Wypych Handbook of Solvents

Figure 23.2.7. Schematic of a permeable reactive barrier. [From Permeable Reactive Barrier Technologies for Contaminant Remediation, EPA/600/R-98/125, 1998].

mary groundwater contaminants were TCE, PCE and cis-1,2-DCE (cDCE). The lithology of the site has been characterized as alluvial-fluvial clay, silt, sand and gravel, with an aquifer extending 5 to 60 ft below ground surface. The lithology is complex in this region and separates the aquifer into two zones with a discontinuous semi-confining aquitard. The mixed TCE, PCE, cDCE plume was ca. 10,000 ft by 5,000 ft extending along the direction of groundwater flow. Prior to installation of the permeable barrier system, TCE levels exceeded 5,000 g/L, PCE 1,000 g/L. A permeable reactive barrier was constructed with the dimensions 10 ft wide, 6 ft long, and 25 ft deep with a 2 ft pea gravel layer in front of and behind the cell. The cell was filled with granular zero-valent iron and a steel corrugate wall was constructed on each of the sides of the cell to form a funnel redirecting groundwater flow in that area through the iron cell. After nearly 4 years of operation, monitoring wells down gradient of the permeable barrier continue to shown non-detect for CHCs.

23.2.4 CONCLUSIONS

There are a number of technologies and strategies for managing hydrocarbon remediation. We have reviewed a number of the more promising, simple, and perhaps higher-technology solutions. However, a number of other demonstrated (pump and treat, air sparging) and emerging technologies do exist.34 The basic themes of preventing migration passively, and removal of contaminant via degradation (biotic and abiotic) are seen in all the technologies. The proper use of particular technologies and strategies is very dependent on the extent and type of contamination, the site characteristics (hydrology, lithology, etc), the cleanup goals, and applicable regulations to name a few. Unfortunately, there are no hard and fast rules for the use of a particular technology; past experience suggests that the more that is known about site characteristics the greater the success of technology application.

REFERENCES

1J.G. Mueller, C.E. Cerniglia, and P.H. Pritchard. in Bioremediation: Principles and Applications, R.L. Crawford and D.L. Crawford, Ed., Cambridge University Press, Cambridge UK, 1996, pp. 125.

2L.P. Wackett, in Bioremediation: Principles and Applications, R.L. Crawford and D.L. Crawford, Ed., Cambridge University Press, Cambridge UK, 1996, pp. 300.

3F.J. Millero and M.L. Sohn, Chemical Oceanography, CRC Press, Boca Raton, FL, 1991.

4M. Nishmura and E.W. Baker, Geochemica et Cosmochimica Acta, 50, 299 (1986).

5D.J. Hopper, in Developments in Biodegradation of Hydrocarbons, R.J. Watkinson, Ed., Applied Science Publishers, London., 1978, pp. 85.

6M. Blumer, Scientific American, 234, 35, (1976).

7 R.A. Rasmussen, M.A.R. Kahlil, and R.W. Dalluage, J. of Geophysical Research, 85, 7350, (1980).

8M.S. Reisch, Chemical and Engineering News, 72(15), 12, (1994).

9R.D. Norris, Handbook of Bioremediation, Lewis Publishers, Boca Raton, FL, 1994.

10P.E. Flathman, E.J. Douglas and J.H. Exner, Bioremediation: Field Experience, Lewis Publishers, Boca Raton, FL, 1994.

11M.T. Montgomery, T.J. Boyd, B.J. Spargo, J.G. Mueller, R.B. Coffin, and D.C. Smith, in In Situ Bioremediation and Efficacy Monitoring, B.J. Spargo, Ed., Naval Research Laboratory, Washington, DC, NRL/PU/6115—96-317, 1996, pp. 123.

12T.J. Boyd, B.J. Spargo, and M.T. Mongtomery, in In Situ Bioremediation and Efficacy Monitoring, B.J. Spargo,Ed., Naval Research Laboratory, Washington, DC, NRL/PU/6115—96-317, 1996, pp. 113.

13C.A. Kelley, B.A. Trust, and R.B. Coffin, Envir. Sci. Technol., 31, 2469 (1997).

14D.F. Berry, A.J. Francis and J.-M. Bollag, Microbiol. Rev., 51, 43, (1987)

15E. Arvin, B. Jensen, E.M. Godsy and D. Grbic-Galic, in: International Conference on Physiochemical and Biological Detoxification of Hazardous Wastes, Y.C. Wu (Ed.), 1988, p828.

16M.D. Mikesell and S.A. Boyd, Appl. Env. Microbiol., 52, 861, (1986).

17S.L Woods, J.F. Ferguson, and M.M. Benjamin, Env. Sci. Technol., 23, 62, (1989).

18A.J. Frisbie and L. Nies, Bioremediation Journal, 1, 65, (1997).

19J. Dolfing and J.M. Tiedje, FEMS Microbiol. Ecol., 38, 293, (1986).

20Y.Yang and P.L. McCarthy, Environ Sci. Technol., 32, 3591, (1999).

21E.M. Godsy and D.F. Goerlitz. U.S. Geological Survey Water-Supply Paper 2285, (1986).

22J.R. Mihelcic, and R. G. Luthy, Appl. Environ. Microbiol., 54, 1182, (1988).

23J.R. Mihelcic and R.G. Luthy, Appl. Environ. Microbiol., 54, 1188, (1988).

24W.R. Mahaffey, UPRR, In Situ Treatment Process Development Program, Milestone II Report, Volume 3/ 4, (1988).

25B. Al-Bashir, T. Cseh, R. Leduc, and R. Samson, Appl. Microbiol. Biotechnology, 34, 414, (1990).

26J. Thierren, G.B. Davis, C. Barber, B.M. Patterson, F. Pribac, T.R. Power and M. Lambert, Groundwater, 33, 469, (1995).

27A.A.M. Langenhoff, A.J.B. Zehnder and G. Schraa, Biodegradation, 7, 267, (1996).

28D. L. McNally, J.R. Mihelcic and D. R. Lueking, Environ. Sci. Technol., 32(17), 2633, (1998).

29R.F. VanDolah, P.H. Wendt, and E.L. Wenner, South Carolina Coastal Council, NA87AA-D-CZ068. (1990)

30J. Mueller, M. Ohr, B. Wardwell, and F. Lakhwala, Soil & Groundwater Cleanup, Oct/Nov, 8, (1999).

31W.E. Allmon, L.G. Everett, A.T. Lightner, B. Alleman, T.J. Boyd, and B.J. Spargo, Naval Research Laboratory, Washington, DC, NRL/PU/6115—99-384, (1999).

32B. Trowbridge, V. Jurka, G. Beyke and G. Smith, in Second International Symposium on Remediation of Chlorinated and Recalcitrant Compounds, Battelle Press, Columbus, OH, 2000.

33U.S. EPA, In Situ Remediation Technology Status Report: Treatment Walla, EPA 542-K-94-004, Washington D.C., 1995.

34S.K. Sikdar and R.L. Irvine, Bioremediation: Principles and Practice, Battelle Press, Columbus OH, 1997.

24

Protection

George Wypych

ChemTec Laboratories, Inc., Toronto, Canada

24.1 GLOVES

Many types of gloves are manufactured for different purposes. Proper gloves selection is important to ensure that the solvent or other chemical compound cannot penetrate through the glove where its subsequent evaporation would be prevented by the glove itself. Exposure to solvent entrapped between the glove and the skin is more severe than the exposure to solvent without glove.

The first requirement in the selection of a glove is that the materials from which gloves are produced are not dissolved or swollen by solvent. This alone is not sufficient. The other important requirement in glove selection is permeability of all of the materials in its structure. Permeability is measured according to ASTM Standard F 739 or European Standard EN 374. Permeability results are usually expressed in mg of permeate which penetrates 1 m2 of material per minute. Good materials for gloves should have permeability below 1 mg m-2 min-1. Materials having permeability in the range from 1 to 10 mg m-2 min-1 may still be considered as suitable materials.

Relative to permeability, materials are rated by a five point scale of the permeation index number. The best choice of glove material has a permeation index number = 0. If the material has index 1 (permeability in the range from 1 to 10 mg m-2 min-1), the glove can be eventually accepted for harmful chemicals. Any higher index number makes justification for its use more difficult and in plain language such a glove should not be used with harmful chemicals.

Breakthrough time is another measure of glove fitness for purpose. This parameter measures the time in minutes during which a measurable amount of a particular chemical compound penetrated through a particular garment. Specialized monographs give data on breakthrough times for a large number of gloves and other protective clothing and numerous penetrants.1,2 These sources1,2 are the best collections of data which should be considered in glove selection. There is a relationship between permeation rate (and thus permeation index number) and breakthrough time. For practical purposes gloves are selected based on the assumption that they should resist penetrant breakthrough for more than eight hours. Such gloves are generally considered to have permeability index number = 0.

In addition to the properties of protective clothing materials, the toxicity of the penetrant should be considered. For less toxic solvents, materials with a permeation index

number of 1 or even 2 may still be cautiously considered but will be less acceptable for more toxic penetrants.

Monitoring the quality of protection during use is not less important. Materials are not permanent. Frequent inspection of gloves is therefore very important. Any mechanical damage will compromise protection properties. The presence of cuts, cracks, or holes immediately renders the gloves useless. Gloves should be inspected for changes of color, texture, or hardening which are signs of material degradation.

It should be borne in mind that protective clothing is not universal for all chemical materials. For this reason, protection against one penetrant does not suggest that the glove has protecting qualities against the other materials. Mixtures of solvents behave in a different manner than do pure components. The temperature at which exposure occurs is also an important factor. Generally as temperature increases, permeability increases.

Table 24.1 gives general guidance regarding the applicability of different glove materials for different groups of solvents. Note that glove materials are not equal. They vary with the formulation used by a specific manufacturer and the thickness of the protective layer. For each selection, the manufacturer’s specification should be consulted to estimate previously discussed parameters. The best practice requires that gloves are tested for particular conditions of their use. The other good option is to consult results of measurement included in the specialized monographs.1,2

Table 24.1. General guidelines for selection of gloves for different groups of solvents

*PE/EVAl/PE = polyethylene/ethylene vinyl alcohol/polyethylene

The above suggested selections are based on the test data included in the monograph.1 Only the gloves which have a permeability index number = 0 were included. However, since solvents in each group frequently have diverse physical properties, in some specific cases the selection for that group may not be the most suitable for a particular member of the group. It should be also considered that some manufacturers have several grades of gloves in the same generic group of polymer therefore their specification should always be consulted.

24.2 SUIT MATERIALS

The selection of suit material is more complex because not only physical properties of the components but also the design of suit and structure of laminate used will determine its barrier properties. As a whole, these are usually proprietary and difficult to compare. The information in Table 24.1 can be used for general guidance but the industrial hygienist should make a full evaluation of the performance of the protective clothing in particular conditions and application.

24.3 RESPIRATORY PROTECTION

The selection of a respirator, general suggestions for its use, the adsorption capacity of filters, and breakthrough time are reviewed below.

The selection of respirator is based on the nature of respiratory hazards such as permissible exposure limits, established concentration immediately dangerous to life, actual concentration of hazardous substances, and amount of oxygen. When using filters, the ambient air must contain at least 20% oxygen at sea level. Filter protection should not be used for unknown contaminants and contaminants that are immediately dangerous to life and health.

Permissible exposure limits and actual concentration determine (among other factors) the breakthrough time as discussed below.

Only approved respirators should be used. Each country has a body which can approve respirators for use. In the USA, respirators are approved jointly by the National Institute for Occupational Safety and Health (US Department of Health and Human Services) and the Mine Safety and Health Administration (Department of Labor).

In addition to the the above parameters determining respirator selection, the following factors are also considered: nature of operation process, location of hazardous area (especially in respect to supply of respirable air), employee activity and intensity of effort required to perform the work (determines the amount of air which must be supplied to lungs), physical characteristics and limitations of various respirators.

The selection of respirator must be done with a full consideration of these many factors which require specialized knowledge going beyond this discussion. Further information on this subject can be found in the specialized monograph.3

Respirators can be generally divided into two main groups: air-purifying respirators and atmosphere-supplying respirators. The first group is more common and for this reason will be discussed in more detail below. Air-purifying respirators are still divided into non-powered and powered and these are further divided into gas/vapor and particle removing. Our main interest here is given to vapor-removing, non-powered respirators which are the most common in industry and laboratories in solvent applications.

Two additional subjects are integral part of good protection: respirator fit testing and training of users. Non-powered, vapor-removing respirators are also termed as negative pressure respirators. This means that respirator is under positive pressure during exhalation and under negative pressure during inhalation. If the respirator does not fit the user properly, some air from the surroundings will be drawn into the respirator during inhalation because of leaks. This will result in a diminishing efficiency of protection. For this reason, each user should be given help from the employer in selecting the most suitable type and size of respirator for the particular individual. In addition, the reasons for fitting should be clearly explained so that they are fully understood by the employee. It is only the employee who may later assure that the respirator is used properly and this will depend on his/her full understanding of the principles.

The first matter of importance is the rate of breathing under various conditions.The amount of air we breathe depends on our energy requirements or more precisely on the intensity with which we expand energy. If no work is performed, the average human being requires about 10 l of air per minute. The rate of breathing increases with the intensity of work (light work 20-30, heavy work 70-100 l/min). The use of a filter reduces air flow rate due to the pressure drop and many respirators cannot cope with high rates of flow which becomes the one important limitation of negative pressure respirators that must be evaluated during the selection process.

The pressure drop in the filter depends on its design. Chemical cartridges used for solvent adsorption are filled with activated carbon or activated charcoal which are amorphous forms of carbon characterized by their ability to rapidly absorb many gases and vapors. The carbon is obtained by pyrolysis of wood, nutshells, animal bones, petroleum products, and other carbonaceous materials. Activated carbon for respirators usually comes from coconut shells or coal after activation at temperature in the range from 800 to 900oC. It has a porous structure with a surface area of 10,000 m2/g. On the one hand, maximizing surface contributes to increased capacity on the other it may lead to an increased pressure drop during breathing (depending on particles shapes and sizes). It is thus important to consider both capacity of the filter and its pressure drop.

The adsorption of vapor is a physical process which can be reversed. Desorption of vapor does not require a high energy and is equilibrium driven (equilibrium relative to the concentration of vapor in surrounding atmosphere and distribution of adsorbed vapor in

ddiameter of granule

Gmass velocity through the cartridge

ηviscosity of air-vapor stream

Ddiffusion coefficient

This equation gives information on the relevance of major parameters of performance of filters. Breakthrough time increases with the increase of the following parameters: adsorption capacity of carbon, its density, its volume, and the cross-sectional area of the adsorbent bed and size of the granules. It decreases with increased flow rate, concentration of solvent, and an increase in the value of the diffusion coefficient. The toxicity of solvent plays a role here as well because with the increase of solvent toxicity, the breakthrough concentration is decreased which decreases breakthrough time. Breakthrough time for 3M cartridges can be calculated using available software by providing the type of solvent, its concentration, and type of work (light, medium, heavy). In addition, relative humidity is accounted for in the calculations. The adsorption of vapors is not affected by humidity below 50% but decreases rapidly as the relative humidity increases above 50%. Adsorption temperature is also an essential factor.

The above discussion shows that, although there is generally one type of cartridge used for organic vapor, all cartridges are not the same in terms of performance. The conditions of use of these respirators determine if they can perform specific protective functions. Considering that one cartridge, typically disposed after one day work may contain 40 g of solvent which would otherwise be inhaled, the selection and use of respirators is not a trivial matter and should be given serious attention.

REFERENCES

1K Forsberg, L H Keith, Chemical Protective Closing. Performance Index. 2nd Ed., John Wiley & Sons, New York, 1999.

2K Forsberg, S Z Mansdorf, Quick Selection Guide to Chemical Protective Clothing. 3rd Ed., John Wiley & Sons, 1997.

3W H Revoir, C-T Bien, Respiratory Protection Handbook, Lewis Publishers, Boca Raton, 1997.

25

New Trends Based on Patent Literature

George Wypych

ChemTec Laboratories, Inc., Toronto, Canada

Changes in production methods and the increased emphasis on environmental protection have produced continuous changes in solvent use and in the technology of solvent processing. The aim of this chapter is to analyze existing patent literature to illustrate the trends in

•the development of new solvents

•the use of solvents in various branches of industry

•the new methods of solvent processing with emphasis on solvent recycling.

25.1NEW SOLVENTS

The developments and introduction of new solvents are discussed in Chapter 21 (supercritical fluids and ionic liquids) and Chapter 3 (terpenes). These three generic groups of materials are emerging technologies studied to address environmental concerns.

Cleaning solvents are used in many industrial applications. These solvents have typically been highly volatile, toxic, and flammable. Dichloromethane, methyl ethyl ketone, toluene, xylene are frequently used for cleaning. They have all negative features contributing to potential hazards such as high volatility, flammability, and toxicity, and they influence the natural balance of the environment. If they are to be replaced, their replacements must have equal performance − a difficult task considering their excellent cleaning properties. Two recent patents1,2 suggest alternative solutions. 1-methyl-2-pyrrolidone is a suitable substitute for dichloromethane and methyl ethyl ketone in terms of its solvent abilities. It is less flammable and less volatile but its high cost prohibits its use in many applications. When it is blended with an alicyclic carbonate, a polar solvent, and terpene, a non-polar component, cost reaches an acceptable level and the blend can be used for cleaning paint equipment, reclamation of silkscreens, cleaning offset print rollers, printing surfaces, and as a general purpose cleaner.1,2

The removal of soiling and graffiti from exterior coatings requires the use of substantial quantities of solvents. Paint removers such as dichloromethane, benzene or toluene all of which which are hazardous solvents are commonly used. Several applications are needed before complete removal is achieved. Anti-graffiti coatings which are based on