1. Define the Problem

Design a processing plant that produces ethanol at the following specifications:

• Ethanol Output: 10 % of United States market production (15.7 million kg/year)

• Composition: 85 wt. % ethanol, 15 wt.% water

• Cost: Less than $2.90 per gallon (the present price)

• Method: Fermentation using the microorganism Zymomonas mobilis

2. Define the Reaction

This is an anaerobic reaction in which the bacterium Z. mobilis uses glucose to form ethanol and carbon dioxide. Small amounts of acetate and glycerine are produced. If oxygen is introduced to the reaction, the production of acetate and glycerine increase, thus decreasing the purity of the desired ethanol product. It is important, therefore, to keep this reaction as void of oxygen as possible.

3. Find the Raw Materials

The raw material we are interested in acquiring for this project is glucose, the carbon source for the bacteria. Since Z. mobilis cannot break down any complex sources of glucose (e.g. cellulose, corn starch, etc.), the glucose must be introduced to the reactor in original form.

What are some sources of glucose?

• Purified Glucose (also known as Dextrose in the chemical industry) ($1.12 per kg)
• High Glucose Corn Syrup ($0.144 per lb)

Physical properties (for these substances must be found before any further design calculations can be done)

4. Attain Data from a Laboratory Fermentation Experiment

We also need to know how different variables can affect the reaction. In order to do this, we need to look over data from an actual laboratory scale fermenation. Fermentation at three different temperatures were run in order to observe the effect of temperature on ethanol production. We have data here from the three different fermenations on Excel spreadsheets. Using the data, choose the fermentation which yielded the most ethanol (mass) in the shortest time. Choose from the following experiments.

• Fermentation at 25 degrees C
• Fermentation at 30 degrees C
• Fermentation at 35 degrees C

Record the following from the experiment:

• temperature
• max ethanol concentration
• time to produce maximum ethanol concentration
• initial and final liquid volumes in fermentor
• initial and final glucose feed masses
• concentrations of glucose in feed and in initial liquid volume

5. Calculate the amount of raw material and product output from the fermenation.

• Temperature = 30 deg C
• Max ethanol concentration = 85 g/L
• Time to produce maximum ethanol concentration = 30.0 h
• Initial volume = 6.0 L; final volume = 11.78 L
• Initial glucose solution mass = 18175 g; Final glucose solution mass = 13894
• Concentrations of glucose in feed = 500 g/L; in initial liquid volume = 100 g/L

A. Find mass of glucose feed used:

final glucose mass - initial glucose mass = Total mass of glucose solution

18175 g - 13894 g = 4281 g glucose solution

B. Find volume of glucose solution:

4281 g solution / (1500 g/L solution) = 2.854 L solution

C. Find the mass of glucose used:

Mass of glucose from feed = 2.854 L solution * 500 g/L glucose in solution = 1427 g glucose

Mass of glucose in initial volume = 6.0 L * 100 g/L glucose = 600 g glucose

glucose from feed + glucose in initial volume = Total glucose used

1427 g glucose + 600 g glucose = 2027 g glucose

D. Find mass of ethanol produced:

Mass of ethanol produced = (max concentration of ethanol)(volume of fermented broth at that time of max concentration)

1001.3 g ethanol = 85 g/L ethanol * 11.78 L fermented broth

Therefore, 2027 g glucose yielded 1001.3 g ethanol

We need to scale up these values for raw materials and product output to meet our goal.

6. Scale-Up Procedure

It's not a cut and dry solution. The basic procedure is to pick a volume for the fermentor (that is proportional in dimensions and operation to the lab fermentor). After that, calculate how much ethanol this size fermentor might produce and then see if it will make the necessary ethanol at a price that is lower than today's prices.

The Iterative Procedure:

1. Pick a volume from 500 - 1000 cu. meters.

2. Calculate how much ethanol is made in one year by one reactor. If it's not enough to meet our goal or if it costs more than the present price of $2.90 per gallon, then calculate how many reactors of that volume working at the same time might yield the adequate result. If the answer is more than five reactors, go to step 1 and choose a larger volume. Repeat Step 2.

3. If still not enough ethanol can be made or if it is too expensive, then this means that another production method using fermentation must be explored.