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Case Studies

 
  Reducing Pollution at the Source
 

Reactive Distillation

In the November 1999 AIChE Annual Meeting, Professors M. Doherty and M. Malone of the University of Massachusetts Department of Chemical Engineering presented their findings on the topic "Recent Advances in Reactive Distillation." In comparing the traditional versus the reactive distillation methods, such as in the production of methyl acetate example below (click to enlarge), the latter methods have the advantage of being able to:

  • Improve Selectivity
    - Reduce Raw Materials Usage
    - Reduce Byproducts Prevent Pollution
  • Reduce Energy Use
  • Handle Difficult Separations
    - Avoid Separating Reactants
    - Eliminate/Reduce Solvents
  • Enhance Overall Rates
  • "Beat" Low Equilibrium Constants

Example: Production of Methyl Acetate

 

Traditional vs. Reactive Distillation (click to enlarge)

 
You may also view the slides (PDF, 985 KB) presented at the meeting, which include summary findings of the project, as well as highlights on future research needs.
 
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  Reducing Pollution at the Source to Protect
Human Health and the Environment

Reducing Automobile Emissions and Saving Energy

William Obenchain and Marcel van Schaik of the American Iron and Steel Institute, and Pete Peterson of the U.S. Steel Group conducted a case study on the UltraLight Steel Auto Body-Advanced Vehicle Concepts (ULSAB-AVC), in which reductions in automobile emissions and improvements in gas mileage were observed as a result of using lightweight steel in the construction of cars.

The ULSAB-AVC is a complete conceptual design for steel intensive compact and mid-size sedans. The designs were developed by a consortium of 33 steelmakers from around the world. The designs specify gasoline and diesel powered models; in the U. S. combined driving cycle the mid-sized sedan will achieve 52 miles per gallon when powered with a gasoline engine and 68 miles per gallon if equipped with a diesel engine. This equates to only 0.32 (diesel) - 0.38 (gasoline) lbs of CO2 per mile.

 

ULSAB-AVC: Comparison of Mileage and CO2 Emissions

  U.S. C.A.F.E. standard ULSAB-AVC
Gasoline
ULSAB-ABC
Diesel
U.S. combined [mpg] 27.5 52 68
CO2 Emission [g/km] 204 108 92
CAFE = Corporate Average Fuel Economy Standards for automobiles and trucks
 

In addition, the automobiles are designed to achieve "Five Star" crash safety rating based on the anticipated 2004 safety standards, and will cost no more to build than traditionally engineered vehicles. By comparison, the 2000 fleet of midsize automobiles in the USA averages 28.6 mpg (DoE Transportation Energy Data Book, 2001 Ed.) and is not designed to meet the same stringent safety requirements as ULSAB-AVC. The ULSAB-AVC utilizes advanced high-tech steels and modern engineering and manufacturing techniques that are available to automobile and auto parts manufacturers.

To learn more on the subject, view the "Reducing Automobile Emissions and Saving Energy" report (PDF, 5 MB).
 
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Minimizing Hazardous Chemicals in the Paper Industry

Carl Houtman of the USDA Forest Product Service and of the University of Wisconsin at Madison conducted a case study on minimizing the use of hazardous chemicals in the paper industry. To eliminate the use of and exposure to hazardous chemicals in the bleaching process, a new delignification agent (a polyoxometalate, or POM) is used to provide the basis for closed-mill bleaching technology. This technology eliminates the use of a hazardous chemical while maintaining effective lignin removal. The two flow charts below (click to enlarge) compare the traditional bleach process and the new "green" process using POM.

 

Traditional bleaching process (click to enlarge)

 

Green process via POM (click to enlarge)

 
While this delignification process completely eliminates beach plant effluent, it requires increased steam and energy usage as well as new capital equipment. As demonstrated in the table below, the trade-offs are that the POM process requires higher process flow temperature and has a high steam requirement to run the oxidative reactor. Furthermore, the increased capital cost in mills already built prohibits immediate implementation.
 

Paper Bleaching: Comparison of Process Stream and Energy Inputs

  Process Stream Inputs (m3/MT) Energy Inputs
NaOH O2 H2SO4 ClO2 H2O2 POM Electricity
(kW-hr/MT)
Steam
(kg/MT)
POM   137       0.27 277 2858
DEop 24 5 5 18.3 6   281 1693
POM = polyoxometalate process, uses no ClO2 or NaOH
DEop = traditional method of bleaching
 
Engineers will soon be moving the POM process to the pilot plant phase while continuing to research and test the final product. The challenge will be to reduce process temperature and to eliminate the oxidative reactor to decrease steam requirements.
 
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  Protecting Human Health

Minimizing Worker Exposure to Mist in the Auto Industry

Exposure to mist from machining fluids can cause serious health problems, including cancer, respiratory problems, and allergic reactions. To limit exposure from inhalation of this mist, Professors Manke, Gulari, and Smolinski of the Wayne State University Department of Chemical Engineering and Materials Science tested the effect of adding polymers to both water-based and straight-oil machining fluids. A cost-effective method of reducing mist from oil-based fluids has already been widely implemented in the auto industry. For water-based fluids, however, the economics of mist suppression techniques are not yet as favorable, and engineers continue to look for practical ways to meet this challenge.

For straight oil fluids, polyisobutylene (PIB) can be added to control mist. An addition of 70 ppm of PIB results in a 40% reduction in average mist levels and a 67% reduction in peak mist levels (click to enlarge following figures). This additive has been used extensively in auto manufacturing facilities. Its costs are relatively low and only weekly replacement is required.

 

Photograph of mist suppression with PIB (click to enlarge)

Graph of mist suppression with PIB (click to enlarge)

To control mist from water-based machining fluids, engineers are exploring the use of polyethylene oxide (PEO) for this purpose. The results are promising.  However, high treatment levels are needed (up to 500 pm), the polymer is relatively costly, and daily replacement is required. To improve the economics of treatment for water-based fluids, researchers are investigating optimization of polymer-surface interactions and synthesis of "designer" antimisting systems.
To learn more on the subject, view the slide presentation (PDF, 539 KB) entitled "Suppression of Machining Fluid Misting by Polymer Additives".
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Reducing Worker Exposure to Solid Particulate

Using engineering controls to eliminate manual dumping of bags, as shown in the figures below, can substantially reduce exposure to particulates in the workplace and the need for personal protective equipment such as respirators.

Reducing worker exposure to solid particulates.

 
Note that the "greener" liquid system, while protecting workers from the risks of dust inhalation, introduces potential water releases that must be evaluated for risks to human health and the environment.

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