Preview this Book. Add to Wish List. Close Preview. Toggle navigation Additional Book Information. Description Table of Contents. Summary Written with a diverse audience in mind, this book describes the current status, development, and future prospects for the critical technology of second-generation biorefineries, specifically with a focus on lignocellulosic materials as feedstock.
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It provides an overview of the issues behind this technological transition, and it provides, in depth, the science and technology related to cellulose for production of bioethanol and other biofuels. The book also highlights the main emerging routes that will serve as the source of important bio-generated products in the future. Request an e-inspection copy. Share this Title.
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Recommend to Librarian. Related Titles. Biofuels: Biotechnology, Chemistry, and Sustainable Development. Shopping Cart Summary. Items Subtotal. View Cart. Industry experience, both in the USA and Europe, demonstrated that farmers need to be educated in the benefits that they will obtain from the deployment of this industry. The industry must provide the relevant key information to farmers in the regions where a 2G facility is going to be constructed to create the proper atmosphere.
The extra income for rural areas will increase the profitability of traditional farming. The possibility of utilizing marginal land for the growth of biomass to be used as feedstock for biofuels is a major advantage of the lignocellulosic biofuel industry. A large amount of work has been aimed at the development of viable energy crops; these kind crops are easily adapted to the environment and ground conditions.
To have a bankable project, it is necessary to have sufficient feedstock to assure the economic return of the project. This kind of contract is new for farmers and to biomass suppliers who usually work on an annual basis. Creation of agricultural associations will be an important step on the path to reaching these agreements.
Supply is not only a cost problem but it is also a location issue. Nowadays, facility location is determined by feedstock availability over a very limited distance, not more than miles. To have available feedstock in a short radius, the facilities are placed in relatively remote areas, this in turn increase the rest of the production costs, such as, utilities, personnel and final product transport logistics. One solution could be to create centralized markets or biomass reference markets that allow homogeneous supply routes, e.
This would decrease logistic costs and provide higher versatility to all facilities. Standardization of biomass from different feedstocks, defining specifications regarding polysaccharide content that could be reached by more than one agriculture residue or energy crop will help to advance the 2G industry. If future facilities are able to process a mix of feedstock, the industry will reach the flexibility required to provide more freedom for the location of the facilities, and the number of potential facilities per region will probably increase.
As such, an area to develop is the optimization of productive processes for lignocellulosic biofuels so that they operate simultaneously with different raw materials; this will make the technology less dependent on local feedstock from a given location. Once the biomass is harvested, collected and transported to the facility location, the next step is to process and convert it into a liquid biofuel.
The procedure is mainly divided into four processes Fig. In all of these areas, there is still room for technology improvement. Lignocellulosic process converting the biomass into biofuels and coproducts. Process step for conversion of agricultural residues into ethanol. Source : Abengoa. For a 25 Mgal facility, almost tons of biomass per day is required. The stored biomass must meet at least two key specifications: moisture content and ash content.
The output from the biomass handling goes to the biofuel process conversion area and if the facility has an integrated biomass boiler, part of the biomass will be allocated to be burned. Biofuel conversion starts with pretreatment, which consists of an acid or alkaline soak system that saturates the feedstock with dilute strong acid or base. The soaking system also removes a significant amount of sand, which can cause severe erosive damage to the equipment.
The soaked biomass is pretreated in a continuous steam explosion reactor. The pretreatment process solubilizes the hemicellulosic sugars, primarily xylose and arabinose, and greatly improves the cellulose digestibility through disintegration from lignin. The pretreatment process is followed by a conditioning step to adjust pH, temperature and total solids content. Sufficient residence time in the saccharification tanks is maintained for the conversion of the cellulose into monomeric glucose and hemicellulose to glucose, xylose and other sugars of lower concentration.
The saccharification is followed by simultaneous fermentation of xylose and glucose to ethanol using a genetically modified strain of brewer's yeast Saccharomyces cerevisiae. In this case, it is necessary to include solid—liquid separation steps that permit the sugar to be purified to a level that can be used in further processes.
Lignocellulose biorefineries - ifeu - Institut für Energie- und Umweltforschung Heidelberg GmbH
In a standard 2G facility, ethanol is distilled and dehydrated using conventional distillation and molecular sieve steps. The raw materials can be used in soil amendment because composition allows to increase organic C content and provides porosity to substrates that facilitate seed germination and plant root development. However, depending on the location or on the type of project, other areas, such as a biomass boiler or wastewater treatment plant, have to be included within the facility to comply with environmental legislation or to generate the vapour needed for plant operation.
The facility cost should take into account both the capital cost needed per gallon Capex and the cost to operate the plant Opex. Both are influenced by the kind of project. There are three main types of projects:. This is a plant by itself. It needs a complete value chain management.
Its location influences the Capex and also the logistics of biomass supply and ethanol sales. In terms of Capex, it needs the construction of the core process, biomass handling, pretreatment, enzymatic hydrolysis, fermentation and distillation; and also auxiliary operation units such as cogeneration and a waste water treatment plant; these usually significantly increase the overall cost.
In this concept some existing infrastructures and operations can be shared thanks to the proximity of other industries. This model requires at a minimum the construction of the process area.
The value chain for feedstock procurement and logistic must be completely developed. The construction of auxiliary operations units is limited. The whole value chain is completely integrated within a 1G facility, taking advantage of the synergies in feedstock supply and product logistics.
The construction of auxiliary operation units is not necessary. The aim of the two last configurations is to decrease the cost of the auxiliary or complementary operation units and focus the efforts on reducing the cost of the technological core areas. Some other issues, such as cake and syrup destination need, however, to be solved.
After feedstock availability, reducing the investment cost through the reduction in the auxiliary equipment is the second step towards making a commercially viable project. The challenge, to the industry, is to be as flexible as possible to increase the potential locations where to place viable technical and economical projects. There are a range of alternatives, outside improving the logistic model, where the industry is working to reduce operational capital costs.
These include enzyme cost reduction by improving activity, valorization of the lignin contained in the raw material, increasing the pretreatment efficiency or improving the yeast production organism. The location of a plant will definitively influence the overall facility layout. Investment costs will differ significantly depending on the configuration required.
Absence of synergies with external utilities concomitantly results in an increase in storage equipment and logistical costs. Equipment cost area distribution of a general lignocellulosic greenfield facility. As described above, the first step in a lignocellulosic facility is to prepare the biomass for processing. This is critical because it influences all of the downstream processing. We can distinguish two main steps, one where biomass is just preprocessed to obtain the designed PSD and, in the subsequent step, the biomass is pretreated to make hemicellulose and cellulose accessible for cellulases.
For the biomass handling area, the main objective is an appropriate delivery of milled feedstock to the pretreatment system with a consistent quality that meets the required specifications in terms of particle size and total ash content. As mentioned in the feedstock section, the logistics model is critical to obtain a homogenous stream at the beginning of the process. No special innovations have been made in this area, but some experts are starting to develop different methodologies that will improve the facility performance and also the integrated logistic model.
Once the biomass has gone through the handling system, the next step is the pretreatment that will release the oligomers to be transformed into sugars. This is a critical step in lignocellulosic biofuel production. Each market player has developed their own technology as the feedstock defines the pretreatment technology and conditions. One of the main hurdles that the industry faces is that the pretreatment needs to be optimized for each raw material, limiting the flexibility of the plant to process different feedstocks.
That is why more versatile pretreatments are required so as the process becomes less raw material dependent. A number of technologies are available today for the pretreatment of lignocellulose, including, chemical, physical and biological processes. Some of these technologies have already been commercialized and are well known, whereas others are still at lab scale. Each industrial player has developed its own pretreatment technology. The 2G commercial technologies are protected by a number of patents that guard the technology while the economic viability of the projects are improved.
This is why different pretreatment have been considered. As a result of the violent decompression, the structure of lignocellulose is disrupted and the fibres are opened up, leaving sugar polymers more accessible to the subsequent enzymatic hydrolysis Stelte, As no chemicals other than water are used, equipment corrosion is minimal and requirements for the reactor metallurgy are less demanding. Also, the level of release of chemicals that may act as inhibitors in the saccharification or fermentation steps is very low.
The main drawbacks of steam explosion are related to the mildness of the process which limits the effectiveness of the pretreatment and demands the use of very high enzyme loads in the saccharification step. Another option is the use of dilute acid in the pretreatment, this involves the use of dilute aqueous solutions of inorganic acid HCl, H 2 SO 4 combined with temperature.
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This pretreatment results in good depolymerization and release of hemicellulose and cellulose. Compared to steam explosion, dilute acid pretreatment is more efficient for woody samples. As acidic conditions allow partial depolymerization of hemicellulose and cellulose, the enzyme loading required is lower compared to simple steam explosion. However, this kind of pretreatment requires high capital investment due to the special reactor metallurgy; operational costs are also higher. It is well known that aqueous ammonia treatment allows biomass delignification without a significant degradation of sugars.
However, the effectiveness of this pretreatment with some feedstock, such as woody biomass residues is rather limited Yang and Wyman, Commercial pretreatments for corn stover, wheat straw and sugar cane straw are currently being optimized, however, one of the main challenges that the sector must overcome in the coming years is to enhance process versatility to be able to deal with more than one raw material at a time.
Lignin removal is another key step in the development of the biofuel industry; in the current methodology, lignin is maintained until the distillation phase. However, there are several pretreatment technologies in development that try to separate the components of the biomass in different streams, one of the most promising is the use of ionic liquids ILs which are able to dissolve lignocellulose under mild conditions, resulting in more accessible cellulose and recovery of lignin in the raw material.
Nevertheless, there are still challenges to the industrial deployment of this technology, including high cost and regeneration of ILs Tadesse and Luque, Searching for other alternatives may reduce costs and increase the possibility of using lignin in new ways that are not currently used to add value.
Further discussion on the lignin issue follows below. The main challenges in pretreatment are as follows: development of a versatile technology that can reach appropriated levels of pretreated biomass material independently of the raw material used; generation of combination plants that can more easily process under milder conditions to allow optimization both economically and environmentally; to optimize pretreatment processes using less corrosive chemicals making construction materials cheaper and as consequence reduce the initial investment in particular, steel alloys resistant to acid or base.
After the material is conditioned in the pretreatment area, the next step, the enzymatic hydrolysis or saccharification is one of the most critical factors in lignocellulosic biofuel production, and represents one of the main technology development areas. Why this difference? The answer is the enzymatic cocktail needed for 2G. Today only about three companies have commercialized this kind of cocktail: Novozymes, Dupont and Abengoa.
Nowadays, this cost contribution is achieved at least at a demo scale by the enzymatic cocktail developed by Abengoa, although the performance on a regular basis at commercial scale is still a pending issue. Reported commercial data indicate that the three commercial cocktails may operate within the same range. How can these cocktails be improved?
The most relevant aspect is the use of thermophilic enzymes because the increase in temperature prevents hydrolysates from being contaminated and, therefore, the loss of raw material; this increases the overall performance of the process. Another factor is that the total solid ratios at which the technology can work is relatively low compared with 1G, this is due to the lower yield per tonne of raw material introduced and the longer residence times needed. Although the enzymes would work even better at lower solid concentration, this is the minimum ratio at which ethanol concentrations are reached.
One of the main improvements that can be made is to increase the performance of the enzyme cocktail at higher total solid, or at least reaching optimum performance at current levels. As noted above, the 2G enzyme cocktail seems to be a niche market with very few players. A significant increase in the volume of 2G enzyme market is required to provide producers with the equity to optimize their cost structure. Enzyme producers need to be involved in the industrial development process if they want 2G facilities to achieve their nominal capacity.
If the market is converted into an oligopoly with few competitors gaining most of the value from the 2G technology, the development of the industry globally will become difficult. Enzyme developers need to be involved in the industry growth, participating in different ways with not only the industrial developers but also with other stakeholders. The current fermentation technology produces ethanol, although other alternative alcohols or bioproducts can be synthesized, e.
Very efficient yeasts have been designed and optimized to ferment xylose and glucose simultaneously. Another very important aspect is to shorten the fermentation time; this could lead to a reduction in the number of fermenters per plant with a consequent saving in the initial investment. In addition, it should be possible to work at different pHs or temperatures, to improve the propagation phase. In this area, unlike at the enzyme market, there is no risk of an oligopoly which could cap the market and there is still room for improvement in terms of operational conditions to decrease the overall costs.