Somewhere along the timeline of a given chemical plant process a manager will (or at least should) ask the question: “can we run this process in a more efficient and safer manner”? Chemists and engineers may be set to work finding ways to extract more profit from a process.
There are numerous ways any given process may be improved. How that is done specifically depends on the process, obviously. But certain generalities can be made that serve as a guideline in thinking through the process.
In this essay I will limit my comments to batch or semi-batch processing and to specialty and fine chemicals. Continuous processes and commoditized products are out of the scope of this essay.
Batch and Semi-Batch
A batch process is one in which a vessel is charged with raw materials which are allowed to react to form a desired product. A semi-batch process is one in which raw materials are metered into the vessel over the course of the reaction. From a process safety perspective, the big difference between the two is that the batch reaction is the one with all of the reaction energy contained in the vessel from the start. A semi-batch process is one in which the energy is metered in based on the limitations of heat transfer capacity.
Commodity Chemicals
Some chemicals are commodity products and others are specialty or fine products. A commodity chemical is a product which is produced at a large (relative) scale, commonly in a continuous process, and is subject to price pressures generated by national or global scale competition. There are exceptions, naturally. Generic drugs or semiconductor chemicals may be commoditized but manufactured by relatively small scale batch processing though still subject to commodity market dynamics.
A commodity chemical product is one which has numerous producers offering similar specifications and varying mostly by price, often resulting in strong competition. As a result of the large scale and the great competition, commodity chemicals are often priced at low dollar-per-unit levels. Owing to the basic nature of commodity chemicals in manufacturing, it is not uncommon for commodity chemical sales volume to be an economic indicator.
Here is an important economic point in thinking about commodity vs non-commodity chemicals. Commodity chemicals typically have a cost structure featuring large raw material or energy costs. Commodity processing is all about the dilution of overhead into high volume. Commodity cost structures may be quite immobilized by fixed raw material and/or energy costs.
Commodity chemicals are commonly used for mass production of other goods. Examples of commodity chemicals include NaOH, soda ash, potash, sulfur, sulfuric acid, HCl, chlorine, BTX, ethylene, propylene, butanol, ethanol, methanol, naphtha, methane, hydrogen, ammonia, etc. These are materials bought and sold by the railcar and whose sales volumes indicate the health and vigor of entire nations. Other, lower volume, chemicals are commoditized as well. Additives and treatment chemicals for commodity consumer goods like pigments, solvents, plasticizers, dyes, food processing additives, lubricants, polymer additives, metal treatment chemicals, agrichemicals, etc. These goods are sold on the large scale for their performance modification or other properties.
Specialty and Fine Chemicals
Specialty and fine chemical products are commonly sold in lower volumes for a broad range of manufacturing and formulation activity. There is no sharp line of demarcation between commodity and high volume fine chemicals. Commoditization is less a manufacturing phenomenon and more of a market phenomenon. The same is true for specialty and fine chemicals.
Specialty and fine chemicals are an important part of the total chemicals market sector. There are tens of thousands of chemical entities on the market. Most are deeply obscure, in demand only by a few researchers. A common growth strategy of catalog companies is to increase the number of catalog offerings, thus snagging new customers by providing specialized precursors to those who do not want to make a science project out of starting materials. This business strategy has helped to grow the well known chemical catalogs to their immense size.
A specialty chemical is a material that feeds into a particular use, or is valuable or usable only to a particular end user. Commonly, a specialty chemical may be used for a single application by a single customer or a few narrow applications for a few customers. A specialty chemical is often part of an intellectual property package whose use and identity is highly controlled. The specialty chemical, like a fine chemical, may be covered under process patents that limit manufacturing practices.
A specialty chemical may be of technical grade (i.e., 60 to 95 % purity) or it may be highly purified. It might be of a complex composition and specifiable only under bulk properties like viscosity, flash point, or color. Or a specialty chemical might be highly purified and have sharply defined specs requiring spectroscopy, chromatography, XRD, % ee, or elemental analysis. A specialty chemical might also be a fine chemical in the sense that its composition is in the public domain, but its application is just obscure or covered by a patent.
Generally, a fine chemical is a substance whose composition is in the public domain and is refined to some commercially viable level. A fine chemical may be a reagent or a substrate and may be used by anyone technically qualified to handle it. Very often, the composition of a fine chemical is understood to a high level. Fine chemicals may be starting materials for the manufacture of other substances, or may be used directly in an application where it remains chemically intact at the retail level. An example would be an emulsion stabilizer or some polymer additive.
Specialty and fine chemicals are not mathematically distinct definitions. The differeces are based on market behavior and intellectual property. Examples exist which may find a home under both definitions. For the most part, a specialty chemicals manufacturer is a producer of customized materials with a limited base of potential customers.
The Prime Directive
Here is the central business imperative of any chemical plant- we want to run the reaction as fast as possible without taking undue risks. Labor costs and other overhead accumulate with process time, Δt. Any given batch fine or specialty plant has x gallons of capacity available for use 24 x 7 every year. The key to profitable operation is to get maximum product output per unit time. That means maximum space yield and/or maximum rate. Decreasing production time is equivalent to increasing plant capacity.
Production risk divides into two principal domains: 1) safety and 2) economic. While it is possible to have an economic risk without a significant safety risk, the practical fact is that all safety risks are also economic risks. So in the execution of a process improvement, very practical thinking has to guide the work.
Cost Drivers
Commoditized chemicals are often disproportionately raw material or energy cost intensive relative to specialty and fine chemicals. High volume, low margin products that have been in a competitive market a while have most likely been optimized such that the labor contribution to overhead has long been minimized. For a given plant, significant improvements to the cost structure may not be easily found in the labor column if the major costs are raw mats. Except as follows. Relocating a plant to a country with lower labor and/or tax costs. Commodity production follows the labor cost gradient from a high-cost labor pool to a lower-cost labor pool.
Process intensification on chemical products that have been commoditized for a long time is difficult. Besides relocation of the manufacturing site, a step change in processing technology may be needed to improve process economics. Fundamentally new chemistry (or catalyst!) or reactor type or in materials handling may be needed to justify a change.
Whereas commoditized chemical costs may be driven by raw material or energy costs, specialty and fine chemicals are most likely to have a cost structure driven by labor and overhead. A dominance by labor cost contribution will be especially true early in the life of the chemical product. The early developmental period in the market life of a fine or specialty product is the time when competition is likely to be minimal and price pressures lowest.
Early in the life of a fine or specialty chemical product is the time when the end user is struggling to understand the market picture. This is the commercial development period. While the end user (customer) is certainly trying to contain costs, low volume may cause the buyer to rely on a single supplier for a time. This gives the vendor a chance to log enough process iterations to bring the production costs more in line with expectations.
When pricing smaller volume products, every effort should be made to pad the costs in anticipation of process upsets and low yields. And for high margin. R&D and scaleup costs are typically highest early in the life of a product. Margins should be high enough early on so that the early production pays for the development. Customers will not be enthused about this. They’ll want you to “partner” with them and get some skin in the game early. Try to avoid this, politely.
A small volume fine or specialty product should be heavy in labor costs. Over time, and as price pressure from customers mount, the vendor should be able to accept price concessions through improvements in labor contribution. This is wiggle room. A smart vendor will never price a new product too close to raw mat cost since the inevitable movement of price is downward.
Low volume specialty or fine chemicals are often not subject to the same sort of pricing dynamiocs as the commodity chemicals. This category of chemical manufacture is more obscure and the products may not be manufactured constantly or in large lots.
Importantly, lower volume fine and specialty chemicals are commonly purchased on a spot buy basis rather than a supply contract. Owing to the lack of long term certainty of cash flow, spot buy prices are always higher than contract prices.
Process Intensification. The benefits.
The business of making a reaction execute in a shorter time or in a higher batch space yield or batch chemical yield is called process intensification. The idea of intensification is to produce more product per unit batch volume of processing equipment and/or per unit batch time. Every chemical plant has a fixed number of operable reactor gallon hours per year. Given that conventional chemical batch reactors are fixtures that are very expensive to modify or change out, it is desirable to focus effort on getting the maximum product out of those limited reactor gallon hours.
In a competitive market, one way to grow is to find advantageous economies of scale and pass some of that improvement along in the form of more attractive pricing. The ability to maximize the throughput of product in fixed equipment is the ability to dilute overhead expenses into a greater number of kgs of product and direct more cash into the profit column.
Process intensification almost always involves doing something faster, hotter, at higher pressure, or in increased concentration. That is the intensification part. An exception might be an alternate process that affords a higher chemical or space yield, or faster rxn rate without undue risks. One should always be on the lookout for these plums.
Process Intensification. The down side.
The attactive part of process intensification is quite plain. But there is a down side that may or may not be apparent in any given intensification project. It is a change that could bring plant operations closer to the release of hazardous energy.
The question that any process intensification project should squarely address is the matter of the accumulation of hazardous energy. This can be manifested in many ways.
For example, you increase the concentration of your reaction mixture in your process. This is a space yield intensifying improvement that has the benefit of advantageous bimolecular kinetics. You get more product per batch and you increase the reaction rate by increasing the reagent concentrations. Reagent feed times are nominally increased, but probably not to a deleterious extent.
Naturally, there are consequences to consider. Is there an induction period to look out for? The thermal consequences of this may be magnified at higher space yields.
Does the intensified process produce excessive and unwanted side products?
Does the process generate a precipitate or increase the viscosity of the reaction mass? Increased viscosity has a deleterious effect on heat transfer and mixing efficiency. Slurry formation may be enhanced and consequently produce problems with discharge and pumping of the reactor contents. Filtration may be problematic as well.
Furthermore, as a result of reagent addition the reaction mixture may have a greater density that the initial solution in the vessel, diminishing power transfer efficiency in agitation. Effectively you may end up vortexing an inner band of reaction mass with poor flow along heat transfer surfaces.
Cavitation at the impeller tips may occur and attenuate the efficiency of heat transfer. Heating a viscous two phase reaction mass may lead to localized overheating along the reactor jacket if it is rigged for heat. I have seen this lead to flash boiling of volatile solvents along the jacket surface with an increase in pot pressure.
Another form of process intensifiaction is through the application of higher reaction temperature and/or pressure. Increasing the reaction temperature could be as easy as using a higher boiling s0lvent. Or it could entail higher pressure as well. Whereas most operations can easily accommodate a higher boiling solvent, higher pressure will require specialized pressure vessels. These are less common, in fact, they are part of a manufacturing subspecialty in their own right.
To summarize, intensify a commodity chemical process is more likely to involve addressing raw materials, energy inputs, and material handling. Conversely, while specialty and fine chemical processing could benefit from the above areas of concern, unit labor cost is likely to be a target for process improvement. Labor cost is something that can be minimized most easily by process intensification and quite likely without fundamental equipment changes.
From time to time, all processes should be re-examined for efficiency and safety improvements. But the operator should expect consequences in any process change.
Lamentations on Chemistry 