Category ENERGY

Birth of Nuclear Energy

The alpha decay of U-238 occurs naturally, but in the 1930s Otto Hahn, Lise Meitner, and Fritz Strassman began to study the neutron-induced radioactive decay of ura­nium. Bombardment of a target nucleus with neutrons can result in elastic collisions (the neutron just bounces off with a loss of energy), inelastic scattering (leaving the target nucleus in an excited state and the neutron with less energy), capture of the

Mass number (number of nucleons in nucleus)

FIGURE 9.1 Binding energy per nucleon versus mass number. (From Wikimedia Commons. http://en. wikipedia. Org/wiki/File:Binding_energy_curve_-_common_isotopes. svg. Accessed June 10, 2013.)

neutron by the target nucleus (this gives an excited state compound nucleus that then decays), or fragmentation (fission)...

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NUCLEAR CHEMISTRY BASICS

9.2.1 General Chemistry Review

The energy conversions we have examined thus far have relied primarily upon cap­turing the energy of chemical reactions that center on electron transfer or excitation. We have been able to ignore, if you will, the rest of the atom—until now. Nuclear power comes about from release of the binding energy of elemental particles that make up the nucleus of atoms. Because of the fundamental relationship between matter and energy (E = mc2), the loss of a tiny amount of mass in a nuclear reaction translates into a huge amount of energy. Understanding nuclear power requires a quick review of some nuclear nomenclature and basic general chemistry.

A nucleon refers to either a proton or a neutron in the nucleus of an atom made up, of course, of positively charged prot...

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Nuclear Energy

9.1 INTRODUCTION

As noted in the introduction to this book, there are several relevant topics that would not be covered even though there is legitimate claim to their inclusion. Given that limitation, why include nuclear power? After all, it is a topic that is highly contro­versial with respect to sustainability and certainly one with a clouded history. Yet the following two quotes from expert scientists well summarize the need to consider nuclear energy:

To the extent that we live in a hydrocarbon-limited world, generate too much CO2, and major hydropower opportunities have been exhausted worldwide, new nuclear power stations must be considered.

Tad W. Patzek, Cockrell Family Regents Chair, Petroleum and Geosystems Engineering, University of Texas at Austin

and David Pimentel, Professor ...

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8.6.3.5 Conclusions

The production of FAE biodiesel has well-established and reliable technology behind it and biofuel plays a minor, but significant, role in many areas of the globe. Industrial-scale applications have much room for improvement, however, and in the end analysis, FAE biodiesel is a first-generation biofuel that, in many instances, competes with food production. New methods of biodiesel production have been developed that are based on crop residues and LCB such as switchgrass. These methods—Fischer-Tropsch diesel, hydrotreated vegetable oils, and hydrotreating of waste cooking oils—offer additional promise in that they do not play into the “food versus fuel” debate and they produce a higher-performance diesel (Bezergianni and Dimitriadis 2013)...

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Process Conditions

Lipase catalysis takes place, as expected, at lower temperatures and in general must be carried out at temperatures below 60°C, at which point the lipase is deactivated. However, catalysis of FAEE biodiesel produced from soybean oil with Novozym 435 gave the optimum yield of 92% when carried out at 65°C (Brusamarelo et al. 2010). Just as for the catalysts described in the previous sections, a large excess of the alco­hol must be used in order to present a favorable equilibrium. The alcohol is also a necessary reaction component in that it acts as a solvent and reduces the viscosity of the reaction mixture. However, some lipases are inhibited by alcohols, particularly shorter-chain alcohols such as methanol or ethanol...

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Immobilization

Because of the high cost associated with these enzymes their practical application requires immobilization in or on some solid material that allows their easy recov­ery. Immobilization of the lipase on a solid inert material not only results in cost

savings due to recycling, it also stabilizes the lipase. As a result, fixed bed reactors (such as described in Section 8.5.3.2) are preferred for enzyme-catalyzed continu­ous biodiesel manufacture (as opposed to a reactor that would subject the lipase to too much shear stress) (Ribeiro et al. 2011)...

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Lipases

Triacylglycerides are lipids and the enzymes known to catalyze lipid esterification, hydrolysis, and transesterification (and, hence, biodiesel production) are, logically enough, lipases. These enzymes are widely distributed in nature, being produced by microorganisms as well as plants and animals. Microorganismal lipases from the genera Candida, Rhizopus, and Pseudomonas are the primary sources for industrial applications. Lipases are especially active for lipophilic substrates, so fatty acid esters of over 10 carbon atoms are good substrates. They do not require cofactors (a cofactor is a small molecule that must associate with the enzyme to activate it) and they are stable in the presence of organic solvents...

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Enzymatic Catalysis

Given that the production of FAE biodiesel is based on a biological feedstock it stands to reason that biological catalysis is an option. Indeed, enzymatic catalysis of FAE biodiesel production is a well-studied phenomenon for the usual good reasons: enzymatic catalysis leads to a much milder, greener chemical transformation given a lower temperature of reaction and absence of harsh acids and bases. The issues associated with enzymatic catalysis are also unsurprising, that is, high cost and com­petitive inhibition by impurities in the feedstock.

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