Biomass Valorization by Davide Ravelli

Biomass Valorization

Sustainable Methods for the Production of Chemicals

 

Editors

 

Prof. Davide Ravelli

Chiara Samorì

 

 

 

Logo: Wiley

Foreword

Why bother with biomass conversion? It seems so difficult compared to converting hydrocarbons into products. People used to think that we were about to run out of fossil fuels, but that was a red herring – there is enough left in the ground to serve us for hundreds of years. So, if running out of hydrocarbons is not the problem, then why are we trying to convert biomass? The problem is in the consequences of hydrocarbon usage, not in the depletion of hydrocarbons. Those consequences are severe. Fossil fuel resources are heavily contaminated with sulfur, mercury, and other pollutants. Many products from such feedstocks are persistent, leading to problems such as plastics in the oceans. However, most importantly, burning fossil‐based fuels or incinerating fossil‐based products generates carbon dioxide while the production of the feedstocks consumes no CO2.

Now, imagine a sustainable future – a future in which all of our needs are met with products made from renewable resources, and those same products are themselves recycled into new products. The feedstocks are nontoxic, the products are biodegradable, and greenhouse gas emissions are completely offset by CO2 consumption. Everyone would agree with that as a desirable goal, but we are a long way from that future. There is so much work to do before we get there. We as a society are married to our petrochemical past in so many ways, from the products we choose to make, the ways in which we make those products, and even what we teach our future chemists and chemical engineers at the universities. We need to divorce ourselves from our petrochemical past in order to bring about that sustainable future.

Make no mistake about it. That divorce is going to be messy, but it is still worth doing. At first, we thought that it would be easy. Just make existing products from biomass instead of fossil fuels. It sounds so simple, but study after study has shown that the environmental impact of transforming biomass into traditional chemical products is usually more harmful than making the same products from fossil fuels. So, what are we going to do? We have to be smarter about it. Those traditional chemical products were chosen in the past because they were easy to make from hydrocarbons. Why cannot we choose new chemical products? Let us choose chemical products that are easy to make from biomass!

Choosing new products is not the only task on our To Do list. There is a long list of tasks ahead of us. We have to

  • increase our knowledge of biomass conversions.
  • evaluate new conversion processes and products in terms of potential environmental impact, not just as an afterthought but during the design stage,
  • use only renewable energy in the biomass conversion processes,
  • develop less energetically costly ways of removing organic products from water, given that water is often the solvent for fermentations and other standard techniques for biomass transformations,
  • build up supply chains from producers of raw biomass, through transportation and conversion to platform chemicals, all the way to manufacture finished products,
  • seek new sustainable feedstocks and new platform chemicals, keeping in mind their potential availability at industrial scale and the environmental impact of using such feedstocks at scale,
  • design our new products so that they can be recycled efficiently, can biodegrade if discarded, and do not themselves lead to environmental crises,
  • change how organic chemistry is taught at the universities so that biomass feedstocks become the norm.

That sounds like a lot of work, but do not despair. There are so many talented people working on biomass conversion, such as the authors and editors of this volume, that each of these items on our “To Do” list can be achieved. The sheer variety of approaches described in the following chapters assures me that there is great hope for the future of biomass conversion. Many of you, the readers, are also developing new technologies for sustainable chemical manufacturing. We will attain that sustainable future, and this book demonstrates that we are making progress toward that goal.

My commendations to Chiara Samorì and Davide Ravelli for putting this work together, to the authors for their many contributions to the book and the field, and indeed to everyone in the green and sustainable chemistry research community for their efforts in developing the chemistry that will make sustainable living a reality.

August 2020

Philip Jessop

Queen's University

Preface

It is nowadays apparent that the chemistry of the future will involve the exploitation of biomass‐based renewable materials, the currently available stock of fossil resources being doomed to exhaustion. This transition may indeed bring about several benefits because having recourse to renewable resources should limit the impact human activities are having on climate change.

Currently, the use of biomass by mankind is limited to addressing a few specific needs, notably fulfilling the feed demand and supplementing energy production in addition to the fossil fuel portfolio. The impact of these activities on the net primary production (NPP) of terrestrial and marine biomass can be accounted for by considering the human appropriation of net primary production (HANPP) parameter, which corresponds to all the human alterations of photosynthetic production in the ecosystems. This constant HANPP represents a significant fraction of the NPP and has a huge impact on ecosystems because it reduces the amount of energy available to other species, influences biodiversity, and alters water, energy, and carbon flows within food webs, also modifying the distribution of resources. In the prospected future scenario of a massive use in industry, biomass will at some point become a scarce resource, and its utilization should be considered wisely, accordingly. In particular, the entire substitution of fossil fuels with biomass for energy production purposes is unrealistic because of the huge amount of biomass that should be devoted at this end. Furthermore, one may argue if this kind of application is the best use possible of biomass, fully exploiting its characteristics in terms of chemical composition.

Through history, a variety of biomass constituents have been employed in the preparation of valuable drugs, flavors, and fragrances, or to provide, especially in the second half of the nineteenth century, commodity materials such as cellulose esters (nitrate and acetate) and oxidized linseed oil (linoleum). Indeed, there exist different options of using biomass to produce chemicals. Nowadays, let apart the use of wood in the paper industry, bio‐based surfactants, lubricants, coatings/dyes, additives for plastics and solvents (mostly based on vegetable oils/animal fats, sugar, or starch) are the most important applications of biomass in chemistry. As for future applications, the question is still open; however, it can be anticipated that the use of biomass for chemicals production is a much more sustainable option than having recourse to it for energetic purposes. Furthermore, in addition to merely duplicating existing products deriving from fossil resources, the chemistry of biomass opens the opportunity to develop a new portfolio of products, having no equivalence among those presently manufactured by classical synthetic routes from hydrocarbons. A subsidiary advantage is that the development of bioproducts requires fewer legislative constraints.

Accordingly, there is an increasing interest in developing suitable techniques to tackle the valorization of biomass to produce chemicals and this area is expected to further expand in the future. Along the same line, bio‐based waste materials, to be included in a circular economy perspective, can likewise contribute significantly. Independently from the actual biomass employed, this is a challenging area because inhomogeneous materials with variable composition must be processed with tailored technologies. The book “Biomass Valorization: Sustainable Methods for the Production of Chemicals” is intended to present the state of the art of the different strategies available nowadays to convert biomass into useful building blocks/commodity chemicals.

Each chapter features an introductory section, detailing the core details of the described technology and showcasing the typical chemical pathways that can be activated by having recourse to it. Next, peculiar advantages and limitations of the described strategy in the processing of biomass are described. Finally, relevant examples from the recent literature are reported, with attention to the organic chemistry perspective, also indicating how the different approaches can modify and valorize the native functionalities present in the starting biomass.

After an introductory section (Chapter 1), intended to set the stage and describe how biomass can contribute to the production of chemicals, the rest of the book has been organized according to the diverse approaches that can be exploited, also highlighting the potential, challenges, and innovative solutions associated with them. Biomass valorization processes have been explored using catalytic routes, including acid catalysis (Chapter 2), base catalysis (Chapter 3), metal catalysis (Chapter 4), and biocatalysis (Chapter 5). Various thermal strategies that can be applied for the valorization of biomass involve pyrolysis (Chapter 6) and thermochemical–biological hybrid processes (Chapter 7). Different advanced/unconventional strategies have also shown great promise, such as those involving electrochemical (Chapter 8) and photochemical (Chapter 9) means, microwave treatment (Chapter 10), ultrasound‐assisted approaches (Chapter 11), and mechanochemical approaches (Chapter 12). As a final contribution, biomass processing from an industrial perspective is assessed (Chapter 13).

There is no doubt that in the future, the production of chemicals will be based on the exploitation of biomass and the time has come to find the best methods to address this challenge and put it into practice.

November 2020

Chiara Samorì, University of Bologna, Italy

Davide Ravelli, University of Pavia, Italy