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How to turn vegetable waste into clean fuels

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Plant biomass, that is, organic matter from plants such as wood and agricultural and industrial waste, is the largest source of renewable materials on Earth. It is available in large quantities at low cost and represents a decisive potential source for energy production, to obtain (bio)fuels for transport, as well as bioproducts and renewable raw materials that can be used to produce plastics.

Biomass allows energy to be obtained by being subjected to various processes. Through combustion, it produces heat and electricity; through thermochemical processes, it is transformed into fuel gas; and through biochemical processes, it is transformed into biogas or bioethanol (two products that can be used to produce electrical energy). biomass can also be converted into biodiesel or synthesis gas (syngas), from which chemicals (such as plastics) and liquid fuels can be synthesized.

“Residual biomass is a renewable fuel that exists in large quantities in Spain,” explains researcher Juan Adánez, from the Institute of Carbochemistry (ICB). “In addition to agricultural and forestry waste, it includes waste of organic origin, such as sewage sludge, livestock waste or municipal waste.. It can be used for the production of energy, biofuels or chemical products with neutral CO emissions.two into the atmosphere, or even to achieve negative CO emissionstwo if the COtwo generated in these processes is captured and stored”, he adds.

Adánez’s team is studying how to use biomass to obtain energy and synthesis gas through non-polluting processes, that is, processes that allow simultaneously capture the COtwo of the waste at low cost and store it. It would be a useful technology to reduce greenhouse gas emissions. The capture of these gases is essential: it is essential to remove COtwo of the atmosphere to achieve the goal of the 2015 Paris Agreement, which limited the average global warming to 1.5 °C compared to pre-industrial levels.

Biomass, like wood from trees, removes COtwo naturally from the atmosphere by converting it into organic matter. In this way, when these organic residues are used as fuel, this COtwo returns to the atmosphere, but without increasing the proportion of gases in the environment (zero or neutral emissions are considered). If the energy use of biomass is added to the technology of capturing COtwonegative CO emissions are achievedtwo and remove it from the atmosphere efficiently and at low cost.

The technology investigated by Adánez’s team allows control of CO emissionstwo in industrial processes. It puts the fuel from these processes (biomass, used oils, etc.) in contact with a metal oxide or oxygen carrier. In this way, this oxide supplies the oxygen necessary for both combustion and gasification, without putting it in contact with the air.

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As a result, the products of combustion (COtwo and water) do not contain nitrogen and it is not necessary to separate the COtwo for capture and storage, instead it can be captured directly. Similarly, in gasification, the quality of the synthesis gas is improved -because it lacks nitrogen- and the need to use high-purity oxygen is avoided, which significantly reduces the operating costs of the process.

In these investigations, the process is developed from the laboratory to its application at a semi-industrial level. “We develop oxygen carriers with suitable characteristics for both combustion and gasification or reforming,” says Adánez.

This technology could be applied in industrial plants with CO capturetwo from the combustion of biomass and wasteas well as in hydrogen production plants, synthetic biofuels, fertilizers and biorefineries.

Refining of plant remains

One of the instruments to produce fuel from biomass are the biorefineries, a type of refinery that converts biomass (plant dry matter, specifically lignocellulose) into other beneficial by-products, such as biofuels and chemicals.

Biorefineries can produce various chemical products by fractionating an initial raw material (biomass) into multiple intermediate products (carbohydrates, lignin, lipids), which can in turn be transformed into value-added products.

Researchers from the Institute of Catalysis and Petrochemistry (ICP) lead a ambitious project to develop a biorefinery that generates fuel and renewable chemicals from plant waste, in a sustainable way. The project, called Fraction, has received 6.2 million euros from the European public-private consortium BBI-JU (Bio-based Industries Joint Undertaking).

The project is based on a novel method for treating plant residues, fractioning their components and extracting those that are most useful. “This initiative aims to establish that multiple renewable materials and chemical products can be produced from lignocellulosic biomass in a sustainable way and at competitive prices, replacing many of the products that we use today and that come from oil, such as beverage bottles, packaging for plastics, paint solvents…”, explains David Martin AlonsoICP researcher.

“To achieve this, the Fraction project will use an innovative and flexible organosolv process (biomass treatment that uses an organic compound instead of water as a solvent) that allows treating lignocellulosic waste (pine, birch, bagasse, corrugated cardboard, etc.) to split and separately obtain its three main components: high-quality cellulose, hemicelluloses and lignin”, explains Manuel López Granados, coordinator of the project.

These components can be used both for the production of ethanol, which can be used as biofuel, as well as other raw materials, polymers and resins, solvents for paints, surface coatings or to produce plastics for packaging or plastic bottles.

The Fraction project is coordinated by the ICP in a multidisciplinary consortium with 12 partners from eight European countries. Members include two large industrial partners, five research or technology centers and five small and medium-sized companies. “The Fraction project covers the entire value chain for each product until the end of its useful life, with industrial involvement, and includes members who are strongly interested in the subsequent scaling of the technology for future commercialization at the end of the project,” says López. Pomegranates.

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Improvement in obtaining bioethanol

At the Institute of Natural Resources and Agrobiology of Seville (IRNAS), the group led by Jose Carlos del Río works on the recovery of plant biomass for the production of biofuels, bioproducts and biomaterials. One of these products is a biofuel, the second generation bioethanol (2G), obtained from plants and plant residues that do not compete with crops used for food and do not cause an increase in their price. 2G bioethanol, or cellulosic alcohol, is obtained from polysaccharides (cellulose and hemicelluloses) present in plant matter.

“Plant cell wall polysaccharides, especially cellulose, can be converted into neutral sugars by a process called enzymatic hydrolysis. Those neutral sugars can then be converted to ethanol through fermentation. However, this degradation process has an important obstacle, lignin, a complex and highly recalcitrant aromatic polymer that surrounds the polysaccharides of the cell wall, and that must be eliminated”, explains José Carlos del Río.

“In order to partially degrade or eliminate lignin, it is necessary to carry out a pretreatment of the lignocellulosic biomass, so that the cellulose is more accessible to the enzymes of the hydrolysis process. There are various types of pretreatment, but generally they all use aggressive chemical products,” explains Del Río.

As an alternative, the IRNAS researchers They are working on the development of more environmentally friendly biotechnological pretreatments that achieve a more selective removal of lignin from biomass.. “The pretreatments developed by IRNAS to degrade lignin are based on the use of enzymes from fungi such as laccases. However, the direct action of laccases on lignin is restricted to phenolic units that only represent a small percentage of the lignin polymer, a fact that limits their biotechnological application”, indicates the researcher.

“An alternative proposed by our group has been the joint use of laccases with redox mediators, simple compounds that form stable diffusible radicals, and that once oxidized by the enzyme, these oxidize and degrade lignin”, he details. The results obtained by IRNAS are very promising.

The EU has set the goal of ensuring that at least 32% of transport fuels come from renewable sources by 2030, according to the Renewable Energy Directive 2018/2001. The development of biofuels from biomass contributes to the decarbonisation of the transport sector, one of the largest emitters of greenhouse gases.

Reference article: https://www.csic.es/es/actualidad-del-csic/biorrefinerias-para-conversión-residuos-vegetales-en-combustible-renovable

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Environment section contact: crisisclimatica@prensaiberica.es

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