EPA Safety

Hazard Assessment and Procedures
The chemicals involved in this process are benzene, propylene, benzene and p-diisopropylbenzene. Although each chemical posed a hazard, benzene is the most hazardous. All chemicals should be utilized with safety in mind however; benzene must be handled with care. The health effects of benzene range from dizziness to cancer. Therefore, special precautions must be taken to ensure safety within the facility. In fact, in any workplace where benzene is used, stored or transported, workers must be aware of benzene’s properties, toxicity and safety procedures to meet the requirements of the OSHA Benzene Standard (29 CFR 1910.1028). Therefore, an annual training program will be implemented at the facility that ensures that all employees are knowledgeable of benzene policies and procedures. The OSHA Benzene Standard also provides permissible exposure limits for employees. In the event of an accidental release of benzene, the release must be reported to the appropriate authority, cleaned immediately while removing all sources of ignition. The storage and handling of feed chemicals has been responsible for some many explosions, including the Bhopal disaster in 1984. The plant accidently released methyl isocyanate gas into the environment. The accident stole the lives of 3,787 people. The effects of the gas leak are still seen today in Bhopal. The use of internal floating roof storage tanks are recommended for benzene bulk storage to ensure that the facility is safe from accidental releases and the tanks will be maintained according to state and local regulations.

First, source reduction was considered to reduce the amount of benzene released. Therefore, most of the benzene used in the process is recycled back into the process. The stream was then minimized and analyzed to determine if the direct release of benzene to the environment was a feasible option. Unfortunately, the risk was not in the allowable range therefore, waste treatment must be used. Gas adsorption was considered as a method of treating the recycle stream. However, the purge stream in conjunction with waste removal was more financially sound than utilizing carbon in a gas adsorber to remove the cumene in the recycle stream.

Production of cumene is a vital process for the use of phenol in industry. The recommended design of a cumene plant is to feed pure propylene and benzene to a reactor at molar flow rates of 102.3 and 105.6 kmol/h, respectively followed by two distillation columns. The yield of cumene produced is in accordance with the design specifications given. An economic analysis of the process yielded a net present value of $53.11 million after 12 years with only a 30% probability of failure.
The proposed process has been evaluated for environmental and safety hazards. It has been designed in accordance to all EPA standards and regulations with minimal release of toxic chemicals. This process is believed to be an economically and environmentally sound investment.

Huge Mistake!!!!!

While conducting the final economic analysis it was found that our total profit for the design process was -$22,000,0000. That is an extremely high number. We were floored with these results. After the culmination of our hard work to only make a negative profit hurt us deeply. We had to start back at the drawing board even after a few of team members were extremely frustrated that the deadline was quickly approaching.

Being the ever astute engineers that we are we figured out that it wasn't out utility cost that was killing our profit margins but the purchase costs for the raw materials. The specification of 2:1 or even 4:1 benzene ratio to propylene was found to be too high.

Economic Analysis

For this process it was determined that the COMd is $116.79 million. The fixed capital cost (FCIL) of process was found to be $3.97 million with a working capital of $9.69 million. The total cost of the raw materials (CRM), propylene and benzene, is $92.79 million. The process, which has benzene and di-isopropyl benzene as waste products, has a waste treatment cost (CWT) of $981,000. The total utilities cost (CUT) for the process was found to be $361,000. The total cost of labor (COL) was found to be $106,000. A total summary for the cost of manufacturing can be found in the file CAPCOSTanalysis.xlsx.

The revenue generated from the sale of cumene is $134.25 million dollars. Completing a cash flow analysis on the process shows the generation of a profit in year four of operation with a cash flow of $4.03 million. At the end of 12 years (2 years for construction and 10 years of operation) proposed plant would have a net present value (NPV) of $53.11 million. The discounted cash flow rate of return (DCFROR) is 63.11%. Based on the Monte Carlo Analysis of the NPV there is a 26% chance that the proposed process will not turn a profit. The median NPV is $39 million. Approximately 58% of the calculated values lie above the projected NPV for the process, $53.11 million. The summary for the Cash Flow and Monte Carlo analyses can also be found in CAPCOSTanalysis.xlsx.

Nearing the End

The project is almost done. Two more days to go. We are now doing the final optimization of the process and doing the final economic analysis of the process.

Over the weekend we had a minor setback. A team member received news that her grandmother passed and was understandably unable to work for two days, but the show must go on. The other two team members pressed forward with finalizing the final process. The final process was determined to feeding the pure benzene and propylene, mixed at a point in the stream (inter-stream mixing), to a heat exchanger. The mixture would then be fed to the reactor. The reactor effluent would be sent to a distillation column that would separate benzene to be recycled to the feed. The bottoms from that column would be fed to a second column where cumene would be separate for selling.

We are currently working on the economic cost evaluation and the environmental analysis of our process. Stay tuned for more updates for our senior design project

 

~JDB

Week 2 Progress Report

Progress Report for Week 2 of Design of Cumene Production Facility

Team #: Mia Barrington, Jessica Blanding, Robert Duncanson

Goals for Week 1:

1. Evaluate alternate separation sequences.
   
   
2. Carry out flash and distillation column (shortcut and rigorous) simulations.
   
3. Optimize process units and include recycle.
   
   

Summary of Accomplishments for Week 1:

1. Team members decided on a final sequence of processes that would yield the correct amount of cumene
   
2. After running simulation in ASPEN is was determined that a flash separator to separate the propylene first would not be cost effective because of the low level of separation that would be achieved. Therefore, It was determined to just use a single distillation column to separate the benzene from the cumene.
   
3. Sensitivity analysis was run in ASPEN and the optimal process units were determined
   

Difficulties Encountered:

Aspen at times can be difficult to operate. Robert and Jessica spent an hours trying to get ASPEN to run the simulation. ASPEN had to be shut down and a new simulation started in order for the simulation to run.

CAPCOST is confusing. Jessica is having difficulty figuring out how to specify the equipment requirement in CAPCOST

Suggestion:

Extend the project a week and move the last test to final weeks to allow students to have more time to prepare a better report. Team Members expressed concern that the project is not feasible to complete in 3 weeks especially when the project description specifies that 4 weeks are necessary.

Team Activities in Week 12

Member (s)	Task	Time spent (h)
Robert and Jessica	ASPEN simulation on reactor and sensitivity analysis	4
Mia, Robert and Jessica	Final PFD	4
Jessica	CAPCOST simulation	5
Mia, Robert	ASPEN simulation on distillation column and sensitivity analysis	6
Total (h)		19

 

Goals for Week 3:

1. Finish Equipment Costing
   
2. Finish final report
   
3. Submit project
   

 

Project Timeline (listed tasks are for illustrative purpose only, modify and expand as necessary)

Task

Week 1

Week 2

Week 3

Week 4

Preliminaries

Gross Profit and hand calculations of reactor sizing.

Consideration of Alternatives

Preliminary PFD

Recommended Design

Base case simulation

Sensitivity&Optimization

Heat Integration

Economic Analysis

Equipment Sizing &Costing

Profitability Analysis

Monte Carlo Analysis

Safety and Environmental

Hazard Identification

Waste Mitigation&Treatment

Preparation of Written Report

 

Aspen Reactor

Aspen has been a tough program to crack. Following the tutorials turned out to be more work than we thought. We had to simulate the reactor kinetics of the cumene production using our hand calculations as a basis for our operating specifications. We used a mixer and a simple Rplug packed bed reactor model. We stuck with our 350 C temperature as well as the 35 bar pressure.

Aspen Plus overall seems to be a more intuitive program than chemcad but it still has its flaws. Setting up the reactor and specifying the components: propylene, benzene, cumene, and dissopropylbenzene. The SRK method was used as this was as suggestion that was read some where.

First run of aspen yielded nonsensical results. It showed that our propylene was comopletely reacted and we acheived 100% conversion. This was impossible due to all the text books drilling in our heads how achieving 100% conversion would need insane reactor volumes or specifications that aren't economically possible. This is generally why we assume conversions less than ideal (there is a reason why we call it ideal after all)generally around 98-60% at least. We realized quickly that our preexponential factors or reactor kinetics must be wrong. The little trick in Aspen is the need to specify the preexponential factor in SI units. Changing this and doing some basic SI conversion yielded acceptable results.

We then did a design specification to get the actual size of the reactor at 95% conversion. This was the key size of the reactor that everythign would be based on the 95% conversion.

We also ran a sensitivy analysis to determine the effects of pressure and temperature on reactor size. We also showed how temperature effects selectivity and how pressure had little to no effect on selectivity which makes sense.

There are the following results and we figured an optimal range of reactor size, temperature, and pressure that we would like to operate the reactor in order to get our correct design specifications.








From the graphs one could see how as the pressure increases the reactor volume decreases. However, there is a trade off between high pressure, reactor volume, and the cost of each. The optimal range seems to be between 25-45 bar for trying to keep the reactor volume around 30-10 cubic meters.

The T vs Volume chart highlights as well how the lower the temperature the greater the volume needs to be and there is associated cost between higher temperature and reactor volume. Since the selectivity increases with lower temperature chart 3. There is a need to balance both these variables to achieve the necessary design specifications.

These charts provided a calming feeling that we're at least on track with everything and just need to begin the next phase of our design. Our next step in our process would be to fire up a heat exchanger (excuse the pun) and a distillation column and do the same procedures with obtaining 99% product of cumene.


~RSD

Aspen Plus

Doing some preliminary chemical reactor simulations. It turns out doing the first trial simulation that the simulation returned no errors. However, it showed that all propylene reacted and there was literally 0.8ish kmol/hr of the undesired product formed. There might have been some miscalculations with converting the pre-exponential factor to the appropriate units for aspen.

Another idea is to actually employ a sensitivity analysis on the reactor plotting temperature vs. reactor volume and pressure vs reactor volume to see the result effects to get some type of idea of an ideal operating range/volume. There is a note that selectivity increases when temperature is lower but that will undoubtedly increase the size of the reactor. There seems to be some what of a balancing act and whatever we choose we have to justify such choices.

~RSD

Progress.

One of the hardest part about senior design and this project is figuring out what is the purpose of all of this. Trying to set up a logical flow path on how to solve this Cumene design project in ways that make sense to me was one of the more difficult tasks. The first step we chose was to do some preliminary calculations to determine the flow rates into and out of the reactor. Since the production of cumene depends primarily on the reaction of benzene and propylene with a minor side reaction we needed to focus our attentions on this process first. All other resulting flow rates and separations will come after our analysis of the reactor. Seems simple doesn't it? Well not when you took mass and energy balances 2 years ago and when you spent what seems like a survey of reactor kinetics this past summer (whoever devised spending 6 weeks on this course needs to be slapped). Its a good thing I'm good at teaching myself and learning material on my own or we'd be SOL!

Anyhow what we did was set up a basic spreadsheet to do material balances around the reactor. Since we know the rate of cumene production we needed we could easily determine the other concentrations by converting everything into molar flow rates. We chose in this system that fraction conversion of propylene to be around 95% (a number we made up it just feels good to say 95%). We also chose to feed benzene in excess a 4:1 ratio. In order to get a good grasp on our mass balance spreadsheet we neglected the 2nd reaction first in order to make sure we understood those fundamental concepts of reaction mass balances.

From the balances we were able to determine the required amount of benzene and propylene that needed to be fed into the reactor as well as the resulting flow rates out of the reactor and the reactor volume.

This was also done for 5:1 ratio of benzene to propylene. As well as incorporating both reactions to solve for the reactor size. These are just preliminary calculations that will be used in Aspen Plus to see whether when in the ballpark or way off base.

The reactor volumes for those approaches were around 8-9 cubic meters. Then involving the 2nd reaction the results were as follows:



With a volume of around 10 I'm somewhat confident we're doing the right approach. It isn't too small or too large (as big as a football field) then now its on to simulation the fun part...

Ran into a few simple mathematical mistakes due to the ti-89. Ti-89 was solving for the integral in the wrong manner returning numbers that were completely off. Solving the integral by hand even though time consuming as well as using other programs such as polymath and math.com helped confirm these results. Checking and rechecking numbers is one of the most annoying things about this design project.

~RSD

The Times are Changing

"For every complicated problem, there is an answer that is
short, simple and wrong"
H.L. Mencken

The majority of the team members are out of town...That doesn't stop Senior Design though...
Continuing on we're trying to size our Reactor

There are two ways to do this:
1. The Chemist’s Approach: Build larger sizes of
laboratory equipment and experimentally measure all
the process variables.
2. The Engineer’s Approach: Develop process models for
each unit and solve these equations to estimate the
mass and energy flow rates. Use these rates to
determine size..

A process model is a set of equations, including the
necessary input data to solve the equations, that allow us to
predict the behavior of a chemical process system.

The Engineer's approach seems better nothing against my Chemist folks...but after all we are Chemical Engineers.

Progress Report for Week 1 of Design of Cumene Production Facility

Team #: 13

Goals for Week 1:

1. Researched alternative technologies for process, and market analysis

2. Calculation of Gross Annual Profit for Process

3. Hand calculations for reactor sizing and comparison to Aspen Plus simulation

4. Development of preliminary PFD

5. Examine environmentally friendly processes and waste treatment.

Summary of Accomplishments for Week 1:

1. The gross annual profit was found to be $49,725,183.41. This is the maximum amount of profit expected at 90% conversion under ideal conditions neglecting such factors as startup cost and equipment.

2. Calculations were completed by hand to obtain molar flow rates. However, the volume and conversion need to be calculated.

Team Activities in Week 1

Member (s)	Task	Time spent (h)
Mia Barrington	Background research.	9
Robert Duncanson and Jessica Blanding	Preliminary reactor sizing and gross profit calculations.	10
Total (h)		19

Goals for Week 2:

1. Evaluate alternate separation sequences.
2. Carry out flash and distillation column (shortcut and rigorous) simulations.
3. Optimize process units and include recycle.

The overall objective of this project is to create a process to generate 100,000 metric tons per year of cumene using benzene and propylene. The target design is achieving a 99% purity of cumene. We start by analyzing the kinetics of the problem.

Based on the given rate law and rate constant. We can begin to deduce information about the specifications of our reactor. The second reaction proceeds faster than the first reaction because the pre-exponential factor A is higher than the first reaction. It could be difficult to optimize the two equations but because the activation energy has a similar relationship we can optimize the reactions by operating at a low temperature. At low temperatures, the reaction favors the alkylation reaction. A short residence time or short reactor will also help maximize the selectivity of reaction A. We would also have excess benzene fed into the reactor at a high flow rate in order to minimize the amount of propylene that reacts with cumene to form an undesired product. Moderate pressures will be used.

However, when using lower temperatures, a larger reactor becomes necessary. Therefore, the temperature and reactor size must be optimized. We would not use high temperatures or high pressures because the reaction would then favor the undesired product.

The alkylation reaction is highly exothermic. Therefore, we would like to utilize that heat to minimize utility costs and equipment.

Hand Calculations

To find the flow rates

For a ration of fresh feed to recycle feed of 1:3

Problems

1. Calculating the design specifications (volume at a specified conversion with initial guesses for the molar flows of benzene and propylene) for a PBR with multiple reactions.

2. We are still optimizing the temperatures and pressures used throughout the process and would like further guidance as to how we can more efficiently find the best operating conditions.

~Mia B.
~Jessica B.
~RSD