Biorefinery biomass

Conversion efficiency and robust fermentation of mixed-sugar lignocellulose-derived hydrolysates are critical for producing ethanol at low cost to realize a commercially viable biorefinery. Biomass sugars are typically released by thermochemical pretreatment followed by enzymatic hydrolysis of chopped or milled biomass. The pretreated soluble fraction of biomass is called the hydrolysate and the hydrolysate containing the insoluble... 

One can envisage the future production of liquid fuels and commodity chemicals in a biorefinery Biomass is first subjected to extraction to remove waxes and essential oils. Various options are possible for conversion of the remaining biofeedstock, which consists primarily of lignocellulose. It can be converted to synthesis gas (CO + H2) by gasification, for example, and subsequently to methanol. Alternatively, it can be subjected to hydrothermal upgrading (HTU), affording liquid biofuels from which known transport fuels and bulk chemicals can be produced. An appealing option is bioconversion to ethanol by fermentation. The ethanol can be used directly as a liquid fuel and/or converted to ethylene as a base chemical. Such a hiorefinery is depicted in Fig. 8.1. 

Advances in biorefineries Biomass and waste supply chain exploitation... 

For example, in a (thermochemical) biorefinery, biomass is converted into energy carriers such as transportation fuels (e.g., ethanol), heat, and power and/or chemicals. In terms of energy content, the amount of biomass for (transportation) fuels and CHP (e.g., by combustion) is much higher than the amount used for the production of chemicals. However, in terms of added value, chemicals can provide a significant contribution to the overall cost effeaiveness of the refinery. When the main product of a biorefinery is (hemi) cellulose bioethanol, the lignin ends up in a residue that mostly is used as a fuel to generate heat. The economics of the biorefinery will benefit much from the valorization of this lignin-rich residue to value-added aromatic chemicals. 

Alternatively, an entirely new downstream process and product chain, using renewable raw materials, can be conceived (the biorefinery ). The chemistry will be more focused on that of oxohydrocarbons (particularly carbohydrates) rather than hydrocarbons. Understanding the materials chemistry of biomass and related products would need to be enhanced. However, work has already been undertaken to identify the top sugar-derived intermediates (Figure 1.9) on which down-stream chemical processing might be derived. 

Biomass is a renewable resource from which various useful chemicals and fuels can be produced. Glycerol, obtained as a co-product of the transesterification of vegetable oils to produce biodiesel, is a potential building block to be processed in biorefineries (1,2). Attention has been recently paid to the conversion of glycerol to chemicals, such as propanediols (3, 4), acrolein (5, 6), or glyceric acid (7, 8). 

The additional interesting part of Fig. 1.12 is the biorefinery, which uses biomass and waste, produces waste products C02 and ash, both to be recycled for the production of biofuels, heat and electricity and biomaterials. These biomaterials are highly oxygen functionalized for products such as alcohols, carboxylic acids and esters. A currently produced bioplastic is poly(lactic acid). A main cost factor is separation. 

A biorefinery scheme to produce chemicals from non-food biomass is given in Fig. 1.16. 

This chapter surveys different process options to convert terpenes, plant oils, carbohydrates and lignocellulosic materials into valuable chemicals and polymers. Three different strategies of conversion processes integrated in a biorefinery scheme are proposed from biomass to bioproducts via degraded molecules , from platform molecules to bioproducts , and from biomass to bioproducts via new synthesis routes . Selected examples representative of the three options are given. Attention is focused on conversions based on one-pot reactions involving one or several catalytic steps that could be used to replace conventional synthetic routes developed for hydrocarbons. 

The expansion of the market, however, will depend considerably on the possibility of an efficient use of other biomass sources, particularly lignocellulosic-based materials, fast growing dedicated crops, and waste resources. Effective integration of bioethanol production into biorefineries will also be a key aspect in decreasing the price by a better use of all the components of biomass. 

A biorefinery maximizes the value derived from the complex biomass feedstock by (a) optimal use and valorization of feedstock, (b) optimization and integration of processes for better efficiency, and (c) optimization of inputs (water, energy, etc.) and waste recycling/treatment. Integrated production of bioproducts, especially for bulk chemicals, biofuels, biolubricants and polymers, can improve their competitiveness and eco-efficiency. However, although a few examples of biorefineries already exist (Chapters 3 and 6), many improvements are still needed to enhance the process [5] ... 

Valorization, retreatment or disposal of co-products and wastes from biorefinery by catalytic treatments. This includes the utilization of plant and biomass fractions that are residual after the production of, for example, bioethanol and from other production chains (e.g., production of methane). 

To convert these feedstocks into useful chemicals, mainly fermentation, chemical modification or thermochemical methods were applied. However, these processes were later abandoned in favor of the more economic and efficient processes based on fossil resources, in particular oil. Easier transport and more stable chemical composition (biomass feedstocks are highly diverse, depending on the source) are two relevant additional factors in favor of fossil fuels. Therefore, although the concept of biorefinery is attractive, there are several barriers to economically feasible. 

However, most of these routes are still economically unattractive and the possibility of creating an equivalent petrochemistry based on biomass, which depends on raising the conversion efficiency and establishing cascades in which the residues of one product serve as inputs for another, still suffers from the relatively unattractive products derived from hemicellulose and lignin. Therefore, to bring back biomass into the chemical business , the utilization of biomass must be enhanced by integrating it into biorefinery (Fig. 2). 

Figure 4 gives an alternative scheme of possible biomass conversion pathways. Depending on the type of available biomasses and the objective products, each biorefinery will implement a different production and conversion scheme. 

Fig. 4 Schematic flowsheet of possible biomass conversion pathways in a biorefinery.

The alternative pathway is the biochemical route. It processes starches/sugars into ethanol, a standard technology with installations world-wide, but in a biorefinery the start is the whole-plant material or biomass residues containing hemicel-lulose, which is broken into sugars that then can be fermented to ethanol and/or other alcohols such as butanol. As mentioned before, there is the need to develop novel and/or improved biocatalysts for alternative organic fuels, such as biobutanol, by fermentation processes. 

The valorization of by-products in biomass conversion is a key factor for introducing a biomass based energy and chemistry. There is the need to develop new (catalytic) solutions for the utilization of plant and biomass fractions that are residual after the production of bioethanol and other biofuels or production chains. Valorization, retreatment or disposal of co-products and wastes from a biorefinery is also an important consideration in the overall bioreftnery system, because, for example, the production of waste water will be much larger than in oil-based refineries. A typical oil-based refinery treats about 25 000 t d-1 and produces about 15 000 t d 1 of waste water. The relative amount of waste water may increase by a factor 10 or more, depending on the type of feed and production, in a biorefinery. Evidently, new solutions are needed, including improved catalytic methods to eliminate some of the toxic chemicals present in the waste water (e.g., phenols). 

A thorough analysis of value chains and the development of alternative value chains starting from biomass derived feedstocks, including assessment of the economic viability of the transformation of the chains, is required. This should be followed by the identification of easy entry points for the implementation of novel value chains. Technical key issues are generic methods to cope with the variability of raw materials derived from biomass and higher susceptibility to contamination by microorganisms and suitable catalysts for biorefineries. 

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