As the global population continues to grow so does our need for energy and materials. The depletion of fossil fuels and its increasing demand raises concerns of how we will secure a continuous supply of product and meet the future generations needs. The issue of supply and demand isn’t the only concern, as burning of fossil fuels also releases greenhouse gases into the atmosphere causing global warming. [6] Some of the alternatives to fossil fuels are shale gas and coal. Various chemical companies have been looking into the opportunities created by shale gas and oil for chemical production due to it affordability. However, this has been limited due to the environmental concerns including; groundwater contamination during the fracking process and its links to increasing seismic activities. The use of coal for chemical production is also limited and is not a way to secure future energy supply. The use of sustainable and renewable raw materials such as biomass and bio-waste has become an area of interest for the industry and could be the answer for sustainable low carbon chemical production. [4]
The current chemical production is mainly oil centric. Natural petroleum is chemically saturated and consists of C-C bonds therefore isn’t a product of much use. This is why the process of cracking is used to replace the C-C bonds with C-C bonds which is a more useful unsaturated product. The products of the cracking process are smaller chain alkenes (C1-C8) which are the most useful starting material for 90% by weight of all useful synthesised organic compounds. [1] It is estimated that 80% by weight of all the chemicals produced by the petroleum industry is used for polymers. In theory, all the chemicals for plastics can be derived from renewable sources such as biomass but the process of doing this is not always chemically feasible.[9]
Biomass is an inexpensive and abundant source of carbon the cost of production of which is dependent on the region it is being produced in.[8] Biomass is all organic material derived from green plants as a result of photosynthesis. It includes a wide range of organic materials and is composed of cellulose, lignin, lipids, sugars starches and more. Waste biomass such as food residue and animal waste has the potential to be converted into fuel for transportation and for the production of biomaterials.[14] Current production of bio-based chemicals and fuels are mainly done from sugar/starch and oil containing crops. However, these raise some social problems as these feedstocks are also used for food purposes. An alternative could be to use waste and lignocellulosic biomass which do not compete with food or land.[6]
Biomass can be processed through two main processes, thermochemical which produces a mix of oils and gases and biochemical. The thermochemical conversion processes include direct combustion, pyrolosis, gasification and liquefaction. [14] Syngas is a product of thermochemical gasification which is carried out at high temperature of approximately 1000C and is usually used to produce heat, power and chemical derivatives. It can also be fermented into methanol and ethanol. Syngas is a mixture consisting mainly of CO2 and H2, it is considered a chemical platform for bio refineries. [6] Platform chemicals are intermediates from which new products are derived. Oils extracted form plants and biomass have various uses in the food sector, biofuels and more. [7]
The advantage of using biomass over petroleum sources for chemicals and fuels is mainly because of the carbon neutrality of the biomass derived fuels along with the fact that these are biodegradable and sustainable products. Current bio based chemicals only represent a minor fraction of the industry due to their high costs. Therefore, one of the most important research in developing biomass chemicals is to be able to reduce the cost of their production, this is where catalytic conversion has become subject to wide research. It has been estimated that by 2050 at least 30% by weight of chemicals will be derived from biomass based feedstocks. [10] Other major concerns for the usage of biomass is that it would get in the way of production of food crops. One solution is to use non-food biomass crops for production of biochemicals.[15]
Plants convert carbon dioxide and water into primary and secondary metabolite bio-chemicals in the process we know as photosynthesis. Primary metabolites are carbohydrates and lignin which are present in large volume and can be converted into biofuels. Secondary metabolites are high value chemicals and are found in lower volumes. They can be used to produce high value chemicals such as food flavours and pharmaceuticals. [12]
Solid biomass can be converted to liquid to be used as fuel by the Fischer-Tropsch (FT) synthesis. In this process, the biomass is first gassified with air, oxygen and steam to produce raw bio- syngas. The bio syngas then goes through a cleaning process to remove any contaminants. FT synthesis of the clean syngas is carried out in a catalytic reactor to produce renewable liquid fuels. The FT synthesis is a process of producing liquid hydrocarbons from synthesis gas therefore the feedstock can also be coal and natural gas. [13]
Dimethyl ether can be produced by the dehydration of methanol which is initially formed from syngas. DME is more preferable than methanol and plays an alternative role to it. It is the smallest aliphatic ether which is also non toxic and non corrosive. DME can be used as alternative to diesel fuel because of its high cetane number and low emission of CO and nitrogen oxides. DME can also be used as an alternative fuel for cooking due to its similar properties to liquifued petroleum gas.[5]
5 hydroxymethylfurfural (HMF) is a deriviative of furan compound and was listed as one of the top 10 value added bio-based chemicals by the US department of energy. It is considered one of the most promising platform molecules that can be converted into a variety of chemicals. HMF can be naturally produced by the thermal decomposition of carbohydrates. HMF and its deriviatives can be used in a variety of food sources specifically processed foods. One of the major advantages of HMF derivative based plastics are that they are generally biodegradable therefore creates an opportunity for a green low carbon economy. [15]