Eric Flint: Grantville Gazette Volume 24

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 Derivatives

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?".