Representative raw materials

As far as possible, these R&D tests should use representative samples of the actual raw materials, fuel, water, reagents and additives, filter aid, active carbon, and IX resins that would be expected to be used in the final plant. As discussed previously, a synthetic mixture of pure laboratory chemicals from the bottles on the shelf cannot duplicate in many cases the exact complex physical structure and/or the large number of impurities in these raw materials. Similarly, whenever it is intended to use combustion gases in direct contact with the process streams (e.g., in a calciner or a dryer), the exact composition of the fuel can be significant. Such combustion gases can contain ash particles or gaseous impurities that can contaminate the products or would need to be treated in the waste streams or can accumu- late in the plant.

It has often been found in real cases that the use of certain raw materials

in such tests did result in serious, nonexpected problems. For example, in solvent extraction processes, some impurities can precipitate as fine solids causing the liquid–liquid mixture to emulsify and, thus, preventing the normal operation of the process. In one particular case, the raw material contained an impurity with oxidizing power, which attacked and destroyed the organic extracting reagent used. In hydrometallurgy and salt processes, the precipitation of solids that stick or build on the walls of the equipment and pipes can stop a plant. Some natural streams can, when heated, release some dissolved noncondensable gases, which may

disturb the vapor–liquid equilibrium, and/or (at least) need to be collected and vented properly. Other problems can be the precipitation of colloid suspensions, coloring phenomena, etc. Such troubles may be serious enough to “kill” sooner or later the proposed industrial process at least in its original form, so it is very important to discover and diagnose them as early as possible. Possible solutions can include pretreatments or even changing the source of the problematic raw material.

Unfortunately, it often happens that, despite all reasonable efforts, rep- resentative samples of all the actual raw materials cannot always be readily procured from the beginning of the experimental program.

First Situation — This difficult situation has been typically found, for instance, when a new mineral deposit was being explored and small samples of the expected raw materials can only be separated and reconstituted from small drilling rig cores in quantities hardly enough for the analytical and preliminary bench tests.

Second Situation — Another typical case has been the development and demonstration of a proposed process, which was intended to handle an effluent stream expected from a “future” operation that was still at the design or construction stage.

Third Situation — This situation has been also encountered now and again in the development of large-scale biotechnology processes, which typ- ically consist of two separate parts:

1. The fermentation section, which is producing a broth containing a valuable product (e.g., a carboxylic acid)

2. The recovery section, intended for the separation of such valuable product from the broth into a pure, concentrated, marketable form These two sections are generally developed and even designed sepa- rately by two specialized groups, and they are often built in different plots “across the road.” Obviously, all the characteristics of the new recovery process are derived from the exact composition of the expected fermentation broth, as defined at the time of the project justification. But it often happened that while the “recovery” group was developing, designing, and building their processing unit, the “fermentation” group was continuing their efforts to improve their part. They would aim at a better productivity (which is the average production rate per unit volume of fermentor) and/or a better yield on the raw materials. This can be quite natural from their point of view, but the resulting changes in the broth composition (mostly with regard to the associated impurities) can have serious (negative) effects on the recov- ery process, as developed.

A mutual understanding and coordination between these two groups should be obvious, but often can be delicate in real life and may have to be imposed from above. To be fair, the fermentation group is not always informed of the downstream development (“What do these biologists know about our separation processes?”). But, at least in one case known to the

author, when the fermentation group was informed that one of the impurities generated by the microorganism constituted a very serious separation prob- lem, they found a genetic “trick” to prevent this particular impurity and replace it with a less problematic one.

In such cases, where representative samples of the actual raw materials cannot always be readily procured from the beginning, an experimental pro- gram on “synthetic” mixtures can only be done as an exploratory work aimed at the preliminary process design. The results need to be clearly marked as such, and this situation reflected in the safety factors included in the economic analysis. Repeated tests should be scheduled for later, in the exact selected conditions, as soon as the actual representative samples can be obtained.