Hamid A. Al-Megren

Recyclable, strong thermosets and organogels via paraformaldehyde condensation with diamines

Recyclable Thermoset Polymers The high mechanical strength and durability of thermoset polymers are exploited in applications such as composite materials, where they form the matrix surrounding carbon fibers. The thermally driven polymerization reaction is usually irreversible, so it is difficult to recycle the constituent monomers and to remove and repair portions of a composite part. García et al. (p. 732; see the Perspective by Long) now describe a family of polymers formed by condensation of paraformaldehyde with bisanilines that could form hard thermoset polymers or, when more oxygenated, produce self-healing gels. Strong acid digestion allowed recovery of the bisaniline monomers. A strong polymer formed by heating can be digested with strong acid to recover and recycle its bisaniline monomers. [Also see Perspective by Long] Nitrogen-based thermoset polymers have many industrial applications (for example, in composites), but are difficult to recycle or rework. We report a simple one-pot, low-temperature polycondensation between paraformaldehyde and 4,4ʹ-oxydianiline (ODA) that forms hemiaminal dynamic covalent networks (HDCNs), which can further cyclize at high temperatures, producing poly(hexahydrotriazine)s (PHTs). Both materials are strong thermosetting polymers, and the PHTs exhibited very high Young’s moduli (up to ~14.0 gigapascals and up to 20 gigapascals when reinforced with surface-treated carbon nanotubes), excellent solvent resistance, and resistance to environmental stress cracking. However, both HDCNs and PHTs could be digested at low pH (<2) to recover the bisaniline monomers. By simply using different diamine monomers, the HDCN- and PHT-forming reactions afford extremely versatile materials platforms. For example, when poly(ethylene glycol) (PEG) diamine monomers were used to form HDCNs, elastic organogels formed that exhibited self-healing properties.

Advanced chemical recycling of poly(ethylene terephthalate) through organocatalytic aminolysis

We report the effective organocatalysis of the aminolytic depolymerization of waste poly(ethylene terephthalate) (PET) using 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) producing a broad range of crystalline terephthalamides. This diverse set of monomers possesses great potential as building blocks for high performance materials with desirable thermal and mechanical properties deriving from the terephthalic moiety and amide hydrogen bonding. Further, a computational study established mechanistic insight into self-catalyzed and organocatalyzed aminolysis of terephthalic esters, suggesting that the bifunctionality of TBD particularly concerning activation of the carbonyl group differentiates TBD from other organic bases.

Computational investigations on base-catalyzed diaryl ether formation.

We report investigations with the dispersion-corrected B3LYP density functional method on mechanisms and energetics for reactions of group I metal phenoxides with halobenzenes as models for polyether formation. Calculated barriers for ether formation from para-substituted fluorobenzenes are well correlated with the electron-donating or -withdrawing properties of the substituent at the para position. These trends have also been explained with the distortion/interaction energy theory model which show that the major component of the activation energy is the energy required to distort the arylfluoride reactant into the geometry that it adopts at the transition state. Resonance-stabilized aryl anion intermediates (Meisenheimer complexes) are predicted to be energetically disfavored in reactions involving fluorobenzenes with a single electron-withdrawing group at the para position of the arene, but are formed when the fluorobenzenes are very electron-deficient, or when chelating substituents at the ortho position of the aryl ring are capable of binding with the metal cation, or both. Our results suggest that the presence of the metal cation does not increase the rate of reaction, but plays an important role in these reactions by binding the fluoride or nitrite leaving group and facilitating displacement. We have found that the barrier to reaction decreases as the size of the metal cation increases among a series of group I metal phenoxides due to the fact that the phenoxide becomes less distorted in the transition state as the size of the metal increases.

Textural characterizations and catalytic properties of quasispherical nanosized molybdenum disulfide

Synthesis of sphere nanostructured MoS(2) is reported. Characterization of the synthesized MoS(2) was investigated by X-ray diffraction, nitrogen adsorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that the obtained MoS(2) is composed of layers that bend to form mostly spheres, with an average diameter of approximately 180 nm. The growth in crystallinity is mainly due to the increased number of the round-stacked layers of MoS(2). The catalytic activity and selectivity of the synthesized nanostructured MoS(2) for the dibenzothiophene hydrodesulfurization were investigated. The closed-circle MoS(2) layers exhibited a high selectivity for the direct sulfur removal.

The Catalyst Selectivity Index (CSI): A Framework and Metric to Assess the Impact of Catalyst Efficiency Enhancements upon Energy and CO2 Footprints

Heterogeneous catalysts are not only a venerable part of our chemical and industrial heritage, but they also occupy a pivotal, central role in the advancement of modern chemistry, chemical processes and chemical technologies. The broad field of catalysis has also emerged as a critical, enabling science and technology in the modern development of “Green Chemistry”, with the avowed aim of achieving green and sustainable processes. Thus a widely utilized metric, the environmental E factor—characterizing the waste-to-product ratio for a chemical industrial process—permits one to assess the potential deleterious environmental impact of an entire chemical process in terms of excessive solvent usage. As the many (and entirely reasonable) societal pressures grow, requiring chemists and chemical engineers not only to develop manufacturing processes using new sources of energy, but also to decrease the energy/carbon footprint of existing chemical processes, these issues become ever more pressing. On that road to a green and more sustainable future for chemistry and energy, we note that, as far as we are aware, little effort has been directed towards a direct evaluation of the quantitative impacts that advances or improvements in a catalyst’s performance or efficiency would have on the overall energy or carbon (CO2) footprint balance and corresponding greenhouse gas (GHG) emissions of chemical processes and manufacturing technologies. Therefore, this present research was motivated by the premise that the sustainability impact of advances in catalysis science and technology, especially heterogeneous catalysis—the core of large-scale manufacturing processes—must move from a qualitative to a more quantitative form of assessment. This, then, is the exciting challenge of developing a new paradigm for catalysis science which embodies—in a truly quantitative form—its impact on sustainability in chemical, industrial processes. Towards that goal, we present here the concept, definition, design and development of what we term the Catalyst Sensitivity Index (CSI) to provide a measurable index as to how efficiency or performance enhancements of a heterogeneous catalyst will directly impact upon the fossil energy consumption and GHG emissions balance across several prototypical fuel production and conversion technologies, e.g. hydrocarbon fuels synthesized using algae-to-biodiesel, algae-to-jet biofuel, coal-to-liquid and gas-to-liquid processes, together with fuel upgrading processes using fluidized catalytic cracking of heavy oil, hydrocracking of heavy oil and also the production of hydrogen from steam methane reforming. Traditionally, the performance of a catalyst is defined by a combination of its activity or efficiency (its turnover frequency), its selectivity and stability (its turnover number), all of which are direct manifestations of the intrinsic physicochemical properties of the heterogeneous catalyst itself under specific working conditions. We will, of course, retain these definitions of the catalytic process, but now attempt to place discussions about a catalyst’s performance onto a new foundation by investigating the effect of improvements in the catalyst’s efficiency or performance on the resulting total energy and total CO2 footprint for these prototypical fuel production and fuel conversion processes. The CSI should help the academic and industrial chemical communities, not only to highlight the current ‘best practice catalysts’, but also draw specific conclusions as to what energy and CO2 emissions saving one could anticipate with higher efficiency/higher performance from heterogeneous catalysts in a particular fuel synthesis or conversion process or technology. Our aim is to place discussions about advances in the science and technology of catalysis onto a firm foundation in the context of GHG emissions. We believe that thinking about (and attempting to quantify) total energy and CO2 emissions reductions associated with advances in catalysis science from a complete energy life cycle analysis perspective is extremely important. The CSI will help identify processes where the most critical advances in catalyst efficiency are needed in terms of their potential impact in the transition to a more sustainable future for fuel production and conversion technologies.

Rapid Production of High‐Purity Hydrogen Fuel through Microwave‐Promoted Deep Catalytic Dehydrogenation of Liquid Alkanes with Abundant Metals

Hydrogen as an energy carrier promises a sustainable energy revolution. However, one of the greatest challenges for any future hydrogen economy is the necessity for large scale hydrogen production not involving concurrent CO2 production. The high intrinsic hydrogen content of liquid-range alkane hydrocarbons (including diesel) offers a potential route to CO2 -free hydrogen production through their catalytic deep dehydrogenation. We report here a means of rapidly liberating high-purity hydrogen by microwave-promoted catalytic dehydrogenation of liquid alkanes using Fe and Ni particles supported on silicon carbide. A H2 production selectivity from all evolved gases of some 98 %, is achieved with less than a fraction of a percent of adventitious CO and CO2 . The major co-product is solid, elemental carbon.

Advances in the study of coke formation over zeolite catalysts in the methanol-to-hydrocarbon process

Methanol-to-hydrocarbon (MTH) process over acidic zeolite catalysts has been widely utilised to yield many types of hydrocarbons, some of which are eventually converted into the highly dehydrogenated (graphitized) carbonaceous species (cokes). The coking process can be divided into two parallel pathways based on the accepted hydrocarbon pool theory. From extensive investigations, it is reasonable to conclude that inner zeollite cavity/channel reactions at acidic sites generate cokes. However, coke formation and accumulation over the zeolite external surfaces play a major role in reaction deactivation as they contribute a great portion to the total coke amount. Herein we have reviewed previous literatures and included some recent works from KOPRC in understanding the nature and mechanism of coke formation, particularly during an H-ZSM-5 catalysed MTH reaction. We specially conclude that rapid aromatics formation at the zeolite crystalite edges is the main reason for later stage coke accumulation on the zeolite external surfaces. Accordingly, the catalyst deactivation is in a great certain to arise at those edge areas due to having the earliest contact with the incoming methanol reactant. The final coke structure is therefore built up with layers of poly-aromatics, as the potential sp2 carbons leading to pre-graphite structure. We have proposed a coke formation model particularly for the acidic catalyst, which we believe will be of assistance in understanding—and hence minimising—the coke formation mechanisms.

Wax: A benign hydrogen-storage material that rapidly releases H2-rich gases through microwave-assisted catalytic decomposition

Hydrogen is often described as the fuel of the future, especially for application in hydrogen powered fuel-cell vehicles (HFCV’s). However, its widespread implementation in this role has been thwarted by the lack of a lightweight, safe, on-board hydrogen storage material. Here we show that benign, readily-available hydrocarbon wax is capable of rapidly releasing large amounts of hydrogen through microwave-assisted catalytic decomposition. This discovery offers a new material and system for safe and efficient hydrogen storage and could facilitate its application in a HFCV. Importantly, hydrogen storage materials made of wax can be manufactured through completely sustainable processes utilizing biomass or other renewable feedstocks.

Chapter 10 – The Indirect and Direct Conversion of CO2 into Higher Carbon Fuels

This review examines the concept of transforming CO 2 ultimately into high hydrocarbon fuels as a means of closing the carbon cycle. It is noted that this in effect is two challenges and must address not only the environmental impact, but also the need for clean renewable energy. It describes the two potential routes; Indirect routes which covers the generation of syngas via the Dry Methane Reforming process and the subsequent conversion of syngas into hydrocarbons via the Fischer-Tropsch process. Examination of the concept of methanol to hydrocarbons is also dealt with; while this is a more convoluted process compared to Fischer-Tropsch it allows production of gasoline range hydrocarbons with octane number enhancement properties. Direct routes are also described briefly and examine the concept of the chemical transformation of CO 2 into fuels, in this section the limitations of such a process of demonstrated, with specific emphasis on the reduction of catalyst choice, due to reduced activity towards CO 2 compared to CO. As such to overcome these limitations specific additives may be employed. The chapter concludes with a critical examination of the future perspectives for such processes and with specific emphasis upon potential areas of research to improve the viability of widespread application. In particular it is commented that perhaps the biggest and most difficult challenge for closing the carbon cycle arises from the need for a clean, cheap and most importantly renewable source of H 2 .

The Herman F. Mark Polymer Chemistry Award

Professor Ken Wagener at the University of Florida is the most recent recipient of the highest award provided by the Polymer Division of the American Chemical Society. This honor is called the Herman F. Mark Polymer Chemistry Award to recognize outstanding research accomplishments and contributions to the advancement of polymer science through teaching, research, technical leadership and scientific writings. A symposium was held in September 2013 in Indianapolis, Indiana, USA to celebrate this award; the first five papers in this issue of the Applied Petrochemical Research Journal represent part of the science that was presented at that time. The 2013 winner, Prof. Ken Wagener, joins a distinguished list of former recipients like Paul J. Flory, Carl S. Marvel, Maurice L. Huggins, Herman F. Mark, John D. Ferry, Charles G. Overberger, Walter H. Stockmayer, Michael Szwarc, Ed J. Vandenberg, Harry R. Allcock, James E. McGrath, James Economy, Murray Goodman, Robert Grubbs, Henry K. Hall, Jr, Robert W. Lenz, Leo Mandelkern, Otto Vogl, William J. MacKnight, Donald R. Paul, Robert Langer, Jean Frechet, and Kris Matyjaszewski. Herman Mark was a pioneer in the field of polymer science. Born in 1895, he chose the path of science for his life work, first establishing a strong reputation in X-ray diffraction of macromolecules. He worked in industry (IG Farben) for some time where he also proved to be an excellent synthetic polymer chemist. He then moved to the University of Vienna as a Professor of Physical Chemistry, followed by migration to Canada, which eventually led him to the Polytechnic Institute of Brooklyn in New York. His work there was the first in polymer education in the USA, and it was at this location where he spent the majority of his academic career. Brooklyn Poly, as it was known then, was the leader in polymer education in the United States, truly pioneering the educational component of polymer science for decades. Herman Mark firmly established his place in history as being among the first generation of polymer chemists. The award was established in 1976. In 1989, the award was named the Herman F. Mark Polymer Chemistry Award. The award in his name is conferred every other year by the Polymer Division of the American Chemical Society.