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Entry

Biorefinery Based on Multiple Raw Materials and Wastes for the Production of Energy: A Proposal Tailored to Southwestern Europe

by
Sergio Nogales-Delgado
*,
Carmen María Álvez-Medina
and
Juan Félix González González
Department of Applied Physics, University of Extremadura, Avda. De Elvas s/n, 06006 Badajoz, Spain
*
Author to whom correspondence should be addressed.
Encyclopedia 2024, 4(4), 1381-1395; https://doi.org/10.3390/encyclopedia4040090
Submission received: 29 July 2024 / Revised: 18 September 2024 / Accepted: 20 September 2024 / Published: 24 September 2024
(This article belongs to the Section Engineering)
Browse Figures
Review Reports Versions Notes

Definition

:
In this entry, the possibility of the implementation of a biorefinery based on multiple raw materials (from agricultural wastes, vegetable oils, etc.) is covered, pointing out the available technology to interconnect different processes so that the atom economy of the process is as high as possible, reducing the environmental impact and improving the efficiency of the energy or products obtained. For this purpose, this model is based on previous works published in the literature. The role of biorefineries is becoming more and more important in the current environmental scenario, as there is a global concern about different environmental issues such as climate change due to GHG emissions, among others. In this sense, a biorefinery presents several advantages such as the use of natural raw materials or wastes, with high atom economy values (that is, all the products are valorized and not released to the environment). As a consequence, the concept of a biorefinery perfectly fits with the Sustainable Development Goals, contributing to the sustainable growth of different regions or countries, regardless of their stage of development. The aim of this entry is the proposal of a biorefinery based on multiple raw materials, using different technologies such as transesterification to produce both biodiesel and biolubricants, steam reforming to produce hydrogen from glycerol or biogas, hydrothermal carbonization of sewage sludge to produce hydrochar, etc. As a result, these technologies have potential for the possible implementation of this biorefinery at the industrial scale, with high conversion and efficiency for most processes included in this biorefinery. However, there are some challenges like the requirement of the further technological development of certain processes. In conclusion, the proposed biorefinery offers a wide range of possibilities to enhance the production of energy and materials (hydrogen, biodiesel, biolubricants, different biofuels, hydrochar, etc.) through green technologies, being an alternative for petrol-based refineries.

1. Introduction

1.1. Current Energy Scenario

In the current global energy scenario, there is an increasing concern about several aspects, such as environmental problems (greenhouse gas emissions, land and water pollution, etc.) or geopolitical issues (such as international conflicts with economic and commercial consequences) that provoke a general worsening of the standard of living of citizens, especially in developing countries. In this sense, the implementation of green policies, including the promotion of a circular economy and green chemistry at the industrial level, could be a very interesting alternative to alleviate these problems [1,2]. Thus, a real contribution to environmental protection could be achieved, as well as a higher energy independence that could neutralize the negative effects of geopolitical conflicts. Finally, these practices could be an important starting point for the sustainable growth of developing countries.

1.2. The Role of Biorefineries

In this context, the role of biorefineries as real alternatives for refineries based on petroleum is becoming more and more important, as their implementation contributes to environmental conservation through green processes and low emissions. Biorefineries can be based on multiple raw materials and technologies to obtain energy and a wide range of products [3,4]. Nonetheless, some points are common in these biorefineries, including:
  • The starting point of these biorefineries are renewable raw materials or wastes that can be valorized. Otherwise, their environmental management would be difficult, costly, and fruitless. Thus, the avoidance of fossil-based products is a key point to reduce many of the abovementioned environmental and geopolitical problems. For instance, there are biorefineries based on different wastes (such as fruit and vegetable wastes [5], including tropic agro-industrial waste [6], or biomass and waste in general [7]), whose implementation can be interesting.
  • Considering that the products obtained are derived from natural sources, their environmental impact if there is an accidental release would be less negative compared to petroleum products. It should be taken into account that some of these processes obtain products that partially retain the molecular structure of their precursors, keeping some characteristics (such as high biodegradability).
  • Different products are obtained, many of them as intermediate compounds that can be reused in further processes depending on the demand. Consequently, biorefineries can be adapted to current energy and product demands. In this sense, when necessary, the production of a certain biorefinery can be centered on goods that are scarce due to geopolitical aspects, as in the case of biofuels when abrupt changes in oil prices occur.
  • The atom economy (or atom efficiency, defined as the amounts of desired products that are obtained compared to the amounts of reagents used, expressed in terms of percentage) of these processes is usually high, due to the high conversions obtained (with the contribution of catalysts in many cases) and the interconnection with other technologies to reuse intermediate products or wastes. As a consequence, low quantities of pollutants are released to the environment, with a subsequent low environmental impact. In any case, other factors such as the economy or social aspects should be taken into account in this context.
  • Lastly, many wastes are derived from local or agricultural sources. Consequently, their valorization in a biorefinery context would imply an important contribution to the sustainable growth of developing countries or regions. In these areas, the main agricultural practices can provide products or wastes that could serve as the basis for the implementation of biorefineries specifically adapted to their specific circumstances. However, the real implementation of a biorefinery can be a challenge, requiring environmental and economic analysis to assess its feasibility.
Therefore, different technologies widely studied in the literature for biomass conversion could be interesting, such as pyrolysis or combustion of biomass [8,9], biodiesel or biolubricant production through transesterification [10,11], biogas production through anaerobic digestion with the production of biomethane and the subsequent valorization of CO2, or biogas reforming [12,13] to produce hydrogen or syngas upgrade to obtain different biofuels through Fischer–Tropsch [14], among many others. These processes and components could be suitable for their inclusion in a biorefinery, as many of the byproducts or wastes obtained in a certain process could be upgraded by using another one, generating synergistic interconnections that result in biorefineries with multiple processes involved.
Indeed, the increasing interest in this field is denoted by the number of registered patents, which could indicate a relevant presence of these processes at the industry level. Thus, Table 1 shows some of the patents related to biorefineries or some of the processes that will be covered in this entry:
As observed in this table (where a short selection of patents is included), there are recent patents mainly focused on the implementation of biorefineries or the possible conversion of traditional facilities to green processes. This fact identifies several points, like the following:
  • There has been a considerable number of patents about the use of biorefineries or green processes and technologies for the last 15 years, proving that this field is becoming a reality nowadays.
  • There is a wide range of raw materials that are used as the basis of these biorefineries, from microalgae to wastes such as spent coffee grounds.
  • The role of catalysts in these patents is essential. Indeed, some patents are exclusively focused on this issue.
  • The conversion of old facilities for biorefinery implementation is also important in these patents, which could be a recurring possibility.
In this sense, both purely scientific works at the laboratory scale and different patents (focused on the industry level) indicate that the role of biorefineries is becoming more and more important in this energy and environmental context.

1.3. Aim and Scope

Considering the above, the aim of this entry was to propose a biorefinery based on multiple raw materials and processes to demonstrate the suitability of multiple green technologies applied to a circular economy. Specifically, this biorefinery would be located in the southwest of Europe, although its location could be different due to the versatility and adaptation to multiple raw materials. In this sense, the city of Badajoz (150,000 city residents) was selected as a location with a great potential due to the nearby presence of a wastewater treatment plant and multiple agricultural areas, which could provide the different wastes or raw materials to feed the whole process. This way, the location was selected to avoid further environmental impacts due to changes in agricultural practices, being adapted to the reality of this region and avoiding the contribution to further environmental problems such as desertification or water stress. Also, the location of this city is interesting, with nearby strategic cities such as Madrid (330 km), Seville (187 km), and Lisbon (188 km). Thus, the shipment of generated products would be feasible, although commercial communications could be improved, as expected with the implementation of railroad lines for high-speed trains between Madrid and Lisbon, among other measures taken by the European Union [23]. For this purpose, different research works of our experienced group, supported by other articles that represent contributions carried out by external researchers, were selected as the basis for this biorefinery, interconnecting different raw materials and their corresponding products or byproducts by using diverse technologies to improve the atom economy of the whole process. Furthermore, the valorization of different wastes that would otherwise be characterized by difficult environmental management was also covered, as in the case of waste cooking oil (WCO). Thus, the novelty of this work consists of showing a feasible example of a biorefinery based on our context, which could also be applied to different scenarios, as many raw materials could be easily adaptable to this biorefinery.

2. Components of the Proposed Biorefinery

2.1. Foundations of the Biorefinery

As explained, the proposed biorefinery is based on agricultural products and wastes, whose processing is linked by the implementation of several processes that have been widely studied by our research group. Thus, this study covers different technologies applied in previous works (from pyrolysis to transesterification), as well as other studies found in the literature that could perfectly fit the foundations of the technologies proposed in this communication. In this sense, different wastes or raw materials were used as starting points, such as different agricultural wastes, oilseed crops (and the corresponding extracted oil), wastewater, or waste cooking oil, among others. It should be noted the variety of sources selected for this study, including materials in different physical states.

2.2. Technologies Included

Thus, different multidisciplinary teams have been working on several technologies to enhance or valorize these wastes, including the following:
  • Biodiesel or biolubricant production through transesterification, which offers a wide range of products that can be used as intermediate products of other processes if suitable purification conditions and further technologies are implemented, as explained in the following section in the case of glycerol [24]. Concerning biodiesel, transesterification is carried out with methanol as a reagent to produce fatty acid methyl esters and glycerol. On the other hand, biolubricant is produced by reacting fatty acid methyl esters with superior alcohols (like pentaerythritol or trimethylolpropane) to produce biolubricants and release methanol (which could be reused in the previous transesterification step).
  • Anaerobic digestion of agricultural wastes was also covered in order to obtain high-quality biogas (with around 60% methane). Thus, the higher the content of methane, the better for the further processing of biogas [25].
  • Once biogas is purified, especially concerning H2S capture (which is essential to avoid the deactivation of catalytic processes through poisoning), biogas can undergo processes like steam reforming to obtain syngas or hydrogen (if purification processes are carried out) [26]. It should be noted that glycerol generated in transesterification to obtain biodiesel can be upgraded by using this technology [27]. Also, biogas can be used in local combustion engines to produce electricity and heat.
  • Purification processes such as pressure swing adsorption or membrane reactors to obtain pure hydrogen from syngas (the flue gas obtained in steam reforming, with variable proportions of hydrogen and carbon monoxide) [28].
  • Also, syngas can be upgraded to biofuels or other compounds through the use of Fischer–Tropsch synthesis, which offers a large variety of products depending on the reagents and chemical conditions [29].

2.3. Assessment of the Biorefinery

In this regard, this study considers the feasibility of the interconnection of different components in a biorefinery based on agricultural wastes, pointing out several factors such as main operating conditions, conversion and byproduct generation, which are essential to assess the suitability of a certain biorefinery. In any case, most of the technologies covered in this study are technologically mature due to the fact that there are industries based on these foundations, as well as the fact that there has been high scientific interest in this field for years or decades.
It should be noted that this proposal is only an example of biorefinery, which can vary depending on multiple factors such as waste, technology availability, or pollution, among others [30,31].
Again, one of the main advantages of a biorefinery is pointed out, like the capability of adaptation to different situations and demands, offering a broad range of possibilities through the use of new products (or wastes) and technologies.
Nevertheless, the proposed biorefinery covers several processes to obtain multiple products that could be a good replacement for petrol-based ones, with key products such as glycerol that can have various uses depending on its purity and technology availability. Moreover, these technologies can be applied to different materials with variable characteristics, enhancing the possibilities of this biorefinery in further adaptations. Finally, some challenges are also covered, with the subsequent search for solutions through research found in the literature.
For this purpose, a review of our own literature (which is specifically focused on technologies applicable to biorefineries), combined with other specific studies that could fit the aim of this study, was carried out, including more than 30 specific works and more than 70 articles in general.

3. Advantages and Challenges of the Proposed Biorefinery

3.1. Main Components Included in the Biorefinery: Characteristics and Advantages

Considering the abovementioned references, the proposed biorefinery is included in Figure 1.
At this point, it should be clarified that, in order to simplify this entry, only the main steps to obtain a specific intermediate or final product are considered. For instance, anaerobic digestion includes many different steps to produce biogas, such as drying processes, which are not covered in this study.
As shown in this figure, many of the previous conditions to consider a biorefinery are clearly represented, such as the use of renewable raw materials or wastes characterized by difficult management, the possibility of reusing different byproducts in the same process, and the wide range of intermediate products that can be directly used or upgraded depending on the market demand. The presence of methanol should be noted, which is one of the few synthetic reagents used in this biorefinery to start the process. Nevertheless, during the second transesterification, methanol can be regenerated and reused in the first transesterification, partially recovering this intermediate product depending on many factors such as the collection system or the use of vacuum. Also, WCO is derived from the culinary use of vegetable oils (although it appears as an isolate waste in the figure). Thus, the main steps carried out in this biorefinery are included in Table 2, covering their main aspects and references.
In these processes, different conversion values can be obtained depending on many different factors such as operating conditions or the nature of the raw material, among others. According to our previous experience, proximate values of conversion can be obtained. Thus, different yields can be obtained in transesterification processes to produce biodiesel (exceeding 96% in many cases), producing glycerol (with approximately 10% w/w related to the original weight of vegetable oil used). On the other hand, around 0.75 Nm3 of biogas with high CH4 percentage (60%) can be obtained per 1 kg of sewage sludge, whereas the conversion of biogas to produce hydrogen is normally above 90%. Regarding HTC, its yield can vary, at around 50% in some cases.
The most interesting points about this biorefinery, apart from the aforementioned advantages, are the following:
  • The nature of the raw materials used (most of them natural sources or wastes) is essential to consider specific technologies. For example, high moisture content in solid wastes (for instance, sewage sludge or its mixture with agricultural waste) is essential to consider the implementation of HTC technologies for their valorization, whereas the use of pyrolysis is recommended for dry products (like agricultural wastes with a previous drying process). Especially interesting is the fact that one single crop, such as cardoon, safflower, or rapeseed, could provide different products that can be used as starting points in this biorefinery, like the corresponding vegetable oil (and the subsequent biodiesel) [32,33], cake (both of them from seeds after mechanical extraction, for example), and different agricultural wastes that can be combined in different processes like pyrolysis or HTC [34], among others. The same happens to gaseous compounds like biogas, whose methane and sulfhydric acid content will determine the performance of processes such as biogas (or methane) steam reforming or its use as biomethane.
  • Similarly, the properties of intermediate products, as well as final products, are vital to consider the final use of these materials. For instance, glycerol can be used in a wide range of applications depending on its purity. High-purity glycerol is recommended for cosmetic use, whereas lower purities are required for energy purposes such as steam reforming [35,36]. Also, the role of viscosity in biodiesel and biolubricants is essential for their use in diesel engines or other industrial processes. On the other hand, syngas obtained in biogas steam reforming can be an interesting starting point for Fischer–Tropsch synthesis, depending on the H2/CO ratio. Otherwise, purification processes could be recommended to obtain pure hydrogen, depending on the final purpose of this technology.
  • The role of catalysts is important in many steps included in this biorefinery in order to make the global process efficient, especially compared to traditional refineries. Indeed, most of the abovementioned processes require the use of catalysts to compete with fossil-based processes. Thus, homogeneous catalysts like sodium or potassium hydroxide or sodium methoxide are popular for their use in transesterification processes [37]. However, further purification processes are required, with the subsequent development of heterogeneous catalysts where only a physical separation after biodiesel or biolubricant production is required. On the other hand, heterogeneous compounds like nickel-based catalysts are normally used in steam reforming, presenting a wide spectrum of alternatives depending on many factors such as deactivation resistance due to different factors like poisoning (on account of the presence of H2S), sintering (due to the use of high temperatures), or coke deposition (because of methane conversion) [38,39]. Among these alternatives, the use of promoters that improve the interaction of the active phase (normally Ni) with the support (for instance, Al2O3, SiO2, etc.) is important, but also the operating conditions of the process (pressure, temperature, or steam-to-carbon ratio, among others). In this sense, new catalysts are being developed to improve some properties such as durability (in the case of heterogeneous catalysts) and efficiency, which is essential to improve the efficiency of the global process. Other catalysts such as zeolite are popular in the case of pyrolysis, whereas homogeneous and heterogeneous catalysts have been used in HTC, many of them focused on reducing tar and char formation such as Na2CO3 or K2CO3 [34]. Interestingly enough, some of these processes, in turn, could produce interesting carbonaceous materials that can act as photocatalytic or catalytic supports in different processes [40].
  • As explained in Table 2, some technologies, such as transesterification and steam reforming, are extremely adaptable to different characteristics of the raw material by making slight modifications. In the case of the former, different alcohols can be used during transesterification to obtain biodiesel (by using methanol) or biolubricants with different viscosity values (by using, for instance, trimethylolpropane or pentaerythritol, among others). Concerning reforming, the foundation of this process is highly adaptable to plenty of reagents such as methane included in biogas, glycerol obtained in transesterification processes, or other hydrocarbons, obtaining relatively similar products like syngas with variable composition. Thus, the versatility of these technologies makes the combination of different routes possible, enhancing the efficiency of the process in general and reducing emissions to the environment.
  • Finally, purification technologies are essential to offer interesting options when one single and pure product is desired for a certain usage. In this sense, purification in biodiesel production is basic in order to obtain a high-quality product for diesel engines (where specific standards are required for their correct performance), obtaining glycerol as a byproduct. On the other hand, technologies for syngas purification to obtain hydrogen are equally interesting, like the use of membrane reactors or pressure swing adsorption. However, not only purification technologies are necessary to offer a high-quality product. As previously explained, there are processes where impurities are a challenge that should be accomplished, especially affecting the poor catalytic performance of the process. In this sense, high acidity in oil is not desired in transesterification processes where NaOH is used as a homogeneous catalyst, whereas the presence of H2S is negative in reforming processes, requiring absorption or adsorption steps to remove this impurity, which is dangerous even at low concentrations (ppm) [41,42].
    Table 2. Main processes involved in the proposed biorefinery.
    Table 2. Main processes involved in the proposed biorefinery.
    ProcessDetailsReferences
    Anaerobic digestionBiogas with high methane content (around 60%) was obtained from different wastes. Requirement of sulfhydric acid capture for further treatments such as steam reforming, to avoid corrosion and poisoning. It should be noted that other alternatives are available, especially concerning digestate, which can be used for different purposes like organic fertilizer or animal bedding, among others.[43,44,45]
    Oil extractionThrough mechanical or chemical processes, high yields can be obtained, with the valorization of cake obtained for animal feeding, fermentation to produce bioethanol or anaerobic digestion.[46,47,48]
    Fischer–TropschIf syngas composition obtained in steam reforming is suitable, then this process is interesting for obtaining different compounds like biofuels or biolubricants, depending on viscosity and high heating values. Other processes to convert syngas in dimethyl ether could be an interesting alternative.[49,50]
    Hydrothermal carbonization In order to produce hydrochar from wastes with high moisture levels, this is an interesting choice. These products can be transformed into activated carbons that can be reused in different processes such as desulfurization to clean biogas. Nevertheless, other interesting products can be obtained from HTC, such as liquid that can be used for fertigation.[34,51,52]
    Pressure swing adsorptionAlong with membrane reactors, it is essential to obtain hydrogen with high purity (over 99%). The quality of syngas is essential to obtain pure hydrogen and to contribute to the durability of membrane reactors.[53,54,55,56]
    PyrolysisIn this case, fast pyrolysis was selected, as it can enhance bio-oil fractions. One of the main products obtained in pyrolysis is carbon, along with oils and synthetic gas. Concerning the former, activated carbons can be generated for multiple purposes.[57,58,59,60,61]
    Steam reformingThis is an interesting process that can be used with multiple materials, such as biogas or glycerol, to obtain hydrogen, among other products. High conversions (exceeding 95%) have been found in the literature, requiring hydrogen purification in many cases.[62,63,64,65]
    TransesterificationDepending on the kind of alcohol, transesterification with methanol provides FAMEs (with high conversion, up to 98%), whereas transesterification with pentaerythritol (or trimethylolpropane) produces biolubricants (with conversions between 90–95% in most cases).[66,67,68,69,70,71,72]
As observed in this table, and considering the fact that most of the processes are based on wastes characterized by difficult environmental management, the conversion and efficiency obtained for certain purposes is relatively high, which contributes to the high atom economy of the process.
Thus, unconverted reagents would be difficult to manage, with the subsequent separation requirement to obtain pure and high-quality products for specific uses. Consequently, apart from the fact that most technologies used in this biorefinery are based on valorizing as many products as possible, conversion is a key point to contribute to high-efficiency processes and, especially, to reduce undesired products that could be discharged into the environment.

3.2. Challenges Related to Biorefinery Implementation

Even though the main advantages of the proposed biorefinery have been discussed in previous subsections, there are also some challenges that should be assessed, included in Figure 2.
As observed in this figure, the main challenges related to the implementation of a biorefinery have to do with environmental, ethical, and economic issues, like the following:
  • Carbon/water footprint: These are interesting factors that are normally included in a life cycle assessment (LCA). Concerning the activity of a biorefinery, all the processes should be controlled “from cradle to grave”, including carbon dioxide generation (directly or through energy consumption from conventional electricity generation) and water pollution. As previously stated, the higher the atom economy, the lower the emissions discharged into the environment, with a subsequent lower environmental impact. This is the reason why the perfect combination of technologies taking part in a biorefinery is required.
  • Waste management: Again, different processes can produce undesirable wastes, which should be valorized by the implementation of further technologies that can bring, at the same time, new environmental challenges. The LCA is an interesting tool to classify these technologies according to their environmental impact, assessing the suitability of their implementation from different points of view.
  • Extraction of raw materials: Equally, every aspect of a biorefinery is monitored from an LCA point of view, including the raw materials or wastes used. For the latter, every effort to valorize them is normally suitable, whereas for the former this is not always true. As explained in the following point, the use of different resources to produce a raw material can determine the suitability of the whole biorefinery.
  • Land usage: In some cases, especially concerning the use of oilseed crops, there are continuous concerns about this issue. Thus, the use of land for this purpose instead of the food sector is problematic. Nevertheless, there are sustainable alternatives, like the use of wastes derived from vegetable oils (for instance, WCO) or different sustainable land practices such as the introduction of safflower or cardoon, which can take part in shifting cultivation to recover soils [66,68].
  • Transportation/shipment: This is a key point in a biorefinery, as these practices could influence different factors such as carbon footprint. On many occasions, the location of a biorefinery is essential to make the most of the raw materials used or products obtained, as observed in the case of Germany [73]. In this case, the biorefinery could be located in Badajoz (Spain), where there is a wastewater treatment plant, and most crops (like cardoon, rapeseed or safflower) have been proven to be suitably grown. Thus, the transportation of wastes or raw materials would be minimized. Regarding the products, they could be locally commercialized for the same reason.
  • Equipment crushing/wear: Obviously, the use of multiple pieces of equipment in a biorefinery implies a decrease in efficiency due to crushing or wear. For instance, a certain reactor with an electric resistance will exhibit lower efficiency over time, requiring more energy to maintain the same working temperature. These factors are important to carry out a suitable LCA of the whole process.
  • Energy costs: With respect to this factor, it is important to consider the energy source used in this biorefinery. For this purpose, different points should be addressed, like the possibility of reusing the energy generated or the implementation of renewable energies (such as solar or wind energy) to reduce energy costs and CO2 emissions.
Also, an issue that should be considered is the presence of multiple disadvantages for each process in the biorefinery, especially focused on the different wastes. For instance, the generation of glycerol during the first transesterification can be a challenge if its purity is not considered, requiring different processes depending on this factor. This way, a perfect adjustment of these technologies, along with suitable technology development (as explained in the following paragraph) should be accomplished.
Finally, there is another interesting factor that should be considered, like the different technological maturity of the processes included in this biorefinery (see Table 3, where the main technological readiness levels are included according to an adaptation made by NASA [74] and the literature included in this review, where different laboratory or industrial levels are explained). Obviously, it could be a challenge to join multiple technologies with different maturity levels, requiring the technological development of the less mature processes. For this purpose, the role of multidisciplinary teams is essential to develop, from environmental and engineering points of view, the techniques employed in this entry for a correct implementation at industry level.
It should be taken into account that the implementation of a biorefinery with these characteristics requires further studies, covering different aspects such as economic impact or life cycle assessment (LCA), in order to check “from cradle to grave” that the materials, processes, and emissions involved in this process do not represent an environmental threat, as observed in several studies about LCA focused on hydrogen production [75], biodiesel synthesis [76,77], or the pyrolysis of sludge [78].
A possible solution to this problem is the capability of biorefineries to produce several products. In our case, biodiesel, biolubricant, glycerol, or hydrogen, among others, are obtained, whereas there are other biorefineries where multiple products are obtained. For instance, a Phaffia Rhodozyma biorefinery was proposed, with interesting biologically active bioplastics as the main products [79], and a biorefinery based on Rhodosporidium Toruloides to obtain different lipids and carotenoids was studied [80], pointing out the relevance of producing multiple products to counter the possible negative economic costs.

4. Conclusions and Prospects

As a conclusion, according to the literature and previous research works carried out by our group, a biorefinery based on multiple wastes was presented, located in southwestern Europe, but with the possibility of implementation in different regions due to its versatility (as it can accept multiple raw materials to obtain vegetable oils or biogas, for instance). This biorefinery could present several advantages from a technical and environmental point of view.
For instance, the proposed biorefinery showed a high variety of products and adaptability, as several final and intermediate products are obtained, which can be easily adapted to current energy or product demands. The versatility of these technologies and products is one of the most interesting characteristics of the proposed biorefinery, offering a high adaptability to different economic scenarios and making it an interesting alternative for fossil-based refineries, as many of the functions of the latter are covered by this green process (including biogas, biodiesel, glycerol, or biolubricant production, among others).
In general, different products can be obtained that can be used as energy sources or interesting compounds in industry, presenting a high atom economy due to the low quantities of wastes that are generated, as many byproducts can be reused as intermediate products for additional processes.
Indeed, some wastes can be reused or valorized thanks to the implementation of innovative or mature technologies such as reforming or different separation processes like membrane reactors or pressure swing adsorption.
In any case, the challenges related to this kind of facility present an interesting area for improvement, requiring the development of new catalysts that can be more resistant to impurities or exhibit longer durability. Also, purification techniques could be useful to improve the catalytic performance of many processes involved in the proposed biorefinery, apart from the obvious maintenance of facilities in general.
Another challenge would be the technological development of new or innovative technologies to valorize wastes. For this purpose, the homogenization of the TRLs of the processes involved in this biorefinery would be necessary, with an important role of multidisciplinary teams to promote industrial-scale facilities. Furthermore, the implementation of some innovative processes such as HTC at the industrial scale is necessary in order to contribute to the better efficiency of the whole process, assessing its suitability through environmental tools such as the LCA or economic studies. This is due to the fact that each process included in the proposed biorefinery has advantages and challenges that should be counterbalanced by the good performance of supplementary processes.
Another challenge is the fact that these technologies are not equally mature, requiring further research for those with lower TRL values, in order to make these processes more efficient and adaptable at the industrial scale. On the other hand, the use of combined technologies in such a complex biorefinery could imply further environmental problems, which should be solved by enhancing tools such as the life cycle assessment. Also, the economic feasibility of these processes should be considered to assess the feasibility of the proposed biorefinery.

Author Contributions

Conceptualization, S.N.-D. and C.M.Á.-M.; methodology, S.N.-D. and C.M.Á.-M.; validation, S.N.-D., C.M.Á.-M. and J.F.G.G.; formal analysis, S.N.-D. and C.M.Á.-M.; investigation, S.N.-D. and C.M.Á.-M.; resources, J.F.G.G.; data curation, S.N.-D. and C.M.Á.-M.; writing—original draft preparation, S.N.-D.; writing—review and editing, S.N.-D.; visualization, S.N.-D., C.M.Á.-M. and J.F.G.G.; supervision, J.F.G.G.; project administration, J.F.G.G.; funding acquisition, J.F.G.G. All authors have read and agreed to the published version of the manuscript.

Funding

The authors would like to thank the “Consejería de Economía, Ciencia y Agenda Digital y la Universidad de Extremadura para regular la concesión directa de una subvención a la Universidad de Extremadura (UEx) para la realización de las líneas de actuación LA4, LA5, LA8, LA9 y LA11 del programa de I+D+I en el Área Energía e Hidrógeno Verde financiadas con los Fondos Next Generation EU, programa incluido en la medida de inversión C17.I1 Planes Complementarios con las Comunidades Autónomas, que forman parte del Componente 17 Reforma Institucional y Fortalecimiento de las Capacidades del Sistema Nacional de Ciencia, Tecnología e Innovación del Plan de Recuperación, Transformación y Resiliencia”.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The data used in this entry were obtained from different works included in the references.

Acknowledgments

The authors would like to thank the contributions of all the colleagues involved in this entry, whose expertise and hard work have made this work possible.

Conflicts of Interest

The authors declare no conflicts of interest.

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Encyclopedia 04 00090 g001
Figure 1. Biorefinery proposal, including main technologies (in white), raw materials (in red), intermediate products (in blue), reagents (in light blue), and products (in yellow). The processes were the following: AD, anaerobic digestion; EXT, oil extraction; FT, Fischer–Tropsch; HTC, hydrothermal carbonization; PSA, pressure swing adsorption; PYROL, pyrolysis; SR, steam reforming; TE, transesterification. Black arrows indicate direct conversion routes, whereas red dashed arrows show possible reuse of intermediate products in the biorefinery.
Figure 1. Biorefinery proposal, including main technologies (in white), raw materials (in red), intermediate products (in blue), reagents (in light blue), and products (in yellow). The processes were the following: AD, anaerobic digestion; EXT, oil extraction; FT, Fischer–Tropsch; HTC, hydrothermal carbonization; PSA, pressure swing adsorption; PYROL, pyrolysis; SR, steam reforming; TE, transesterification. Black arrows indicate direct conversion routes, whereas red dashed arrows show possible reuse of intermediate products in the biorefinery.
Encyclopedia 04 00090 g001
Encyclopedia 04 00090 g002
Figure 2. Main challenges for the implementation of a biorefinery, and the assessment for solution proposal.
Figure 2. Main challenges for the implementation of a biorefinery, and the assessment for solution proposal.
Encyclopedia 04 00090 g002
Table 1. Patents related to biorefineries or processes included in this entry.
Table 1. Patents related to biorefineries or processes included in this entry.
InventorsPatentYearReference
ShuangquanMulti-recycling type kitchen waste biorefinery system2024[15]
Azocar Ulloa et al.Microalgae biorefinery for biofuel and valuable products production2015[16]
Wu et al.Method for preparing phenolic compounds by catalyzing pyrolysis of biorefinery residues with attapulgite catalyst2019[17]
PrandiMethod for converting a conventional oil, petrochemical or chemical plant into a biorefinery2017[18]
Crawford and SchaferEnhancing a biorefinery with an optional vapor recompression unit while maintaining the ability to operate without the vapor recompression unit2016[19]
Rispoli et al.Method for revamping a conventional mineral oils refinery to a biorefinery2012[20]
Bae and ChoAn integrated process for conversion of spent coffee grounds into value-added biochemicals and biofuel2022[21]
Feng et al.Integrated biorefinery process for bagasse2022[22]
Table 3. Technological readiness levels (TRLs) of different technologies included in the biorefinery.
Table 3. Technological readiness levels (TRLs) of different technologies included in the biorefinery.
TechnologyTRL
Anaerobic digestion9
Transesterification9
Biogas steam reforming9
Fischer–Tropsch synthesis5–9
Hydrothermal carbonization1–4
Pyrolysis4–7
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Nogales-Delgado, S.; Álvez-Medina, C.M.; González González, J.F. Biorefinery Based on Multiple Raw Materials and Wastes for the Production of Energy: A Proposal Tailored to Southwestern Europe. Encyclopedia 2024, 4, 1381-1395. https://doi.org/10.3390/encyclopedia4040090

AMA Style

Nogales-Delgado S, Álvez-Medina CM, González González JF. Biorefinery Based on Multiple Raw Materials and Wastes for the Production of Energy: A Proposal Tailored to Southwestern Europe. Encyclopedia. 2024; 4(4):1381-1395. https://doi.org/10.3390/encyclopedia4040090

Chicago/Turabian Style

Nogales-Delgado, Sergio, Carmen María Álvez-Medina, and Juan Félix González González. 2024. "Biorefinery Based on Multiple Raw Materials and Wastes for the Production of Energy: A Proposal Tailored to Southwestern Europe" Encyclopedia 4, no. 4: 1381-1395. https://doi.org/10.3390/encyclopedia4040090

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