J. Angel Menéndez

Microwave Heating Applied to Pyrolysis

The use of microwaves for heating is well established in society, being used in domestic and some industrial processes. However, there is potential for this technology to be introduced and applied to many other industrial heating processes, which offers unique advantages not attained with conventional heating. In this sense, microwave technology is being explored as one method to assist in waste management. Currently, significant quantities of hazardous wastes are generated from a multitude of products and processes. The increase in both the quantity and of the diversity of waste production is now posing significant problems for their effective management. New technologies are being investigated to develop systems which shall support the safe handling, transportation, storage, disposal and destruction of the hazardous constituents of this waste. The recent interest in microwave technologies appears to offer the best solution to waste management, whereby a variety of microwave systems can be designed, developed and tailored to process many waste products. It is possible that microwave technologies shall provide for: (i) a reduction in waste volume, (ii) rapid heating, (iii) selective heating, (iv) enhanced chemical reactivity, (v) the ability to treat waste in-situ, (vi) rapid and flexible processes that can also be controlled remotely, (vii) ease of control, (viii) energy savings, (ix) overall cost effectiveness, (x) portability of equipment and processes, (xi) cleaner energy source compared to some more conventional systems, etc. From existing processes for the harnessing of energy and raw materials from waste, thermochemical conversion routes are suitable candidates for the application of microwave technology. One of the thermochemical processes which is rapidly gaining in importance in this field is pyrolysis. This process not only allows for higher energy recovery from the waste, but it also generates a wide spectrum of products. Hitherto, most published work on the pyrolysis process has dealt with conventional heating systems, although recent interest in microwave-assisted pyrolysis (MP) has highlighted its unique advantages, not within the scope of traditional methods. The aim of this chapter is to emphasize the principles of MP and to show recent research on the application of this technology to waste treatment. As an introduction to the topic, a brief background on the pyrolysis process and the fundamentals of microwave irradiation as an energy source are presented.

Carbon Materials as Catalysts for Decomposition and CO2 Reforming of Methane: A Review

Abstract The decomposition and CO2 reforming of methane, respectively, are promising alternatives to industrial steam methane reforming. In recent years, research has been focused on the development of catalysts that can operate without getting deactivated by carbon deposition, where, in particular, carbon catalysts have shown positive results. In this work, the role of carbon materials in heterogeneous catalysis is assessed and publications on methane decomposition and CO2 reforming of methane over carbon materials are reviewed. The influence of textural properties (BET surface area and micropore volume, etc.) and oxygen surface groups on the catalytic activity of carbon materials are discussed. In addition, this review examines how activated carbon and carbon black catalysts, which are the most commonly used carbon catalysts, are deactivated. Characteristics of the carbon deposits from methane are discussed and the influence of the reactivity to CO2 of fresh carbon and carbonaceous deposits for high and steady conversion during CO2 reforming of CH4 are also considered.

Microcalorimetric study of acid sites on ammonia- and acid-pretreated activated carbon

Abstract This study was designed to determine the value of microcalorimetry as a probe of acid/base sites on carbon surfaces. Calorimetric studies of ammonia adsorption on acid and ammonia pretreated activated carbon (BDH) samples demonstrated that the technique does titrate acid sites (at equilibrium) according to their relative strengths. However, only in conjunction with other techniques, including Boehm titration, point of zero charge (PZC) and temperature programmed desorption (TPD) is it possible to determine the probable identity of the acid sites present on a given carbon. Collective consideration of the data from all techniques suggests that ammonia pretreatments create a surface whose chemistry is completely different from that of the original carbon. Not only are new acidic sites created, but a high concentration of basic sites are introduced as well. Thus, the final surface is clearly amphoteric, to an extent which is largely dictated by the pretreatment temperature.

Continuous flow nanocatalysis: reaction pathways in the conversion of levulinic acid to valuable chemicals

The selective production of 2-methyltetrahydrofuran from levulinic acid has been effectively conducted using designed Cu based catalysts and compared with a commercial Pd/C system under microwave irradiation. Optimised conditions for the most active catalysts Cu-MINT (>90% conversion, 75% selectivity to MTHF) and Pd/C (78% conversion, 92% selectivity to MTHF) were further translated into a continuous flow process using the proposed catalysts to find out the deactivation of Cu-MINT under flow conditions (79 vs. 13% conversion with a switch in selectivity to products after 30 min in flow), the high stability of Pd/C (73 vs. 70% conversion at stable selectivity under analogous conditions to those of Cu-MINT) but, most importantly, different relevant pathways to valuable products from levulinic acid depending on the type of catalyst employed.

On the use of calorimetric techniques for the characterization of carbons: A brief review

In this paper, the use of calorimetric techniques to characterize different carbon materials is reviewed. The focus of the review is on the use of calorimetric techniques to assess chemical properties of carbons (e.g. nature of surface groups, hydrophobic/hydrophilic character, acidic/basic behavior, etc.), and a small section is dedicated to the application of calorimetry in determining the physical properties of carbons (e.g. surface areas, pore size distribution, etc.). The following techniques are described: immersion and flow-adsorption calorimetry and gas-adsorption microcalorimetry. Several representative examples of the use of calorimetry techniques to evaluate both physical and chemical properties are presented. It is demonstrated that calorimetry has provided unique insights into the structure and chemistry of active sites on the surface of various carbons.

Pyrone‐Like Structures as Novel Oxygen‐Based Organic Superbases

these pyrone-like compounds are combina-tions of non-neighbouring carbonyl and ether oxygen atoms atthe edges of a graphene layer. Thus, this generic designationwould include not only g-pyrone derivatives but also struc-tures where the two oxygen atoms are located in differentrings. Although there are no reported data, within ourknowledge, for these latter pyrone-like systems, we haverecently demonstrated using ab initio calculations that theyshow a broad spectrum of base strength (around 12 pK

Chapter 6 – The Basicity of Carbons

This chapter covers most of the aspects related to the capacity of some carbon materials to act as proton sinks. The first section is devoted to some fundamental definitions, historical background, relevance, and, particularly, the assessment of the basicity of carbons. The concept of basic site on the surface of carbons is also introduced. Four types of basic sites, namely oxygen surface functional groups, heteroatom (other than oxygen) surface functional groups, basal planes and edges, and inorganic (or mineral) matter, are proposed as the main contributors to the basicity of carbon materials. The main core of the chapter describes these four families in terms of occurrence, relative basic strength, and accessibility. Special attention is paid to some of the controversies that still remain when ascribing the basicity of carbon materials to one particular site over the rest. Finally, some open questions are drawn to stress the need for further fundamental research in the field of carbon basicity.

Microwave-induced low temperature pyrolysis of macroalgae for unprecedented hydrogen-enriched syngas production

An efficient methodology based on low temperature microwave-induced pyrolysis has been developed for syngas production from macroalgae. The protocol provided unprecedented hydrogen production, with switchable H2/CO ratios depending on pyrolysis conditions which were found to remarkably improve conventional pyrolysis experiments even at significantly higher temperatures (400 vs. 800 °C). Arcing effects under microwave irradiation, which result in an interesting observed pseudo-catalytic effect promoted by the metal oxides contained in macroalgae, seem to account for the improved results.

Mixtures of Steel-Making Slag and Carbons as Catalyst for Microwave-Assisted Dry Reforming of CH4

The use of steel-making slag as catalysts for microwave-assisted dry reforming of CH4 was studied. Two carbon materials (an activated carbon and a metallurgical coke), mixtures of the carbon materials and Fe-rich slag, and mixtures of the carbon materials and Ni/Al2O3 were tested as catalysts. The mixtures of slag with carbons gave rise to higher and steadier conversions than those achieved over the carbon materials alone. In addition, the use of the metallurgical coke mixed with metal-rich catalysts gave rise to remarkable results. Thus, no CH4 and CO2 conversions were achieved when coke was used alone, whereas high conversions were obtained when it was mixed with the metal-rich catalysts.

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.