ETHANOL INDUSTRIAL TECHNOLOGIES RESEARCH OVERVIEW
FROM FIELD TO FUEL
The state of the art in Brazil is advanced compared to developed countries. Research conducted in Brazil by the private and public sectors brought an important contribution in terms of:
· Equipment and process design;
· Bagasse high pressure feeding technology and requirements bagasse must fulfill;
· Corrosion abrasion and material engineering;
· Lignin-cellulose material pretreatment.
· By-products formation and removal.
· Hexoses fermentation and integration of hydrolysis to sugar cane processing to ethanol, sugar and power;
· Process and energy consumption optimization.
Research lines in the BIOEN Division of Ethanol Industrial Technologies should now address:
· The use of bagasse and trash from cane processing, including the characterization and development of procedures for physical pretreatment of this raw material;
· Development of physical and chemical methods of pretreatment of raw material with the aim of disengaging the strong crystalline not attackable of lignin cellulose;
· Development of both acid catalyzed and biocatalyzed processes for saccharification;
· Development of high performance cellulases;
· Hydrolysis liquor treatment purifying in order to remove fermentation inhibitors;
· Pentoses and hexoses efficient fermentation processes, including the development of microorganism strains;
· Energy optimization of hydrolysis processes;
· Effluent disposal and environmental friendly accepted processes
The work to be done does not stop at scientific level, basic and process engineering as well as feasibility studies must be done in order to arrive to a commercial process
Fermentation processes convert sugar raw material to ethanol. Ideally, it must be fast, efficient, flexible, and with low costs in terms of initial investments, maintenance, control, inputs and work.
Brazilian ethanol fermentation process must and can be improved in terms of yield, integration, micro organisms’ population and by-products control, final ethanol concentration, batch time and equipment design and maintenance.
There are several ways to improve fermentation process yield, including the use of high convertible carbon sugarcane varieties and incremental gains from:
· Reducing waste volume due increasing of ethanol content and/or waste recycle into the process;
· Reducing use or substitution of sulfuric acid;
· Reducing use or substitution of antibiotics;
· Reducing use or substitution of nitrogen and potassium;
· Reducing centrifugation costs from cellular recycling;
· Standardization of analytical procedures.
Additionally, due the dual nature of sugar/ethanol facilities, it is required high flexibility and resilience to easily shifting between ethanol or sugar production, and to deal with different sugarcane composition or maturation.
Microbiological studies about yeast ecology and population dynamics are perhaps one of essential themes to improve fermentation. Sugarcane juice fermented by yeasts with high alcoholic tolerance will increase its alcoholic content and therefore minimize steam consumption in the distillation and residues produced.
It is also important to develop yeasts with high thermal tolerance given that control of temperature becomes more expensive as temperature of cooling water increases, due the necessity of significantly amounts of energy to water pumping around fermentation tanks.
Ecology of the alcoholic fermentation process must be controlled, avoiding the development of contaminant bacteria that today cause productivity reduction and increasing costs with biocides and antibiotics. Flocculation problems in fermentation reactors, caused from undesirable yeasts or bacteria in proper ambient conditions.
Succession patterns of yeast ecology during fermentation cycle need to be better understood. This is essential to improve the composition and genetic quality of fermentation starters.
Finally, it is important to expend efforts in research of new process technologies. Some have been recently proposed, as the vacuum extractive fermentation, which provides a better productivity – tree fold higher – and lower steam consumption and residues production at distillation. The whole cost reduction with this system is estimated to be as high as 10%.
The mainly research goal in distillation consists of reducing steam consumption by introduction of multiple stage distillation processes. In the new energy sugarcane paradigm it would facilitate energy balance optimization of the industrial facilities.
Also the diffusion of molecular sieves and evaluation of vacuum distillation, absorption and pervaporation processes, as forms to extract anhydrous ethanol, should be considered. These technologies could substitute petrochemical products and reduce steam consumption.
Technological alternatives for treatment and use of distilling residues (vinasse), as for example, biodigestion and concentration, should be re-analyzed under the light of the new paradigm. Leaves blanket on field could change nutritional requirements.
Vinasse, so far has been applied as fertilizing, however research is still necessary in following topics: technologies of concentration, strategies of applications, measurement of environmental impacts and evaluation of impacts of biodigested vinasse effluent versus in natura vinasse. Other possibilities include vinasse combustion and protein production. It is important to point out that development of adequate solutions to each producing region becomes necessary, according to its local characteristics.
Other by-products of industrial operations, like filter cake, fusel oil and boiler leached ashes could be also subject of study, aiming recycling and environmental benefits.
Finally, it is necessary to reduce the water use for processing. CTC (at Piracicaba-SP) has developed several approaches to reducing industrial water consumption. Water use can be reduced of current 3m3/t to less than 1m3/t, producing less effluent and reducing costs, facing the governmental trend to enforce taxes for rivers water use.
Regarding thermodynamic cycle of generation and use of energy, the sector is beginning to change from using old 22 bar boilers to use 40 and up to 60 bar units. This change is motivated by energy saving considerations, involving the modification of procedures and systems that allow for more efficient electricity generation. A more relevant technological improvement, gasification technology, will also make energy generation more efficient, however it still needs to be developed and demonstrated.
An equally important task is to comply with the obligation of sugarcane harvesting without burning, which will imply is the collection of trash and its subsequent burning in boilers.
Two environment related topics are energy overall optimization of industry and controlling of burning emissions from industry facilities.
Thermo-chemical processes called BTL ("biomass to liquids") include pyrolysis and gasification technologies to be developed and compared with usual biochemical routes.
Pyrolysis is the chemical decomposition of organic materials by heating in the absence of oxygen or any other reagents, except possibly steam. The pyrolysis (or devolatilization) process occurs as the carbonaceous particle heats up. Volatiles are released and char is produced, resulting in up to 70% weight loss for coal. The process is dependent on the properties of the carbonaceous material and determines the structure and composition of the char, which will then undergo gasification reactions.
The gasification process occurs as the char reacts with carbon dioxide and steam to produce carbon monoxide and hydrogen. The resulting gas is called synthesis gas and may be more efficiently converted to energy such as electricity than would be possible by direct combustion of the biomass, as the biomass is first combusted in a boiler and the heat is used to produce steam to drive a steam turbine. Synthesis gas could be converted into liquid fuels (ethanol, 1-butanol or others) when passing in catalytic stream beds (Fischer-Tropsch process).
Other alternative is the biodigestion of the entire crop, that has potential in generating liquid fuels at lower costs to the ones of the oil.