Grantville Gazette Volume 24 Page 23

  Thermodynamics/Gibbs Free Energy. There are reference books in Grantville (e.g., the CRC Handbook of Chemistry and Physics) which have tables of thermodynamic values for various elements, cations, anions and solids. You can use these tables to predict whether a reaction involving those entities can occur spontaneously.

  Rate. Loosely speaking, the equilibrium is the endpoint of a chemical reaction, and rate is how quickly it gets there. For a reaction to be commercially feasible, it must not only have an equilibrium favoring the products, it must have a high enough reaction rate. Unfortunately, the prediction of reaction rate is difficult and at the very least requires a knowledge of the exact reaction mechanism. Reaction rates increase with concentration (more chance for the reactants to collide) and temperature. Reactions of ions in solution tend to be fast. Other reactions are slower, as some (but not all) of the bonds holding the reactants together will need to be broken.

  Planning. In general, synthetic strategies depend on either displacing one metal with another which is higher in the electromotive series, or on causing two soluble salts to react to form an insoluble product, a gas, or water. (See appendix table 1-2.)

  Electrochemistry

  Electrochemistry studies the use of spontaneous chemical reactions to create an electric current (as in a battery) or the use of an applied electrical voltage to force a chemical reaction to occur (as in an electrolytic cell).

  If the electromotive potential of a reaction is less than zero, then the reaction won't occur spontaneously. But you can still make it happen by applying electricity. The voltage has to be high enough to counteract the negative potential of the reaction, and the current will determine how much product is produced. The reaction will not be 100% efficient, so you will have to use more current than what is theoretically required.

  An electrolytic cell has an electrolyte and two electrodes (cathode and anode). The electrolyte may be a solution or a molten salt; the key point is that it contains mobile ions. An ion is an atom or molecule which has lost one or more electrons giving it a positive charge (cation), or gained one or more electrons, yielding a negative charge (anion). The voltage drives the movement of cations toward the cathode, where they are reduced, and of anions toward the anode, where they are oxidized.

  At the anode and cathode, the products may undergo further reaction to form secondary products. In a two compartment diaphragm or membrane cell, some kind of barrier prevents undesired reactions between anode and cathode species. For example, in the chloralkali process, hydroxide ions are allowed to react with sodium ions in the cathode compartment (making caustic soda), but not with chloride ions in the anode compartment. And recombination of sodium and chloride ions is also inhibited.

  In 1633, Dr. Phil built a "wet cell" battery with a dilute sulfuric acid electrolyte and a zinc electrode. Offord, "Dr. Phil Zinkens a Bundle" (Grantville Gazette 7). That story doesn't reveal the identity of the second electrode, but it would probably be copper, see Boatright, "So You Want to Do Telecommunications in 1633?" ( Grantville Gazette 2).

  Here, we are more concerned with electrolysis, which is the decomposition of a chemical by electricity. Dr. Gribbleflotz experimented with electrolysis of an unspecified salt in Offord and Boatright, "The Dr. Gribbleflotz Chronicles, Part 2: Dr. Phil's Amazing Essence Of Fire Tablets" (Grantville Gazette 7)

  In the old time line, water was decomposed into hydrogen and oxygen in 1800; sodium and potassium were isolated by electrolysis of their salts in 1807.

  The first electrochemical reaction of industrial importance was probably in the purification of platinum. In 1991, the principal electrochemical products were caustic soda, chlorine, aluminum, copper, zinc, chromium, sodium chlorate, caustic potash, magnesium, sodium, manganese dioxide, permanganates, manganese, perchlorates, and titanium. (KirkOthmer9:125). The most common electrolyte was probably sodium chloride.

  Electricity is supplied by power plants as high voltage alternating current, but for electrochemical use, this needs to be rectified into direct current and stepped down by transformers to a lower voltage.

  Catalysts

  What appears to be a single reaction may occur through a series of steps (addition, elimination, substitution and rearrangement), each with its own molecularity (the number of reacting molecules) and own rate law (a mathematical relationship between the rate of the reaction step and the concentration of the reactants). The slowest step determines the rate of the overall reaction.

  Catalysts increase (or decrease, so-called negative catalysts) the rate of a chemical reaction without participating in the net reaction. They have no effect on the equilibrium concentrations of the reactants and products.

  Johann Dobereiner discovered that the rate of the conversion of alcohol to acetic acid (1816) or acetic aldehyde (1832) could be increased by conducting the reaction in the presence of platinum wire. He created (1823) a lighter in which the hydrogen flame was produced by the action of sulfuric acid on zinc, in the vicinity of a platinum sponge (EA "Dobereiner"; Jentoft). In 1817, Humphrey Davy studied the effect of wires of different metals on the rate of reaction of coal-gas with oxygen. The term "catalysis" was coined by Jons Jakob Berzelius, who used it to explain additional phenomena, including the rapid decomposition of hydrogen peroxide by metals.

  EA "Catalyst" says that "many common catalysts are powders of metals or of metallic compounds," and by way of example mentions that platinum catalyzes the hydrogenation of double bonds. It also indicates that acids can be catalysts; "sulfuric acid catalyzes the isomerization of hydrocarbons."

  EA "Platinum" says that for use as a catalyst, platinum is used in powdery ("platinum black", from reduction of platinum chloride) or spongy form, and there is reference to its use in production of nitric acid.

  Further "data mining" EA will identify other catalysts, which I have tried to logically group below: metals: palladium, neodymium, samarium, rhenium, lutetium, ruthenium, molybdenum, silver, mercury, nickel, iron, rhodium, a platinum-rhodium alloy (for preparation of hydrocyanic acid from ammonia, methane and air, or preparation of nitric acid or ammonium nitrate), copper, unidentified transition metals, metal oxides: iron oxide (to catalyze the direct combination of nitrogen and hydrogen in the Haber Process, EA "Ammonia"), manganese dioxide (to speed the thermal decomposition of potassium chlorate to produce oxygen, EA "Chemical Reactions"), platinum dioxide (from fusion of chloroplatinic acid with sodium nitrate), copper oxides, chromium zinc oxide (used in methanol production), scandium oxide, cadmium oxide, lead oxide (litharge), acids: hydrobromic acid, chromic acid, hydrogen fluoride, hydrochloric acid (for nitrobenzene), miscellaneous: copper acetate, aluminum chloride, certain organotin compounds, nickel-aluminum sulfide, sodium nitrate (for manufacture of sulfuric acid), sodium ethylate, peroxides, hot alcoholic solution of potassium cyanide, lithium acetate, n-butyllithium, coordination compounds of zirconium, phosphorus pentaflouride, water (!).

  EA apparently overlooks the organometallic catalysts, which were rather important in the late twentieth century.

  It is important to note that many catalysts are reaction-specific. Hence, there is going to be a lot of educated trial-and-error going on; systematically testing the effect of each of a series of potential catalysts to see if any of them facilitate a reaction of interest.

  A good example of this is the screening carried out by Bosch to make the Haber nitrogen fixation process feasible commercially. Haber initially identified osmium and uranium, both of which were quite expensive, as effective catalysts. Bosch set up test reactors, and tested 4,000 different catalysts over five years, finding that an impure iron oxide catalyst was cheap and operable. (McGrayne 66; KirkOthmer5:323).

  Just to complicate matters further, modern catalysts aren't necessarily simple materials. Because the catalytic material is expensive, it is usually advantageous to use it in small amounts, and disperse it on a support material with a high surface area. Gamma-alumina is the most popular support. (KirkOthmer 5:347).

 
There are also catalytic promoters. These are substances which don't act as catalysts themselves, but which potentiate the activity of the "real" catalyst. There are both chemical promoters which change the surface chemistry, and textural promoters which alter the physical characteristics. Alkali metals have been used as chemical promoters.

  Catalysts can be deactivated as a result of fouling (they are physically masked by deposited material), poisoning (feed impurities which reduce their catalytic activity), and physical change (e.g., sintering). Catalysts may in turn be regenerated.

  The modern catalyst for ammonia synthesis is a combination of iron oxide as the catalyst, aluminum and calcium oxide as textural promoters, and potassium as a chemical promoter.

  Some catalysts-common acids, finely divided metals (e.g. platinum), and some metal oxides-can be put to work in the 1632verse in fairly short order. Others are rare materials, or of a complex composition or structure, and it will take years, if not decades, of work to duplicate them.

  Temperature Control

  Temperature affects both the rate and the completeness of a reaction. A typical rule of thumb is that for every 10њC increase in temperature, the reaction rate will double. The effect of the temperature on the completeness of a reaction depends on whether it is endothermic (needs heat) or exothermic (releases heat). Higher temperatures favor endothermic reactions and hinder exothermic ones.

  There are other considerations. Too high a temperature can result in side reactions, including decomposition. So, depending on the reaction, you may want to heat things up, keep the temperature from increasing above a certain point, or bring it below room temperature.

  If a reaction is temperature sensitive, then you need a good thermometer. For industrial work, you might prefer a thermostat which controls a heating or cooling device. In 1634, the Essen Instrument Company is manufacturing precision mercury thermometers. (Mackey, "Ounces of Prevention," Grantville Gazette 5). I would expect that simple spirit thermometers are being made, too.

  Both heating and cooling processes are slower to start, and stop, when the reaction is on an industrial scale. As the volume increases, the ratio of the heating or cooling surface to the volume decreases.

  In the laboratory, if an elevated temperature is needed for a reaction, the chemist will use a gas-burning Bunsen burner. This can reach a temperature close to 900њC. Up-time, natural gas is used, but Dr. Phil has an alcohol burner in 1633. Offord and Boatright, "Dr. Phil's Amazing Essence of Fire Tablets," Grantville Gazette 7).

  On the industrial scale, you may be burning some kind of fuel, which heats air or water surrounding the vessel, or passing through tubes in the vessel. Steam distillation falls in this category. Or you may be converting electrical energy into heat energy. Or running two industrial processes alongside each other, one providing heat for the other.

  Chemical reactions tend to be more efficient when the reactants are all in the liquid phase. Solids react only at their surfaces, and gases are low in density. If one of the reactants is solid at room temperature, then to put it in the liquid phase, it must be dissolved or melted. And melting requires heat.

  In some cases, it is possible to drastically lower the melting point of the substance of interest by adding a second substance, known as a "flux". Sodium, potassium and lead oxides lower the melting point of glass from 1700њ C. to perhaps 900-1200. Aluminum oxide melts at 2054њ C., but it can be dissolved in cryolite, which is molten at a little less than 1000њ C.

  You may also be trying to lower the melting point of the waste material. For example, in smelting copper, you may want to make sure that the silica forms a very liquid slag, that the copper can sink through. So iron oxide is added.

  Smelting metals typically requires a reducing agent (e.g. carbon) and heat. For tin or lead oxide, a campfire (600-650њC) is good enough, but copper requires a temperature of 700-800 and forgeable iron, 1100њC.

  Combustion processes cannot exceed the "adiabatic combustion temperature," which, for combustion in air, is about 2000њ C for natural gas, 2150 for oil and 2200 for coal. The fuel is the source of carbon and the air is the source of oxygen. The limiting temperature is a function of the heating value of the fuel, the specific heat capacity of the fuel and the air (and the combustion products), the ratio of fuel to air, and the air and fuel inlet temperatures (Wikipedia, "Combustion"). Even higher temperatures are achievable with rocket engine fuels/oxidizers.

  The practical combustion temperatures for industrial chemistry are much lower than the theoretic limit. It is difficult to achieve complete combustion if there is insufficient air, heat is lost (radiated out; carried away by exhaust gases), and so forth. To ensure complete combustion, it is customary to use an excess of air, but air dilution then reduces the temperature of combustion.

  In 1920, a coal furnace could achieve a temperature of 1600њC without a blast, and 1800њC with one. A gas-fired furnace, with hot air, both the gas and air under pressure, could reach about 2000њC. (Marsh, 46). For higher temperatures, you need to heat by means other than combustion.

  An electric arc furnace uses an electric current to heat a conductive material. That could be an ionic compound, or a conductive metal. Perhaps the first industrial use of the electric arc furnace was in the production of calcium carbide by heating lime and coke to 2000њC (1888). Electric arc furnaces came to play an important role in small-scale steelmaking.

  Another option for sidestepping the practical combustion temperature limit is to use a solar furnace. Temperatures of 3000њC have been achieved by focusing solar radiation.

  The higher the temperature our technology will generate, the more options we have for chemical synthesis.

  To chill things down, you can put the vessel in ice, an alcohol bath, dry ice (solid carbon dioxide), or in liquid nitrogen. (for availability of CO2 and nitrogen, see part 2, and Huston, "Refrigeration and the 1632 World" (Grantville Gazette 17)).

  Atmosphere Control

  Some reactions cannot be conducted in the air, because it would react. If so, the air is replaced with an inert gas, like nitrogen or argon.

  Or you may need an atmosphere whose pressure is higher or lower than normal. It is important to compare the number of gas molecules at the beginning and end of the reaction. If that number decreases (as in ammonia synthesis), increasing the pressure will cause the reaction to shift (per Le Chatelier's Principle) in favor of reducing the pressure, which means in favor of fewer gas molecules, and thus in the forward direction. On the other hand, if the number of gas molecules is increased by the forward reaction, then you want to conduct the reaction under lower-than-normal pressure.

  To change the pressure, you need two things: a pump, and a vessel with walls strong enough to withstand the pressures generated.

  Vacuums may be needed to pull out a gaseous product (to drive a chemical reaction), or to lower the boiling points of the compounds in an organic residue (as in vacuum distillation). Vacuum pumps have been scavenged from refrigerators. (Gorg Huff, "Other People's Money," Grantville Gazette 3)

  Elevated pressure also may be used to keep the reactants in the liquid phase, or to facilitate a gas phase reaction. In the mid-nineteenth century, autoclaves were built which could achieve pressures of 725-1150 psi (14.7 psi is normal atmospheric pressure). A 1901 ammonia synthesis used a 1450 psi autoclave. In the early twentieth century, large-scale continuous feed reactors had been built which could handle 2000-5000 psi. By the 1990s, there were operations using 51,000 psi. (Kirk-Othmer/"High Pressure Technology").

  High pressure vessels are typically thick -walled, and composed of gun steels. During the 50s, the preferred alloy was nickel-chromium-molybdenum, and later an alloy which additionally contained vanadium gained favor.

  The down-timers' only experience with "pressure vessels" is of a rather specialized nature: cannon barrels. These have to resist the internal pressures generated by the explosion. For a given thickness, bronze is better than cast iron, and the down-timers are familiar wi
th the concept of the "built-up" cannon, in which hot hoops or jackets are fit over the barrel and allowed to cool and shrink.

  In 1773-91, Woolwich conducted experiments on muskets, reporting a maximum internal pressure of 2,000 atmospheres. (Ingalls). A Civil War era 15-inch Rodman gun, charged with 130 pounds of black powder, will experience 25,000 psi (1700 atmospheres) pressure. (NPS).

  While explosives are not exactly a preferred source of pressure (they're dangerous, and don't lend themselves to continuous processing), Alfred Noble "packed steel tubes with gunopowder or cordite and heated them until they exploded with tremendous force, briefly attaining pressures of 8,000 atmospheres at more than 5,000њC." (Hazen 35).

  The up-timers include some steam engine enthusiasts, and a locomotive boiler can be considered a high pressure vessel suitable for continuous processing. Canon is a little vague on the issue, but it appears that there is at least one true locomotive on the main line by September 1633 (Flint, 1633, Chapter 33). That locomotive, of course, is generating high pressure steam. I suspect, based on the nineteenth-century locomotive data which the designers will be studying, that it has a steam pressure in the 75-200 psi range. That's still short of even a nineteenth-century autoclave, but it's a start.

  To some extent, it will be possible to compensate for having weaker alloys by increasing the thickness of the vessel wall. However, that increases the expense of the vessel and, if it's externally heated or cooled, it impairs heat transfer. In addition, increasing vessel thickness doesn't address the Achilles' heel(s) of the system: the openings needed in order to add raw materials, withdraw product and perhaps supply or remove heat.