Enzymatic Activation Of Alkanes Constraints And Prospects High School
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Stephanopoulos outlined the currently envisioned routes for biological methane activation and conversion to chemical products and biofuels. An overall pathway of methane activation to an active intermediate CH 3X and a possible assimilation route leading to the synthesis of some product like 3-hydroxybutyrate or butanol was shown. Assimilation can proceed via methanol, which is dehydrogenated to formaldehyde, and processing the latter to an intermediate metabolite of the pentose phosphate pathway. Methane activation is presently possible via anaerobic methanotrophic consortia and aerobic methanotrophs that utilize the activity of a methane monooxygenase enzyme. A challenge with the biological production of certain chemicals like methanol or butanol is the low titers in which the products are made, leading to high energy requirements for recycling huge amounts of water. However, other products like lactic acid, succinic acid, polyhydroxybutyrate (PHB), and lipids may be produced at high concentrations without issues of toxicity to the microorganisms.Anaerobic consortia have the potential of methane activation at high efficiency, but they exhibit low rates and operate as a mixed culture whereby methane oxidation is coupled with sulfate reduction catalyzed by sulfur-reducing bacteria.
No single culture of anaerobic methanotrophs has been isolated yet. Aerobic methanotrophs exhibit a higher rate of methane oxidation albeit at lower energetic efficiency.
Various products have been detected to be naturally synthesized in aerobic methanotrophs, such as lipids (potential for biodiesel production) and the polymer PHB, but their concentrations are low (below 1g/L) (;; ). There is potential in engineering natural aerobic methanotrophs to either increase the figures of merit of naturally produced compounds such as the above, or to endow the host organisms with the pathways required for the synthesis of other products of interest. However, the biological toolkit required for the genetic modulation of these organisms remains underdeveloped, said Stephanopoulos.On the other hand, Stephanopoulos noted, model organisms like E. Coli have been engineered for the production of numerous products from carbohydrates and other substrates. These organisms could be further engineered to allow them to utilize methane, which would enable a seamless system whereby methane is activated by these model organisms, converted to an intermediate such as methanol, and the latter converted to the product of choice. Although many of the concepts for such a scheme have been worked out for other systems, formidable challenges remain in achieving the same for the activation and conversion of methane to target products. Stephanopoulos stressed that more research in this area will help develop the basic biological tools and platform strains required to realize this vision.
In addition, he listed two technologies that are nearing industrial use: (A) short contact time catalytic partial oxidation and (B) oxygen transfer membranes as well as two emerging technologies for converting methane into syngas: (C) chemical looping and (D) dry reforming.Each of these technologies has its own unique limitations and challenges, which if addressed satisfactorily would improve the economics of the processes using these technologies. DiscussionFollowing the presentation, this group spent much of its time identifying four key objectives for research aimed at improvement of the available commercial processes, said Maria Flytzani-Stephanopoulos, distinguished professor and the Robert and Marcy Haber Endowed Professor in Energy Sustainability at Tufts University. Are many new tools available that could generate transformational results through studies of catalysts and catalytic processes. These included environmental transmission electron microscopy, atmospheric pressure X-ray photoelectron spectroscopy, and simulated moving bed chromatography, the latter which could be used to develop new separations technologies.
The group discussed the potential of accelerated screening, characterization, and synthesis tools for developing improved catalysts, and of work in the area of intrinsically safe design to improve the safety and reliability of oxidation reactions. Gaffney stated that the national laboratories possess many of these tools and the expertise to use them, and there is a value with making these tools and the associated staff expertise available to the nation. Finally, this group noted that for the development and widespread use of standardized practices with regard to catalyst formation and use, reactor methodologies, and standard operating procedures are not yet the norm in this field.In his introductory presentation to the third working group, Israel Wachs, the G. Whitney Snyder Professor of Chemical Engineering and director of the Operando Molecular Spectroscopy and Catalysis Research Laboratory at Lehigh University, described the mechanistic work that his group has performed to better understand the factors influencing the catalytic activity of a promising ZSM-5–supported molybdenum catalyst that achieves the dehydro-aromatization of methane to liquid aromatics, primarily benzene, and hydrogen (, ). This catalyst, he said, first converts methane into ethylene and further reactions at the catalyst produce a mixture of chemicals, of which 70 to 80 percent are aromatics. The catalyst is eventually deactivated by coke formation, though it can be completely regenerated by oxidation treatment in a second reactor. DiscussionFollowing this presentation, the group’s discussion, as reported by Monty Alger, director of the Pennsylvania State University’s Institute for Natural Gas Research and professor of chemical engineering at Pennsylvania State University, started by identifying two reasons for why it would be desirable to develop industrial processes for converting methane to aromatics: the substantial price spread between methane and naphtha and the increasing demand for aromatics that is starting to outstrip capacity.
Because of the low cost of ethane in the United States, more ethane than naphtha is being used to produce ethylene, which produces fewer aromatics as byproducts. The group then discussed the barriers. To commercialization of the process Wachs described, starting with the energy input required to drive this endothermic reaction and the lack of reactors designed to deliver and manage the high temperature at which this reaction occurs. managing heat and mass transfer;. catalytic selectivity;.
product separation and purification;. catalyst cost and supply security; and.
catalyst lifetime and regeneration.Marks said that there have been many attempts using a variety of conditions and heterogeneous catalysts to achieve the direct conversion of methane to methanol (;;;;; ), but any selectivity in the process was achieved at the expense of conversion and typical yields are 1 to 3 percent. Researchers at the Gas Technology Institute are reported to be developing a room-temperature, high-efficiency process to convert methane into methanol and hydrogen using metal oxide catalysts that are continuously regenerated. Catalysis at the University of Washington, reported, the discussion raised the point that future environmental policies could serve as a driver for the development and commercialization of smaller plants for processing stranded and flared gas using some of the technologies Marks outlined in his presentation.
Current methods of managing the oxidants required for direct conversion could be improved, the group noted, and it would help to some way reduce the cost of separating oxygen from air or to develop an air-recyclable oxidant such as the process used in one variant of the Wacker reaction that recycles copper (I) to copper (II). Improved methods for separating methanol from the water used in some schemes will be helpful, too, and despite advances in mechanistic understanding, there is still room for a better fundamental understanding of the catalytic activation of the carbon–hydrogen bond. The group also noted that electrocatalytic methane activation is a new approach that highlights ways to think about entirely new concepts for catalyzing conversion of methane to methanol, and, in this arena, opportunities exist for more efficient energy production using direct methane fuel cells, but new catalytic materials are seriously lacking.The working group then discussed some of the challenges to making current approaches viable, starting with reducing the temperature of some of the reactions and improve their selectivity.
For homogeneous systems, separations can be an issue. Two overarching challenges facing catalytic conversion of methane using either heterogeneous or homogeneous catalysts include avoiding coking, in which carbonaceous deposits form on heterogeneous catalysts and thereby limit catalytic activity, and developing new ligands for homogeneous catalysts that are stable under reaction conditions. Homogeneous organometallic catalysts that have enjoyed success in major catalytic processes such as hydrogenation, metathesis, and hydroformylation typically employ ligands such as phosphines that are unstable under the conditions required for methane oxidation, which generally involve strong oxidants, strongly acidic media, and water.Other promising but higher-risk approaches being taken included the development of movable, small-scale plants for use with stranded and flared methane, and the development of oxidants that do not need separating from the product mix. The discussion raised the question of whether it would be a better idea to convert methane to dimethyl ether, whether it would be possible to develop an oxidant that did not need separation, and if routes to methanol through syngas in an integrated process could prove viable.
Another promising avenue the group noted was to get experts in heterogeneous, homogenous, biocatalytic, and electrocatalytic processes and catalyst supports together in a forum such as this workshop to generate new ideas. Goldberg said there is currently not financial support available to convene such a forum. Ronmental issues and lifecycle analysis in decision making. He also said the same question could be asked for ethane-to-ethylene processes and noted that every time he hears that a particular area is mature, some development comes along that proves that idea wrong.
In his opinion, research with the biggest potential for producing a breakthrough involves taking an entirely different approach to catalysis, such as the idea of combining different types of catalytic processes. Wachs added that the pulp and paper industry, the largest user of methanol as the feedstock for producing formaldehyde, strongly desires a one-step process for methane to formaldehyde or methane to methanol. Mark Barteau from the University of Michigan stressed the importance of considering the carbon budget of a process as well as the economic budget. “I think it would be a great tragedy if we had a scientific breakthrough that lowered the capital cost of a process and also lowered the carbon efficiency,” he said.Maughon commented that if the question is about prioritizing where to spend research dollars, the answer from Dow’s perspective would be that methane-to-methanol conversion would not be a high priority, and he would guess that ExxonMobil would say the same thing. Stangland responded by saying that while it may not be Dow’s priority, methane-to-methanol conversion might be a priority for the nation as it considers how best to use the nation’s natural resources, though he agreed that methane-to-methanol conversion likely would not be a top priority given the potential for some of the other areas the working groups discussed to produce game-changing catalytic solutions for using methane to produce value-added chemicals.
Santiesteban added that research prioritization should also consider what might be beneficial in the long term. “The chemical industry goes through cycles, and so we need to be ready for different situations,” said Santiesteban. “The technology we have now was not developed in 1 day.
It was developed by people who had a vision and it is our responsibility to create a vision for tomorrow.”In that vein, Alexis Bell from the University of California, Berkeley, commented that industry may take a short-term view, but it depends on researchers at the national laboratories and universities to take a longer-term view and develop the science and basic engineering that would later enable industry to implement a technology if it made sense at that time. By the same token, added Goldberg, the basic science behind methane-to-methanol conversion is providing knowledge about how to selectively activate and functionalize the carbon-hydrogen bond and how to use oxygen effectively as an oxidant in a potential industrial process.
Enzymatic Activation Of Alkanes Constraints And Prospects High School Photos Of Diplomas Templates
Ultimately, that knowledge may not lead to a future process for making methanol, but it could lead to processes for using methane as a feedstock to make other valuable chemicals. Alger, agreeing with Goldberg, said that history has shown that most of the great inventions resulted from research not.
Directly related to that invention. What is important, he said, is the cross-fertilization among fields that results in knowledge generated in one field being applied to problems in another technology area where the market is demanding a solution.Shannon Stahl from the University of Wisconsin–Madison also commented on the importance of cross-fertilization and stressed the importance of including researchers from industry in any cross-disciplinary discussions and programs.
He also suggested that the federal funding agencies consider funding a new type of program that would bring together small teams of researchers, including those from industry, to work on a focused problem as a complement to large center programs and individual investigator grants. In his opinion, this type of mid-sized team approach would provide a good return on investment and afford the opportunity to respond quickly to a research need. Alger seconded this idea and noted how little time professors have today to engage in the type of cross-disciplinary conversations this field is lacking.