Psychrometric Chart

As you may have seen in one of my earlier posts, graphs, charts and tables are extremely helpful tools for a chemical engineer. With so many different combinations of temperature, humidity, pressure, mass fraction, etc; charts efficiently organize data and provide an engineer with a quick method to determine a quantity. In ChE 031, we frequently use charts and tables to determine values for our system balance problems. Recently, the class was introduced to psychrometric charts, which are imperative in solving humidity problems.

Psychrometric Chart

The chart looks complicated, but once you understand how to use it, it is a great asset in solving questions. On the right y-axis there are mass fractions for (kg water/kg dry air). Given humid air, there is always a specific ration of water to dry air. On the x-axis, there is the dry bulb temperature, which is basically the absolute temperature that the humid air is at. Those are the simple components, the real fun starts on the inside of the chart. The vertical bowed lines indicate the relative humidity of the air. So, if given the relative humidity and temperature, you could determine the desired point on the graph and then trace across to find the mass fraction of water. If given any two values, you can always find the third. The upper left boundary of the chart is a curved line that contains important information. There are perpendicular lines to the boundary which are used to determine the values provided by the upper left boundary. Along the boundary exists the wet bulb temperature, which deals with the temperature of the evaporation at 100% saturated air. Extended past the boundary on the stair-like straight lines are enthalpy values. If given conditions for humid air, you can plot the point on the chart, and then determine all these quantities explained above. This chart is extremely useful when given a humid air system.

Dehumidifier

Above is an example of a dehumidifier. Humid air is cooled so water condenses and then a stream of lower humidity (or none) is released. If faced with a question like this, there are many different parameters that could be given. With the help of the psychrometric chart, you could determine the heat released to produce a certain amount of liquid water or determine the leaving conditions, among many other possibilities. There process for humidifying air is similar, but in this case liquid water is heated until it becomes a vapor and then it is put into an air stream in order to increase the humidity. The psychrometric chart makes life much easier when dealing with humidity balance problems.

Diels-Alder Reactions

What’s the Diel with Alder reactions? (I’ll stick to my day job) In organic chemistry, we study the reactions and properties that govern organic life. For the majority, we examine molecules and reactions that contain carbon, hydrogen, oxygen, and nitrogen. These elements are the basis for all organic material, with carbon being the most important. (the common expression being carbon-based lifeform). Organic chemistry is an extremely broad topic, but when boiled down, organic chemists aim to figure out how to produce different material. This is referred to as synthesizing a material. An organic chemist has to figure out how to get from point A to point B, it’s kind of like solving a maze. One of the major components of class is learning and employing mechanisms for reactions. Mechanisms describe how a reaction occurs and in what order. One such mechanism/reaction is the Diels-Alder reaction, which I first learned about in lecture and then actually carried out in lab.

Diels-Alder Reaction

The Diels-Alder reaction is very significant because it forms carbon-carbon bonds. The chemists whom the reaction is named after received the Nobel Prize in Chemistry for the novel discovery. The image above explains the mechanism for the reaction. A diene (2 carbon-carbon double bonds) reacts with a dienophile (C=C) to produce a six carbon ring with a single double bond. This ring is called cyclohexene. The red arrows indicate the movement of electrons which exist in the pi pairs. Pi pair bonds form double bonds. The reaction if fairly simple, it always occurs the same way with the same groups reacting. The only difference is that there can be other substituents (molecules) on the diene or dienophile, or the reactants can be rings. The Diels-Alder reaction solely refers to the above reaction, but by altering the diene and dienophile, the final product can be altered to something the chemist desires.

After learning about the reaction, I was able to complete a Diels-Alder Reaction in organic lab. We started with dicyclopentadiene which had to be “cracked” into cyclopentadiene. Cyclopentadiene acts as the diene for the reaction. To “crack” the dicyclopentadiene, we used fractional distillation, which involves boiling the mixture to remove a certain compound by recondensing it. Cyclopentadiene has a much lower boiling point than the original substance, so we were able to remove it and use for the reaction. Next, we dissolved maleic anhydride in several solvents and then slowly added the cyclopentadiene. Maleic anhydride is a while solid and acts as the dienophile in the reaction. After setting the reaction on ice, we observed the Diels-Alder reaction, with the product being cis-Norbornene-5,6-endo-dicarboxylic Anhydride (I’ll call it the “product”). This is a perfect example of how a complex substance can be produced based on the simple Diels-Alder mechanism. The product is an interesting white crystalline structure that looks like snow. To recover and purify the product, we used a recrystallizing technique by heating, cooling, and then filtering. This lab was a great way to get tangible reinforcement from what was taught in lecture. Check out the pictures below that highlight the product from the lab.

Reaction

Crystal Product

W.L. Gore Campus Event

The question on nearly every college student’s mind is, “What am I going to do after graduation?” It recently hit me that I can’t stay in school forever. For the last 15 years all I’ve known is school, never really worrying about the future; I’ve had summers off and been able to financially rely on my parents. The easy life is quickly coming to an end.

As a sophomore, my first priority is doing well in classes and learning as much as I can. However, on the back burner I am starting to look into internships, co-ops, and an eventual job. Lehigh runs a co-op program in which students work at a company for their junior fall semester and summer before senior year. Comparatively, internships take place over the summer and winter breaks, with summer employment lasting about 12 weeks. I am considering both co-op and internships for this upcoming summer. To help students network and meet employers, Lehigh sets up forums for companies to come in and inform students about what they do and possible job opportunities. Unlike the large job convention on Goodman, these forums allow for a more intimate setting where students can get more one-on-one time with employers and really get a feel for the company.

Last week, W.L. Gore and Associates held an event on campus in which they had employees talk about what they do at Gore and provide some information about their internship program. Gore is probably most recognizable for their Gore-tex brand, which is waterproof consumer clothing. This includes jackets, outerwear, and shoes. Gore-tex clothing is just the tip of the iceberg for Gore. They also produce military and fireman clothing, medical products, fibers, electronics, and filtration units among many other products. I had no idea about all that Gore produced. Check out their site here http://www.gore.com/en_xx/

Gore-tex

Pharmaceuticals

 

 

 

 

 

All of Gore’s products are derived from PTFE which is a type of polymer. It’s truly incredible all the products that can be made from a single type of material. I think it speaks volumes to the ingenuity and creativity that Gore exudes. On the left are traditional Gore-tex gloves which are perfectly waterproof. On a completely different spectrum, I was very intrigued by the pharmaceutical department at Gore. Using PTFE, they produce all types of material used in the human body. They make patches that can be put in a person’s body to cover a certain area and will remain in the body forever, without harming the host. Gore also produces sutures and catheters which are instrumental in surgery. They can engineer the material to dissolve into the body after a certain period of time or remain intact forever. I found the most interesting Gore product to be small tubes used to keep heart valves or capillaries open. If a person has blocked valve, doctors obviously need a way to keep it open. Gore’s device begins by attaching to the end of a catheter at the same diameter of the catheter. This allows the doctor to safely move the catheter and place the Gore tube in the correct location. When in place, the tube is activated and it expands, opening the valve or pathway. Some tubes have anchors which keep them in place while others eventually dissolve. The products that Gore produces are incredible and it was awesome to learn about.

Possibly the most interesting aspect of Gore, a Fortune 5oo Company, is the workplace environment. Gore has all their department factories (ie fabrics, medical, electronic, etc) within 20 minutes of each other in Newark, DE (also Arizona). This allows employees to easily travel between facilities and collaborate. The employees who spoke at the event really emphasized how they were given freedom to investigate ideas that interested them and use innovation to create products. I’m interested in research and development, so the product development field at Gore really spiked my interest. The employee speakers also said that if they were bored or “hit a wall” in a certain position, they could move to a new position that appealed to them, increasing their effectiveness. I truly enjoyed learning about Gore and I plan on doing some more research before applications for internships are due. I’m excited for the future and ready to explore other companies that, like Gore, could be a possible employer.

Spectrochemical Series — Chem Lab

One of the most striking features of transition metal compounds is their wide range of colors, especially solutions of transition metals. The intensity and particular color of the solution varies depending on the identity of the ligand attached to it. A ligand is simply an ion or molecule that attaches to a central atom (eg. Cl-,NO2-). In the lab, we first sythesized (Cu(en)2(H2O)2)I2. The ligand in this case is en complex. The starting material was copper (II) acetate monohydrate. Ethylenediamine (en) is slowly added which acts as the ligand. Water and ethanol are added in several steps, along with the solution being filtrated using a Buchner funnel, to obtain the final crystal product.

(Cu(en)2(H2O)2)I2 Crystals

Our yield was much smaller than the picture (~.10 g). The next part of the lab allowed us to develop a spectrochemical series of copper. We made several different solutions containing copper and a ligand. The solutions all started with copper nitrate (Cu(NO3)2) which is light blue in color. We studied the effect of the ligands: ammonia, chloride, ethylenediamine (en), nitrite, and water. The en came from the crystals synthesized in the first part. Each of these ligands was added to copper nitrate and it changed the color of the solution. By determining the absorbance of each solution, we are able to develop a spectrochemical series of the ligands. This series ranks the ligands from high field to low field. The wavelength that each solution absorbs corresponds to the strength of its field.

Color Wheel with Wavelengths

We used a spectrometer to determine the absorbance of each solution. Briefly, when material emits a color, that means it is absorbing the opposite color. For example, if you are wearing a red shirt, it absorbs green light. We measured the maximum wavelength that each solution absorbed, which produced a scale for the series. Copper and nitrite produce a  yellow-green solution. When we found the maximum wavelength, it was 398 nm. So, the compound absorbed violet light, while emitting green-yellow light. I will post pictures of each color at the end of the post, see if you can estimate the wavelength that each absorbs.

In the end, we were able to develop a ranking of ligands and compare it to literature (known) values. This lab was very interesting because it dealt with inorganic material (copper metal). Just how different metals burn with different colors, they also produce different colors depending on what it attached to them. The semester is winding down, and I only have two chemistry labs left. It has been really helpful to physically perform what is learned in class through lab. I definitely think it allows me to learn material better and be able to apply it to other situations. Check out the pictures of various solutions and try to determine what wavelength they absorb. Remember, the complimentary color to the visible color is absorbed (across the color wheel).

Chloride

Ammonia (left)

en

Water

Spring 2014 Semester

It’s that time of year again, class registration. The second round of exams is winding down and the topic on everybody’s mind is what classes they are going to take next semester. I think juniors and seniors have already registered, my registration as a sophomore status is next Tuesday and first-years sometime later next week. Registration is sort of the tale of two cities, Arts & Sciences and Business students have more freedom in choosing classes. They are able to fill their requirements with classes that peak their interests and truly pertain to career paths they wish to pursue. Meanwhile, engineers have a more structured curriculum, so there is less freedom to take different classes. In the ChemE department, there is a handout which organizes all required classes and provides a recommended time line of when to take each class. For this reason, my toughest part of registering is making sure I can fit all needed classes with the times and (hopefully) avoid early start times. Here is my schedule so far for next semester:

Spring 2014

My schedule is not quite finalized, I still need a HU/SS class to total 18 credits. ECE 083 is required for ChemE and unfortunately it starts at 8 AM, but it’s better to get out of the way now than later. I have two ChE classes, 210 which is Thermodynamics and 179 which is professional development. From what I’ve heard, in professional development information about careers is presented and you are able to develop an idea of what industry you are interested in. CHM 112 is organic chemistry 2, which will hopefully be an easy transition from Organic 1 (I’m taking currently). Last is BIOS 41 which is Introductory Biology. ChemE’s must fulfill a biology elective, there are several choices and I still haven’t 100% decided which to take. I really haven’t had any classes other than math and science, so I’m excited to have a humanities or social science elective.

As a whole, this semester will be challenging (aren’t they all?) but after it’s over, it will mark the halfway point of my college career. That’s kind of crazy to think about. Hopefully I can hammer out a schedule and be ready for 7 AM registration on Tuesday.

Organic Chemistry Gets Explosive

I did a double-take when I first read the experiment guide for one of my recent organic chemistry labs. “We get to blow something up?” I thought there had to be a mistake, there’s no way they would trust some college students with an explosive material. But there was no mistake, the objective of the experiment was to produce silver acetylide (Ag2C2) which is a greyish solid. Silver acetylide is shock and heat sensitive, which means it will detonate with an increase in temperature or any type of shock. When it is dry, the solid will explode given the slightest shock. This lab experience was both exciting and nerve-racking.

Silver Acetylide

The explosive nature of the compound is derived from acetylene, whose structure is two carbons bonded with a triple bond. Acetylene is a clear gas that is odorless, poisonous, and flammable. We had no vessel to hold the gas after producing it, so it immediately had to be used to synthesize a solid, Ag2C2. To produce acetylene, distilled water was added to calcium carbide (CaC2). Calcium carbide is a greyish/white solid that looks like small pebbles. Due to its dangerous properties, the acetylene was directly transferred to another solution after it was produced. Silver acetylide (Ag2C2) forms with the reaction of acetylene and silver nitrate (AgNO3). The acetylene was funneled from the initial reaction into the bottom of a graduated cylinder which held silver nitrate. This allowed the acetylene (a gas) to bubble through the silver nitrate liquid solution and solid silver acetylide formed.

Reaction of Acetylene and Silver Nitrate

Apparatus

After all of the water and calcium carbide reacted and bubbles ceased eluting through the silver nitrate, the solid had to be filtered off. We used vacuum filtration to isolate the solid silver acetylide, but made sure to keep the solid slightly hydrated. As I indicated earlier, if the silver acetylide became too dry, it would detonate with movement (shock). The silver acetylide was placed in a foil holder and was then placed on a heat source. We stepped back and closed the hood to allow the solid to explode. The intended explosion was one pop, but mine ended having an initial pop and then a series of tiny pops, like a machine gun, several minutes later. We then had to be very careful cleaning up. There was the occasional “snap” on our table where tiny pieces of the solid ended up. To negate the substance’s tendency to explode, the solid could be put in water. Therefore, we cleaned the lab table with very wet paper towels and soaked all equipment in water and then cleaned everything very thoroughly. Overall, the lab was very exciting and I learned a lot about the physical properties of acetylene. Interestingly, acetylene will produce an explosive solid when reacted with other metals, not just silver.

One interesting fact about the explosion of the solid is that only solid products are formed when it detonates. In nearly all explosions, gas is released at detonation, but solid carbon and solid silver are the only products when silver acetylide explodes. Apart from the excitement of the explosive lab, I learned about safety and always being careful in a lab setting. It is very important to be aware of ones surroundings and focus when chemicals are present. If you mix the wrong chemicals, it can produce something poisonous or explosive, like in our lab. This lab was effective at demonstrating how to treat chemicals in a lab and handle them with care. Not to mention, we got to blow something up.

The Art of Charts

The main focus of system problems evaluated in ChE 31, and in chemical systems in general, is how the substances react to changes in the surrounding parameters. That is, changes in pressure, temperature, and new products being added to the system. For a simple example, if a solution needs to be heated to evaporate water from a desired solid product, a chemical engineer can determine what temperature and pressure is most effective for the system to accomplish the task. It is essential to understand how materials will behave, given certain parameters, in order to determine the balance on a chemical system.

There is nearly infinite combinations of materials that can be studied at different parameters. It is impossible to have a simple list of values to quantify all the factors of a chemical system. With the ability to alter pressure, temperature and many other properties of a single system, chemical engineers need a method to simply present information about the system. In order to find a solution to a problem, an engineer must be able to easily find values at different parameters. For this reason, chemical engineers rely heavily on charts, graphs and tables. Charts effectively present information about substance(s) and make it easy to determine the value one needs. In ChE 31, I am constantly using charts in the textbook to find constants and numbers to solve material balances. For example, there is a table in my textbook that presents the vapor pressure of water based on the temperature and mass fraction of water. Here are three different charts that I have used so far:

MgSO4 Phase Diagram

This is an MgSO4 Phase Diagram. It’s difficult to explain in text, but at different temperatures MgSO4 exists as a saturated solution (in water) and as crystals (hydrated). Given a temperature, one can determine the mass percentage of MgSO4 in the solution and in the crystals using the diagram. The diagram can also be used to determine the phase (solid/liquid) and concentration of MgSO4 at different temperatures.

This is a Pxy or Txy diagram. The difference between the two different diagrams is one has a constant pressure and one is at a constant temperature. These diagrams are used when you have a closed volume with two different substances that are in the liquid and gas phases. Different materials condense/evaporate at different temperatures and are based on the temperature and pressure of the system. Basically, you use either a given temperature or pressure to determine the molar percentage (x-axis) of each substance in the solution. For example, if the liquid composition of benzene is 30%, the composition of Toluene is 70%. The compositions of vapor would be different.

Ternary Phase Diagram

Lastly is a ternary phase diagram. We haven’t used these much so far, but they are utilized when you have a solution of three different materials. Usually, one of the substances (A) dissolves in the other two. The diagram is used to determine how much of substance A dissolves in each of the other two solvents, based on the amount of each solvent in the system.

As a whole, charts are extremely helpful in efficiently presenting useful information. It is imperative to be able to understand and use these diagrams to solve problems and be a successful engineer.