of the US Department of Agriculture and the US Department of Energy is the additional supply of 1 billion tons biomass for a prize of 35 US dollars per ton per year for the industrial chemical and biotechnological utilisation, without restriction of today's applications of biomass from agriculture and forestry. The European Commission and the US Department of Energy have come to an agreement for co-operation in this field (US Department of Energy (DOE), 2005). Based on the European biomass action plan of 2006 both strategic EU-projects, (1) BIOPOL, European Biorefineries: Concepts, Status & Policy Implications and (2) Biorefinery Euroview (Current situation and potential of the biorefinery concept in the EU: strategic framework and guidelines for its development) began preparation for the 7th EU framework program.
In order to minimise food-feed-fuel conflicts and in order to use biomass most efficiently, it is therefore necessary to develop strategies and ideas for how one might use biomass fractions, in particular green biomass and agricultural residues, such as straw more efficiently. In future developments, food- and feed-processing residues should therefore also become part of biorefinery strategies since either particular waste fractions may be too small for a cost-efficient specific valorisation treatment in situ or the diverse technologies necessary are not available. Fibre-containing food-processing residues may then be pre-treated and processed with other cellulosic material from other sources in order to produce ethanol or other platform chemicals. Foodprocessing residues have, however, a special feature one has to be aware of. Due to their high water content and endogenous enzymatic activity, foodprocessing residues have a comparatively low biological stability and are prone to uncontrolled degradation and spoilage including rapid autoxidation. To avoid extra costs for transportation and conservation, the use of foodprocessing residues should also become part of a regional biomass utilisation network. Thus advanced oil crop biorefineries could produce oil for food, proteins for functional products and straw for platform chemicals and lignin.
1.2.2 Principles of Biorefineries
Biomass is similar to petroleum as it has a complex composition. Therefore its primary separation into main groups of substances is appropriate. Subsequent treatment and processing of those substances leads to a whole palette of products. Petrol-chemistry is based on the principle of separating hydrocarbons simply and in a pure form in refineries. In efficient product lines, a system based on family trees has been built, in which basic chemicals, intermediate products and sophisticated products are produced. This principle of petroleum refineries must be transferred to biorefineries. Biomass contains C:H:O:N, a feature that petroleum does not have and therefore complicates processing. The biotechnological conversion will therefore become, beside the chemical, a big player in the future (Figure 1.2).
Thus biomass can already be modified within the process of genesis in such a way that it is adapted for the purpose of subsequent processing and can particularly target products that have already been formed. For those products the term 'precursors' is used.
Plant biomass always consists of the basic products such as carbohydrates, lignin, proteins and fats, besides various substances such as vitamins, dyes, flavours and aromatic essences of different chemical structures. Biorefineries combine the essential technologies between biological raw materials and the industrial intermediates and final products (Figure 1.3).
Excerpted from Advanced Oil Crop Biorefineries by Abbas Kazmi. Copyright © 2012 Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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