Arcal Chemicals, Inc., Woodbine, Md.
Go Back To Back To Original Design
I am amazed that the new manager changed or was allowed to change the process based on the advice of an “experienced” operator and he did not consult the company’s technical personnel about the changes. Why didn’t anyone ask if the operator was a qualified chemist or chemical engineer? Changes made without a science and technology basis should have been a no-no, at least in my book.
If the company wants to get back to producing the desired product, then I suggest the following:
1. Go back to the original process as designed and get the plant producing quality product as was being done before the “new manager” made the process changes.
2. Get the process technologists involved to review the operator’s suggestions and understand the basis for the modifications.
3. Rationalize the changes suggested by the operator. Cost reduction changes should be based on science, chemistry and chemical engineering rather than on the operator’s experience.
4. Technical staff should test out the operator’s suggested changes in a pilot plant or even in the plant (if there is no pilot plant) under very strict supervision. This will let the company understand how the changes will work out in an operating plant.
5. The operator’s suggestion indicates there are opportunities to lower the cost of manufacture. Time and effort are needed to pursue all avenues to achieve necessary cost reductions.
6. The company needs to review its operating practices and should not allow changes to be made in the process without complete understanding of the changes and their impact.
Girish Malhotra, PE, president
EPCOT International, Pepper Pike, Ohio
Change One Variable At A Time
This situation is what management of change was meant to avoid. In addition, it seems like bad experimentation to change several variables at once.
N2 is meant to protect the alkyl lithium from oxidation. Using air, especially plant air with its relatively high concentration of water — typically, 0.02 lb of water per lb of dry air at 20°F dew point — means that the catalyst and the 1-butyne, 3-chloro are exposed not only to oxygen but also to water. Depending on the availability of metal catalysts, this could pose more than a contamination or yield problem — it could be a safety problem.
DI water is slightly acidic, pH 4.5–5. Hard water, especially well water, typically is slightly basic. The EPA recommends water should have a pH of between 6.5 and 8.5; rainwater has a pH of about 5.3. Acid helps dissolve salts but also catalyzes the conversion of alkynes to a ketone, a side reaction, instead of allowing them to be carried away to distillation. So, there would be slight benefit to raising the pH. However, DI water has consistent properties, well water does not. Water, by itself, is a necessary part of the quenching process: R-Li+ reacts with water to form an alkyl compound and LiOH.
The 2-isopropanol is also part of the quench solution. Without it, the alkyl lithium could become a hazard. In addition, trying to do distillation without the liquid in the trays will be difficult. I wonder if this is causing the impurity problem?
As for chilling, this probably is required to improve the density difference between the organic and aqueous phases. Without it, some organics, especially polar ones, will be drawn to the water. Take samples near the phase break to determine the driving force between the two phases. I think you’ll find a problem.
The trickle bed is a fast, highly efficient means of removing organic compounds in trace amounts from water. The residence time reported is 20–90 seconds. However, these beds typically are designed for a certain maximum organic loading that you exceeded by “dumping” organics during quenching and decanting. You should look at the economics again; consider increasing the capacity of your wastewater system if your changes warrant it.
Dirk Willard, contract process engineer
Jedson Engineering, Cincinnati, Ohio
We use N2 at 31 psig to drive 2,200 gallons of a viscous polymer at 235°F through an electrically heat traced and insulated 2-in., sch-10, 347-ft line from a reactor, which, once emptied, is ready for the next batch (Figure 1). This takes about 210 minutes. Initially, we can put about 25 gpm through the pipe. By the time we’re done, the polymer viscosity has doubled from 380 cP and the flow has dropped to 13.8 gpm. The polymer specific gravity is about 1.05 at 235°F. The reactor is rated for 40 psig. Originally, we used lobe pumps; we switched to the pressurized system because of monomer emissions, contamination of pump barrier fluid, a heel in the reactor, and shearing by the pump. Even with N2, the product continues to cross-link, resulting in the increased viscosity and the slowed-down transfer. Measurements show that the apparent viscosity increases to 1,200 cP for a 3-in. line and 3,600 cP for a 4-in. line. How can we speed up the process? The production manager wants the transfer only to take 30 minutes but believes that boosting the polymer flow rate will substantially increase the N2 demand. What do you think?
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