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Chemistry

Separation agents

Sustainable solvents dissolve pulp and can be widely used in industry

EDUARDO CESARFor many people chemistry is something that can be dangerous. In popular opinion it is associated with industrialized food that can do harm, weapons of mass destruction or pollution. As a reaction to this situation and taking into consideration environmental aspects and sustainable production, the concept of “green chemistry” began to gain strength as from the 1990’s. This is the incentive needed for using renewable raw material and biodegradable products for replacing substances that are harmful to human health and the environment. At the University of São Paulo (USP), a team led by Professor Omar El Seoud, from the Chemistry Institute (IQ), is dedicated to taking these principles forward. With support from FAPESP, they are working on a line of research, the objective of which is to develop the so-called “green solvents,” which cause a low environmental impact and are recyclable.

These are ionic compounds, comprising ions, molecules or atoms that gain or lose electrons during a process and, because of this, have a special electrical charge. They constitute an alternative to traditional solvents, derived from oil, which are used in the production of plastics, paints, adhesives and detergents. Ionic liquids provide greater chemical and thermal stability. Because of this they are safe, are not inflammable and do not evaporate, which considerably reduces the risk of causing fires and explosions. They are also relatively easy to obtain. “From a nitrogenized organic compound, imidazole, and common elements, like chlorine, bromine and iodine, it is possible to produce 144 ionic liquids and a large number of derivatives, most with application potential,” says Seoud. “This number is impressive when compared with the small number of volatile organic solvents (VOS) derived from oil and used industrially.” There are at least 10 oil-derived solvents produced in Brazil. According to the Brazilian Petroleum Agency (ANP), production in 2010 reached 2.4 million cubic meters and is a market that has revenues of R$ 5 billion a year. Still very much beginning in Brazil, the market in green solvents already has sales of some US$ 3.5 billion a year worldwide, and production of 5 million tons, according to information from the Brasil Econômico newspaper. North American market research company, Global Industry Analysts, announced last year that green solvents grew at an annual average production rate of 4.2% between 2001 and 2010.

Vegetable fiber
The importance given worldwide to the new possibilities of green solvents is extensive and covers ionic liquids that can be used, for example, in the production of second generation ethanol from agricultural waste. The first stage in this process involves the removal of lignin, a type of glue that binds together the components of vegetable fiber. One of the routes that is being researched is to dissolve the material in ionic liquid and separate the lignin by adding another solvent (acetone). “This vegetable mass is separated and then fermented, which generates glucose and then ethanol,” he explains. “The ionic liquid is also recovered and recycled in the process.” This type of liquid can also be used in producing pulp derivatives, like filtration and hemodialysis membranes, fibers and thickeners in the food industry.

“We use ionic liquids as efficient solvents for dissolving pulp fibers that are commercially interesting, like cotton, sisal and eucalyptus. After it has been dissolved the fiber is transformed into the derivative.” Researchers are also studying the so-called tensioactive ionic liquids (TILs), which have the same basic structures as common liquids but are capable of changing the surface tension of water, hence the name. They can be used as bactericides and for recovering water that has been contaminated with polychlorate organic substances. “In this case, the TIL is added to the contaminated water and forms aggregates called mycelia, which dissolve the organic contaminants,” explains Seoud. “The solution then goes through an ultrafiltration stage using special membranes and, under pressure, the water is cleaned in a specific filter and the aggregate, with the mycelium containing the pollutant, is retained for subsequent safe disposal. The technique can also be adjusted for removing heavy metals, inorganic contaminants that come from various metallurgical processes.” Still without a patent, Professor Seoud says that there are no immediate prospects of these green solvents being licensed to an industry, for example.

Ionic liquids are not the only solvents that can be considered green. There are already similar products in the market produced from glycerine, a by-product of the manufacture of biodiesel, in which for every 1000 liters of this biofuel, almost 100 liters of waste remains. An example is Augeo SL 191, a solvent for paints and varnishes used in automotive painting and repainting, industrial paints, wood and leather, which was launched in 2009 by Rhodia in Brazil. According to the company this solvent evaporates slowly and has little volatile organic compound, which enables greater productivity and less consumption in the paint and varnish manufacturing process. Along the same lines, the company launched Augeo Clean at the end of 2010, which is a variety of solvent, also derived from glycerine, for use as a raw material in the segment of products used in household and industrial cleaning. The multinational, which was bought at the beginning of the year by Belgian company Solvay, guarantees that the new products created in the company’s laboratories in Brazil, if they obey sustainability criteria, can replace similar products derived from oil and traditionally used in solvent formulae.

The projects
1. Synthesis, properties and applications of functionalized tensioactives and biopolymers: a green chemistry focus (nº 2004/15400-5); Modality Thematic project, Coordinator Omar Abou El Seoud – USP; Investment R$ 513,625.20 and US$ 184,476.24 (FAPESP)
2. ‘Green’ solvents: chemistry and applications of ionic liquids in catalysis: colloids and derivatives from biopolymers (nº 2010/03629-9); Modality Thematic project; Coordinator Omar Abou El Seoud – USP; Investment R$ 590,427.90 and US$ 73,111.88 (FAPESP)

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