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Ethanol Production and the Determination of Density in the Distilling Process

Supplier: B-R Controls
13 February, 2006

Ethanol use as a transportation fuel can be traced back to Henry Ford and other early automobile pioneers. It has always played a role as a supplement to oil-based fuels, and clean air programs in the 1990s have boosted the production considerably in recent years.

Ethanol for use as a high-octane renewable fuel is produced by the fermentation of molasses, corn and other grain products. In the future it may also be economically produced from "biomass" or agricultural wastes.

Production of ethanol starts with grain (corn, barley or sorghum), cellulose or molasses. Yeast is added to the starting products which are then cooked and the mixture is fermented to produce CO2 and a mixture of around 18% ethanol. This mixture is then cooked in a still until the ethanol concentration increases to about 50%. For industrial ethanol production the product is transferred to a rectifying still where the concentration is increased to 95% (190 proof), and finally to dewatering where it reaches 100% (200 Proof).1

At the rectifier columns (190 Proof) and condenser (200 Proof) it is recommended that ethanol producers monitor the density and H2O content of the ethanol stream as a quality control check.

The outlet of the condensor is the crucial last stage in the production of ethanol and an absolute quality check point for ethanol producers. After fermentation, a multi-column distillation system strips the alcohol from the mash by boiling. After the final column, the 95% (190 proof) alcohol goes to dehydration where the remaining water is removed to produce 200Proof alcohol as a last step in this process.

If ethanol has significant amounts of water in it (5% is a significant amount) its molecular structure will make it act more like water than ethanol when mixed with hydrocarbon solutions such as petrol. When "wet" ethanol is mixed with petrol, the ethanol will separate out with all the ethanol settling to the bottom of the vessel and the petrol to the top.2

The measurement of % H2O is crucial at this point.

1. History of Ethanol Production: June 2002;
Prepared by Joshua K. Buchheit; Rural Enterprise and Alternative Agricultural Development Initiative

2. Ethanol 101- Dehydration by Dr. Scott Kohl,
Technical Connections, http://www.ethanol.org/documents/Ethanol101.7.pdfHow

How is the density measured?

The alcohol monitoring system from Anton Paar is a highly accurate density transducer which continuously measures the density, %H2O and alcohol (ethanol) concentration (%v/v or %w/w). It consists of a density transducer DPRn427i and an mPDS evaluation unit. Its high accuracy and reliability ensure efficient quality control and product monitoring.

Inside the DPRn 427(I) transducer is an oscillating U-tube system. It is excited and kept oscillating at its resonant frequency by two coils and an electronic circuit. The oscillation period and sample temperature are measured and transferred to an evaluation unit (mPDS 2000V3) for data processing and control purposes.

Your benefits

The Anton Paar Alcohol Monitor gives you an accuracy of 0.03%, equivalent to fine laboratory instruments (and unavailable through conventional flow meters). Installing an Alcohol Monitor increases the profitability of an ethanol plant and pays off in a very short time.

The Anton Paar density systems are unmatched for accuracy, reliability and performance. As they incorporate explosion-proof transformers and transducers, Anton Paar measuring systems are quickly gaining acceptance at ethanol plants around the world.

Alcohol Monitor - Features at a glance

  • High resolution and repeatability up to 0.01% w/w (90 to 100%)
  • Short response time (< 1 sec.)
  • No moving parts, ensures long working life
  • Robust housing for operation under harsh process environments
  • Water-proof to IP65
  • Built-in high resolution temperature measurement
  • Intrinsically safe to EEx ia IIC T6 (optional)
  • All wetted parts made of Hastelloy C276

System configuration

  • DPRn 427 I intrinsically safe density transducer
  • mPDS 2000V3 evaluation unit
  • IPS 501 Intrinsically safe barrier
  • Alcohol software: % alcohol, % H2O, temperature, density, Proof
  • DAVIS Windows-based recording software (optional)

Technical specifications:

Measuring Range:

Alcohol: 0 to 200 Proof

Water: 0 to 100%

Temperature: -25 to 125 °C

Accuracy & repeatability:

Density: 0.00005g/cm3 / 0.00001g/cm3

Alcohol: 0.05%w/w / 0.02%w/w ( 0 - 90% range)

Alcohol: 0.03%w/w / 0.01%w/w ( 0 - 90% range)

mPDS 2000V3 evaluation unit


  • External product type selection for 255 products
  • 4 analog inputs
  • 3 analog outputs
  • 2 relays for limit monitoring
  • Serial interface RS 232/RS 485

For further information or to discuss your application requirements please visit our website or contact us using the email feature below.