Chemicals I Have Known (and Made) – Acrylonitrile

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The last chemical I wrote about, hydrogen peroxide, I described as a cute, cuddly chemical. The next chemical I was involved with was anything but cuddly. Acrylonitrile, or Acrylo as we called it, is an organic chemical that is used to make acrylic plastics and fibers. By itself, it has toxicity as it will release cyanide within the body. But the process to make the chemical is also very nasty, and especially so where we made it in Memphis. A little background first, though.

I received a promotion and gained the title of Production Supervisor in the Acrylo process. This was a big enough process that it had two production supervisors. I was placed in charge of planning the annual shutdown, which required intense logistical planning. I served as a backup to the real process supervisor. He was a Memphis native who had come up from the hourly wage roll to his exempt role position. He actually was a classmate of Elvis Presley when they were both in junior high school, but he did not have any good stories about their shared time. So I had the advantage of being able to learn about supervision while only occasionally really taking charge.

chemical plant

The Acrylo process is a huge process, more like an oil refinery than a standard chemical plant. It had six huge reactors where the chemicals propylene, ammonia, and oxygen (from air) are mixed with a catalyst in fluidized bed reactors. These reactors were about 12′ in diameter, and some 40′ tall. The reaction itself creates significant heat, so the reactors are full of tubes containing water which turn into steam that helps to drive the later separation processes. Once the chemicals have reacted, the off-gases are sent into an absorbing tower. This tower was over 100′ tall, and about 15′ in diameter. After the gases are absorbed in water, it is necessary to separate out the other reaction products. The primary one is hydrogen cyanide, which I wrote about earlier. There were two distillation towers used to separate and purify the hydrogen cyanide, which was then sent by pipeline to the other part of the plant that produced cyanide as its primary product. I remember that one of the pumps that transferred the cyanide developed a leaky seal, and since it was several months before the scheduled shutdown, the solution was to barricade off a section of the process with good old yellow and black warning rope, guaranteed to be a barrier against all chemicals. NOT! In fact, even beyond the tape, you could taste the cyanide, and this is how I became sensitive to cyanide and was able to easily pass the sniff test during my annual physical at the plant. It does not smell like bitter almonds, rather, it is an unpleasant sensation that grabs at the back of the throat.

Once the cyanide was removed, the crude acrylonitrile had to be separated out of the ammonia-laden water. There were a total of five distillation towers, each with a different purpose, until finally the refined acrylonitrile was pure enough to go into the storage tanks. One of the distillation towers actually concentrated another byproduct, acetonitrile, which is used as a solvent. Eventually though, the ammonia-laden water was neutralized with sulfuric acid, and had to be disposed of. Now every other commercial acrylo plant in the US was in a location where the waste stream could be injected into the earth in a deep well. In Memphis with its extensive aquifer system near the Mississippi River, this was not a viable option. So when the plant was built in the 1960’s, and energy was extremely cheap, the solution implemented was to incinerate this stream. We had three huge stacks that could be used to “thermally oxidize” the solution, and release nitrogen, water, and sulfur dioxide to the atmosphere. We were the 2nd largest sulfur dioxide emitter in western Tennessee. Only the Tennessee Valley Authority’s coal-fired power plant was a larger source. As you can imagine, when the dual energy shocks of the 1970’s came, burning a water waste stream put a larger and larger burden on profitability. So much so that when our plant suffered a major freezing incident one winter, that proved to be the final straw that led to the plant’s closure and eventual dismantlement. Chemical plants really, really do not like cold, freezing weather. And seeing 12″ diameter burst water pipes start to leak when they finally thaw is not something I ever want to witness again.

But before the process was closed, there were some really wild times I had. One in particular involved a one ton cylinder of sulfur dioxide. Now pure sulfur dioxide was used as a polymerization inhibitor in the vapor space in the columns where cyanide was purified. So we had tubing running from the cylinder up to the tops of the distillation towers. Even though sulfur dioxide boiled at 14ºF, it took a little extra push to ensure that enough gas flowed up to where it was needed. So we had a simple plywood enclosure where we kept the cylinder, and we had steam coils underneath the cylinder. Such a complex system couldn’t ever go wrong, could it? Well, it did go wrong, and the fusible plug in the cylinder that kept it from over-pressurizing, that plug melted and began to release the content of the cylinder to the atmosphere. That was one of the days where the other Process Supervisor wasn’t there, and I was in charge. I had to direct the evacuation of the adjacent laboratory and technical building, but what saved us was one operator who was able to get onto a forklift with breathing air, and pulled the cylinder out, where it could be sealed by hammering a wooden plug into the hole where the fusible plug had been. We prevented releasing the entire cylinder contents, which could have affected a large area, including US 51 highway which ran parallel to the plant.

To this day I don’t remember what we did to get another cylinder in and fix the tubing that had torn away when the cylinder was pulled out, but I do remember that we didn’t create a huge environmental incident.

When we finally did get into our planned shutdown, the biggest job was the replacement of our 100+’ tall absorbing tower. We got cranes in that were able to lift the entire tower – the big crane to lift from the top, a smaller crane to guide the bottom section. Then the process was reversed so that the new column was installed. We did this on a weekend when most of the lab people and other technical engineers weren’t around. My job? To run the video camera that captured the move. Somewhere there was a VHS tape that documents the replacement of this absorbing tower, which was used for about one year before the entire process was shut down.

Propylene is the main reactant to make acrylo. It has properties very similar to its chemical cousin, propane. So you know those long cylindrical tanks that hold propane? We had four big tanks that held the propylene. One thing that most folks don’t know about chemical piping is that there is almost always a little bit of leakage that comes out of valves and flanges. And for whatever reason, propylene attracts wasps. So going up on the storage tanks was a bit of an adventure. It was necessary to keep watch in order to knock down wasp nests before they got too big.

One other similarity to a refinery was that the residual gases from all of the columns was released through a flare stack. This stack was 175′ tall at its tip, and one of the tasks for the shutdown was to inspect the flare. I, being a novice supervisor, didn’t always think about my decisions. We had an intern who had his own pilot’s license, and was clearly unafraid of heights. So he asked, and I gave permission, for him to do the inspection on his own, and trusted him to do it safely. If he had an accident, my career would have been over at that time. But he completed the inspection, and came down safely. It was only years later after I gained more experience that I realized what a risk I took with his life and with my own career in my company.

The equipment for this process was huge. We used air as an ingredient. So it was a 2500 horsepower air compressor that fed the reactors. That was one impressive motor that ran that compressor.

Of all of the chemical processes I worked with, this one was by far the “dirtiest”. We emitted tons per day of sulfur dioxide. We sometimes had cyanide leakage. We had another wastewater stream that did go to the sewer system, that we had to monitor for compounds that had the nitrile (or cyanide) functional group – the CN on the end of the molecule. Before I worked in the process, they had tried to see if they could use the ammonium sulfate waste stream as a fertilizer for soils that needed acidification. They had a section of ground near the plant set up to receive the waste, and monitored the soil to see how it worked. Spoiler alert – it didn’t work.

One thing that I appreciated in my time in this process was that we had a Superintendent who believed that his supervisors should know what we were expecting workers to do. So all of us had to put on self-breathing air packs (like scuba tanks), put on chemical-proof suits, and disassemble and reassemble a flange with its bolts. It did show me how exhausting working in that type of environment was. When I took off the suit, I was drenched in sweat. But in my mind, I thank my old supervisor’s supervisor for giving me a taste of what it really is like to work in such an environment.

In the Memphis plant where I worked, there were four large chemical processes. I’ve shared the stories of three of them. One more to go.

 

Chemicals I Have Made – Hydrogen Peroxide

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It’s such a cute, cuddly chemical. Found in its brown plastic container in medicine cabinets across the world, it is poured on cuts and scrapes where it foams up in bubbles. Safe enough to be used as a mouth rinse. Good old 3% hydrogen peroxide! But let me assure you, what is safe at 3% strength, is not safe at 35% concentration. Or at 70% strength. Hydrogen peroxide, or H202 , is a chemical that must be given a great deal of respect. In my career, I worked in a process that made H202 for several years, and I’ve seen examples of its power.

When tank cars were loaded with H202, the hoses would still contain some of the liquid in the lines. There was an attitude that since this was not an organic material, and since the decomposition products were water and oxygen, it was not worthwhile to ensure that the last drops were purged out of the line. So a metal box was filled with steel scraps, metal shavings, and other pieces of metal with a high surface area. This box was used to decompose the peroxide before it ran into our cypress-lined trench system. On one occasion, significantly more peroxide ran down into the box than was intended, and not all of the peroxide decomposed before it entered the tar-covered cypress trench. Decomposition continued, and the heat released along with the enriched oxygen environment inside the trench, actually caused the trench to begin smoldering. The fire alarm was sounded, and the investigation showed that the fire was essentially caused – by water. That is the power inherent in industrial strength H202.

Before I worked at the plant, they had a specialized still that concentrated peroxide to 90% purity. That strength was used as a rocket fuel, and as a propellant for torpedoes. I never heard of any stories about accidents with that grade, but it would take very little in order to release the energy found in that strong of a chemical. After I left the Memphis Plant, I heard about something that happened to a tank car outside of the plant. Tank cars for peroxide were made of about 1/2″ thick aluminum. One night, a tank car essentially exploded, opening up the top like a pop can. The thought is that someone playing with a rifle, shot the tank car. There is a little organic material that sits atop commercial grade H202, which reacted to form organic peroxides. The energy from a rifle shot caused the organic peroxide to detonate, which triggered the release of the oxygen from the decomposing peroxide. I saw the car on a trip back to the plant. It clearly showed that there is a lot of energy available with 70% H202. I have searched diligently on the internet but I can find no on-line evidence of this incident.  One can only imagine what would have happened if this incident occurred after 9/11.

The process for making H202 is complex. An organic solution called working solution is the key to creating the H202 molecule, which then recycles to begin the process again. The working solution first enters the hydrogenators, where hydrogen gas contacts a catalyst of palladium chloride coated out as palladium metal on alumina particles. The palladium chloride comes in a solution form in 5 gallon pails, costing multiple thousands of dollars per pail. After the catalyst is filtered out, the working solution goes into the oxidizers, where air is blown through the solution. Hydrogen grabs onto the oxygen, and forms H202, which then is extracted with water, and concentrated in distillation stills. The working solution then returns and is ready to run through the loop once more.

That is a highly simplified version of the process. In practice, there is art involved. The active chemicals in the working solution can degrade over time. Therefore it is necessary to divert a side stream of working solution to flow through alumina, where the impurities that form in the hydrogenation step absorb onto the alumina. The whole process with the catalyst and the hydrogenation step is labor intensive, and it is always necessary to withdraw a portion of the catalyst and replace with fresh catalyst. To prevent that expense, and to achieve higher yield, the plant I worked at had invested in what is called a fixed bed hydrogenation system. This had shown impressive results in lab-scale testing, and in pilot plant testing, where 5-gallon sized vessels were used to prove the effectiveness before you built a 1000-gallon facility for commercial production. The new commercial facility was commissioned, and put in service.

But problems developed very rapidly. Even though the pilot plant testing did not show it, the commercial scale facility developed some hot spots inside the hydrogenator. This caused the active compound in the working solution to degrade much more rapidly than inside of the fluid bed hydrogenators. Since the investment in the working solution was several million dollars, it became imperative to find some way to reverse the damage. Lab work was expedited, and a solution was identified. They needed some engineer to manage the project and get the equipment ordered, installed, and functioning. I was plucked from the cyanide unit(see  Chemicals I have made – Hydrogen Cyanide ) and put in charge of the project.

It was a true baptism into project management. I got to travel to see the vessel that we were buying in the fabrication shop, up in the extreme northwest corner of New Jersey. There you were more likely to see a black bear than to see a Joisey girl. But the best part of the project was that I got to install and program a Programmable Logic Controller (PLC). Now this was back in 1980, and these were brand new toys  tools that used all of the advances in semi-conductors that were available. You could replace a whole rack of single-function logic switches, with a single unit that could do nearly unlimited functions. I had a lot of fun learning the ladder logic that went with this, and getting the system to work as intended. We started up our treatment unit – and it didn’t solve the problem. The working solution was still getting degraded, even when the fixed bed unit was operated at only a fraction of its intended production rate. The equipment I installed was abandoned, and the large fixed bed unit was shut down and eventually dismantled. But I had learned valuable skills and had managed a significant project by myself.

The manufacture of H202 is not different by chemical manufacturers. At the time I worked to make H202, all manufacturers used the process I described. Eventually, the unit I worked at was sold to another company in exchange for one of the other companies processes. I left H202 when I got a promotion to be a process supervisor for the manufacture of acrylonitrile. But that’s another story for another time.

 

Chemicals I Have Known (and Made) – Hydrogen Cyanide

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As I look back on my career in industry, I realize that I became inured to the chemicals I dealt with and produced. I will be posting occasionally on some of the materials I worked with and made during the first part of my career. The first chemical I worked with was hydrocyanic acid – a simple molecule consisting of a hydrogen atom, a carbon atom, and a nitrogen atom (HCN). This molecule is so simple that there are molecular clouds in space where HCN is found, released from stars that have synthesized carbon and nitrogen in their core. But HCN has a well-known reputation as a poison, one that prevents oxygenated blood from being able to deliver their life-giving load to cells. Once oxygen transport ceases, energy production in a cell stops, and the cell and the organism that contains the cell dies.

 

So at the chemical plant I worked at, one of the requirements to work in the cyanide area was to ensure that I could detect cyanide leaks so I would not wander into an area with a fatal concentration. This was done by means of a sniff test. Three beakers of water were set on a tray. Two were plain water, and the third had a concentration of cyanide in it that resulted in small amounts of cyanide vapor in the air above the beaker. To pass the test, you had to tell which beaker held the cyanide. The first time I took the test, I was guessing somewhat. None of this “bitter almonds” smell, just something that was a little off. By the last time I took the test, almost 10 years later, I picked up the beaker with the cyanide and before it made it halfway to my nose, I put it back down on the tray and said “That’s the one.” What was originally too faint for me to be certain had become so overwhelmingly repugnant over the course of a decade that it gagged me.

 

Cyanide. What’s it good for? Hydrogen cyanide is used in quite a few chemical processes as a feed stock. One of the chemical processes is used to make another chemical called methyl methacrylate (MMA), used in acrylic paints and in plastics like Plexiglass. My chemical plant made MMA as well, but that’s a story for another day. The other main use of cyanide was to make sodium cyanide, which is used in the mining of precious metals. Sodium cyanide solutions are able to leach small concentrations of gold, silver, and other precious metals out of ore, allowing it to be concentrated and extracted into product. Our plant produced sodium cyanide as well as HCN. Some HCN is shipped to other locations for use. When it was shipped, the tank cars that contained it were painted in a distinctive manner. They had red stripes on them – one that circled the car lengthwise, and one that circled the circumference of the car, forming a cross on both sides of the car where the stripes collided. These cars were called candy stripers in the trade.

 

Hydrogen cyanide is produced when ammonia, natural gas, and air are heated and passed over a platinum – rhodium gauze mesh. The off-gases are then absorbed, and the cyanide produced is concentrated and purified. At our plant, HCN was stored in tanks surrounded by dikes. One of our safety features was flare guns mounted on posts throughout the tank farm. If the worst happened, and liquid cyanide were to leak out onto the surface of the dike, folks were instructed to fire a flare gun and set the liquid on fire. HCN is volatile (78ºF boiling point), but the vapor will not explode. Instead, it will undergo a deflagration where the combustion wave front is slower than the speed of sound. Other gases like methane will explode, where the combustion wave front is faster than the speed of sound, which causes the pressure wave that creates damage in an explosion. So for HCN, it is much better to let it burn and eliminate the toxic vapors evaporating from the liquid surface.

 

One day in 1979, I was out at the plant on a Saturday. I remember that Dr. Jenks was there on that day as well, and he invited me into his office. Dr. Jenks was one of those older generation chemists who knew everything about the chemistry and processes. He had a wooden box in his office, about 18″ on the narrow sides, and about 10′ long. In that box was the replacement platinum/ rhodium gauze for the catalyst change. At that time, when precious metal prices were at a 30 year high, his office held about 2 million dollars in platinum and rhodium. I was impressed.

 

My main job in manufacturing support was in the waste treatment process. As you can imagine, the waste water from these cyanide processes needed special treatment and segregation from other waste water. The “state of the art” water collection system consisted of cypress lined trenches, with cypress boards covering the top. This ran downhill to the bottom of the plant, where we had the Trade Waste water treatment facility. Waste water came into a collection point, where sodium hydroxide was added to make sure that the water was basic. If cyanide ions were in an acidic solution, cyanide vapor would be released above the solution, and that is not a good thing. So once the pH was adjusted to make the waste basic, then it would be mixed with liquid chlorine. Our plant produced sodium metal and liquid chlorine, so we had only to send the chlorine down a pipe to the water treatment plant, and mix it in with the waste water. When the chlorine hit the basic water, it produced chlorine bleach solution (sodium hypochlorite). Bleach attacks the cyanide and converts it to a non-toxic degradation product. To ensure that the reaction took place, after treatment the water was diverted into what were called 8-hour ponds. These ponds were on either side of the treatment building, and were unlined ponds where the water was held until the reaction was complete. Then the water was released into a baffled chamber called the one hour pond where it was analyzed to make sure that all of the cyanide was destroyed, and after the last test, the water was combined with the other sewer waste and went into the City of Memphis sewage treatment system. Unfortunately at the time, our interceptor sewer did not hook up to the sewage treatment system, and the water along with all of the domestic wastewater was discharged directly into the Mississippi River. Environmental protection has definitely improved in the 40 years since I was working in this process.

 

I would imagine that the staffing situation for the Trade Waste process has also improved. Back when I worked at the plant, there was a single operator who was stationed at the treatment plant. This individual sat in a central control room, and on either side of the control room were the chlorine injectors with the liquid chlorine flowing through them. Now, I don’t know about you, but I would be hesitant to work by myself, with cyanide-laden waters and liquid chlorine surrounding my office, but back in the late ’70’s, I didn’t think as much about the implications of what could go wrong. The plant had a safety procedure where the person working in a remote location had to check in with the main control room at least once per hour. Believe me, at that time, so much could have gone wrong in an hour’s time that the operator could have been dead for 59 minutes. But it never did at that facility during at least the first 30+ years of operation. Looking now at the facility on Google earth, it is obvious that they have made significant changes and improved the safety of the treatment operation. But some of the facilities look similar to what I worked with 40 years ago.

 

There’s much more I could go into. Cyanide has some amazing chemistry, and the waste treatment is almost an art unto itself. I did some large-scale testing there where we added a hydrogen peroxide waste stream that was what I considered to be fun chemistry. But it was definitely a good process to work on for my first real production support for making a nasty chemical.

Why so close? Chemical plants and oil refineries, and water.

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Chemicals, oil, and water are linked eternally in a faustian bargain. In order to produce most chemicals, and all petroleum products, it is necessary to have access to immense quantities of water. Thus, the infrastructure for these industries is found in the low-lying areas alongside of rivers, and within the inlets and bays along the coastline of the oceans. When the inevitable floods happen, the potential for releases of chemicals and oil, and even explosions as seen in Crosby Texas this week can and will occur.

Why is there this dependence on huge quantities of water? In order to make many chemical reactions occur, it is necessary to provide heat. That heat normally comes in the form of steam. Steam is also used to enable separations of chemicals through distillation. The tall columns seen in chemical plants and refineries are usually distillation towers, where products and wastes are drawn off at various levels in the towers. These products must then be condensed, and they are condensed in heat exchangers with water being used to cause the vapors to condense. The chemicals and the water don’t mix in these condensers, since they are found on opposite sides of the heat exchangers. But immense quantities of water are used in heat exchangers, and the water is thus warmed, reducing its effectiveness in condensing and cooling chemicals.

The water used in heat exchangers and condensers may only be used once. This is single-use water and it is necessary to have a large volume of water nearby in order to release the warmed water without adverse ecological impact. If the water is reused, then it is necessary to cool the water back down in order to use it again. This is done in cooling towers, and you normally will see the plumes of water vapor coming up from these large structures, where water is cooled through evaporation as it drips on down through the wooden framework of a cooling tower. Cooling towers increase the concentration of salts in the water, since a portion of the water is lost to evaporation and may have many cycles through the cooling tower before being discarded to a body of water.

Since it takes lots of energy to move large quantities of water, and lots of money to run long lengths of piping, most chemical plants are found just adjacent to the water. They are sited so that they are above the normal flooding levels, but when unprecedented flooding happens like with Harvey, they are supremely vulnerable to damage from water. In my career in the chemical industry, I worked at two plants (in Tennessee and in West Virginia) that were situated along rivers. The plant in Tennessee did have problems long after I left when flooding from the Mississippi caused backwater flooding that buried part of the plant, which was situated on a smaller feeder stream. Fortunately, it didn’t cause the release of chemicals, and was not a large problem, but it highlights how close proximity to water comes with its own set of risks.

I have been to plants in Texas that were totally inundated from the floods this week. One along the end of the Houston Ship channel, that immense concentration of oil and chemical plants along Texas 225. The other was in Beaumont, situated right next to the marshlands leading to the Gulf of Mexico. The facilities at these plants are designed to be safe and to be able to be shut down without causing chemical releases. But. There are limits to what you can do and still be safe. When you have feet of floodwaters covering a site, then the power of the water can do things that cannot be controlled. Water can erode pipe supports, and the dangling piping will bend and break, releasing the contents of the lines. Floodwaters can shove vehicles and boats into pumps and piping, causing them to break. Even in the normal process of shutting down facilities, excess venting and flaring of flammable and toxic compounds can happen, which can cause irritation and concern among the neighbors of these facilities.

Just as there is a faustian bargain between these facilities and water, there is another relationship that comes into play. That is the relationship between the workers and their families, and their proximity to the plant. Very often the workers for these facilities are found in the neighborhoods surrounding the plants. Entire generations of workers have grown up nearly in the shadow of the towers of refineries and chemical plants. This is especially true in the region around the Houston Ship Channel. The towns of La Porte, Pasadena, Deer Park, and Baytown have a symbiotic relationship with their industrial behemoths. Only a single road separates the residential areas from the properties of the oil and chemical companies. Quite literally, the companies and the towns are all in the same boat at times like now.

The plant that had the explosions this week was a different type of chemical plant. This plant was not adjacent to a large body of water. What it manufactured was a chemical that is essential in the manufacture of plastics, but by its own nature, it was extremely unstable. In my chemical plant in West Virginia, we also manufactured a similar material. These materials are known as polymerization initiators, and they make it possible for chemicals like ethylene (two carbons bound by double bonds) to react with each other, and form long chains that we know as plastics (polyethylene). The materials we produced in West Virginia also have to be kept refrigerated or they will grow unstable and catch fire. Part of the lore of the plant involved the time when the manufacturing line for this material had a problem, and the temperature rose to the point where the chemical decomposed and ignited. That fire was remembered long after everyone who worked during the fire had left the plant. What made the situation in Texas worse, was that the organic peroxides they made are not only flammable but are explosive when they decompose.

Part of the manufacturing process for chemical plants involves process hazards reviews. In these reviews, the participants go through a systematic review of the inherent hazards of the process and facilities, and determine if there were adequate safeguards to prevent incidents and injuries. Sometimes a significant hazard is discovered, one that had not been previously considered, and then the management of the plant faces the task of getting the fix done to remove the hazard. Since it takes time to implement new facilities (and get the authorization to spend the money to build facilities), normally there are administrative controls that are put in place to temporarily mitigate the risks. But even though I participated in many process hazards reviews in my career, I do not remember ever having considered the case of having my plant submerged in multiple feet of floodwater, and having no way to get anything working for days at a time. I imagine that the chemical and refining industries will have to go through substantial work trying to come up with new safeguards that will prevent releases and explosions such as are being seen in Texas now.