Ethanol Production Flowsheet

sucrose feed rate 1000 kg/h

5006000

water feed rate 5000 kg/h

20012000

Mixer

Reactor

Distillation

Directions

This simulation performs steady-state mass balances on a three-unit ethanol process: a mixer, a fermentation reactor, and a distillation column.

Drag the sucrose feed rate slider to set the mass flow of sucrose entering the mixer in stream S1.
Drag the water feed rate slider to set the mass flow of water entering the mixer in stream S2.
Every stream label updates immediately. Each label lists the mass flow rate of each species in that stream and the total flow, all in kg/h and reported to four significant figures.

Yeast enters the mixer as its own feed stream, SY, set at 5 % of the combined sucrose and water feed, so it is fixed by the two sliders rather than set independently. In the reactor, 95 % of the sucrose ferments; the carbon dioxide produced leaves as vent stream S7, so it never reaches the column. The column sends 99 % of the entering ethanol overhead at the ethanol–water azeotrope composition (95.6 wt % ethanol) in stream S5, and everything else leaves in the bottoms stream S6.

Things to try

Hold the sucrose feed fixed and change the water feed. Notice which stream flows change and which do not, and explain why.
Double the sucrose feed and check whether the ethanol product in S5 also doubles.
Add the total flows of S5, S6, and S7 and compare the sum with S1 + S2 + the yeast added, to confirm that overall mass is conserved.

Open Details for the equations behind the numbers, or Guided inquiry to download a worksheet that walks through degree-of-freedom analysis and the balances for each unit.

Details

All balances are steady state, so for each species accumulation is zero and input plus generation equals output plus consumption.

Fermentation reaction

\( \mathrm{C_{12}H_{22}O_{11}} + \mathrm{H_2O} \;\rightarrow\; 4\,\mathrm{C_2H_5OH} + 4\,\mathrm{CO_2} \)

Mixer

The mixer combines three feeds: sucrose, water, and yeast. The yeast feed is set at a fixed fraction of the raw sucrose plus water feed,

\( \dot m_{Y} = f_Y \left( \dot m_{1,S} + \dot m_{2,W} \right) \)

and each species passes through unchanged:

\( \dot m_{3,S} = \dot m_{1,S} \qquad \dot m_{3,W} = \dot m_{2,W} \qquad \dot m_{3,Y} = \dot m_{Y} \)

Reactor

Sucrose is the limiting reactant and is converted to the extent \( X \). The molar extent of reaction is

\( \xi = X \, \dfrac{\dot m_{3,S}}{M_S} \)

Species balances across the reactor, with 1 mol of water consumed and 4 mol each of ethanol and carbon dioxide produced per mole of sucrose reacted:

\( \dot m_{4,S} = (1 - X)\,\dot m_{3,S} \)

\( \dot m_{4,W} = \dot m_{3,W} - \xi \, M_W \)

\( \dot m_{4,E} = 4\,\xi \, M_E \)

\( \dot m_{7,C} = 4\,\xi \, M_C \)

\( \dot m_{4,Y} = \dot m_{3,Y} \)

Yeast is inert in the balance, and the carbon dioxide leaves entirely in the vent stream S7.

Distillation column

The column is specified by an ethanol recovery to the distillate and a distillate composition at the azeotrope:

\( \dot m_{5,E} = R \, \dot m_{4,E} \qquad \dot m_{5,W} = \dot m_{5,E}\,\dfrac{1 - x_E}{x_E} \)

Sucrose and yeast are nonvolatile, so the bottoms stream carries everything the distillate does not:

\( \dot m_{6,i} = \dot m_{4,i} - \dot m_{5,i} \)

Overall check

\( \dot m_{1} + \dot m_{2} + \dot m_{Y} = \dot m_{5} + \dot m_{6} + \dot m_{7} \)

Symbols

symbol	meaning	value / units
\( \dot m_{j,i} \)	mass flow rate of species \(i\) in stream \(j\)	kg/h
\( \dot m_{j} \)	total mass flow rate of stream \(j\)	kg/h
\( \dot m_{Y} \)	yeast feed rate to the mixer, stream SY	kg/h
\( \xi \)	molar extent of the fermentation reaction	mol/h
\( X \)	fractional conversion of sucrose in the reactor	0.95
\( f_Y \)	yeast loading, fraction of the raw feed \( \dot m_{1} + \dot m_{2} \)	0.05
\( R \)	fractional recovery of ethanol to the distillate	0.99
\( x_E \)	ethanol mass fraction in the distillate (azeotrope)	0.956
\( M_S \)	molar mass of sucrose	342.30 g/mol
\( M_W \)	molar mass of water	18.015 g/mol
\( M_E \)	molar mass of ethanol	46.07 g/mol
\( M_C \)	molar mass of carbon dioxide	44.01 g/mol

Species subscripts: \(S\) sucrose, \(W\) water, \(E\) ethanol, \(C\) carbon dioxide, \(Y\) yeast. Streams: S1 sucrose feed, S2 water feed, SY yeast feed, S3 reactor feed, S4 column feed, S5 ethanol product, S6 bottoms, S7 carbon dioxide vent.

Guided inquiry

The guided inquiry activity is downloading as a PDF. It is a classroom or self-study worksheet that uses this simulator to work through degree-of-freedom analysis, system boundaries for multi-unit processes, non-reactive balances on the mixer, reactive balances on the fermenter, and separation balances on the column.

If the download does not start automatically, use the link below.

Download the activity (PDF)

About

This simulation was generated by Professor David L. Silverstein and Dr. Loyal Murphy of the University of Mississippi using Google Gemini. It was modified for LearnChemE using Claude AI. Prepared for LearnChemE with support from the National Science Foundation, grants DUE 2336987 and 2336988, in collaboration with Washington State University. Questions and comments: LearnChemE@gmail.com