Eric Flint: Grantville Gazette Volume 24

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.