DOCSLIB.ORG

Study of Chemical Process Structures for Process Synthesis

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Study of Chemical Process Structures for Process Synthesis STUDY OF CHEMICAL PROCESS STRUCTURES FOR PROCESS SYNTHESIS Hiroshi OAKI and Masaru ISHIDA Research Laboratory of Resources Utilization, Tokyo Institute of Technology, Yokohama227 Whenthermodynamic characteristics of processes are represented by a vector on the (JH, TqJS) diagram, the processes may be classified into six types: heating, separation, refrigeration, heat source, mixing, and refrigerant. Based on this classification, which is quite appropriate to process synthesis, the analogy between chemical reactions and physical operations is discussed. Since a chemical process system is considered to be an isolated system, the criterion for those processes to constitute a process system is examined and a new criterion based on the dissipation factor, D=T0JS/JH9 is proposed. It is shown that there are only six basic patterns for the combination of processes to makeup a process system. Whenan endergonicprocess and an exergonic one constitute a process systemand the former process is carried out with the help of the latter, the exergy transformation between these two processes becomes an important factor. The concept of the ideality index is introduced and the relationship between this ideality index and the dissipation factor Dis discussed. state to another2\ we mayevaluate the changes in Introduction enthalpy, AH, and entropy, AS, for each process. In chemical engineering, the process has usually Then we may describe thermodynamic character- been classified according to the type of equipment or istics of the process by a vector on the {AH, TQAS) operations such as heat generation, heat transfer, diagram shown in Fig. 1. distillation, absorption, extraction, and so on8>11). In this diagram, the enthalpy change is chosen as Such classification is suitable for equipment design abscissa and the entropy change multiplied by the calculations. However, based on this classification, ambient temperature To is selected as ordinate. Then many kinds of chemical reactions have been cate- the axis for Ae=0is represented by the oblique line gorized into only one group. given by AH=T0AS, since the exergy function e is In the previous paper7\ the authors proposed a new defined as methodto analyze a chemical process system from the e=H-T0S (1) viewpoint of exergy transformation between the target Therefore, we may divide the plane shown in Fig. 1 process and coupled processes such as exergy donors, into six regions by these three lines, AH=0(ordinate), exergy acceptors, accelerators, and mediators. It AS=0 (abscissa), and As=0 (oblique line). As will was shownthat there maybe several patterns for coupl- be explained later, these six regions may be called ing between the target and the coupled processes. Fromthat discussion, it was concluded that such clas- heating, separation, refrigeration, heat source, mixing, sification of processes based on type of equipments is and refrigerant types. not suitable for the energy analysis or synthesis of processes. The purpose of this paper is to classify processes into six types from the viewpoint of thermodynamics. Based on such classification, the criterion for several processes to constitute a process system is discussed. Finally, the efficiency of the exergy transformation in a basic binary process system is obtained. 1. Classification of Processes on (AH, TQAS) Plane Since a process is the transition ofa system from one Received April 10, 1981. Correspondence concerning this article should be addressed to H. Oaki. Fig. 1 Six types of processes on (AH, T0JS) diagram VOL. 15 NO. 1 1982 51 and O<Z)<1, corresponding to region (4) in Fig. 1. Since this substance maygive heat to the other material, this region is called heat source type. 4) Refrigerant The vector for heating a substance to the temperature To is located in region (6) in Fig. 1. Since this process maybe coupled with the refrigera- tion process, this region is called refrigerant type. Figure 2 summarizes the characteristics of the vec- tors of these four types of thermal processes to give and Fig. 2 Vectors for thermal processes at various take a certain amount of heat. As the temperature T temperatures on (dH, T0JS) diagram is increased, the vector approaches the abscissa, giv- ing rise to D=0. On the other hand, as the tempera- The vector (AH, T0AS) for a process may also be ture is decreased, the effect of the entropy change is specified by the values of AHand the slope, T0AS/AH. increased, resulting in D=ooat T=0 K. Therefore, The later indicates the increase in entropy per unit the direction of the vector for these thermal processes enthalpy increase and maybe called the dissipation is significantly affected by temperature. factor, D. 1. 2 Polytropic processes D= T0AS/AH (2) Compression and expansion are important proc- By this dimensionless factor, the increase in exergy esses in chemical industry. The changes in enthalpy for the process is given as follows. and entropy of n moles of an ideal gas from the state Ae=AH(l -D) (3) at T± and P1 to T2 and P2 can be obtained as follows. Whena computer is utilized to analyze or to synthe- JH=n^2cpdT=ncp(T2 - T1) (6) size a process, this dissipation factor D maybe used as a quantitative parameter denoting the direction of the vector on the {AH, T0AS)diagram. ,HL>--»l:H"(iro* co Let us examine several typical processes and draw Then the dissipation factor for a polytropic process, their vectors on the (AH, T0AS) diagram. i>Kw=const3)4), is given as 1. 1 Thermal processes 1) Heating Whenn moles ofa certain substance is AH (cp/cm)Tln W heated from Tt to T2, the dissipation factor D for this where m is the polytropic exponent and cm is the poly- heating process is obtained as tropic molar heat capacity3} defined by ToncX"dInT }n(TlT^ cm=cv(r-m)/(l -m) (9) V- ?t2 = lo~^-j^-=i o/i ln (4) ncA dT T2~Tl Wehave m=l and cm=oofor isothermal compres- sion, giving rise to D=oo, while m=y9cm=0, and D= 0 for adiabatic compression. Consequently, the where Tln, denned by (r2-TO/ln (r2/r0, is the loga- direction of the vector ofpolytropic processesis affected rithmic mean of Tx and T2 and the heat capacity cp is by the exponent m. assumedto be constant over that temperature range. Since the heating process above the ambient tem- 1. 3 Separation and mixing 1) Separation The changes in enthalpy and entropy perature TQgives AH>0 and O<Z><1, its vector is are positive and negative, respectively, in regular located in region (1) in Fig. 1. Hence, this region is separation processes and their dissipation factor be- called heating type. comes negative. Hence, their vector (AH, T0AS) Aheat sink at a constant temperature T is a special appears in region (2) in Fig. 1. case for such heating processes. Since T1 and T2 in For example, when 250 moles of aqueous solution Eq. (4) are equal to T9 the dissipation factor for such a of 40 mol% methanol is distilled and separated into heat sink is given by aqueous solutions of 95.8 mol%methanol and 5.8 D= T0/T (5) mol%methanol, we have 2) Refrigeration Refrigeration is the process of {100 CH3OH+150 H2O}-»{91 CH3OH+4 H2O} cooling a substance to a temperature below the am- +{9 CH3OH+ 146 H2O} (10) bient temperature To. Since Eq. (4) holds also for J#=0.18 kJ4), T0AS=~55.l kJ4), Ae=553 kJ this process, its vector appears in region (3) in Fig. 1. Hence, this region is called refrigeration type. and 3) Heat source Cooling a certain substance at high D=-306 temperature to a temperature above To gives AH<0 where the brackets in Eq. (10) mean the mixture. 52 JOURNAL OF CHEMICAL ENGINEERING OF JAPAN The exergy increase of the above separation process is almost equal to that of the decomposition of a mole of methane or the refrigeration of 16 moles of nitrogen from 298 K to 100K, as shown in Fig. 3. However, the methodsto realize these endergonic processes are quite different from each other, as will be discussed in detail in the next section. Therefore, the process of which the vector is located in region (2) in Fig. 1 is called separation type. 2) Mixing Since mixing is the reverse of separa- tion, the changes in enthalpy and entropy are usually Fig. 3 Three kinds of endergonic processes with negative and positive, respectively. Therefore, its almost equivalent amount of As vector (AH, T0AS) appears in region (5) in Fig. 1. Hence, this region is called mixing type. 1. 4 Chemical reaction To perform detailed energy analyses for chemical reactions, information about concentrations of both reactants and products are required. Then the changes in enthalpy, entropy, exergy, and the dissipation factor for reactions can be calculated. For primary discussions for process synthesis, however, the stand- Fig. 4 Examples of endergonic reactions ard dissipation factor D°, defined by the following equation, may be utilized. D°=T0AS0/AH (ll) where S° is the entropy of each componentunder unit pressure. Figure 4 shows the vectors on the (AH, T0AS) diagram for several endergonic reactions based on thermodynamic data compiled in the literatures1>9). Figure 5 shows those for exergonic reactions. Since the vector of the reverse reaction appears in the op- posite direction, all six types can be observed in chemi- cal reactions. The reactants of exergonic reactions with negative or small positive values of D such as ATP, shown in Fig. 5, have been called high-energy compounds5 }. Figure 6 shows the effect of temperature on the value of dissipation factor D. It is found that D for chemi- cal reactions is almost constant over a wide range of temperature.
Load more

Recommended publications
  • Effects in Reversible Exothermic Reactions
    Effects in reversible exothermic reactions. Effect of Temperature on Equilibrium A temperature change occurs when temperature is increased or decreased by the flow of heat. This shifts chemical equilibria toward the products or reactants, which can be determined by studying the reaction and deciding whether it is endothermic or exothermic. Introduction Le Châtelier's principle states that a change in temperature, pressure, or concentration of reactants in an equilibrated system will stimulate a response that partially off-sets the change to establish a new equilibrium. In the case of changing temperature, adding or removing of heat shifts the equilibrium. However, reactions invariably involve changes in enthalpy, with energy (typically in the form of heat, but can involve light) either being absorbed or released during the reaction. Some chemical reactions -- like burning wood or exploding TNT -- release heat to their surroundings. Chemists call these exothermic reactions. Increasing the temperature affects an exothermic reaction in two different ways: by changing the rate of the reaction and by changing the balance between products and reactants at the end of the reaction. Generally speaking, your reaction will speed up because a higher temperature means more heat and energy in your system. However, in some cases, raising the temperature might shift equilibrium and prevent some of your reaction from occurring Reaction Rates Nearly all reactions go faster as the temperature increases -- exothermic reactions included. The reaction between oxygen in the air and the chemicals in the tip of a match, for example, is so slow at room temperature that nothing seems to happen. When you heat up the tip of the match by striking it against the striker strip on the box, however, the temperature increases and with it the rate of the reaction until it burns with a hot flame.
    [Show full text]
  • Review Of: General Comments
    January 15, 2013 Review of: Quantifying drivers of chemical disequilibrium in the Earth’s atmosphere E. Simoncini, N. Virgo , and A. Kleidon Earth Syst. Dynam. Discuss., 3, 1287–1320, 2012 Reviewer: Elbert Branscomb General Comments This paper addresses questions of significant general interest, namely how to es- timate the power needed to maintain atmospheric chemical disequilibria, what the magnitude of that power is in the important case of the CH4=O2 disequilib- rium found in the earth’s atmosphere, and the issue of whether the result, and in particular the general approach, might aid in detecting life on other planets. The thermodynamic approach taken to estimating the power is presented as the paper’s main contribution. The manuscript seems clearly within the scope of ESD. However, in my judgment the manuscript does not rise above the threshold sufficient to justify publication either with regard to significance or original contribution. At the same time, I do not view the shortfall as being so great, or beyond reasonable dispute, that I would object to being overridden on this judgment by other reviewers or editors. In summary, my reasons for this negative decision come down to two points. First, to my mind the case is not made that power calculations of the type considered could in any practical case assist in deciding whether some distant planet was ‘metabolizing‘. The analysis presented in effect argues against this idea - as the authors themselves essentially acknowledge with commendable candor; the powers predicted are too small and, more importantly, no practical strategy seems to exist for determining, for a distant planet, either the needed production fluxes (required to estimate the power by the proposed method) or what fraction of the power involved could not be explainable as due to abiotic processes.
    [Show full text]
  • An Introduction to Metabolism
    CAMPBELL BIOLOGY IN FOCUS URRY • CAIN • WASSERMAN • MINORSKY • REECE 6 An Introduction to Metabolism Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge, Simon Fraser University © 2016 Pearson Education, Inc. SECOND EDITION The Energy of Life . The living cell is a miniature chemical factory where thousands of reactions occur . The cell extracts energy and applies energy to perform work . Some organisms even convert energy to light, as in bioluminescence © 2016 Pearson Education, Inc. Figure 6.1 © 2016 Pearson Education, Inc. Concept 6.1: An organism’s metabolism transforms matter and energy . Metabolism is the totality of an organism’s chemical reactions . Metabolism is an emergent property of life that arises from interactions between molecules within the cell © 2016 Pearson Education, Inc. Metabolic Pathways . A metabolic pathway begins with a specific molecule and ends with a product . Each step is catalyzed by a specific enzyme © 2016 Pearson Education, Inc. Figure 6.UN01 Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1 Reaction 2 Reaction 3 Starting Product molecule © 2016 Pearson Education, Inc. Catabolic pathways release energy by breaking down complex molecules into simpler compounds . One example of catabolism is cellular respiration, the breakdown of glucose and other organic fuels to carbon dioxide and water © 2016 Pearson Education, Inc. Anabolic pathways consume energy to build complex molecules from simpler ones . The synthesis of proteins from amino acids is an example of anabolism . Bioenergetics is the study of how energy flows through living organisms © 2016 Pearson Education, Inc. Forms of Energy . Energy is the capacity to cause change . Energy exists in various forms, some of which can perform work © 2016 Pearson Education, Inc.
    [Show full text]
  • CH4103 Organic and Biological Chemistry LCM Lectures 1-8
    CH4103 Organic and Biological Chemistry LCM Lectures 1-8 Dr Louis C. Morrill School of Chemistry, Cardiff University Main Building, Rm 1.47B [email protected] Autumn Semester For further information see Learning Central: CH4103/Learning Materials/LCM 1 Unit 1: Recap In Unit 1 with Dr Elliott you have learnt some key fundamentals in O-Chem: • Drawing and naming organic compounds (Lecture 1) • Molecular shape and hybridisation - sp3, sp2 and sp (Lecture 2) • Constitutional and stereoisomers (Lectures 3-7) • Conformations of acyclic and cyclic organic structures (Lectures 4 and 5) • Conjugation and resonance (Lecture 8) • Reactive intermediates – carbocations, carbanions and radicals (Lectures 8 and 9) • Acids and bases – pH and pKa (Lecture 9) These are the first tools in your synthetic toolbox and are essential knowledge – please revise these topics diligently. Further supporting learning materials can be found on Learning Central and within Organic Chemistry 2nd Ed. (J. Clayden, N. Greeves and S. Warren) – Chapters 1-8. For further information see Learning Central: CH4103/Learning Materials/LCM 2 Unit 2: Lecture Synopsis • Lecture 1: Describing an Organic Reaction. Homolytic vs heterolytic bond breaking, bond dissociation energy (BDE), enthalpy and ΔH°, entropy and ΔS°, Gibbs free energy and ΔG°, equilibria. • Lecture 2: Reaction Kinetics and the Hammond Postulate. Differentiating thermodynamics and kinetics, rate laws, activation energy (Ea), the Arrhenius equation, free energy diagrams, intermediates and transition states, the Hammond postulate. • Lecture 3: Curly Arrows for Electron Movement. How molecules interact, nucleophiles and electrophiles, use of curly arrows to represent electron movement, curly arrows for nucleophilic attack / substitution, loss of a leaving group / elimination, proton transfers and carbocation rearrangements.
    [Show full text]
  • AP Biology Notes Outline Enduring Understanding 2.A Big Idea 2
    AP Biology Notes Outline Enduring Understanding 2.A Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis. Enduring Understanding 2.A: Growth, reproduction and maintenance of the organization of living systems require free energy and matter. Learning Objectives: Essential Knowledge 2.A.1: All living systems require constant input of free energy. – (2.1) The student is able to explain how biological systems use free energy based on empirical data that all organisms require constant energy input to maintain organization, to grow and to reproduce. – (2.2) The student is able to justify a scientific claim that free energy is required for living systems to maintain organization, to grow or to reproduce, but that multiple strategies exist in different living systems. – (2.3) The student is able to predict how changes in free energy availability affect organisms, populations and ecosystems. Essential Knowledge 2.A.2: Organisms capture and store free energy for use in biological processes. – (2.4) The student is able to use representations to pose scientific questions about what mechanisms and structural features allow organisms to capture, store and use free energy. – (2.5) The student is able to construct explanations of the mechanisms and structural features of cells that allow organisms to capture, store or use free energy. Essential Knowledge 2.A.3: Organisms must exchange matter with the environment to grow, reproduce and maintain organization. – (2.6) The student is able to use calculated surface area-to-volume ratios to predict which cell(s) might eliminate wastes or procure nutrients faster by diffusion.
    [Show full text]
  • How Cells Obtain Energy 91 4 | HOW CELLS OBTAIN ENERGY
    Concepts of Biology Chapter 4 | How Cells Obtain Energy 91 4 | HOW CELLS OBTAIN ENERGY Figure 4.1 A hummingbird needs energy to maintain prolonged flight. The bird obtains its energy from taking in food and transforming the energy contained in food molecules into forms of energy to power its flight through a series of biochemical reactions. (credit: modification of work by Cory Zanker) Chapter Outline 4.1: Energy and Metabolism 4.2: Glycolysis 4.3: Citric Acid Cycle and Oxidative Phosphorylation 4.4: Fermentation 4.5: Connections to Other Metabolic Pathways Introduction Virtually every task performed by living organisms requires energy. Energy is needed to perform heavy labor and exercise, but humans also use energy while thinking, and even during sleep. In fact, the living cells of every organism constantly use energy. Nutrients and other molecules are imported into the cell, metabolized (broken down) and possibly synthesized into new molecules, modified if needed, transported around the cell, and possibly distributed to the entire organism. For example, the large proteins that make up muscles are built from smaller molecules imported from dietary amino acids. Complex carbohydrates are broken down into simple sugars that the cell uses for energy. Just as energy is required to both build and demolish a building, energy is required for the synthesis and breakdown of molecules as well as the transport of molecules into and out of cells. In addition, processes such as ingesting and breaking down pathogenic bacteria and viruses, exporting wastes and toxins, and movement of the cell require energy. From where, and in what form, does this energy come? How do living cells obtain energy, and how do they use it? This chapter will discuss different forms of energy and the physical laws that govern energy transfer.
    [Show full text]
  • Basis of High Energy of Hydrolysis of ATP
    BIOENERGITICS DR ANITHA N Bioenergetics is the quantitative study of energy relationships and energy conversion in biological systems. DR ANITHA N Energy • Energy can exist in two states: – Kinetic energy – energy of motion. – Potential energy – stored energy. • Chemical energy – potential energy stored in bonds, released when bonds are broken. • Energy can be transformed form one state to another. DR ANITHA N A diver has more potential Diving converts energy on the platform potential energy to than in the water. kinetic energy. DR ANITHA N Climbing up converts the kinetic A diver has less potential energy of muscle movement energy in the water to potential energy. than on the platform. Different forms of energy: Mechanical (kinetic and potential) Light, sound, heat, electrical (including magnetic) and chemical energy Conversion of mass and energy Inter-conversion of subatomic particle. Physics Various energy forms: Light, electromagnetic, Kinetic, heat, potential, sound and wave Interactions between atoms through electrons in outer orbit of atoms at various temperature, Chemistry pressure and pH and solvent condition. Interaction between macromolecules, atoms in similar way as in chemistry except at normal temperature, pressure, Biochemistry around neutral pH and strictly in aqueous Media.DR ANITHA N The Laws of Energy Transformation • Thermodynamics is the study of energy transformations • A isolated system, is isolated from its surroundings • In an open system, energy and matter can be transferred between the system and its surroundings
    [Show full text]
  • Activation of O2 and NO in Heme-Copper Oxidases –
    Chem Soc Rev View Article Online REVIEW ARTICLE View Journal | View Issue Activation of O2 and NO in heme-copper oxidases – mechanistic insights from Cite this: Chem. Soc. Rev., 2020, 49,7301 computational modelling Margareta R. A. Blomberg Heme-copper oxidases are transmembrane enzymes involved in aerobic and anaerobic respiration. The largest subgroup contains the cytochrome c oxidases (CcO), which reduce molecular oxygen to water. A significant part of the free energy released in this exergonic process is conserved as an electrochemical gradient across the membrane, via two processes, electrogenic chemistry and proton pumping. A deviant subgroup is the cytochrome c dependent NO reductases (cNOR), which reduce nitric oxide to nitrous oxide and water. This is also an exergonic reaction, but in this case none of the released free energy is conserved. Computational studies applying hybrid density functional theory to cluster models of the bimetallic active sites in the heme-copper oxidases are reviewed. To obtain a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. reliable description of the reaction mechanisms, energy profiles of the entire catalytic cycles, including the reduction steps have to be constructed. This requires a careful combination of computational results with certain experimental data. Computational studies have elucidated mechanistic details of the chemical parts of the reactions, involving cleavage and formation of covalent bonds, which have not been obtainable from pure experimental investigations. Important insights regarding the mechanisms of energy conservation have also been gained. The computational studies show that the reduction potentials of the active site cofactors in the CcOs are large enough to afford electrogenic chemistry and proton pumping, i.e.
    [Show full text]
  • Endergonic Reactions in Metabolism
    CAMPBELL TENTH BIOLOGY EDITION Reece • Urry • Cain • Wasserman • Minorsky • Jackson 8 An Introduction to Metabolism Lecture Presentation by Nicole Tunbridge and Kathleen Fitzpatrick © 2014 Pearson Education, Inc. The Energy of Life . The living cell is a miniature chemical factory where thousands of reactions occur . The cell extracts energy stored in sugars and other fuels and applies energy to perform work . Some organisms even convert energy to light, as in bioluminescence © 2014 Pearson Education, Inc. Figure 8.1 © 2014 Pearson Education, Inc. Figure 8.1a © 2014 Pearson Education, Inc. Concept 8.1: An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics . Metabolism is the totality of an organism’s chemical reactions . Metabolism is an emergent property of life that arises from orderly interactions between molecules © 2014 Pearson Education, Inc. Organization of the Chemistry of Life into Metabolic Pathways . A metabolic pathway begins with a specific molecule and ends with a product . Each step is catalyzed by a specific enzyme © 2014 Pearson Education, Inc. Figure 8.UN01 Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1 Reaction 2 Reaction 3 Starting Product molecule © 2014 Pearson Education, Inc. Catabolic pathways release energy by breaking down complex molecules into simpler compounds . Cellular respiration, the breakdown of glucose in the presence of oxygen, is an example of a pathway of catabolism © 2014 Pearson Education, Inc. Anabolic pathways consume energy to build complex molecules from simpler ones . The synthesis of protein from amino acids is an example of anabolism . Bioenergetics is the study of how energy flows through living organisms © 2014 Pearson Education, Inc.
    [Show full text]
  • Endergonic Reactions.  ATP “Shuttles” Energy Around the Cell from Exergonic Reactions to Endergonic Reactions
    Chapter 5 The Working Cell: Chemical Energetics and Enzymes I. Energy: The capacity to do work. The ability to change matter Can exist in two forms: 1. Kinetic energy: Energy of motion. Energy that is actively performing work. Examples: Heat: Energy of particles in motion. Light: Energy of photons of light 2. Potential energy: Stored energy due to position or arrangement of matter. Examples: Chemical energy: Potential energy of molecules due to the arrangement of atoms. The most important type of energy for living organisms. Position: Bicycle at the top of a hill. Kinds of Energy Chemical Nuclear Electrical Electromagnetic Light Mechanical Heat Sound II. Energy Transformation Energy can be converted from one kind to another. Transformations are inefficient, generating heat. Examples: Light energy -------- --> Chemical energy (sugar) + Heat Chemical energy -- ---> Mechanical energy + Heat Electrical energy --- --> Light energy + Heat Chemical energy --- --> Biological work + Heat Heat is easily measured energy, because all other forms of energy can be converted to heat. From a biological standpoint, heat is a poor kind of energy which is not very useful to do work. Why? Because heat is lost to the environment. III. All energy transformations are subject to the First and Second Laws of Thermodynamics 1. First Law of Thermodynamics: Energy can be transformed (e.g.: chemical to mechanical), but cannot be created nor destroyed. The total amount of energy in the universe is constant. Biological Consequence: Living organisms cannot create the energy they need to live. They must capture it from their environment. Sources of energy used by living organisms: Sun and chemical energy.
    [Show full text]
  • Biochemistry Steady State
    JWCL281_c16_557-592.qxd 2/26/10 11:10 AM Page 559 Introduction to Metabolism CHAPTER 16 1 Metabolic Pathways obtained from other organisms, ultimately phototrophs. 2 Organic Reaction Mechanisms This free energy is most often coupled to endergonic reac- A. Chemical Logic tions through the intermediate synthesis of “high-energy” B. Group-Transfer Reactions phosphate compounds such as adenosine triphosphate C. Oxidations and Reductions (ATP; Section 16-4). In addition to being completely oxi- D. Eliminations, Isomerizations, and Rearrangements dized, nutrients are broken down in a series of metabolic E. Reactions That Make and Break Carbon–Carbon Bonds reactions to common intermediates that are used as precur- 3 Experimental Approaches to the Study of Metabolism sors in the synthesis of other biological molecules. A. Metabolic Inhibitors, Growth Studies, A remarkable property of living systems is that, despite and Biochemical Genetics the complexity of their internal processes, they maintain a B. Isotopes in Biochemistry steady state. This is strikingly demonstrated by the observa- C. Isolated Organs, Cells, and Subcellular Organelles tion that, over a 40-year time span, a normal human adult D. Systems Biology consumes literally tons of nutrients and imbibes over 20,000 L 4 Thermodynamics of Phosphate Compounds of water, but does so without significant weight change. This A. Phosphoryl-Transfer Reactions steady state is maintained by a sophisticated set of metabolic B. Rationalizing the “Energy” in “High-Energy” Compounds regulatory systems. In this introductory chapter to metabo- C. The Role of ATP lism, we outline the general characteristics of metabolic 5 Oxidation–Reduction Reactions pathways, study the main types of chemical reactions that A.
    [Show full text]
  • Fundamentals and Applications of Photocatalytic CO2 Methanation
    REVIEW ARTICLE https://doi.org/10.1038/s41467-019-10996-2 OPEN Fundamentals and applications of photocatalytic CO2 methanation Ulrich Ulmer1, Thomas Dingle1,2, Paul N. Duchesne1, Robert H. Morris 1, Alexandra Tavasoli1,2, Thomas Wood1 & Geoffrey A. Ozin 1 The extraction and combustion of fossil natural gas, consisting primarily of methane, gen- erates vast amounts of greenhouse gases that contribute to climate change. However, as a 1234567890():,; result of recent research efforts, “solar methane” can now be produced through the photo- catalytic conversion of carbon dioxide and water to methane and oxygen. This approach could play an integral role in realizing a sustainable energy economy by closing the carbon cycle and enabling the efficient storage and transportation of intermittent solar energy within the chemical bonds of methane molecules. In this article, we explore the latest research and development activities involving the light-assisted conversion of carbon dioxide to methane. he combustion of natural gas (NG), which is used for heating, electricity generation and as 1 Ta chemical feedstock, accounts for 20 wt% of global CO2 emissions . While demand for NG is predicted to rise in the coming decades, known fossil fuel reserves are projected to 2 last for only another 60 years . Thus, a non-fossil-based, sustainable source of methane (CH4), the main component of NG, is needed in order to satisfy the growing demand for this important fuel and chemical feedstock while simultaneously reducing the environmental impact of its use. Sustainable production of “synthetic” natural gas (SNG) is possible through the conversion of CO2 and water (H2O) into CH4 and oxygen (O2) using renewable energy such as sunlight.
    [Show full text]