The rising price of natural gas and high emission rate of greenhouse gases from fossil fuels open new areas of research for sustainable alternatives. A wide variety of industrial chemicals are produced from petroleum based feedstock, which can be produced from biomass feedstock.
The chemical production complex of thirteen existing plants in the lower Mississippi River corridor is used as a base case, and new plants that can use biomass as raw materials are integrated into the existing plants. These plants employ processes like fermentation, transesterification, anaerobic digestion, and gasification. Sustainable costs are included with economic and environmental costs to demonstrate how new plants can be integrated into sustainable complexes.
Fermentation of starch (corn), sugar (sugarcane) or lignocellulosic biomass like corn stover or switch grass produces ethanol in presence of suitable enzymes. The processes for conversion depend on the feedstock used. Ethanol is readily converted to ethylene in a process that uses an activated alumina catalyst in a fluidized bed at 300oC with a 99% conversion. Ethylene is the starting chemical for a wide range of industrial commodity chemicals like polyethylene, ethylene oxide and acetaldehyde. An integration of a plant for ethanol based on biomass feedstock will be a starting point for the production of the above commodity chemicals.
Transesterification is the addition of an alcohol such as methanol or ethanol to break the triglycerides in natural oils to fatty acid esters and a glycerol molecule. The fatty acid esters can be modified and polymerized using epoxydation or hydroformylation. Markets that can make use of lipid and vegetable oil based feedstock includes lubricants and hydraulic fluids, solvents, polymers and resins, plasticizers, printing inks, adhesives and surfactants, cosmetics, pharmaceuticals etc..
Transesterification using soybean oil produces approximately 10% by weight of glycerol. Glycerol can be introduced into the propylene chain to produce chemicals. These chemicals are currently produced from natural gas. For example, Glycerol can be converted in a low pressure and temperature (200 psi and 200oC) catalytic process by hydrogenolysis to produce propylene glycol. Algae can be a source for producing natural oils. Algae grow easily in photobioreactors in the presence of sunlight and a carbon dioxide source. Power plant exhaust gases can be an excellent source for the growth of algae with nitrogen oxides present in the exhaust acting as a nutrient source. Some strains of algae are known to secrete the oils, thereby making it easy to extract the oil without involving complex separation and harvesting steps. A plant for the transesterification of oils to esters and glycerol is integrated into the base case design.
Anaerobic digestion of biomass yields carboxylic acids, methane and carbon dioxide in the presence of mixed culture of bacteria. The production of methane can be inhibited by using iodoform or bromoform to produce carboxylic acids like acetic acid and butyric acid. These acids can be further converted to ketones and reacted with cellulose to form cellulose acetate. The MixAlco process produces a mixture of alcohols from the anaerobic digestion of biomass. A plant for the anaerobic digestion of biomass for the production of carboxylic acids and ketones is integrated into the base case design.
Thermal conversion such as gasification and pyrolysis can be used to convert biomass to chemicals. Biomass gasification is the conversion of biomass to synthesis gas, a mixture of carbon monoxide and hydrogen. Pyrolysis is the direct thermal decomposition of the organic components in biomass in the absence of oxygen to yield an array of useful products like liquid and solid derivatives and fuel gases. Typically, gasification reactors comprise of a vertical reactor that has drying, pyrolysis and combustion zones. Synthesis gas leaves the top of the reactor and molten slag leaves the bottom of the reactor. Synthesis gas is used in the chemical production complex of the lower Mississippi River corridor to produce ammonia and methanol. Currently, ammonia and methanol are produced using synthesis gas from natural gas, naphtha or refinery light gas.
Thus, biomass feedstock based glycerin from transesterification process and ethanol from fermentation process are the building block chemicals that are currently produced from fossil feedstock. Gasification produces syngas which can be used in the production of ammonia and methanol. The industrial scale design of these processes is being integrated in the chemical production complex in the lower Mississippi river corridor. Other chemicals like acetic acid and ketones can be produced from anaerobic fermentation of biomass.
New plants that use biomass as raw materials are integrated into the chemical production complex of existing plants in the lower Mississippi River corridor. A superstructure of plants includes the base case of existing plants, a transesterification process, a fermentation process, an anaerobic digestion process and a gasification process. These processes are simulated in AspenŽ HYSYS and then exported to AspenŽ ICARUS PROCESS EVALUATOR for economic evauation. The designs for the rest of the processes are being done, and results will be available soon in the white paper.
The results from the optimal design will be presented in the conference. Four cases will be presented. These cases include (a) release of all carbon dioxide to the atmosphere from the existing and new processes, (b) the utilization of carbon dioxide for producing chemicals and adding value to the overall complex, (c) the utilization of carbon dioxide for the production of algae as biomass for the chemical complex and (d) the sequestration of carbon dioxide in underground wells.
The Chemical Complex Analysis System was used to determine the best configuration of plants in a chemical complex based on economic, energy, environmental and sustainable costs. It incorporates a flowsheeting component where simulations of the plants in the complex are entered. Each plant simulation from AspenŽ HYSYS is converted into a process or block flow diagram with material and energy balances, rate equations, equilibrium relations and thermodynamic and transport properties for the process units and heat exchanger networks. Multi-criteria optimization is being used with Monte Carlo simulation to determine the optimal configuration of plants in chemical production complex and sensitivity to prices, costs and sustainability credits/costs for the four cases above will be presented.
A detailed white paper on this research is available at http://www.mpri.lsu.edu/Integrating_Biomass_Feedstocks_into_Chemical_Production_Complexes_-_a_White_Paper.pdf