a new scenario for green & sustainable chemical production

A New Scenario for Green & Sustainable Chemical Production

Siglinda Perathoner* and Gabriele Centi*Dipartimento di Ingegneria Elettronica, Chimica ed Ingegneria Industriale, University of Messina, INSTM/CASPE

(Lab. of Catalysis for Sustainable Production and Energy) and ERIC (European Research Institute of Catalysis), V.le F.

Stagno D’Alcontres 31, 98166 Messina (Italy). V.le F. Stagno D’Alcontres 31, 98166 Messina (Italy)

(Received: Feb. 10, 2014; Accepted: Apr. 15, 2014; Published Online: ??; DOI: 10.1002/jccs.201400080)

This perspective paper introduces the changing landscape for green & sustainable chemical production,by discussing three key aspects, in relation especially to the possible routes in using biomass and CO2 asnew raw materials: i) introduction of renewable energy in the chemical production chain, ii) from bio-refineries to bio-factories, and iii) moving to a new landscape for raw materials. It is remarked how theyare challenging, but at the same time open chemical industry to innovation and competiveness. This is acritical element particularly in the transitions to new economies.

Keywords: Green & sustainable chemistry; Biomass chemical utilization; CO2 chemical utiliza-tion.

J. Chin. Chem. Soc. 2014, 61, 000-000 © 2014 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1

JOURNAL OF THE CHINESE

Review CHEMICAL SOCIETY

Special Issue for Green & Sustainable Chemistry

* Corresponding author. Tel: +39-90-6765609; Fax: +39-90-391518; Email: [email protected], [email protected]

Siglinda Perathoner took his degree in Chemistry at the University of Bologna (Italy) in

1984 and her PhD in Chemical Science in 1988 working on photophysics and photo-

chemistry of supramolecular systems. From 2001 she joined the University of Messina

and is associate professor of Industrial Chemistry presently. Her recent research interests

include nanostructured zeolites, catalytic membranes, catalysts for waste water purifica-

tion and remediation, photo(electro)catalytic conversion of carbon dioxide, and fuel

cells.

Gabriele Centi completed his industrial chemistry studies at the University of Bologna (It-

aly) and is actually Professor of Industrial Chemistry at the University of Messina (Italy).

He is a former President of the European Federation of Catalysis Societies, and was

Co-ordinator of the European Network of Excellence on catalysis IDECAT. He is

co-Chairman of the Editorial Board of ChemSusChem and Chief Editor of the book series

Studies in Surface Science and Catalysis (Elsevier) and Green Energy (De Gruyter). His

research interests lie in the development of industrial heterogeneous catalysts for sustain-

able chemical processes, environmental protection, and clean energy.

INTRODUCTION

Economic history teaches that the industrial produc-tion does not follow linear trends, but is characterized bycycles of consecutives periods of renewal, prosperity, re-cession and depression.1 Cycles of about 55 years havebeen observed in the last two centuries. The various indus-tries become synchronized and mutually reinforce, andthus also chemical production follows this trend.2 We are atthe end of one of these cycles, with the new one character-ized by a global structural change in the economy from par-asitic to symbiotic economic growth and/or a sustainable“green” path of growth, having as landmark the reorganisa-tion of energy infrastructure.3 This will have a major im-pact on the chemical production, that should turn towards alow-carbon economy on a global scale.4

Increasing competitiveness in a global market, whilstdrastically reducing resource and energy inefficiency andenvironmental impact of industrial activities, is becomingthe critical objective for the chemical and energy industry,although with different priorities in the different world re-gions. Nevertheless, it is important to analyze the new sce-nario for green & sustainable chemical production, fromthe perspective of moving to a low-carbon economy, be-cause scientists should create the background knowledgeto develop new processes and solutions for chemical indus-try.

This is even more important in a changing scenarioduring a new economic cycle, because the transition to thenew system is typically fast and non-linear. Being the de-velopment of chemical industry always associated to push-ing forces such as the availability of new raw materials andenergy sources, and pulling forces such as societal needs, itis necessary to analyze the new scenario for green & sus-tainable chemical production from these viewpoints.

The twelve principles of green chemistry,5 eg.1. Prevention,2. Atom Economy,3. Less Hazardous Chemical Syntheses,4. Designing Safer Chemicals,5. Safer Solvents and Auxiliaries,6. Design for Energy Efficiency,7. Use of Renewable Feedstocks,8. Reduce Derivatives,9. Catalysis,

10. Design for Degradation,11. Real-time analysis for Pollution Prevention,12. Inherently Safer Chemistry for Accident Preven-

tionare an important conceptual framework. However,

the need to move to a new scenario for the chemical indus-trial production, as outlined above, requires to have abroader vision based on sustainability, competiveness, in-novation and design for the future.1,6

Chemical production is at the basis of manufacturing,which accounts for about 20% of GDP on the average, andplays a key role in the structural transformation of an econ-omy, providing the materials, energy, solutions, etc. neces-sary for the change. For this reason, innovation is at thecore of the modern chemical industry. The transformationto a next generation economy (Economy 3.0, based on dis-tributed & sustainable production) requires chemistry in-novation and represents a great opportunity for the chemi-cal industry. However, it is necessary to anticipate the gamechangers in this scenario, and the opportunities for compa-nies which should overcome an often conservative ap-proach. As economic history teaches, only companies hav-ing an innovative vision are able to transform and take ad-vantages from the new opportunities while traditional sec-tors are declining. A novel and sustainable vision for theindustrial chemical production should thus anticipate thedesign needs for the future.

A systemic change is necessary in the way energy andraw materials are used in the chemical production in aworld with finite resources and a rapidly growing popula-tion. This effort goes largely beyond the correct, but limitedview provided from the twelve principles of green chemis-try. For this reason, we prefer to discuss about sustainablerather than green chemistry.1,6 To remark that major chemi-cal companies are now understanding that this approach isa winning opportunity for increasing competitiveness andinnovation in the chemical industry.7

Biomass as chemical feedstock, (re)use of CO2, wastevalorization and use of renewable energy are at the core ofstrategies of chemical/energy industries for a resource andenergy efficient sustainable future and to move towards alow carbon economy.8,9 New feedstocks, waste reutiliza-tion and introduction of renewable energy in the chemicalproduction chain are key components for resource effi-ciency, but the transition to a new green & sustainablechemical production requires to develop all the technolo-gies necessary i) to increase efficiency in using current rawmaterials (fossil feedstock) and ii) to improve current andfuture processes (in terms of reduction of use of resourcesand energy and environmental impact) as well as to de-

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Review Perathoner and Centi

crease the impact of products on environment and society.Critical components are process intensification, end of lifewaste management and recycle, energy smart distributionand storage, material innovation, etc. This is the reasonwhy a systemic change in chemical production rather thanonly on chemical reactions is required.

This perspective contribution shortly discusses someof these aspects, with focus on key aspects that will re-shape, in our opinion the future for green & sustainablechemical production.

INTRODUCTION OF RENEWABLE ENERGY IN

THE CHEMICAL PRODUCTION CHAIN

Various social and political motivations, besides totechno-economical ones, pushed chemical industry for anincrease in the use of RE:

- the significant developments in RE materials andtechnologies (with thus an increase in efficiency andreduction in costs), making RE production competi-tive over the use of fossil fuels,

- a cost of production largely related to fixed capitalcosts rather than variable costs, which are more diffi-cult to estimate in long-term,

- the renewable portfolio standards mandate in manystates and countries as well as various energy conser-vation measures,

- the legislation on climate changes, including currentand future taxation,

- limits on carbon emissions and other environmentaland political concerns, etc.

On the other hand, the chemical industry is an en-ergy-intensive industry and the second-largest industrialenergy consumer. It uses fossils fuels both as raw materialsand as power and fuel, accounting for about 14% of totalindustrial energy consumption. In US the chemical indus-try is even the largest energy-intensive branch, with 25% ofindustrial consumption in 2009, and the highest energyconsumption per unit of value added. The cost of energyrepresents from 8% up to 50% in the cost structure of mate-rials produced from chemical industry. It is thus evidenthow a progress in energy efficiency could translate imme-diately in an increased competiveness, and also in innova-tion through the research effort necessary in achievingthese objectives. A decrease in resource and energy con-sumption turns immediately into reducing the environmen-tal footprint. It is thus clear that the effort in building a re-source- and energy- efficient chemical industry could bring

a benefit in important components of sustainability.There is thus the need to develop effective ways by

which RE could be integrated into the chemical productionchain. However, the direct use of electrical energy, themain output of current technologies for RE production (so-lar, wind, hydro, etc.), is limited in chemical processes.Heat is the main source of energy utilized in chemical in-dustry, except few exceptions (chlorine and soda produc-tion, for example). Less than about 5-10% of of the fossilfuel input (as energy and raw material) can be substitutedby direct use of electrical energy from RE sources, in orderto reduce carbon footprint.

Solar thermal energy can be in principle coupled witha chemical reaction to provide the heat of reaction, butthere are many technical problems for scaling-up this tech-nology, between all the impossibility to maintain 24 h pro-duction and to guarantee uniform temperature during theday. Intermittency is also a main critical issue for introduc-ing RE into the chemical production chain for RE sourcessuch as wind and solar energy which showed the largestrate of growing in the last years. Discontinuity of electricalenergy production from wind, PV solar cells, etc. is a majordrawback in the chemical production requiring constantpower supply.

A third issue is the transport to long-distance of RE.The areas where RE potential cheap sources are availableare often far from those where chemical production is lo-cated for logistic reasons. Often these RE potential cheapsources are distant from the grid, and the effectiveness oftransporting electrical energy at distances over about 500km is limited. An example could be the large untappedhydropower potential. The global technically exploitablehydropower potential is estimated at more than 16400 TWhper year, but over 80% of the potential is still unexploited.A large part of this unexploited potential is located in re-gions (such as Africa) where the local grid is unable to ac-cept the potential production neither the electrical energycan be transported to other potential users. The cost ofhydropower is competitive over other RE solutions (wind,PV) and especially does not show intermittency.

Exploiting this hydropower potential (but similarly,for other RE sources) requires to develop effective solu-tions to transport to long-distance the produced RE. The ac-tual solutions to store and transport electrical energy (bat-teries, etc.) are not effective for large scale users.10 A cost-effective storage and transport of RE is thus a technicalchallenge (and enabling factor) to enlarge the RE share of

J. Chin. Chem. Soc. 2014, 61, 000-000 © 2014 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.jccs.wiley-vch.de 3


A New Scenario for Green & Sustainable Chemical Production CHEMICAL SOCIETY

energy portfolio, but this can translate to an opportunity forthe chemical industry. In fact, the introduction of RE in thechemical production chain requires to convert renewable tochemical energy, by synthetizing molecules which can beeasy stored and transported, as well as that can be then usedas raw materials in the chemical industry.

There are thus three main issues related to the use ofRE in the chemical production chain and in general to fos-ter a large use of RE:

1. Potential unexploited RE sources- A large part cannot be actually exploited- not-local uses, too remote for transport

2. Using RE in process industry- convert renewable to chemical energy- produce raw materials for (chemical) industry- Intermittency

3. Storage- improved systems for energy storage- devices for chemical energy conversionThe common aspect to address these issues is the re-

use of CO2 to produce liquid chemicals such as methanol(but other are also possible), which can be easy transportedand stored, and that are suitable raw materials for the chem-ical industry.4,8,11,12 The key aspect is that the energy neces-sary to increase the enthalpy from CO2 to the liquid chemi-cal (methanol, for example) is provided from RE sources(Figure 1), either directly (via photons or electrons, or indi-rectly through the formation of renewable H2 (produced us-ing RE sources) which is then utilized in the catalytic pro-cesses of CO2 conversion (to form CH3OH, CH4 or CO, forexample) leading as final result to the incorporation of REin the final product.

The direct route of CO2 conversion using photons(photo-catalysis) is apparently the more challenging and

interesting. Various specific reviews13-16 have been pub-lished on the photoconversion of CO2 on semiconductormaterials. Significant progresses have been made on theunderstanding of the mechanism of light capture and en-ergy transfer to CO2 molecules, but the productivity is stilltwo-three order of magnitude lower than that necessary tostart to consider exploitation. There is also the need tobetter identify bottlenecks. Typical aspects studied in liter-ature regards the use of cocatalysts, the interfacial contactbetween semiconductor and other materials as well as therole of heterojunctions in promoting charge separation, andthe design strategy in semiconductors to improve effective-ness in using visible light portion of solar spectrum. Theseare fundamental and important questions, but we should re-mark that in our opinion a key issue not adequately investi-gated regards the interaction of CO2 and the products ofconversion with surface excited states. This issue repre-sents an intrinsic barrier to increase productivity in CO2

direct photoconversion to the levels necessary for exploita-tion.

Important advances have been made in the electro-catalytic reduction of CO2 and in the design of the elec-trodes for this reaction.17-22 Substantial advances in elec-trodes, electrolyte, and reactor design are still required topermit the development of commercial processes. Re-search has been mainly focused on the design of metal elec-trodes to improve their performance (focusing especiallyon Faradaic efficiency) and on alternative approaches suchas the application of ionic liquids as electrolytes and of mi-croorganisms as co-catalysts. Also these are important as-pects, but the key issue for the possible commercializationis the increase of the productivity and the control of selec-tivity. A key aspect, again scarcely investigated in litera-ture, is the possibility to develop 3D-type (eg. high surfacearea) electrodes. This is not only important to increase theproductivity per electrode area (thus reduce the costs), butalso (somewhat more important) to reduce overpotential inCO2 reduction and limit side reaction of H2 formation. An-other important, but scarcely considered aspect is the en-ergy necessary to recover and separate the products of reac-tion. The development of electrolyteless operations (eg.operating the electrocatalytic CO2 reduction with an elec-trode in contact with a gas-phase rather than a liquid phase)could be a relevant approach to proceed in this direction,but still very limited results are available and there is alsothe need to better understand the fundaments of operationsin these conditions.23-25



Fig. 1. A schematic picture (with reference to enthalpyof molecules) of the different routes by whichRE could be introduced in the carbon dioxidemolecule to produce fuels or chemicals.

The current feasible approach, also in terms of scal-ing-up to commercial solutions, is the production of electri-cal energy by RE sources, the use of this electrical energyin electrolyzers to produce (renewable) H2, and finally thecatalytic hydrogenation of CO2 to methanol (or other prod-ucts, such as DME, higher alcohols and hydrocarbons).The current higher challenge for this route is the possibilityto produce economically renewable H2, which requires tomeet some targets:

- stability of operations under pressure (> 30 bar);- improve in current energy efficiency (> 75-80%);- decrease in fixed capital costs for electrolyzers (< €

300/kWe - kilowatts electrical);- development of large electrolyzers stacks;- in a longer term, substitution of Pt in electrolyzers

and reduction of the overpotential.PEM (polymer electrolyte membrane) electrolyzers

are currently the preferable option for the production of H2

from water, but SOEC device are of increasing relevance,for the possibility to obtain better efficiencies in energyuse.26 The efficiency losses in PEM electrolyzer’s perfor-mance is due to three main aspects:

- electrical resistance,- membrane resistance,- kinetic overpotential.While the first two can be improved by a better cell

engineering and membrane materials, the latter requires abetter understanding of the surface processes and modifi-cations during electrolysis, for example with an advancedin-situ characterization. Other requirements for electro-lyzers are efficient operation under variable load, and sta-bility against frequent power interruption.

Catalysts for CO2 conversion also need to be im-proved.27,28 The catalysts for methanol synthesis (fromsyngas, containing also up to about 3% CO2; small amountsof CO2 promotes reaction rate) are well-established at in-dustrial scale, and significant advances have been madealso recently in the understanding of their reaction mecha-nism.29 However, the performances feeding pure CO2 + H2

(instead of syngas containing less than about 3-4% CO2)are significantly lower. Two are the main motivations:

- CO2/H2 mixture is more oxidant than that of a CO/H2 (syngas) mixture; this is influencing the activestate of the catalyst during reaction,

- water, which forms through rWGS reaction, inhib-its the catalyst activity.

Productivity of the catalysts using CO2/H2 feed is

about one third of that possible with an optimal feed com-position. A partial solution is to perform the process in twoconsecutive reactors, with an intermediate removal of thewater produced after the first rWGS reactor. It is also possi-ble to perform the reaction in a membrane-reactor, where awater permeo-selective membrane is present for in-situ re-moval of the water formed during rWGS reaction. How-ever, the preferable solution is to develop specific im-proved catalysts for direct methanol synthesis using a CO2/H2 feed.

A further challenge is to develop an efficient processbased on micro-reactors, because small scale productions(as the common case for methanol synthesis from CO2 us-ing RE) would require intensifying the process and im-proving energy efficiency. Catalysts have to be also de-signed to operate with micro-reactors. Furthermore, thesemicro-plants have faster shut-down and start-up opera-tions, as will be necessary for a better coupling with inter-mittent renewable energy sources.

It is also important to remark that the use of H2 forproducing methanol from CO2 determines a minimal lossof intrinsic energy,30 while bringing relevant benefits interms of possibility to store/transport RE and integrabilityinto the chemical production chain. Actual electrolyzers al-low an efficiency of about 70-85% with energy consump-tion of 4-6 kWh/Nm3 of H2 produced. Using RE, the effi-ciency decreases to about 60%. As shown in Figure 2, thehydrogenation of CO2 decreases only in minimal part theintrinsic energy, and thus the main parameter influencingthe carbon footprint is the production of H2.

The possibility of effective introduction of RE intothe chemical production value chain thus requires the useof RE to produce chemicals and energy vectors which canbe easy integrated into the actual chemical production. It isthus clear from this perspective that CO2 conversion is thenatural option by which this task of introducing RE into the




Fig. 2. Simplified energy diagram for the energy stor-age-conversion chain using methanol as energystorage medium with flows of electrical energy,heat and chemical exergy. Adapted from ref.30.

chemical production chain can be realized. The critical is-sue remains the cost and availability of renewable H2. Asremarked elsewhere,4,31,32 there are good perspectives toachieve the necessary target costs for producing renewableH2, although availability at large scale could be anotherchallenge.

FROM BIOREFINERIES TO BIO-FACTORIES

Similar to what commented above for RE, there aremany societal and political factors pushing towards a bio-based economy, although they transform in an opportunityfor innovation and competiveness, the effective driver, forthe chemical industry:33-35

- Kyoto and related politics to reduce carbon foot-print,

- security of supply,- agricultural policies,- sustainability,- support of the local economics.Government policies will the drive change in energy/

chemical production towards a bio-based economy througha mix of actions such as mandate fuel mix, subsidies, re-newable targets and carbon targets. This fact determinesdifferent policies at country/regional levels, and thus prior-ities conditioning the evolution of the bio-based economyon country/regional level rather than on global scale. Thereare, however, some general macro-trends which should beshortly commented. A more detailed analysis have been re-ported elsewhere.36-38

The first observation is that biofuel expectations aredecreasing, due to increased availability of non-conven-tional fossil fuels (particularly, shale gas in US and coal inChina), and also some alternative fuels such as those deriv-ing from CO2 using RE. Integration with chemical produc-tion will be a key factor to valorize the higher added valueof chemical production. While biofuels were the priority inthe past, chemicals will be the priority for the future. Forthis reason, we emphasize here the need to pass frombiorefinery to bio-factory concepts. In addition, togetherwith the development in the direction of integral use of bio-mass and minimization of impact on the environment (wa-ter ecosystem, in particular), an effort will be observed to-wards an improvement in energy efficiency and a reductionin CO2 emissions. Large amounts of CO2 are emitted dur-ing fermentation (for example, about one ton CO2 per tonof bioethanol produced) and thus a key target will be thepossibility to minimize these emissions.39

Integration of bio- and solar-refineries, in order to ex-ploit and valorize the CO2 produced in biorefineries as wellas to integrate RE sources in biorefinery production (solarbiorefineries) will be an important future direction.38

There are many possible options to reuse the CO2 pro-

duced in biorefineries, taking into account that streams pro-

duced during fermentation, are characterized by a high CO2

concentration (>99%) and low level of impurities which

can be relatively easy removed.39 Some of the possible op-

tions are listed in Table 1.

An interesting example to evidence some of the pos-

sibilities offered in biorefineries/bio-factories to produce

large-volume chemicals is given from the synthesis of

acrylic acid. There are different possible routes to form

acrylic acid using CO2 and/or biomass as summarized in

Figure 3:- the carboxylation of alkenes, in particular of ethyl-

ene; this is the route actively investigated by BASF;

- the direct carboxylation of ethane to propionic acid

(then dehydrogenated to acrylic acid), but still very

limited yields were obtained.

- the reaction of CO (obtained from CO2) with ethyl-

ene oxide to form propiolactone then converted to

either glacial acrylic acid or acrylate esters. This

route is developed by Novomer using its propri-

etary catalysts.The carboxylation of alkenes has been attempted us-

ing several transition-metal systems. This reaction is alsoof great potential industrial interest. Despite of extensivestudies over the last two decades, the major challenges toclose the catalytic cycle have not yet fully overcome. BASFresearchers have been able to close the catalytic cycle (Fig.4b), but forming sodium acrylate and with relatively low



Table 1. Possible routes to valorise CO2 emissions inbiorefineries

Route Company[a] Ref.

Ethylene[b] + CO2 � Na-acrylate(Acrylic Acid)

BASF 40

3 CO2 + 8 H2[c] � Acetone + 5 H2O Evonik 41

Glucose + CO2 �� Succinic AcidBioamber,Reverdia[d] 42

CO/CO2 gas fermentation �

bioethanol, acetic acid, 2,3 butandiol Lanzatech 43

[a] Examples of companies involved in developing this route.[b] Obtained from bioethanol. [c] Genetic modified acetogens[d] Joint venture DSM + Roquette.

turnover.40,44 A comprehensive review of the different pos-sibilities, and reaction mechanisms, in the carboxylationwith carbon dioxide has been published recently by Riduanand Zhang45 and Yu et al.46 The carbonylation of ethyleneoccurs through the formation of metallolactones, particu-larly of Ni and Pd, but which are quite stable molecules.The difficulty is thus how close the cycle.

Using for example Ni(0), the nickel lactones formedin the oxidative addition step are stable compounds. Thisintermediate does not allow �-H elimination to yield acryl-ic acid due to a long distance between the Ni and �-H atomresulting from ring strain. Without the cleavage of NiCbond, consequent transformation to an acrylate is not possi-ble. Recently, the first catalytic synthesis of acrylate fromCO2 and alkene has been achieved by Limbach et al.40 withdtbpe as ligand (Figure 4). Working on the different stepsof the reactions, they were able to show for the first timethat it is possible to have a catalytic cycle (TON 10) in twoseparate steps. Experimentation is also in progress on theuse of heterogeneous catalysts.

Interesting progresses have been made also on thebioroutes to produce syngas from CO2. The production offuels and chemicals through syngas fermentation offerssome advantages over metal catalytic conversion: the

higher specificity of the biocatalyst, lower energy costs,greater resistance to catalyst poisoning, and independenceof a fixed H2:CO ratio.47

There are several microorganisms, which can pro-duce fuels and chemicals by syngas utilization. These mi-croorganisms are mostly known as acetogens includingClostridium ljungdahlii, Clostridium autoethanogenum,Eurobacterium limosum and others.48 Most use the Wood–Ljungdahl pathway. The fermentation of syngas to ethanolby Clostridium ljungdahlii was developed into a commer-cial process that combines biomass gasification, syngasfermentation and distillation of ethanol from the reactor ef-fluent. Syngas is cooled before it can be introduced into thebioreactor and is coupled to heat recovery (BRI energy;www.brienergy.com). Lanzatech (www.lanzatech.com)process of CO fermentation is currently applied on a 0.4 Mldemonstration facility (Shanghai, China) using steel milloff-gas from a working steel mill.43 INEOS Bio (www.ineosbio.com) also began in 2011 the construction of theirfirst commercial scale plant, the Indian River BioEnergyCenter in Florida. Gas fermentation is thus an establishedtechnology, but it is necessary to use directly CO2 ratherthan CO.

It is known that CODH from Clostridium thermoace-

ticum (a Ni and Fe containing metalloenzyme) catalyzesthe reversible oxidation of CO to CO2. It is possible to cou-ple this enzyme with a semiconductor such as TiO2 whichproduces the electrons necessary for the reduction. A hy-brid enzyme-nanoparticle system was used to achieve anefficient CO2 to CO reduction using visible light as the en-ergy source. Armstrong and coworkers49,50 used either TiO2

nanoparticles modified by attachment of carbon monoxidedehydrogenase (CODH) and a Ru photosensitizer (this sys-tems produces CO at a rate of 250 �mol of CO (g ofTiO2)

-1·h-1 when illuminated with visible light at pH 6 and20 °C) or assemblies of CODH with CdS nanocrystals (inthis case the CO production rate at the best is about 0.5�mol·h-1, but turnover frequency per enzyme molecule isbetter; 0.35 M 2-(N-morpholino)ethanesulfonic acid (MES)was used to buffer the acidifying effect of CO2 in solutionand act as the electron donor).

Additionally, several purple non-sulfur bacteria wereisolated that are able to produce H2 in a process similar tothe WGS reaction. Lazarus et al.51 reported the use of redoxenzymes supported on conducting graphite platelets to per-form WGS reaction efficiently at room temperature. TheH+ reduction reaction is catalyzed by a hydrogenase, Hyd-




Fig. 3. Possible routes to form acrylic acid using CO2

and/or biomass.

Fig. 4. (a) The hypothetic coupling of ethene and CO2.(b) The first catalytic cycle for the formation ofsodium acrylate proposed by BASF research-ers.40 Adapted from ref. 46.

2, from Escherichia coli, and CO oxidation is catalyzed bya carbon monoxide dehydrogenase (CODH-I) from Car-

boxydothermus hydrogenoformans. This system shows aturnover frequency (at 30 °C about least 2.5 s-1 per minutefunctional unit; a CODH/Hyd-2 pair) comparable to con-ventional high-temperature catalysts.

The example discussed above evidence how a new in-novative chemistry, combining homogeneous, heteroge-neous and bio-catalysis, is required to address the newchallenges opened from moving to new sustainable bio-refineries/bio-factories. These are few examples, being notpossible to discuss more in details all the cases due to limitsin this perspective paper. However, it is necessary to brieflymention also the prospects for olefin biorefineries.38

Light olefins are the base building blocks for currentpetrochemistry. They are produced currently for over 98%from fossil fuels, mainly by steam cracking of oil and NG(natural gas) fractions, but new opportunities are givenfrom the use of biomass-derived raw materials (Figure 5).

The dehydration of ethanol produced from biomassfermentation is already at an industrial level. This route de-pends greatly on the cost of production of ethanol. InBrazil, where cheap ethanol is available by sugar fermenta-tion, already a couple of industrial plants (by Braskem,Dow and Solvay Indupa) produce ethylene from bioetha-nol. The catalytic dehydration of ethanol to ethylene couldbe realized industrially with a yield of ethylene over 96-97%, but relatively high temperatures (about 450 °C) arenecessary. Some of the research developments in progressare trying to lower this reaction temperature, although thisis not a critical issue, differently from long-term stability.Doped-zeolites, particularly H-ZSM-5 (for example, 0.5%La-2% P-HZSM-5), are catalysts giving good perfor-mances at low temperatures (200 to 300 °C).

Production of other olefins would require converting

further ethylene, for example by olefin methathesis. Figure5 shows some existing possibilities of conversion of lightolefins. To note that the availability of low-cost natural gas(due to shale-gas) is moving some of the naphtha steamcracking plants for olefin production to ethane steamcracking. This is creating an excess of ethylene, and ashortage of C3 and especially C4 olefins.

Less attractive from the industrial perspective (com-plex, multistep, economic only at a large scale, with severeproblems of purification and quality of products, etc.) is theroute of production of methanol via syngas from biomass(eventually, via intermediate fast pyrolysis). Methanol canbe then converted to olefins (MTO) or selectively to pro-pylene (MTP). The methanol synthesis is well establishedcommercially. MTO/MTP are industrial processes, butwith still critical aspects regarding productivity/deactiva-tion. A shorter alternative path is to produce directly olefinsfrom syngas by the FTO process, although catalysts for thisreaction have to be further improved.

In addition to the routes from bioethanol or syngas,other opportunities are offered through the intermediatesynthesis of C3 or C4 alcohols or diols via fermentationprocesses. There are also microorganism strains whichcould produce directly propylene from glucose media (to-gether with various other hydrocarbons, such as propane,butane, butene, pentene, etc.), but productivities are lowand separation cost high.

There are various other possible routes to producelight olefins from biomass, not indicated in Figure 5 forconciseness. Propylene could be synthetized from 1-pro-panol or 2-propanol produced by fermentation, but actualproductivities of the latter are still low. Currently, it wouldbe preferable to synthetize 1,2-propanediol via biochemi-cal pathways,52 convert it to 2-propanol and finally dehy-drate to propylene. The alternative is the ABE fermentation



Fig. 5. New routes of production of olefins from biomass. Adapted from ref. 38.

process53 leading to ethanol, butanol and acetone, the latterreduced to propylene. ABE fermentation (acetone-butanol-ethanol) with wild and genetically modified strains (fromthe Clostridium family) is known from long time, but hasreceived renewed interest recently. However, there are stillmany aspects to improve in order to produce n-butanol atcommercially attracting prices:

- improve yields of butanol,- expanding substrate utilization,- minimizing energy consumption during separation

and purification.Cost of n-butanol is still high and it would be neces-

sary to develop improved micro-organisms to make com-petitive the synthesis. Furthermore, it is preferable to usedirectly the glycols (1,2-propanediol, for example) ob-tained by catalytic conversion of sugars or other platformmolecules (glycerol, lactic acid) as substitute of those de-rived from fossil fuels (catalysed ring-opening of propyl-ene oxide). Polyol Chemical Inc, for example, producespropylene and ethylene glycols (together with other prod-ucts such as glycerine and butanediol) starting from sorbitol/glucose. The process economics, however, are positiveonly using waste sugar streams.

Butadiene is another interesting olefin which can beproduced from biomass-based routes alternative to thosestarting from fossil fuels (naphtha steam cracking frac-tions, or by dehydrogenation of butane). Butadiene couldbe produced by dehydrogenation of ethanol to acetalde-hyde, followed by aldol condensation and dehydration,over MgO-SiO2 (doped with Na2O) catalysts (Lebedewprocess). Overall yield is about 70% or more.54 Hüls is us-ing this process from over three decades, but butadienecould be economic only using cheap bioethanol.

Butanol dehydration to butenes followed by dehydro-genation to butadiene has been also presented as a valueand economic route.55 An alternative route is to produce2,3-BDO by fermentation of sugars, followed by dehydra-tion to butadiene. Lanzatech has developed on a pilot-scalea fermentation process to produce 2,3-BDO (using CO/H2

as feed). In joint venture with other companies (Invista, aglobal nylon producer interested to convert butadiene toadiponitrile, intermediate to manufacture of Nylon 6,6),Lanzatech is also developing a process to convert 2,3-BDOto butadiene via fermentation (leading in perspective to thesingle-step production of butadiene via gas fermentation).Versalis in joint venture with Genomatica is also develop-ing the production of butadiene via 2,3 BDO obtained by

fermentation. There are good perspectives that these routes(by sugar or gas fermentation) will become commerciallyattractive, but productivity and cost of separation are stillcritical elements.

Other olefins interesting for rubbers are also devel-oped using biomass. Genecor in joint venture with Good-year is developing a bio-isoprene production process, andGlycos Biotechnologies plans also to commercialize theproduction of isoprene from crude glycerine. Global Bio-energies and Gevo/Lanxess are developing processes toproduce isobutene from glucose or from isobutanol, re-spectively. The latter is produced by fermentation, as dem-onstrated on already relatively large scale by Gevo andclaimed to be competitive to the fossil-fuel based route toC4 olefins.

Produce olefins from biomass is thus an area of re-search of great interest in many companies, particularlyventure capital ones. Although it is still necessary to betterunderstand which of these new routes may be proven to beeconomic on a larger scale, it is evident how the new sce-nario for chemical production is fast changing and that ole-fin biorefineries will be probably a major route for the fu-ture scenario of chemical production.

MOVING TO A NEW LANDSCAPE FOR RAW

MATERIALS

Actual chemical production, excluding inorganicproducts, is mainly based on oil. Olefins are the major bulkchemical produced, with about 125, 75 and 10 MTons ofethylene, propylene and butadiene, respectively. Abouthalf of ethylene derives from naphtha steam cracking,while about 35% from steam cracking of NG fractions (theremaining from other sources). Propylene, instead, derivesfor about 65% from naphtha steam cracking, 30% from re-finery processes (FCC, mainly) and in minimal part fromNG fractions (including propane dehydrogenation). Theother main source of bulk chemicals for chemical produc-tion is aromatics (about 43, 40 and 20 Mtons of xylenes,benzene and toluene, respectively). They derive almostcompletely from oil fractions. Methanol is the main prod-uct deriving from NG, via syngas formation. Current meth-anol production is about 50 Mtons, but only a fraction isused for chemical production (about 35% for formaldehydeand 10% for acetic acid as main products deriving frommethanol). Although syngas can derive from other sources,including coal, over 96% of the actual production derivesfrom NG.




There is a large debate whether the availability ofcheap NG due to shale gas is changing this current land-scape for chemical production in terms of an increased useof NG with respect to oil. The cost of NG has droppeddown in the last years, due to shale gas availability. Severalchemical companies are looking to the new opportunitiescreated from shale gas to expand production capacity forethylene, ethylene derivatives (i.e., polyethylene, polyvi-nyl chloride, etc.), ammonia, methanol, propylene, andchlorine.

However, shale gas production tends to decrease, andanalysts predict that NG cost will increase again in the nearfuture (shale gas bubble). In addition, the NG market priceis still high in regions such as Europe where many con-strain in exploiting shale gas resources exist. In addition,ethane steam crackers, with respect to naphtha steam crack-ers produce low amounts of higher olefins. Propylene andcrude C4 are an important factor for the competitiveness ofnaphtha crackers compared to ethane or light feed crackers.The existing supply shortage and the high demand for C3and C4 are increasing their prices and thus the profitabilityof naphtha crackers. Except for n-butane oxidation tomaleic anhydride, the direct use of light alkanes in chemi-cal production is still not competitive with respect to lightolefin use. We thus suggest that notwithstanding the cur-rent large interest on chemical use of shale gas, we will stillsee a limited use of NG for chemical production in theforthcoming years.

Coal has limited usage for chemical production cur-rently, but China is actively pushing its use, via syngas pro-duction and production of methanol and then olefins. How-ever, due to the specific economic and political motivationsfor this choice, as well the severe impact on the environ-ment of this route, it is unlikely that the use of coal forchemical production will largely diffuse worldwide in thefuture.

Biomass and CO2 use, as commented before, may in-stead have the potential to change this landscape. Biomasscurrent use in chemical production accounts for few per-centages of global production, but the use is expanding.Figure 6 reports current estimation,56 but based largely onlinear extrapolations.

We have remarked before that we are in a periodwhere an exponential trend may be expected. In accor-dance, the SPIRE Roadmap57 prepared by the Europeanchemical industry estimates feasible to reduce in process(chemical) industry up to 20% in non-renewable, primary

raw material intensity and up to 30% in fossil energy inten-sity by year 2030 from current levels. This could be achievedfrom a combination of use of biomass (including especiallywaste biomass), CO2 and increased efficiency in using cur-rent raw materials.

We have not discussed here (for conciseness) otherimportant options, such as the conversion of CO2 to lightolefins, being discussed in detail elsewhere.4,8,58 Also forthis reaction, there is still the need to improve catalysts, butthe prospects appear interesting. We have also not dis-cussed here the different routes to produce drop-in (eg.which can directly introduced in the chemical value chain)or non-fungible (eg. non identical to those currently used)intermediates.9 The investment cost necessary to developthe process and the integration of the production within theexisting infrastructure (drop-in products) is largely lowerthan in the case of non-fungible chemicals. Their commer-cial introduction is thus easier.

CONCLUSIONS

The examples discussed here, although limited to fewcases being out of the scope a full analysis of all the novelpossible routes, have shown how a changing landscape forgreen & sustainable chemical production, which requiresalso new conceptual approaches going beyond the princi-ples of green chemistry.

The use of alternative and renewable materials to fos-sil fuels, in particular:

- biomass and bio-waste,- products derived from CO2 + renewable H2, the lat-

ter produced with RE (solar) sourcesopen new scenarios to develop a sustainable and low

carbon footprint chemical production,8,9 particularly in re-gions lacking of other resources. There are many motiva-



Fig. 6. Planned cumulative novel bio-based chemicalscapacity. Adapted from ref. 56.

tions for this transition to a new economy and some of themwere briefly discussed in the introduction. We have fo-cused discussion here on three key aspects of this changingscenario:

- introduction of RE in the chemical productionchain,

- from biorefineries to bio-factories,- moving to a new landscape for raw materials.They are challenging, but at the same time open the

chemical industry to innovation and competiveness, aswell as to a new use of RE.59 These are critical elements inthe transitions to new economies.

In conclusion, the scenario for chemical production isfast evolving and new raw materials, substituting fossil fu-els for sustainability motivations and to develop a low car-bon society, will become a main driver to develop novelproduction routes.

ACKNOWLEDGEMENTS

The authors acknowledge the PRIN10-11 projects“Mechanisms of activation of CO2 for the design of newmaterials for energy and resource efficiency” and “Innova-tive processes for the conversion of algal biomass for theproduction of jet fuel and green diesel” for the financialsupport.

LIST OF ABBREVIATIONS

3D tri-dimensionalABE Acetone–Butanol–EthanolBDO ButandiolCODH Carbon Monoxide DehydrogenaseDME dimethyletherGDP Gross Domestic ProductFCC Fluid Catalytic CrackingFTO Fischer-Tropsch to OlefinMTO Methanol to OlefinMTP Methanol to PropyleneNG Natural GasPEM polymer electrolyte membranePV PhotoVoltaicRE Renewable EnergySOEC Solic Oxide ElectrolyzerSPIRE Sustainable Process Industry through Re-

source and Energy EfficiencyrWGS Reverse Water Gas ShiftTWh teraWatt h-1

US Unites States of America

WGS Water Gas Shift

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