The Catalyst Selectivity Index CSI A Framework

Authors: Tiancun Xiao Tara Shirvani Oliver Inderwildi Sergio GonzalezCortes Hamid AlMegren David King Peter P Edwards

Publish Date: 2015/07/02

Volume: 58, Issue: 10-11, Pages: 682-695

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Abstract

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 wastetoproduct 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 largescale 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 eg hydrocarbon fuels synthesized using algaetobiodiesel algaetojet biofuel coaltoliquid and gastoliquid 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 technologiesCatalyst science and technology remains pivotal to the overwhelming majority of chemical manufacturing processes 1 2 3 As just one example catalyst technologies impact upon almost every aspect of the chemical and petroleum refining and petrochemical industries for fuel generation and conversion for these industries the economic impact of catalysis is currently estimated to be over 10 trillion dollars per year 4 5 6 Moreover catalyst technologies are increasingly integrated into many of the leading pollution control and environmental cleanup processes including the reduction of harmful automobile emissions by catalytic converters and nitrogen oxide emissions from combustion and Volatile OC controls 7 8 Importantly therefore catalysis takes on the role of assisting humankind in environmental sustainable development 9 10Because of this continued substantial impact throughout the global economy and critical issues of environmental sustainability catalysis remains at the forefront of modern multidisciplinary research and development in chemistry 10 11 12 13 14 15 16 New and improved catalytic materials and processes are continually being developed to achieve more rapid catalytic reaction rates increased Turnover Frequencies using milder less energyintensive reaction conditions and enhanced selectivity to produce the desired targeted reaction products with minimal product waste With the advent of Green Chemistry and green sustainable processes in the chemical and energy industries catalysis has been listed as one of the main guiding principles for future chemistry directions 13 14 15 16 To begin to quantify the environmental impact of any chemical process Green Chemistry metrics have been advanced to assess the environmental impact of the manufacture of chemicals in terms of solvent waste and chemical efficiency protocols 7 13 17In the 1990’s the important concept of the Environmental E Factor was advanced and developed by Sheldon to assess the environmental impact and indeed acceptability of chemical manufacturing processes The E Factor is defined as the mass ratio of wastetodesiredproducts specifically it represents the sum of all raw materials input kg minus the desired product then divided by the amount of the final product kg 14 17 18 19 20 21 22 23 24A high E Factor reflects a chemical production or manufacturing process characterized by large amounts of waste and with that a larger more damaging environmental impact obviously an ideal E Factor would be close to zero The evolution of Green Chemistry into industrialscale processes particularly in the pharmaceutical industry is therefore strongly based on the E Factor concept It attempts to target any new process or modifications to an existing process which reduces waste together with the potential utilization of hazardous and toxic solvents or reagents although in the majority of cases catalysts are required to attain the ultimate goal of Green ChemistryCatalysis is also a leading technology to achieve the objective of energy efficiency and the reduction of Green House Gas GHG emissions This is especially true in the application of heterogeneous catalysts as they are a separable and therefore a potentially recyclable entity In light of the necessary—and urgent—development and fostering of Green Chemistry practices in any transition to a sustainable energy future we first pose—and then attempt to answer—the question “What quantitative impacts would advances in catalysis in a particular process—notably advances in a catalyst efficiency taken as a key indicator of catalyst performance—have on the complete “WelltoTank” total energy balance and resulting GHG emissions of important chemical fuel synthesis and fuel conversion pathways”

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