Chemical and Biomolecular Engineering

Official blog of the Lehigh University Chemical Engineers


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Recent Timeline Review

Things have been moving pretty fast lately. I have been busy with doing school work such as finishing homework, preparing for midterms, and making progress on Senior Design Project. My group and I have just finished presenting for the second and last time this semester (phew). It had a good turn out in my opinion since we all worked so hard the night before and many other nights before too. It feels great to get that over with and move on to the next episode.

It has also just occurred to me that there’s 8 more days of school left. One more day this week, two more days next week, three schools days off for Thanksgiving break (can’t wait), and a full 5 day week coming back from break to conclude the school year on Dec. 5th. Tomorrow I’ll have a exciting Physical Chemistry Midterm, in which I’m going to start studying for after this post. And then… …drum roll please… … we dive right into Le-Laf weekend! In case you didn’t know, Lehigh will be playing Lafayette for the 150th time, as part of the “The Rivalry”. Lehigh-Lafayette is the most played rivalry and to honor the 150th meeting, this time it’s going to be played at Yankee Stadium in NYC. So it’s likely that things are going to get a little crazy and people are going to have a lot of fun. I’m actually heading to the city Friday evening and stay over Friday night. Coming back from Le-Laf weekend awaits me on Monday the 2nd Process Control quiz. So hopefully I have time to study for that as I try to complete homework which is also due on Monday. It should take me a few hours to complete the homework, and another few hours to study for the quiz. It’s definitely doable as long as I’m not too tired coming back from Le-Laf Saturday night. Definitely more doable after a few cups of coffee. One magical thing about coffee is that it makes things more doable. Anyway on Tuesday, there’ll be a take-home Polymer Science Midterm due. Once that’s complete, I’ll finally be ready for my Thanksgiving break. I’m going home for Thanksgiving break to spend some time with my family, and also maybe catch up on some sleep and yummy home food.

Lastly a motivational quote to share with all of you out there who might find this helpful.


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Unit Ops Filtration Lab

Hi everyone! For the unit operations lab, each group has to perform 5 randomly selected labs. One of the five that our group did was the Filtration experiment. The filtration experiment is a very interesting one and it can get very messy physically if not careful. Basically, in this experiment, the goal is to filter out the Calcium Carbonate in water; so it’s like liquid chalk in a sense. The filtered out CaCO3 will be collected on filter papers. The filter papers were squeezed between metal filter plates, and they are not sealed tightly, they can splash and white slurry can go anywhere. So it was jokingly recommended by our lab professor that you should wear clothing that you don’t care about being splashed on.

To start the experiment, the pressurized tank was filled, secured and pressurized. Before pressurizing, the top of the tank was off to add 4 kg CaCO3 and 40 L of water for 10% weight volume, and mixed with a long rod. Next, the lid was bolted and air sent to the bottom of the vessel from the air valve on the wall to pressurize and keep slurry mixed. A pressure relief valve on the top of the tank allowed air to flow out to maintain a desired pressure. When ready, a plate was pressed between two filter papers and valves were open in accordance with Figure 1 so the cake and filtrate volume could be collected in 100 mL intervals, where the time at each interval was also be recorded. The slurry entered the filter press and CaCO3 was collected on the filter as the remaining water filtrate exited and collected into a cylinder. Once 1 L of filtrate had been collected all valves were closed and the filter press was loosened to remove the plate and filter paper, as seen in Figure 2. The weight of the cake on the filter paper was taken while wet, then dried and weighed again to determine the percent recovery of CaCO3 for the process. This was repeated four times using one filter plate and five time using two filter plate. When the latter trials were run, an additional plate and filter paper that acted as a gasket to the back end of the press were placed with the original set up so that the slurry could pass through one filter then another, both collecting CaCO3, before exiting.

Here’s a 3D figure of what was described above.Capture


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Chemical Engineering Energy

Energy is used all around us and is  involved in many chemical processes. An energy balance is used to keep track of the energy used in each part of the system. An engineers job is to manage the required energy and find a way to reduce the energy requirement. Two types of systems that engineers deal with are adiabatic and isothermal. An adiabatic process is one in which there is no change in the temperature of the system. Whereas an isothermal system is when no phase changes or chemical reactions take place. Energy always follows the first law of thermodynamics which states that energy can neither be created or destroyed only conserved.  It is impossible to know the exact values of internal energy (U) or enthalpy (H) only the change in theses values. A reference state, mostly 0 or 25 degrees Celsius is used so that values of U and H can be used in problems. One equation used in some energy balance equations is the change in enthalpy plus the change in kinetic and potential energy equals the energy transferred. A problem involving energy balances involves steam tables and using tables of enthalpy found in the back of the textbook.

 


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Last Unit Ops Lab

Tomorrow my lab partner and I will be doing our last Unit Operations Lab for this semester. Now I think about it, this semester has really gone by fast. We only have 13 days of school left this semester. Next week is a full week, and then we’ll have a two day week thanks to Thanksgiving break. And then we’ll come back for another full week and then finals week will start afterwards.

Anyways, in Unit Ops I, we only have to do 5 labs, 2 of which we get 3 weeks to work on; they are the first and last lab. The middle three labs we only get 2 weeks to work on. Also for the first and last lab, we’ll present our lab results by giving oral presentations in front of the entire lab section. However, for the middle 3 labs, we have to present the results by writing final lab reports. So for tomorrow, we’re going to start our last unit ops lab experiment.

The experiment my lab partner and I are going to be doing is the Gas Absorption column experiment. In this experiment, oxygen is being forced to dissolved in a tank of water, which is being pumped into stripper columns going from top to bottom. Meanwhile, a steady stream of Nitrogen is going to flow from the bottom of the column to the top to absorb oxygen in the water into the nitrogen stream. A diagram is shown at the bottom of this post. In the Gas Absorption experiment, we are going to study two different types of packing materials, Raschig Rings vs. Wire mesh, and also the length of the column and its effect on gas absorption characteristics. Concentrations of oxygen in water will be monitored using a probe at the inlet and outlet streams of the tank. It is important to control the flow rate of water so we don’t flood the stripper column. It is also important to maintain a steady Nitrogen Flow. Absorption characteristics such as liquid size mass transfer coefficient, Height of transfer units (HTU), and Number of Transfer Units (NTU) are to be determined.

Capture


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Feed Effluent Heat Exchanger

In our most current Ethylene Oxide production process, the fresh ethylene stream is first mixed with recycled ethylene stream. The mixed ethylene is then combined with fresh oxygen feed at 25C to form a final feed stream of the mixture at 22.7C. Since the feed needs to be heated up to reaction temperature before enter the reactor, and reactor effluent needs to be cooled down, we decided to use a unit called the Feed Effluent Heat Changer (FEHE).

Basically, the way FEHE works is that it preheats the feed by using the heat generated from the exothermic reaction in the reactor. It then cools the hot effluent from the reactor by using the cold fresh feed. FEHE is widely used in high-temperature exothermic adiabatic tubular reactor systems to conserve energy. It applies very well to our system because the partial combustion of ethylene to form EO is very exothermic(generate a lot heat). The reaction occurs in the gas phase, so a tubular Plug Flow Reactor(PFR) is chosen. From a capital-investment and energy standpoint, FEHE is a lot efficient than a network of heater and coolers.. Since it’s a gas to gas heat transfer, the overall heat transfer coefficient is 0.17 kWm-2K-1.

Also, the reason why we need to preheat the inlet stream to a certain minimum temperature is that with a tubular reactor, if the feed temperature is too low, the reactor will quench. Quench means that the reaction will move a low-conversion steady state. However, separate heaters and coolers are easier to control from the controller design standpoint. FEHE is generally harder to control and can give us dynamic control problems. In next semester, we’re going to have to implement the system control concepts into out process since it’s going to be dynamic system with disturbances being introduced. This semester we’re only worrying about the steady state behavior of our process.

Here a picture comparing independent heating and cooling vs. FEHE.

Capture

 

 

 

 

 

 

 

 

And here’s what we have in our EO process flow diagram.

Reactor


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Having the same Birthday Paradox?

In today’s Unit Operations recitation, we stumble upon the famous mathematical problem: The Birthday Paradox.

Basically, we were discussing how the science of probability is very counter intuitive. The professor begins by asking what do we think the probability is that two students in the room have the same birthday. There was about 60 students in the class, so I thought it’s going to be something like 60/365, so pretty low. However, the question is very misleading. In fact, you reach 50% probability with just 23 people, and 99.9% with 70 people. In fact, he’s right. There’s two students who actually share the same birthday. The thing with probability is that it doesn’t always happen, but it’s likely to happen, and it works better when you have a very large random sample. Say you have 500 friends on facebook. It’s over 99.9% that you’ll have two friends share the same birthday, but on same days none of your friends share the same birthday, and on some days three of your friends have the same birthday.

Here’s a picture to demonstrate the probability increase over number of people.

 


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Ethylene Oxide Process Part II

In earlier posts I described what my Senior Design Project is about. If you missed out, you can still check them out here for background, and here for part I of the process.

When the reactor effluent comes out the reactor, you are going to get EO as your product, a large amount of unreacted ethylene, some CO2 and water as side reaction products, and inert Argon. The reason for the large amount of unreacted ethylene is that the reaction needs to be controlled in a low conversion+high selectivity fashion so that side reactions are limited. The effluent is then send to a absorber column.

In the absorber column, water is going to be sent in from the top of the column at a large flowrate. Water is used as the absorbent to absorb the gas EO into liquid water, which would exit from the bottom of the column. The unabsorbed gas such as CO2, Aron, and Ethylene are going to exit from the top of the column, in which the CO2 and Argon are going to be purged from the system. The ethylene will be recycled back so mix with the fresh feed, because ethylene is very expensive and it’s best if none of it gets wasted in the process. Since EO and water provides easy absorption, 5 trays are used. The absorber discharges at 12 bar and 25C for the gas on top, 48C for the liquid process water and EO at the bottom. The bottom stream containing EO will enter the distillation column so that EO and water will get separated.

The Txy diagram shows easy separation between water and EO at 12 bar.

Txy

 

The distillation column has 9 stages and the feed stream comes in at stage 4. The column has a condenser at 85.8C with a reflux ratio of 13.8. A reboiler is also used to vaporize the bottom liquid to the top which is then condensed by the condenser. The EO effluent coming out of the column is in gas phase with a purity of 99.5% Ethylene Oxide. The process water exit stream is being divided into two streams. One stream get recycled back to the abosrber to use as absrobent, while the other stream exits out of the system to avoid accumulations of process water.

 

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