Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

In pursuit of more sustainable and competitive biorefineries, the effective valorisation of lignin is key. An alluring opportunity is the exploitation of lignin as a resource for chemicals. Three technological biorefinery aspects will determine the realisation of a successful lignin-to-chemicals valorisation chain, namely (i) lignocellulose fractionation, (ii) lignin depolymerisation, and (iii) upgrading towards targeted chemicals. This review provides a summary and perspective of the extensive research that has been devoted to each of these three interconnected biorefinery aspects, ranging from industrially well-established techniques to the latest cutting edge innovations. To navigate the reader through the overwhelming collection of literature on each topic, distinct strategies/topics were delineated and summarised in comprehensive overview figures. Upon closer inspection, conceptual principles arise that rationalise the success of certain methodologies, and more importantly, can guide future research to further expand the portfolio of promising technologies. When targeting chemicals, a key objective during the fractionation and depolymerisation stage is to minimise lignin condensation (i.e. formation of resistive carbon–carbon linkages). During fractionation, this can be achieved by either (i) preserving the (native) lignin structure or (ii) by tolerating depolymerisation of the lignin polymer but preventing condensation through chemical quenching or physical removal of reactive intermediates. The latter strategy is also commonly applied in the lignin depolymerisation stage, while an alternative approach is to augment the relative rate of depolymerisation vs. condensation by enhancing the reactivity of the lignin structure towards depolymerisation. Finally, because depolymerised lignins often consist of a complex mixture of various compounds, upgrading of the raw product mixture through convergent transformations embodies a promising approach to decrease the complexity. This particular upgrading approach is termed funneling, and includes both chemocatalytic and biological strategies.

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Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading

Conversion of Biomass into Chemicals over Metal Catalysts

Lignin, a major component of lignocellulose, is the largest source of aromatic building blocks on the planet and harbors great potential to serve as starting material for the production of biobased products. Despite the initial challenges associated with the robust and irregular structure of lignin, the valorization of this intriguing aromatic biopolymer has come a long way: recently, many creative strategies emerged that deliver defined products via catalytic or biocatalytic depolymerization in good yields. The purpose of this review is to provide insight into these novel approaches and the potential application of such emerging new structures for the synthesis of biobased polymers or pharmacologically active molecules. Existing strategies for functionalization or defunctionalization of lignin-based compounds are also summarized. Following the whole value chain from raw lignocellulose through depolymerization to application whenever possible, specific lignin-based compounds emerge that could be in the fu...

Bright Side of Lignin Depolymerization: Toward New Platform Chemicals

Research interest in biomass conversion to fuels and chemicals has increased significantly in the last decade as the necessity for a renewable source of carbon has become more evident. Accordingly, many different reactions and processes to convert biomass into high-value products and fuels have been proposed in the literature. Special attention has been given to the conversion of lignocellulosic biomass, which does not compete with food sources and is widely available as a low cost feedstock. In this review, we start with a brief introduction on lignocellulose and the different chemical structures of its components: cellulose, hemicellulose, and lignin. These three components allow for the production of different chemicals after fractionation. After a brief overview of the main reactions involved in biomass conversion, we focus on those where bimetallic catalysts are playing an important role. Although the reactions are similar for cellulose and hemicellulose, which contain C6 and C5 sugars, respectively, different products are obtained, and therefore, they have been reviewed separately. The third major fraction of lignocellulose that we address is lignin, which has significant challenges to overcome, as its structure makes catalytic processing more challenging. Bimetallic catalysts offer the possibility of enabling lignocellulosic processing to become a larger part of the biofuels and renewable chemical industry. This review summarizes recent results published in the literature for biomass upgrading reactions using bimetallic catalysts.

Bimetallic catalysts for upgrading of biomass to fuels and chemicals

The utilization of biogas produced from organic materials such as agricultural wastes or manure is increasing. However, the raw biogas contains a large share of carbon dioxide which must be removed before utilization in many applications, for example, using the gas as vehicle fuel. The process – biogas upgrading – can be performed with several technologies: water scrubbing, organic solvent scrubbing, amine scrubbing, pressure swing adsorption (PSA), and gas separation membranes. This perspective presents the technologies that are used commercially for biogas upgradin g today, recent developments in the fi eld and compares the technologies with egard to aspects such as technology maturity, investment cost, energy demand and consumables. Emerging technologies for small-scale upgrading and future applications of upgraded biogas such as liquefied biogas are also discussed. It shows that the market situation has changed rapidly in recent years, from being totally dominated by pressure swing adsorption (PSA) and water scrubbing to being more balanced with new technologies (amine scrubbing) reaching significant market shares. There are significant economies of scale for all the technologies investigated, the specific investment costs are similar for plants with a throughput capacity of 1500 Nm3 raw biogas per hour or larger. Biogas production is increasing in Europe and around the globe, and so is the interest in the effi cient use of upgraded biogas as vehicle fuel or in other applications. The market for biogas upgrading will most likely be characterized by harder competition with the establishment of new upgrading technologies and further optimization of the mature ones to decrease operation costs. (Less)

Biogas upgrading – technology overview, comparison and perspectives for the future

Biological valorization of low molecular weight lignin

Biogas production is growing and there is an increasing demand for upgraded bio- gas, to be used as vehicle fuel or injected to the natural gas grid. To enable the efficient use of biogas in these applications the gas must be upgraded, i.e. the carbon dioxide, which constitutes a large part of the raw biogas from the digester, must be separated from the methane. This report aims to evaluate the biogas up- grading technologies that are commercially available and in operation today: amine scrubbers, water scrubbers, PSA units, organic scrubbers and membrane units. The technologies are described in detail by presenting the theory behind the separation mechanism, the upgrading process as a complete system, operational issues and how these are solved, and finally the most important financial data. Furthermore, the best developed cryogenic technologies, which today are being used to purify landfill gas and biogas from some specific components and to lique- fy biogas, are presented. Cryogenic upgrading is an interesting possibility, but as this report shows, the technology still has some important operational issues to resolve. Technologies which are especially focused on small-scale applications are finally presented, however not in as much detail as the other, more common technologies. The report shows that for mid-scale applications, the most common options are all viable. The scrubbing technologies all perform well and have similar costs of investment and operation. The simplicity and reliability of the water scrubber has made this the preferred choice in many applications, but the high purity and very low methane slip from amine scrubbers are important characteristics. Regarding PSA and membrane units, the investment cost for these are about the same as for scrubbers. Furthermore, recent developments of the membrane units have also made it possible to reach low methane slips with this technology. Biogas production is increasing, in Sweden and globally, and the interest for bio- gas upgrading to utilize the gas as vehicle fuel or in other traditional natural gas applications increases as well. The mature technologies will see a market with more and harder competition as new upgrading technologies such as cryogenic upgrading are established, and other technologies optimize the processes to de- crease operation costs. Important issues for the future development of the biogas market relate to the implementation of new policy instruments. The work with the new European standard requirements for gas distributed through the existing gas grids is one issue that possibly can have a large effect on possibilities for distribu- tion of upgraded biogas. However, the future will most probably be fuelled by an increasing amount of upgraded biogas. (Less)

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Christian Hulteberg

Papers

Biogas upgrading – technology overview, comparison and perspectives for the future

Biological valorization of low molecular weight lignin

Biogas upgrading - Review of commercial technologies

The technical feasibility of biomass gasification for hydrogen production

Methanol production from steel-work off-gases and biomass based synthesis gas