by Eric Flint
Solvents
Solvents are used as a medium in which the reactants can find each other, as catalysts (to help the reactants make or break bonds), and to control the temperature of the reaction. The traditional solvent for inorganic chemical reactions is water.
If cold water doesn't dissolve a particular salt, you can try hot water, and, if that fails, a dilute or concentrated solution of an acid (hydrochloric, sulfuric, nitric, hydrofluoric, acetic, etc.). If need be, the inorganic chemist may have recourse to pure acids, carbon disulfide, liquid ammonia, liquid sulfur dioxide, alcohol, benzene, chloroform, acetone, ether, and turpentine. CRC provides detailed information on the solubility of inorganic compounds in various solvents.
The choice of solvent can have interesting consequences. Barium chloride is soluble in water, while silver chloride is not. The reverse is true in liquid ammonia. Hence, in water, barium chloride reacts with silver nitrate to form silver chloride and barium nitrate. The reverse reaction is favored in liquid ammonia. (Purcell, 154).
Sometimes, not only do you not want to use water as a solvent, you need to make sure that there isn't even a trace of water present in the reactor. If so, you will use various dehydrating agents to prepare the reactor and the reactants for use.
While water was the most important solvent in inorganic chemistry, it has a lesser role in organic chemistry. Over twenty different organic compounds are used as solvents, including methanol, ethanol, acetone, acetic anhydride, pyridine, chloroform, diethyl ether, and benzene (Bordwell 201). In winter 1633-34, Henri Beaubriand-Levesque uses turpentine and ether as solvents for natural rubber. (Offord, "Letters from France," Grantville Gazette 12).
The "aprotic solvents" (e.g., dimethyl sulfoxide) are especially interesting because they seem to increase the reactivity of the reagents (M amp;B 492). DMSO can be obtained from the lignin of wood (EA/Dimethyl Sulfoxide).
Measurement Apparatus
The weight, and hence the mass, of a chemical is measured in chemistry labs by using an equal-arm balance. This has two pans, one holding the unknown, the other a known weight. EA/Balance says that the key to precision measurements is to use a knife edge as a fulcrum, whereas EB11/Weighting Machines warns that the knife-edges and their bearings must be extremely hard. All else being equal, a long arm balance will be more sensitive than a short arm one. Precautions must be taken vis-a-vis temperature, humidity, vibration (from air currents or through the ground), and other disturbances.
In industry, where the weights involved are much greater, the measurement will probably be with an unequal arm balance ("steelyard"), a spring scale, or a platform scale with multiplying levers. (EA/Weighing Machines).
The volume of a liquid is measured by introducing it into a graduated cylinder of suitable size. The flow rate of a gas can also be measured (suitable examples exist at homes which buy natural gas for heating purposes).
Temperature is measured, of course, by a thermometer. The first thermometers were of the liquid-in-glass type; first water, then alcohol, and finally mercury. The liquid expands as the temperature rises. Sealing the tube was essential to avoiding pressure effects. Mercury is liquid from -39 to 357њC. To measure higher temperatures, a gas-in-tube thermometer can be used. Hydrogen thermometers are used up to 1100њC, and nitrogen to 1550њC.
There are many other principles on which a thermometer can be constructed. The platinum resistance thermometer (1886) has been used to measure temperatures in the -259 to 630њC range.
Gas pressures are measured with a pressure gauge designed to handle a suitable range of pressures. There are hydrostatic gauges (manometers) which observe the movement of a column of mercury in a U-shaped tube, flexible pressure sensors like the 1849 Bourdon tube (coiled tube which expands and causes arm to rotate) or the diaphragm gauge (membrane deforms under differential pressure), and thermal gauges which detect the change in heat conductivity of a gas. A primitive manometer was invented by Torricelli in 1643. In Grantville, we probably have diaphragm barometers in several homes, and the steam buffs have pressure gauges which can work up to probably ten or twenty times atmospheric pressure. pH is a measure of the acidity or basicity of a solution. You can measure it quantitatively with a pH meter; which is really a voltmeter with a glass electrode sensitive to hydrogen ions. There isn't any useful information about them in the encyclopedias, but it might be possible to reverse engineer them, and, if one of the chemists took a course in chemical analysis, they would be described there.
If a pH meter isn't available, then you can estimate pH by using one or more acid-base indicators. Those are chemicals which change color depending on the pH. The oldest indicator, litmus paper, was known to the down-timers. EA/Indicator mentions that a mixture of methyl orange, methyl red, bromothymol blue and phenolphthalein will change color continuously from red to violet as the pH varies from 3 to 10. Several of these indicators are discussed in slightly more detail in EB11/Indicator.
Safety Equipment
The hazards posed by chemicals are fire, explosion, and irritation, burning or poisoning through inhalation of vapor, or skin or eye contact.
Borosilicate glass or stainless steel vessels, goggles, wash stations, specialized fire extinguishers, and fume hoods are all taken for granted in the late twentieth century laboratory but will be quite new to the down-timers.
For further details on hazard control in industrial processes, see Cooper, "Industrial Safety" (part 1 in Grantville Gazette 17 and part 2 in 18).
Separation Processes
Many naturally occurring inorganic chemicals are found together with other chemicals, from which they must be separated.
Chemical processes may also yield a mixture of products. When the reaction is performed, you have to separate the product from whatever else is present. At the very least, there will be solvent. If the reaction didn't go to completion, then there will be some starting materials still around. If your reactants and solvent weren't pure, then you have to worry either about the original contaminants or what they might have been converted into.
Some reactions, by their very nature, create more than one product. For example, there are decomposition reactions, which break a large molecule into two or more smaller ones. And there are many reactions in which there is a "change of partners" (compound AB reacts with CD to form AC and BD, where A, B, C and D represent pieces of the reactants).
Separation of the mixture usually depends on the physical properties that differentiate the desired chemical from the others with which it is associated. But suppose that you need to separate X (desired) from Y (undesired), and you can't do so directly. Well, there are tricks that depend on the different chemical reactivities of X and Y. You could chemically convert X to Z, separate Z from Y, then convert Z back to X. Or convert Y to Z, and separate X from Z or even convert X to Z and Y to W, separate Z and W, then convert Z back to X.
The more common separation processes, and the related physical properties, are:
Distillation/Boiling/Condensation: Boiling point (vapor pressure)
Recrystallization: Solubility of Pure versus Mixed Solutes
Decanting/Filtration: Solubility in a particular solvent, and particle size
Extraction: Difference in solubility between two immiscible liquids
Stripping: Difference in solubility in a liquid and in a gas
Sedimentation/Centrifugation: Density
Magnetic Separation: Magnetism
The down-timers are familiar with simple boiling (distillation), but not with techniques such as fractional distillation and vacuum distillation. I will discuss the more advanced techniques in a forthcoming article on the organic chemical industry. Since the down-timers have only the vaguest concept of gases, they are unaware of the elements that can be collected by the liquefaction of air.
Recrystallization was used by Birringucio in the sixteenth century to purify leached saltpeter. (Bohm). In the simplest form of recrystallization, the crude material is dissolved in a minimum q
uantity of a single solvent, heated enough to bring it all into solution, and then allowed to cool. The principal component crystallizes out first, in a purer form. I am not sure that the down-timers know about multi-solvent crystallization. In any event, modern chemistry increases the number of solvents from which to choose. We are also now more aware of the importance of initiating the crystallization step by providing a seed crystal or creating a seeding surface.
The down-timers also know that some reactions form precipitates, which can then be separated from the remaining liquid by decanting the latter. And they filtered liquids through felt, paper, and porous stones. (Bolton). However, they only practiced gravity filtration, not vacuum filtration, and their filter materials can be improved upon.
The down-timers have prepared extracts, usually with water, of various plant tissues (and the aforementioned leaching is also a form of extraction). However, they haven't really exploited extraction with organic solvents.
Since the down-timers don't know of any gas other than air, and use air in chemical processes only as an oxidant, they aren't aware of the use of a gas to selectively remove a chemical from a liquid.
Density separation by gravity has been used since antiquity. However, centrifugal separation didn't begin until the nineteenth century (a centrifuge was first used separate cream from milk). A centrifuge artificially achieves a sedimenting force much greater than gravity, and hence can separate materials of different density much faster than gravity can.
The down-timers are barely aware of the existence of magnetism, and they lack powerful magnets. Hence, they haven't performed magnetic separations, e.g., of ferrous from non-ferrous metals in recycling operations.
Scaling Up
In the seventeenth century, there were chemical processes, like dyeing and tanning, which could be called industrial processes. Nonetheless, there was no industrial production of chemicals, with the arguable exception of refining ores to metals.
The first chemical compounds produced in reasonably pure form on a large scale were sulfuric acid (late eighteenth century) and soda ash (early nineteenth century). Hence, the down-time alchemists are not accustomed to operations on an industrial scale.
Nowadays, the scaling up of a chemical process is the work of the chemical engineer. In the nineteenth century, chemists teamed up with mechanical engineers. The emphasis of chemical engineers is on "unit processes"-for example, different types of separation.
There are a variety of process changes that must be made when scaling up from laboratory scale (batch size under a kilogram) to industrial scales (tons of material)(White, 117-18). The most obvious one is that the reaction vessels change from glass to metal, but there are others.
Process development is the redesign of a laboratory process to work on the industrial scale. This development work is done on a "pilot plant" scale, intermediate between the laboratory and industrial scales.
The raw material samples that are run through the pilot plant process are only those that are available, if accepted for production use, in commercial quantities. The idea is to avoid using raw materials that will require synthesis, or extensive purification.
Solvents are chosen, whenever possible, so that they don't present severe fire, explosion or toxicity hazards, and so they are recoverable, in reasonable yield (e.g., at least 85%) for reuse.
Since recovery is incomplete, it is a good idea to find ways of minimizing the amount of solvent needed in the first place.
If expensive liquids are involved in the process, whether as solvents or reactants, mockup studies can be performed. That is, an inexpensive fluid with the right physical properties is used as a surrogate to test flow through the system. (Euzen 16).
Many physical processes are size sensitive because of surface/volume ratio considerations. Heating, cooling or filtering material may take minutes on the lab scale but hours on the industrial scale. Extraction of solute from one liquid to another is also on the slow side. The elongated time scale can cause a variety of problems.
There is a general preference for a short time cycle from beginning to end of the production process, but this can cause other problems. For example, a short time cycle may be achievable only if the temperature is allowed to rise rapidly. A temperature rise that is acceptable on the lab scale may result in a fire or explosion when large quantities are involved. The rate of addition of reactants may need to be reduced to compensate.
Significant byproducts of the reaction need to be identified. If you can obtain samples of these byproducts, you can add them to the product and see how the properties change. In this way, you can determine the tolerance limits to be enforced by quality control personnel on the industrial scale.
Many chemical reactions do not yield a single product, even in theory. Others would do so if the reactants were pure, but the required purity may not be obtainable in the early post-RoF period. Separation processes are chosen so that yield is high; crystallization, if necessary, is preferably the last step, because yields are 90% at best.
Ideally, the byproducts are useful in their own right, and recoverable for sale. For example, Spanish pyrites (iron disulfide) were not only used to make sulfuric acid, they usually contained 3-4% copper, which could be profitably extracted from the cinders. (EB11 "Sulphuric Acid").
The good news is that there are economies of scale. Euzen (9) says, "the capital investment normally required for the transformation of the raw material into a given product varies by the power of 0.7 with the capacity of the unit."
Batch versus continuous. In a batch process, the raw materials are loaded into the reactor, the reaction is carried out to completion, the products are removed, and the reactor is cleaned out, ready to repeat the cycle. In a continuous process, the reactor is (almost) never shut down. As product is pulled out, new raw material is added.
Continuous processes are typically very efficient; they are amenable to production of extremely large volumes at a very low operating cost. In part, that low operating cost is attributable to the relative ease with which a continuous process can be automated.
However, there are a few catches. First, continuous processes typically use equipment specially designed for the process in question. If the demand for the product drops, you have equipment which is going to waste. If there is an emergency demand for a different product, you need to set up a separate (batch) reactor to deal with it.
Second, continuous processes must be much more closely monitored. You need real time, or near real time, surveillance of the levels of all the raw materials and products so that, if you're running a little low on one reactant, you can toss more in. And if the product mix isn't correct, you can try to figure out why, and fix the problem.
Third, and this is related to the first two points, continuous process plants tend to have high start up costs.
Fourth, you are at the mercy of your suppliers (and the transportation infrastructure). If you run out of on one of the reactants because a delivery isn't made, or because the material delivered isn't up to spec, then you may have to shut down the process. Idle equipment "burns" money, it doesn't make money. And with some continuous processes, it is difficult and expensive to "restart." You can alleviate these problems by keeping a large reserve of the raw materials, but even when that is practical (some materials don't store well) it is expensive.
This means that we aren't going to see much in the way of continuous processing during the first decade after RoF.
In parts 2 and 3 we will analyze the prospects for the production of specific elements, molecules and compounds.
Table 1-1: Top Inorganic Chemicals
Sulfuric Acid and Derivatives
Sulfuric Acid* manufacture of sulfates, hydrochloric acid and phosphoric acid; acid catalyst,
Phosphoric Acid rust removal, acidification of foods, phosphate (including fertilizer) manufacture, soft drinks
Aluminum Sulfate mordant, water purification, concrete additive
Limestone Derivativ
es
Calcium Oxide (Lime)* steel and cement manufacture
Sodium Carbonate (Soda)* glass flux; pH adjustment, electrolyte, water softener
Sodium Silicate (Water Glass) cement, egg preservative, timber preservative, porosity-reducer in concrete, fire protection
Industrial Gases
Nitrogen ammonia production, petroleum recovery, perishables protection
Oxygen desulfurization of steel; manufacture of etheylene oxide; welding, rocket fuel oxidizer, oxygen therapy
Carbon Dioxide pressurized gas, fire control, welding, solvent (as liquid), refrigerant (as solid), reagent
Sodium Chloride Derivatives
Sodium Chloride* production of chlorine, chloride, and sodium compounds
Sodium Hydroxide (Caustic Soda)* strong base in soap, paper, detergent, synthetic fiber manufacture
Chlorine disinfecting water, bleaching paper, production of vinyl chloride plastics and chlorinated organics
Hydrochloric Acid* regeneration of ion exchangers, pickling steel, pH control, production of chlorides and chlorinated organics, including PVC
Ammonia* raw material for making nitric acid, ammonium sulfate, chloramine; refrigerant; fertilizer (as water solution); fuel
Nitric Acid* manufacture of nitrates; oxidizing agent
Ammonium Nitrate fertilizer, oxidizing agent (in explosives)
Ammonium Sulfate fertilizer, preparation of ammonium salts, protein precipitant
Titanium Dioxide white pigment, photocatalyst
Potassium Carbonate (Potash)* soap, glass production; drying agent; fire suppressant
Carbon Black* pigment, tire filler
(Source: Chenier, Survey of Industrial Chemistry, Table 2.1. Uses from Wikipedia.)
Finding Your Way in Another Plane
Written by Kevin H. Evans
More than anything else, air travel has become one of the great indicators of up-time connections. Aircraft and other flying devices show, more than anything else, the influence of up-time technology on the 17th century. Perhaps one of the Hallmark questions that gets asked of people who return from a visit to the USE will be, "did you see a flying machine?".
