Scalable processing concepts for microwave pyrolysis

Microwave pyrolysis of biomass has long been recognised to provide potential opportunities for producing a range of bio-based products. Unlike conventional heating, microwave heating occurs through the interaction of biomass with electromagnetic energy, with the biomass heated volumetrically by energy conversion instead of conventional heat transfer mechanisms. With microwave heating pyrolysis can be achieved within a cold surrounding environment, a feat that is not possible with conventional heating processes. This unique phenomenon presents a number of opportunities for processing of biomass feedstocks, which include enhanced product quality and a significantly simplified process flowsheet, both of which improve the economic viability of industrial biomass processing. Examples of the benefits of microwave heating include the elimination of size-reduction and particulate removal steps, and simplification of inert-gas preparation and recycling systems. These are discussed within the paper, along with the enhanced product quality that can be produced as a result. Please click Additional Files below to see the full abstract

Energy consumption estimation in the scaling-up of microwave heating processes

The specific energy consumption of six different microwave-driven processes and equipments has been studied and it was found that the scale used dramatically affects it. Increasing the amount of sample employed from 5 to 100 g leads to a reduction in the specific energy consumption of 90–95%. When the amount of sample is 200 g or higher, the specific energy consumption remains practically constant. This means that to assess the real energy efficiency of a microwave-driven process a minimum mass of about 200 g needs to be used. The energy results can then be easily extrapolated to larger scales. Otherwise, a correlation should be used to avoid overestimated energy values and inaccurate energy efficiencies.The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 311815 (SYNPOL project). D.B. and N.R.R. are also grateful to FICYT of the Government of Principado de Asturias (Spain) and the Ministry of Economy and Competitiveness of Spain (under Project MAT2011-23733), respectively, for their predoctoral research grants. The help of Xerolutions S.L. in providing experimental data is also acknowledged.Peer reviewe

Syngas obtained by microwave pyrolysis of household wastes as feedstock for polyhydroxyalkanoate production in Rhodospirillum rubrum

The massive production of urban and agricultural wastes has promoted a clear need for alternative processes of disposal and waste management. The potential use of municipal solid wastes (MSW) as feedstock for the production of polyhydroxyalkanoates (PHA) by a process known as syngas fermentation is considered herein as an attractive bio-economic strategy to reduce these wastes. In this work, we have evaluated the potential of Rhodospirillum rubrum as microbial cell factory for the synthesis of PHA from syngas produced by microwave pyrolysis of the MSW organic fraction from a European city (Seville). Growth rate, uptake rate, biomass yield and PHA production from syngas in R. rubrum have been analysed. The results revealed the strong robustness of this syngas fermentation where the purity of the syngas is not a critical constraint for PHA production. Microwave-induced pyrolysis is a tangible alternative to standard pyrolysis, because it can reduce cost in terms of energy and time as well as increase syngas production, providing a satisfactory PHA yield.Research leading to these results has received funding from the European Union's Seventh Framework Programme for Research, Technological Development and Demonstration under grant agreement no. 311815 (SYNPOL), and from the Comunidad de Madrid (P2013/MIT2807). D. B. also acknowledges the financial support received from PCTI and FICYT of the Government of the Principado de Asturias.Peer reviewe

Microwave-induced pyrolysis of organic wastes for syngas-derived bioplastics production

Tesis Doctoral presentada por el Ingeniero Químico Daniel Beneroso Vallejo para optar al grado de Doctor por la Universidad de Oviedo, febrero 2016.[EN] Up to 3000 million tons of waste are generated in the European Union every year. Of these, organic solid wastes have the potential to partially satisfy the production of chemicals, whilst the environmental impact can be minimized and the sustainability of the processes increased compared to the production processes based on fossil resources. However, these wastes are complex due to their high heterogeneity and new conversion processes are necessary before they can be converted into high value products; e.g., biodegradable plastics. One possibility is to combine the gasification of wastes to produce simple molecules (mainly H2 and CO, known as syngas), which could then be easily metabolized by bacteria to produce bioplastics. The work conducted for this Thesis has been focused on optimizing the production process of synthesis gas (syngas) from different organic residues by means of a novel technology, microwave-induced pyrolysis as an alternative to the conventional gasification process. The objective is to produce syngas for use as a substrate in a biocatalytic process (fermentation) for the synthesis of bioplastics; mainly, the biopolymer ‘PHB’. This dissertation is divided into the three sections outlined below. The first section comprises the experimental tests performed to evaluate the suitability of various solid organic wastes for producing syngas by means of microwave-induced pyrolysis. These wastes include municipal solid waste (both the organic fraction as well as the plastic fraction), agricultural waste, sewage sludge and algae. First, a comparison with the production of syngas from conventional pyrolysis at different temperatures was carried out. In addition, the most appropriate alternative for valorizing the solid fraction resulting from pyrolysis and its composition as well as the characteristics of the oil fraction were studied. The second section of this Thesis is focused on the influence of key parameters on microwave-induced pyrolysis, such as the concentration of microwave absorbent materials, the moisture content of the residues, the carrier gas used and the dielectric properties of the wastes. Finally, the third section deals with the application of the syngas prepared from wastes to the growth of the bacterium Rhodospirillum rubrum and PHB production. Microwave-induced pyrolysis has been demonstrated to be a highly versatile process as the operating conditions can be easily tailored to produce the most appropriate syngas depending on the requirements of different syngas-fermenting bacteria.[ES] En la Unión Europea se generan anualmente hasta 3000 millones de toneladas de residuos. Entre ellos, los residuos sólidos de origen orgánico tienen un gran potencial para satisfacer parcialmente la producción de productos químicos, reduciéndose el impacto medioambiental e incrementándose la sostenibilidad de los procesos respecto a los basados en recursos fósiles. Sin embargo, este tipo de residuos son complejos debido a su alta heterogeneidad, por lo que se requieren nuevos procesos de conversión que permitan reducir su complejidad en compuestos sencillos antes de convertirlos en productos de alto valor como, por ejemplo, plásticos biodegradables. Una de las posibilidades consiste en combinar la gasificación de los residuos para producir moléculas sencillas (principalmente H2 y CO, más conocido como syngas) con la fermentación de dicho gas para producir bioplásticos. El trabajo realizado durante esta Tesis se ha centrado en la optimización del proceso de producción de gas de síntesis (syngas), a partir de diferentes residuos orgánicos, mediante una novedosa tecnología de pirólisis inducida por microondas como alternativa a un proceso convencional de gasificación. La finalidad del syngas producido es ser utilizado como sustrato en un proceso de biocatálisis (fermentación) para la síntesis de bioplásticos; en particular, del biopolímero PHB. Esta memoria se ha estructurado en las tres secciones que se indican a continuación. La primera sección de esta memoria comprende el trabajo experimental consistente en la evaluación de la idoneidad de diferentes residuos sólidos orgánicos para producir syngas mediante la tecnología de pirólisis inducida por microondas. Para ello, se han utilizado residuos sólidos urbanos (tanto la fracción orgánica como la fracción de plásticos), residuos agrícolas, lodo de depuradora y microalgas, habiéndose llevado a cabo una comparativa con la tecnología de pirólisis convencional a diferentes temperaturas. Además, se han estudiado las características de la fracción de aceites obtenida así como las alternativas más apropiadas para la gestión de la fracción sólida resultante del proceso de pirólisis y su composición. La segunda sección de esta Tesis está centrada en la influencia que diferentes parámetros, como son la concentración de material captador de microondas, la humedad de los residuos, el gas portador o las propiedades dieléctricas de los residuos, tienen en la pirólisis inducida por microondas. Por último, la tercera sección aborda el estudio de aplicación de syngas preparado a partir de residuos en el crecimiento de la bacteria Rhodospirillum rubrum y en la producción del biopolímero PHB. La versatilidad del proceso de pirólisis inducida por microondas es especialmente atractiva, ya que se pueden ajustar las condiciones para producir el syngas más apropiado en función de los requerimientos de las bacterias que llevan a cabo el proceso de fermentación.Peer reviewe

Bioplastics via microwave pyrolysis of wastes

Peer reviewe

Comparing the composition of the synthesis-gas obtained from the pyrolysis of different organic residues for a potential use in the synthesis of bioplastics

In this article we propose the possibility of obtaining syngas from very different and complex organic wastes, such as municipal solid wastes, agricultural residues or sewage sludge, through microwave-induced and conventional pyrolysis at 400 and 800 °C. Microwave heating has proved to be an appropriate way to produce a syngas with CO + H2 concentrations as high as 90 vol% and in large yields (up to 0.83 L g−1waste). In addition, the potential of the syngas produced by this technology as fermentation substrate for the production of bioplastics is discussed. Microwave pyrolysis seems to serve as a novel route into biorefineries to produce valuable biobased products.The research leading to these results has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 311815 (SYNPOL project). D. B. also acknowledges the support received from PCTI and FICYT of the Government of the Principado de Asturias.Peer reviewe

Integrated microwave drying, pyrolysis and gasification for valorisation of organic wastes to syngas

[EN] The development of integrated platforms is desirable in order to improve the efficiency of biorefineries. This study deals with an innovative all-in-one thermochemical process (drying, pyrolysis and gasification) based on the use of microwave energy, which could eliminate the need to pre-dry municipal solid waste in order to produce a high quantity of synthesis gas. Depending on the initial moisture content and pyrolysis time, it is possible to obtain different syngas compositions but only during the first 20 min. Beyond this time the syngas composition remains almost constant. In addition, the moisture content was found to improve the volumetric gas production by almost 50%. The energy consumption of this all-in-one process is discussed by comparing it with the scarce information available in the literature concerning the scaling-up of microwave-assisted processes, which may be more cost-effective at a higher scale.The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 311815 (SYNPOL project). D. Beneroso also acknowledges the financial support received from the PCTI and FICYT of the Government of the Principado de Asturias (Spain).Peer reviewe

Influence of the microwave absorbent and moisture content on the microwave pyrolysis of an organic municipal solid waste

[EN] Microwave pyrolysis is presented in this study as a recycling approach for municipal solid waste treatment. The process is based on the conversion of solid waste to syngas (CO + H2) by means of a microwave absorbent. Experiments to characterise the syngas produced were performed using the char obtained from the pyrolysis of a municipal solid waste as microwave absorbent in the microwave power range of 150–450 W and in an absorbent-to-waste ratio range of 0.2:1 to 1:1 (wt.%:wt.%). A rich-syngas fraction with a high H2 content (c.a. 50–55 vol.%) was obtained and analysed by means of response surface methodology through the interaction between the microwave power and absorbent-to-waste ratio. Moreover, a positive effect of the moisture content on gas production is attained since gasification of the char occurs. Thus, the simple use of a cheap waste-derived char leads to a reduction in the microwave power and economic cost of the process.The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 311815 (SYNPOL project).Peer reviewe

Influence of carrier gas on microwave-induced pyrolysis

Interest in microwave-induced pyrolysis has increased in recent years due to its several advantages over conventional pyrolysis. Most of these advantages are related to the presence of microplasmas in microwave heating, since the pyrolysis reactions that take place in a plasma atmosphere generally produce light molecules, such as H2 and CO. Although the exact nature of these plasmas is as yet unknown, it is likely to be dependent on the ionization of the surrounding gases. For this reason, the influence of different carrier gases (N2, He or no carrier gas) on microwave-induced pyrolysis was chosen as the subject of this study. It was found that microwave-induced pyrolysis can be used to obtain equally good gas compositions and yields after the reactor has been inertized, without the need for a carrier gas.The research leading to these results has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no. 311815 (SYNPOL project). D.B. also acknowledges the support received from PCTI and FICYT of the Government of the Principado de Asturias.Peer Reviewe

Conceptualising engineering student perceptions of synchronous and asynchronous online learning

Students’ perceptions towards synchronous and asynchronous online delivery modes of three engineering courses, in a large UK university is conceptualised, inspired by the Community of Inquiry theoretical framework. Using a qualitative methodology, 76 written student narratives were analysed. An overwhelming focus on the elements that helped them to process the information being taught and to synthesise their understanding (cognitive presence) was found, regardless of thedelivery mode. Furthermore, despite the perceived benefits in terms of time management, narratives of asynchronous learning lacked connectivity between such cognitive elements and those allowing them to interact, share, and communicate their understanding with their peers and teachers (social presence). Student reflections on which delivery mode best supported their learning were conflicting at times, but a balance between cognitive and social presence is recommendedto integrate the opportunities that stem from both