Category Archives: Chemistry

On Running a Plant

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Here is a collection of thoughts on running a chemical plant, listed in no particular order.

  • Always have some extra production capacity. Don’t be tempted to book every hour of plant time with processes.
  • It’s easier to get purchase orders than you think. Corollary: It is easier to overbook a plant than you think.
  • Hire the smartest, hardest working people you can afford. 
  • Never do R&D in the plant. Consider using laboratories for that.
  • You will eventually have an incident or an accident. Make sure the HAZWOPER people drill every now and then.
  • Beware the rag layer. It will confuse the operators.
  • Hot filter cakes can ruin your whole day.
  • Somebody sit and think about how failures might be expected to propagate during an incident.
  • Don’t be an asshole.
  • Watch out for reactions with initiation lag times. They’ll getcha.  Stored energy is scary.
  • Try to get the supplier to send dry, clean solvents. Purifying solvents is always a money losing operation.  The same is true for all starting materials.
  • To the greatest extent possible, try to move solutions around rather than solids. Solids handling is always more difficult.
  • Think about where that butyllithium solution is going to go if there is a spill.
  • Try to decide early on how you would like the next disaster to unfold. This is true for all hazardous operations- plant operations, highway driving, or marriage.

I’m sure there are many more good suggestions from Bloggerspace.

C6D6

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Crap. I nearly had a heart attack the other day. Absentmindedly, I burned an NMR in CDCl3 instead of C6D6. The shifts were all cattywompus. The atropisomerism I was expecting from the amide was nearly non-existent in deuterochloroform and my aromatic peaks were all flibbertygibbet. Cripes! This was no good at all!

So, I went to a nearby diner and thought about it over a plate of hashbrowns with onions, jalapenos, and cheese. While gnawing on the breath-busting composition, the problem of solvents dawned on me like an ice cream headache. Doh!!

That Pesky Brazil Nut Effect

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The Brazil Nut Effect is a type of equilibration process that granular systems with a distribution of particle sizes will undergo. It occurs with agitation and proceeds in such a manner as to result in a final state with the center of mass as low as possible. The equilibrated state results in the larger particles migrating towards the top and the smaller particles filling the void spaces down low. According to the above Wikipedia site, certain container shapes can suppress or enhance this effect.

In the merchant chemical business, suppliers strive to provide customers with the maximum quality that is feasible.  Some applications require high chemical purity and others require less purity. The trick is to pay for the purity that you need.  Excess purity is an unnecessary expense.

In many applications a chemical substance must be both chemically pure and of a certain specific physical form.  For applications where the solid must be blended to form a suspension, a slurry, or it must dissolve rapidly, a small particle size is often desirable. Particle size control and analysis is an art that many synthetic chemists can go through their entire careers and never encounter.

In the process of filtration, solids often compact along surfaces to afford flakes and angular chunks that may retain their shape until they reach the package. Lumps can arise from incomplete washing and drying and may be indicative of chemical inhomogeneity in the bulk material. 

Chemical products that are used in compounding for very exacting applications- catalysts, coatings, polymer compounding- may have specifications that require the absence of lumps in the bulk solid. Free flowing homogeneous powders can be prepared by milling or sieving or even spray drying. Compounds that are air, moisture, or light sensitive may not respond well to excessive handling. Before you accept business involving powdered products with bulk solid specs, you need to demonstrate that it is art that you can actually perform.

This is where a smart buyer is worth their weight in gold. Instead of having their own company take the burden of particle sizing, they make the vendor do it. And if the vendor fails, find another.

Where the Brazil Nut Effect seems to enter my life is when the product finally arrives at the customers facility.  If your nice powder had even a single hidden clump in it, you can bet that on arrival it has migrated to the surface to greet the frowning customer. I have received digital photographs of this from customers who wished to drive home the point. So, you just buck up and apologize as sweetly as you can manage and give them your FedEx number so they can send it back.

Analytical Life Without NMR

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We synthetikkers live in the gilded age of NMR. This analytical method is so fast and so rich in quantitative and structural details that we may forget what it’s like to produce materials that aren’t amenable to NMR rigged for liquid samples and H, C, F, B, Si, and P.

I’ve been busy making metal oxides and various complexes for sale that lend themselves to a very short list of analytical methods. When you make compounds for sale you have a responsibility to provide an unambiguous assay of purity for the lot.  Compounds that are poorly soluble, paramagnetic, or lack NMR active nuclei can be problematic for NMR assay in a production setting. Yeah yeah, I know- get a solid state NMR. Well, we don’t have one and it ain’t gonna happen in my lifetime. Meanwhile, I have 200 g of new product that needs to get certed and into inventory.

Lately I have been taking cues from catalog company web-sites and exploring other methodologies. Complexometric titrations for metals assay, AA, gravimetric AgX for halides, Karl Fischer for water, Loss On Drying (LOD) for volatiles (water, solvents), combustion analysis (C, H, & N), Glow Discharge MS (the Big Hammer) for refractory metal oxides, XRD for anything that could be in the xtal database, melting points, TGA, and I’m turning back to FTIR. 

I haven’t been using FTIR in a quantitative way, just looking for a “Conforms to Structure” result. But nonetheless, in the preparation of new compounds for the product list it is a life saver. I can convince myself that the desired ligands are there and use other methods to try to quantitate their wt %.

I always feel better if we can come up with 3 methods that corroborate the composition. You don’t always have to come up with methods that are on the specification either. It is reasonable to report results on a Certificate of Analysis that are “Report Only” and show general conformance rather than some percentage quantity.  Examples might be appearance, color, or even an NMR spectrum.

I have only recently begun to use XRD and am a mere novice in its intracies. I have sent solid solutions where components that I knew to be there were not detectable. I have also sent samples that came back with % compositions of several xtal phases. For characterization of production lots, it has utility in the detection of certain components. Amorphous phases and random, solid solutions are a blind spot for the method. On the other hand, there is ca one half million compounds in the database so it can detect xtal phases down to ~ 1%.

I have learned an expensive lesson in regard to ICP MS. The method is quite blind or unreliable with certain elements. Sulfur and halides in particular. A sample can be loaded with sulfur (often as sulfate) and the assay will come back with a wildly low value. An ICPMS assay of rare earth metal oxides can support a claim for 99.99 % total rare earth oxides. A GDMS of the same sample may show that it is 99.8x % in metals and even lower if you include halides, sulfur, and phosphorus. 

To be fair to purveyors of ICP MS, it is quite sensitive but standards at the lower limit of detection may not be available. Sub ppm numbers without an explanation of conditions and error are to be taken with skepticism.  Everything looks like a dogs lunch once you get down to the sub ppm level.

Breaking Bad

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The AMC channel on cable is running a series called Breaking Bad. It is about a high school chemistry teacher who, for various reasons, begins to make high quality methamphetamine with a former student. It is actually quite interesting to watch. Never before have I seen so many details of chemical synthesis on an entertainment tv program.

The 2nd episode portrays a lecture on chirality to a chemistry class. The technical details seem well researched and the dramatic situations are unexpected and novel. I have to say that it is quite well done.

The teacher is a kind of anti-hero. We can identify with him to a point. But where we depart from him is where he breaks bad. The scenes of a chemist working in a respirator and tighty-whities may frighten some viewers. Caution is advised.

et Al. A Gathering in Memory of Albert I. Meyers.

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Colorado State University has announced “a gathering in memory of a remarkable life” in honor of University Distinguished Professor Albert I. Meyers. It will be held Friday, February 22, 2008, at 10:30 a.m. in the Arizona Room at the Hilton Fort Collins. You may recall that this hotel is 2 blocks south of the Chemistry Building.

RSVP:       csn (at) lamar dot colostate dot edu

This event is being managed by the Director of Development at the College of Natural Sciences at CSU. (I am hesitant to post names and phone numbers that can be collated by web crawlers)

I’ll definitely be there.

Bicarbonate Vulcanism

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I’m taking thursday off to judge a middle school science fair. Should be a hoot.  I don’t know what I’ll say if I see an 8th grader with a volcano experiment. Hopefully we’ll see some hypotheses, measurement, data reduction, and conclusions rather than just demonstrations. I’ll try not to make anyone cry.

Update:  By my estimation, the science fair was a success. I was impressed by the number of students who obtained results that did not align with their hypotheses. I made a point of suggesting to them that experiments which give results that are unexpected are the most interesting of all.  We talked about what success really means in experimentation. Most seemed relieved to hear that their efforts weren’t wasted.

After we discussed this, I placed an epistemological time bomb in their consciousness. I asked the question “When people speak with great certainty but never do experiments, what are you going to think about their assertions?”

There were no volcano displays. That is elementary school stuff. But there were several Mentos/Coke Cola research studies. One kid built a potato cannon that used hairspray and a lantern igniter to launch the spuds. I predict that this kid will eventually lose body parts.

Bis, Tris, Tetrakis

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For many seasons, Th’ Gaussling was the keeper of part numbers and nomenclature in his village.  Fellow peasants would stumble out from the dark and dank mines to plead for new part numbers and names for the new products. As always, outsiders are surprised to learn that this is an actual “job”, but in fact it is. When you make new stuff, eventually you have to call it something. And what you call it has to be recognizable to the barbarian tribes outside the walls.

Peasants and grandees alike would take the names in gratitude for the everpresent fear was that they themselves would be called to toil in the muck of nomenclature as I have.

The dark world of nomenclature is split into two hemispheres- IUPAC and CAS. I don’t know what the deal is with Beilstein. It seems to be a sinking ship with a few deckhands polishing the brass knobs as the bow submerges.  Arguably, CAS has become the default system for nomenclature and identification in much of the world. The CASRN is increasingly the standard for unambiguous substance identification. The US EPA relies upon CAS to keep track of the TSCA inventory. Chemical sellers all over the world rely on the CASRN system to identify products and as a search term to attract internet search engines to their websites.

The major problem that I have encountered is that nomenclature from the 9th collective index (9CI) is often incompatible with our accounting system. The system does not accomodate Greek letters (kappa and eta) and the numbering system leads to sorting and format problems with list generation and subsequent retrieval. The complex system of numbering schemes and nested hierarchies plays havoc with the system as well, if for no other reason than the character count exceeds what is permissable in the data field.

Even more troublesome, the complex names are largely inaccessable to non-chemists. It is very hard for administrative assistants and temps to comprehend accounting data when they are fundamentally unsure of what the identity of the product is and why various materials show up in the bill of materials. To non-technical folks on the business side, chemical names are often just a complicated character string that is prone to data entry errors.

I’ll have to admit that nomenclature from earlier indices (6CI to 8CI) is often more user friendly in this regard. So when it is time to choose a name, 9CI doesn’t always win. This is a propagation step in the retention of obsolete nomenclature and I am guilty as hell of keeping it going.

Unhappy Chemicals

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We all have experiences with chemicals that stick in our memory. Experiences where we have witnessed just what chemical potential really means.  Proton or electron transfer can be downright frightening sometimes. Rude and abrupt phase changes or angry exotherms. Sometimes nature rages back at our feeble attempts to take the dragon out for a walk on a short leash.

I can name many exciting materials, but I think that chlorosulfonic acid is one of the more exciting and obnoxious substances that isn’t explosive or neurotoxic.  What are your favorites?

Skeptical of Hydrogen as a Mass Market Fuel

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If one examines the composition of propellants and explosives, what you find is that the successful and desirable compositions are those substances that decompose to produce many more moles of decomposition products than moles of starting materials.  As a result, modern propellant compositions have not just a preponderance of nitrogen atoms, but also more skeletal C-N or N-N linkages that replace C-C linkages. Dinitrogen as a decomposition product is more atom efficient in producing PV work than is CO2 or H2O if only because a molar volume of N2 contains only 2 moles of atoms as opposed to 3. 

Designers of explosives and propellants are principally concerned with doing work (W=Fd=PV) against the environment. It could be moving soil, forming a shock wave, or a accelerating a projectile out of a tube. Some particular mass needs to be accelerated over a distance and extracting the last bit of work from the expanding gases is desirable.

PV work is performed by evolving lots of -kJ/mol from heat of formation and arranging for the expanding gas to do something useful. In the case of propellants, dinitrogen formation yields a healthy heat of formation produced from making a triple bond. Hot gases want to expand and move whatever they are in contact with. The more molar volumes of gas generated, the more work that can be done. 

Some of the above line of thinking applies to the combustion of hydrocarbons as well, though the necessary formation of triatomic gases lowers the atom efficiency. The combination of C=O and H-O bonds being formed leads to a net evolution of heat compared to heat absorbed in breaking C-C, C-H, and O-O bonds. Properly chosen fuels and oxidizers provide a net increase in moles of gaseous products leading to an increase in molar gas volume.

Now, consider the case of the combustion of hydrogen and oxygen to produce water: 2 H2 + O2 –> 2 HOH.   In this reaction three moles of gas react to produce only 2 moles of  gas. There is a net loss in molar volume of 1/3 at constant presssure.  Obviously H2 reacts violently with O2 to produce PV work.  Hydrogen can be used to power an Otto cycle engine. But the net loss of molar volume across the reaction would appear to be a drawback to this system compared to others. The question I have is, how does this figure into the overall efficiency of H2 as a fuel?? 

Hydrogen is known to be problematic in engines due to what is called a cooling effect.

One of the key issues to consider with hydrogen economics is the fact that every last molecule has to be manufactured from hydrogen rich feedstocks using energy input. Hydrocarbons have to be cracked in some way, water has to be electrolyzed, or metals have to be oxidized with acid to produce dihydrogen. 

Given that H2 has to be manufactured by cracking hydrocarbon resources or electrolysis of water, does it make sense to use H2 as an automotive fuel? Why not just combust the hydrocarbon that was cracked to give up the H2 in the first place? Better yet, combust H2 at a centrally located gas turbine power plant and distribute the energy as electricity.

Hydrogen isn’t easily liquified (like propane) and the compressed gas requires heavy containment. 

With xtal ball in hand, the more I peer into the next 50 years, the more the future appears to be electrically powered. Todays hydrogen and ethanol schemes found in the popular media result from our collective unwillingness to address the real problem: How do we modify our behaviour to consume fewer kilowatt-hours (or BTU’s) per capita?

The answer is that we need to live closer to work, drive fewer miles, divert fewer hydrocarbons into disposable products, and generally consume fewer kg of resources per capita. Hydrocarbons are a very valuable resource- we’re fighting in the middle east over access to oil output in that part of the world. 

Petroleum distillates have a wonderful combination of attributes that make them valuable. Petroleum distillates have high energy density, they are liquid in ordinary conditions and hence can be pumped and atomized, they offer a choice of flash points, and are reasonably safe for people to handle. This is a splendid set of properties! We should be more appreciative and take better care of how we use it.

For Americans, a glimse of the future can be had for the price of a plane ticket to Japan or Europe. Higher population density, smaller portions of most things, and a larger fraction of income spent on energy.