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Dimethyl Sulfide (C2H6S) Thermo Properties

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CHEG 231011 Thermodynamics I

Project Report

Dimethyl Sulfide (C2H6S)

This project focuses on the thermodynamic properties of dimethyl sulfide (C2H6S).
This report mainly consist of a basic introduction for C2H6S from chemical, physical, environmental, industrial sights, a methodology part to show how to generate the thermodynamic charts and a rankine refrigeration cycle for C2H6S, a result part of all the charts and cycle I get from mat lab and other calculation methods, a brief discussion part between the thermodynamic charts and the chemical, physical, environmental, industrial significance.

1. Basic chemistry.
Structure: [pic] [pic]
Molecular weight: 62.134
Boiling Point: 38 °C (311 °K)
Freezing Point: -98.72 °C (174.88 °K)
Triple Point Temperature (Ttri): 174.85°K
Critical Temperature (Tc): 503 °K
Critical Pressure (Pc): 55.30 bar
Critical Molar Volume (Vc): 0.2066 L/mol
Critical compressibility factor (Zc):0.273
Acentric factor (ω): 0.191
Antoine Equation Parameters A: 4.28713, B: 1201.134, C: -29.906
2. Compound uses.
Dimethyl sulfide (DMS) is a key compound in global sulfur and carbon cycles.
a) chemical reactant
Dimethyl Sulfide will undergo some types of reactions and used as a source to produce several chemical compounds.
(b) Food and Beverage Component
DMS is a primary aroma and flavor compound to make beer character. It is also used in other food applications like non-alcoholic beverages, ice cream, candy, baked goods, gelatins and puddings, and syrups. But only in very small amount like several parts per million
(c) Presulfiding of Catalysts
Dimethyl sulfide is an economical source for the organic sulfur required in hydro cracking catalysts. The high purity and easy handling of DMS has led to its worldwide use as a presulfiding agent.
(d) Extraction Solvent
Dimethyl sulfide has a distinct advantage as an extraction solvent for it does not form dangerous peroxides. In addition, DMS has a low affinity for mineral acids and will not extract these from water solutions.
(e) Others
Dimethyl sulfide has also applications on Reaction Medium, Ion Exchange Resins Modification of Nylon Fibers, Fiber Spinning, Preparation of Carbonyl Cyanide Catalyst Modifications Ingredient in Gas Odorants Fuel Additive Control of Coke Formation

3. Safety Issues.
Effects of overexposure to the DMS:
Inhalation: high vapor concentrations may cause headache, memory loss, confusion, convulsions, and unconsciousness.
Eyes: can cause irritation or inflammation.
Skin: can cause stinging on contact with subsequent reddening and removal of skin oils.
Ingestion: can cause irritation to mouth, throat, and stomach.
So, when dealing with DMS, such protections are needed.
Personal Protection: safety glasses, chemical goggles, face shield.
Protective Clothing: here splash potential exists; wear chemical worker's goggles and butyl rubber gloves. Other protective equipment such as aprons, rubber boots, face shield, rubber suit may be needed. Also, there should be eye wash stations and safety showers near use areas.
Besides, do not smoke in areas of storage or use. Employees who handle dimethyl sulfide should wash their hands before eating, smoking, or using toilet facilities.

4. Environmental issues
DMS is only soluble in water to the extent of approximately 2 percent.
DMS is quite volatile and will rapidly evaporate. The greatest danger from a spill is fire. DMS is part of the natural reduced sulfur cycle and as such is not expected to cause any long term ecological damage.
Therefore, the environmental damage produced by DMS is quite small.
5. Manufacturing processes
Here is a flow diagram for producing DMS.
First, CH3OH and H2S are feed continuously in a molar ratio of 2 to1 from P1 and P2 and mixed. The mixture then pass through the reactor containing catalyst with a temperature from 250°C and 450°C and pressure of 42.38bar. Such reactions occurred:
The crude product B is cooled and pass through the separator 1(S1) to remove the H20 inside. The two towers (D1 and D2) remove the unreacted H2S, CH3OH, intermediate CH3SH from reaction [pic] and other waist from steam C and E for recycles. On recycling, the CH3SH is also converted into DMS according to
The outlet steam F is passed into final tower (D3), where the lighter DMS is obtained from the top, and the heaver DMDS is obtained from the bottom of the tower.

1. Peng-Robinson EOS and VDW EOS descriptions
Where Tc, Pc, ω is shown in the introduction part, Tr=T/Tc.
Peng-Robinson is a very good equation of state to predict the properties of the given fuild
Where Vm is molar volume, a and b are substance-specific constants.
For DMS, a=13.34 bar L2/mol2, b= 0.09453L/mol

2. Critical properties
The properties at the critical point, eg:Tc,Pc,Vc,Zc
Tc: Critical Temperature. The temperature above which a gas cannot be liquefied, regardless of the pressure applied
Pc: Critical Pressure. The critical pressure of a substance is the pressure required to liquefy a gas at its critical temperature
Vc: Critical molar volume. The volume of a mole of a substance measured when it is at its critical temperature and pressure.
Zc: Critical Compressibility Factor. Get from Pc*Vc/R*Tc to show weather the fluid is behave ideally.

3. Outline of procedures used to generate the thermodynamic charts
a. P-T phase diagram with Peng Robinson EOS including Pvap (T) and Psubl (T).
The basic procedure is like the diagram shown in P306. I set up a Matlab program to plot the P-T diagram. The temperature range for Pvap(T) is from Ttri to Tc. The principle idea of the program is to provide a give T, and use Antoine Equation to guess a value of P to put into the mat lab. Than mat lab will compute the Z(liquid) and Z(vapor), and calculate the fugacity of the liquid and vapor using Z(liquid) and Z(vapor). If the two fugacity are not equal, mat lab will fix the P until f(gas)=f(vapor) and record the P when at that time. After plug in all the values into the program, a P-T phase diagram will appear.
b. P-V phase diagram Tr=0.75, 0.85, 1, 1.15, 1.25 showing equilibrium limits and spinodal limits of stability for the liquid-vapor envelopes.
A total of five isothermal curves will show on the graph. Take the required T and provide a range of volume, plug them into the Peng Robinson EOS. A pressure- volume curve will appear. From Tr=0.75, 0.85,1, I get the equilibrium P at the given T from part a. With the P and T, I can get the V(vap) and V(liquid) from Peng Robinson EOS. Notice V(vap) =V(liquid) when Tr=1. Connect these five V values and the bimodal curve will show up. Spinodal curve is the curve that connect all the point that (dp/dv)T=0 (d^2p/dv^2)T=max and min.
c. Cp(T,P) for a T range between the triple point and crtitical point temperatures with a series of isobars Pr=0.75,0.85,1,1.15 and 1.25
Use the equation on page 212.: P,T
Cp(P,T)=Cp﹡(T)-T∫P=0,T ( )
Use triple product rule and other math rules to rewrite the equation with respect to Peng Robinson EOS with maple. I find the final result to be very complicated equation. Than, plug in all the values and find Cp(P,T) curve.
d. UJT (T) for a T range between the triple point and the critical point temperatures using the Peng-Robinson E.O.S., for several isobars Pr=-0.75,0.85,1.0,1.15,and 1.25
This part is very easy. Just take Cp, V,T values into the equation in page 196 and the curve will appear.

4. Outline of procedures used to construct the Rankine cycle.
Rankine refrigeration cycle is a kind of power generation cycle that are formed by a pump, a boiler, a turbine and a condenser. I designed the cycle start with an isentropic expansion through a turbine to make a high pressure saturated liquid into a low pressure vapor-liquid mixture and generate useful work at the same time. The second step is to go through an isobaric boiler to increase the internal energy of DMS to transform it to a low pressure saturated vapor. Then, vapor DMS come out of the heater will go through an isentropic compression to form high-pressure vapor. The DMS released from step 3 is put through a isobaric condenser and go back to the high pressure saturated liquid. Additional work is needed at step 3 to supply the pump to compress the gas, and we also need some heat in step 2 to increase the internal energy of DMS. Finally, the efficiency of this refrigeration cycle should be calculated by divides the net work produced by the net heat supplied.

1 Thermodynamic charts.
Chart (a): P-T phase diagram
The lower part in blue is the P(sub), the curve in orange is P(vap).

Chart (b): P-V phase diagram
P and V values at equilibrium limit and spinodal limit are getting from maple:
As I mentioned in the methodology part, when Tr=0.75 and 0.85, a VDW loop will appear. This VDW loop only exist when Tr is less than 1 and it violet the stability criteria (dP/dv)T>0.
For better observation, the equilibrium limit and spinodal limit is plot independently below.
|Five points for equilibrium limits | | |
|V(m^3/mol) |7.94E-05 |9.1519E-05 |0.000183437 |0.00149781 |0.004207 |
|P(Pa) |6.54E+05 |1.78E+06 |5530000 |1.78E+06 |6.54E+05 |
|Five points for spinodal limits | | | |
|V(m^3/mol) |1.03E-04 |1.20E-04 |0.000183437 |5.88E-04 |8.38E-04 |
|P(Pa) |-1.79E+07 |-5.70E+06 |5530000 |2.83E+06 |1.88E+06 |

Chart (c) Calculated by maple

I zoomed in the graph in order to see the graph when Pr=0.75,1,1.15,1.25
I also plot the ideal gas limit (Pr = 0.0000001≈0) for DMS.
P.S: There is no experimental data found in the NIST web book.

Chart (d)
(dT/dP)H : Joule-Thomson Coefficient among Pr=0.75, 0.85, 1.0, 1.15, 1.25.
2. Tables of values (process conditions, etc) used in the charts.
|Tc | 503K |
|Ttri | 174.85K |
|Pc | 55.30bar |
|omega(w) |0.191 |
|Antoine Equation Parameters | A: 4.28713, B: 1201.134, C: -29.906 |
|VDW Equation Parameters |a=13.34 bar L^2/mol^2, b= 0.09453L/mol |

3. Annotated Rankine refrigeration cycle drawing.
4. Table of conditions for operation of your Rankine cycle.
Descriptions about the rankine refrigeration cycle:
The H and S values are getting from Peng-Robinson EOS provided by the CD. I choose the point 3 (saturated vapor) at the temperature of the boiling temperature of DMS. Also I set the high pressure saturated liquid (point 1) temperature to be 432.8. These two points are both saturated, so I only need to fix one variable to get all the other thermal data like H and S. The low pressure vapor-liquid mixture (point 2) is in the two phase region of liquid and vapor. And T2=T3.P2=P3. So I define that x percent of the mixture is saturated vapor, and 1-x% of the mixture is saturated liquid. Through S2=S1, I can solve for x, and in order to get the H at that point. Finally, point 4 will be a liquid that is not in equilibrium, through S3=S4 and P3=P4,T3=311K, the T4 is calculated to be 435.373, H is 8878.5128 as shown in the table. Efficiency(n) is get from net work/net heat=33%

1. Discuss your diagrams in detail and compare them to experimental data if available.
Chart (a)
I enlarged the connection part in the first graph. And find a gap of 0.6pa at T=175.85K (Triple point temperature). The reason why this gap exists is because I am using two different equations to get P (sub) and P (vap). But consider that P (vap) are in terms of 10^6 pa, 0.6 par is negligible compare to this. So I can say that the P (sub) and P (vap) are connected at the triple point, and this is exactly true for any substances.

Chart (b)
The equilibrium limits and spinodal limits I plotted are a little different from what I saw in class. I think it’s because I use the Peng Robinson EOS instead of VDW and there is only five points provided to plot the curve. But in general, the curve is reasonable that the point 1,5and point 2, 4 share the same value of P. They have the same value of P because Gliquid=Gvapor and lead to fliquid=fvapor, and making them the equilibrium limits.

Chart (c)
After plot this graph, I found that when Pr=0.85, the curve is much sharp than the other four, the maximum value even goes to 8*10^6, which is unexpected. I guess it is because DMS is a polar fluid. But I do not exactly know why this phenomenon occurred. So I enlarge the other four curves as follows.
Compare all my five curves when Pr=0.75, 0.85, 1, 1.15, 1.25 with the Cp curve shown in P323. All of them share the same properties that they continuously rise to the critical temperature and get to a pick. After just getting to the pick, the curve drops dramatically down.

Chart (d)
Joule-Thomson Coefficient is a factor to measure the substance is suitable to be a refrigerant. It can be observed from the graph that as Pr increase, the Ujt decrease, which make sense that when dp increase, and remain dT un change, (dT/dP)H must be decreasing.

2 Discuss the industrial or environmental significance of your compound and how that relates to its thermodynamic behavior. Industrial: DMS has a boiling temperature of only 38°C, and it is very easy to explode at room temperature. So when dealing with DMS during industrial process, it must make the temperature at high range. On the other hand, DMS should be stored in tightly closed containers, in a cool place. Environmental: DMS is part of the natural reduced sulfur cycle. Therefore, it should have a low entropy difference during phase change and natural reactions. From entropy balance ds/dt=Q+W+∑MΔS+ Sgen is small. So Q term should also be small. Thus, making the Q in energy balance du/dt=Q a small number. And it is also proved that the Cp value of DMS is quite when at room temperature and pressure.

After finish this huge project, I get a better understanding of C2H6S.
I learned a number of useful chemical, physical, environmental, industrial properties.
The difference between C2H6S and C2H6 is just a sulfur atom, but just because of this it is widely used through many industrial processes. From medium reactant, to the food component, and even to control of coke formation, DMS plays a key role in our daily life.
I also learned many thermo properties. Like the P-T diagram, P(vap)T curve, I realized that every single point on that graph represent a equilibrium limit for P and T under different V.
I even made up my own rankine refrigerant cycle with DMS, which I did not expected, because DMS has a quite low Joule-Thomson Coefficient. But DMS is easy to explode, so, making DMS a refrigerant is still not realistic in daily life.

Reference: (United States Patent used in manufacturing process part) (DMS overview by Gaylord chemical) (NIST Web Book) (Cheneo high quality chemical properties search engine)

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