Biological carbon dioxide utilisation in food waste anaerobic digesters

Carbon dioxide (CO2) enrichment of anaerobic digesters (AD) was previously identified as a potential on-site carbon revalorisation strategy. This study addresses the lack of studies investigating this concept in up-scaled units and the need to understand the mechanisms of exogenous CO2 utilisation. Two pilot-scale ADs treating food waste were monitored for 225 days, with the test unit being periodically injected with CO2 using a bubble column. The test AD maintained a CH4 production rate of 0.56 ± 0.13 m3 CH4·(kg VSfed d)−1 and a CH4 concentration in biogas of 68% even when dissolved CO2 levels were increased by a 3 fold over the control unit. An additional uptake of 0.55 kg of exogenous CO2 was achieved in the test AD during the trial period. A 2.5 fold increase in hydrogen (H2) concentration was observed and attributed to CO2 dissolution and to an alteration of the acidogenesis and acetogenesis pathways. A hypothesis for conversion of exogenous CO2 has been proposed, which requires validation by microbial community analysis

Carbon Dioxide Utilisation -The Formate Route

UIDB/50006/2020 CEEC-Individual 2017 Program Contract.The relentless rise of atmospheric CO2 is causing large and unpredictable impacts on the Earth climate, due to the CO2 significant greenhouse effect, besides being responsible for the ocean acidification, with consequent huge impacts in our daily lives and in all forms of life. To stop spiral of destruction, we must actively reduce the CO2 emissions and develop new and more efficient “CO2 sinks”. We should be focused on the opportunities provided by exploiting this novel and huge carbon feedstock to produce de novo fuels and added-value compounds. The conversion of CO2 into formate offers key advantages for carbon recycling, and formate dehydrogenase (FDH) enzymes are at the centre of intense research, due to the “green” advantages the bioconversion can offer, namely substrate and product selectivity and specificity, in reactions run at ambient temperature and pressure and neutral pH. In this chapter, we describe the remarkable recent progress towards efficient and selective FDH-catalysed CO2 reduction to formate. We focus on the enzymes, discussing their structure and mechanism of action. Selected promising studies and successful proof of concepts of FDH-dependent CO2 reduction to formate and beyond are discussed, to highlight the power of FDHs and the challenges this CO2 bioconversion still faces.publishersversionpublishe

Zirconia/Titania Catalysts for Carbon Dioxide Utilisation

Reaction and conversion of CO2 to chemicals is a challenging area of research. The objective of this work is to study and investigate the use of mixed metal oxide Zr/Ti oxide and related catalysts for the conversion and utilisation of CO2. The first reaction studied was propane dehydrogenation using CO2 to produce propene. Then, the study extended to investigate the direct reaction of CO2 as whole molecule with methane, ethane, acetylene, ethylene and propane to synthesis carboxylic acids. The catalysts were prepared in several ways. Four methods were based on coprecipitation of the mixed catalyst from solutions of zirconium (IV) oxynitrate hydrate and titanium (IV) chloride. Other methods involved impregnation, based on titanium (IV) oxide. Catalysts were characterised by nitrogen adsorption, by powder X-ray diffraction, by ammonia temperature programmed desorption and, ultimately, in terms of catalytic activities. The powder X-ray diffraction patterns of the impregnated titania-rich Zr/Ti oxide catalysts showed that ZrO2 dissolved in the solid anatase phase of titania. At higher concentrations, the ZrO2 appeared as a separate tetragonal phase. Low zirconia content Zr/Ti oxide catalysts showed significantly increased surface areas and higher acidities than the individual oxides. A range of other metal oxides were added as third metal oxides in these mixtures, but none had significant impacts on surface areas or on surface acidities. Propane dehydrogenation is thermodynamically limited. The only possible route is a radical mechanism for H2 removal via a surface process. The catalytic activities at low CO2:propane ratio showed that Zr/Ti oxide exhibited the higher activity than single oxides, but activities were all too low to be of economic significance. In contrast, using higher CO2:propane ratio improved the propene yield and selectivity to values comparable to those achieved with the industrial chromium based catalyst. The catalyst showed selectivity to C-H bond breaking to form propene over C-C bond breaking to make ethene. The study demonstrated that CO2 was utilised mainly for the reverse water gas shift reaction (RWGS) to remove hydrogen from the catalyst surface. The study showed that the Zr/Ti oxide catalysts exhibited higher stability compared to the industrial catalysts at slightly higher gas space velocity. Thermogravimetric analysis showed that Zr/Ti oxide catalyst assists coke gasification in the presence of CO2 at 600 oC. The other mixed oxide catalysts generally showed lower surface acidities and higher selectivities to C-C bond breaking products over the desired propene product. The second study was the direct reaction of CO2 with CH4 to produce acetic acid. Again, this reaction is thermodynamically unfavourable and the only possible route must involve a radical species by which reactants are concentrated on the catalyst surface. Evidence of methyl surface species formation in the presence of methane was indeed found over the Zr/Ti oxide catalyst. With CO2 methane reacted with CO2 to form acetic acid over Zr/Ti oxide catalysts. The C-C insertion mechanism is proposed by which methyl surface species formed on the catalyst and reacted with CO2. This was followed by hydrogenation to form acetic acid. Reactions of CO2 with ethane, ethylene, acetylene and propene were also studied, in the hope of observing direct insertion to produce the corresponding carboxylic acid. In fact, lower acids were formed in all cases, suggesting a radical mechanism involving C-C bond breaking over Zr/Ti oxide catalyst. Interestingly, acetic acid was formed with all these precursor hydrocarbons, and it appears that it occurs via C≡C, C=C, C-C and C-H bond breaking

Novel electrosynthetic methods: focus on carbon dioxide utilisation

The release of CO2 into the earth's atmosphere has been increasing exponentially since the dawn of the industrial age. Mainly due to the burning of fossil fuels; needed for power generation this increased amount of CO2 has been a direct cause to the increased greenhouse effect which in turn brings about severe consequences. Various ways of limiting the release CO2 have been developed over the years, with varying degrees of efficiency and success. Carbon Dioxide utilisation (CDU) is a relatively new technique which utilises CO2 rather than storing it. The main challenges associated with this technique stem from a sustainability aspect, therefore research is placed into developing methods which are environmentally friendly as well as energy and cost efficient. Many research groups from around the world have developed various techniques and approaches to incorporate CO2 into a variety of organics ranging from haloalkanes to alkynes. These techniques have ranged from using standard chemical reactions, intricate photocatalysts to using electrochemical processes, all with the main goal of forming a stable C-C bond, however all these methods possess some form of shortcomings. This project addresses the shortcomings in electrochemical methods associated with CO2. The discovery of a novel electrochemical process using non-sacrificial carbon electrodes in the hydrocarboxylation of styrenes was achieved under mild conditions, (10 Volts, 1 atm CO2 pressure, room temperature, non-sacrificial electrodes) was achieved producing the corresponding mono-carboxylic acids in a highly regioselective manner in good to excellent yields (50-85%). The novel method also proved successful in incorporating CO2 in alkynes, dienes, and acrylates as well as the reducing of internal double bonds. Furthermore, mechanistic analysis was undertaken to deduce the mode of action, this included the use of deuterium labelled reagents, cyclopropyl traps as well as common radical traps. This work has shown the potential of non-sacrificial electrochemical cells, by-passing the environmental and efficiency issues attributed with common electrochemical cells. The bonus of high regioselectivity, robustness towards various functional groups and potential to apply to various starting materials further enhances the potential of this method in become a valuable tool in organic synthesis

Selective formation of trimethylene carbonate (TMC): atmospheric pressure carbon dioxide utilization

Carbon dioxide utilisation (CDU) is currently gaining increased interest due to the abundance of CO2 and its possible application as a C1 building block. We herein report the first example of atmospheric pressure carbon dioxide incorporation into oxetane to selectively form trimethylene carbonate (TMC), which is a significant challenge as TMC is thermodynamically less favoured than its corresponding co-polymer

An investigation of reaction parameters for carbon dioxide utilisation

Carbon dioxide emissions per year have risen exponentially. It is widely known the contribution of CO2 to global warming phenomena, so storage/utilisation of carbon dioxide has become a topical issue and an emerging research area. Despite the fact that utilization of CO2 waste would not solve the problem of the huge quantities going to the atmosphere every year as only less than 1% of it could be reused for the industry, recycled carbon dioxide presents itself as a possible cheap and accessible chemical feedstock. The challenge on recycling CO2 is to minimize energy and cost efficiency of any suitable reaction. On previous investigations the electrochemical synthesis of 5-membered cyclic carbonate from epoxides was accomplished under mild conditions and optimized (1 atm CO2 pressure, 60 mA constant current and 50 °C heating). In order to understand the mechanism of this electrochemical process a deep investigation on the variables of the synthesis of cyclic carbonates was carried out and is presented in this thesis. The variables studied include electrochemical system conditions (application of current through Cu/Mg electrodes, electrodes connected on a closed circuit system with no current, an open circuit system where electrodes were there was no connection between them, and reactions without electrodes), temperature of reaction, solvent screening, catalysts, epoxide substituents, concentration of species and ratio of reactants. As a result of the variables optimization, a new, cheap, simple and relatively fast method (5 to 24 hours of reaction time) for cyclic carboxylation of epoxides with CO2 at atmospheric pressure in acetonitrile in the presence of ammonium salt (TBAI) at mild temperatures (50 - 75 °C) has been developed and improved. The concentration of the reactants, especially of the epoxide, was found to be the most important factor on the success of the reaction. The new reaction conditions also allow converting epoxides to carbonates without the help of any cocatalyst or electrochemical system obtaining excellent yields (50-100%) with the important saving on cost and energy of co-catalyst synthesis and recovery. Chlorostyrene oxide (1 M) reacted almost completely (94%) after 24 hours with TBAI (1 M), in 1 mL of acetonitrile at 75 °C and 1 atm pressure of CO2. Epoxide carboxylation under neat conditions was feasible, producing 44% of chlorostyrene carbonate from chlorostyrene oxide in the presence of TBAI at 75 °C and 1 atm pressure of CO2

The twelve principles of CO2 Chemistry

This paper introduces a set of 12 Principles, based on the acronym CO2 CHEMISTRY, which are intended to form a set of criteria for assessing the viability of different processes or reactions for using CO2 as a feedstock for making organic chemicals. The principles aim to highlight the synergy of Carbon Dioxide Utilisation (CDU) with the components of green and sustainable chemistry as well as briefly pointing out the connection to the energy sector

Two Blind Mice: It Is Time for Greater Collaboration between Engineers and Social Scientists around the RDD & D of Industrial Technologies

Within this short communication article, we consider the value that closer and earlier collaboration between engineers and social scientists could offer the research, development, demonstration and deployment (RDD & D) of industrial technologies. We consider perspectives taken from both the social sciences and engineering in order to highlight the prejudices and misunderstandings that currently limit the extent and quality of such collaboration. It is reasoned that the complex engineering challenges of the future demand a move towards greater interdisciplinarity. Current successful approaches towards fostering interdisciplinarity within the Carbon Dioxide Utilisation (CDU) research community are then used to illustrate the benefits of employing a more holistic approach to the design and introduction of new industrial technologies. It is our hope that this article will catalyse similar collaborative research efforts within other sectors

The Social Acceptance of Carbon Dioxide Utilisation: A Review and Research Agenda

CO2 utilisation technologies—also called carbon dioxide utilisation (CDU) and carbon capture and utilisation (CCU)—convert CO2 via physical, chemical, or biological processes into carbon-based products. CO2 utilisation technologies are viewed as a means of helping to address climate change and broadening the raw material base for commodities that can be sold to generate economic revenue. However, while technical research and development into the feasibility of CO2 utilisation options are accelerating rapidly; at present, there has been limited research into the social acceptance of the technology and CO2-derived products. This review article outlines and explores three key dimensions of social acceptance (i.e., socio-political, market, and community acceptance) pertaining to innovation within CO2 utilisation. The article highlights the importance of considering issues of social acceptance as an aspect of the research, development, demonstration, and deployment process for CO2 utilisation and explores how key stakeholders operating on each dimension might affect the innovation pathways, investment, and siting decisions relating to CO2 utilisation facilities and CO2-derived products. Beyond providing a state-of-the-art review of current research into the social acceptance of CO2 utilisation, this article also outlines an agenda for future research in the field

Investigating public perceptions of Carbon Dioxide Utilisation (CDU) technology: a mixed methods study

Carbon Dioxide Utilisation (CDU) technologies hold promise for helping to limit atmospheric releases of CO2 while generating saleable products. However, while there is growing investment in the research and development required to bring CDU to market, to date there has been very little systematic research into public perceptions of the technology. The current research reports upon the findings of a series of six qualitative focus groups (and an associated questionnaire) held with members of the UK public in order to discuss the perceived benefits and risks of CDU technology. The findings reveal that public awareness of CDU is currently very low and that there is a desire to learn more about the technology. While our participants did, on average, appear to develop an overall positive attitude towards CDU, this attitude was both tentative and was associated with a number of caveats. The implications for the findings in terms of the development of communication and broader strategies of public engagements are outlined