DRAFT

VINYL CHLORIDE MONOMER EMISSIONS 
FROM THE POLYVINYL CHLORIDE PROCESSING INDUSTRIES

Report to
U. S. Environmental Protection Agency
Research Triangle Park, North Carolina

V.      TOTAL U.S. EMISSIONS OF VINYL CHLORIDE MONOMER
FROM POLYVINYL CHLORIDE COMPOUNDING AND FABRICATING

Table V-1 lists estimates of the total U.S. emission rate of VCM from PVC compounding and fabricating processes. These totals are based on 1974 production rates of PVC products and on representative VCM levels in the various types of resins in late 1974. Bases for the various estimates are discussed in some detail in Section IV above.

Table V-2 shows the estimated annual VCM emissions from all stages of PVC product manufacture, starting with the monomer production and proceeding to PVC polymerization and thence to fabrication. As shown in this table PVC fabrication processes, including compounding, account for less than one-half of one percent of the total VCM emissions in the U.S. Fabrication excluding compounding amounts to about one one-hundredth of one percent of total U.S. emissions.

V-1

TABLE       V-1
TOTAL U.S. EMISSION RATE OF VCM FROM POLYVINYL CHLORIDE PROCESSING 

                                 Estimated VCM
                                 Emission Rate*
Process                             kg/year      (lbs/yr)

A.   Flexible PVC
1.   Compounding                   220,000      (480,000)
2.   Extrusion                      <3,000       (<6,000)
3.   Calendering                    <4,000       (<1,000)
4.   Molding                          <400         (<800)

B.   Rigid PVC
1.   Compounding                   300,000      (660,000)
2.   Extrusion                      <4,000      (<10,000)
3.   Molding                        <1,000       (<2,000)
C.   Plastisols, Organosols,          
     Solution and Latex Fabrication  2,000        (4,500)

* Based on 1974 production rates and late 1974 VCM contents of resins.

V-2

TABLE       V-2
ANNUAL VINYL CHLORIDE EMISSIONS - 1974 

                                      Amount      Subtotal of U.S.     Total U.S.  Percent of Total
                        Emissions    Produced  Emissions by Process   Emissions    U.S. Emissions
Process             (kg/kg produced)   (kg)            (kg)              (kg)
A.  Monomer Production  2.5 x 10-3   2.2 x 109            -            5.7 x 106        4.0
B.  Polymerization          -        2.4 x 109            -            1.3 x 108       95.4
Suspension Process     3.9 x 10-2    1.9 x 109        7.6 x 107            -              -
Dispersion Process     6.0 x 10-2    2.8 x 108        1.7 x 107            -              -
Solution Process       1.8 x 10-2    5.9 x 107        1.0 x 106            -              -
Bulk Process           2.4 x 10-2    1.2 x 108        2.9 x 106            -              -

C.  Fabrication Processes  -         2.3 x 109           -            5-6 x 105        0.4

V-3

VI.    CURRENT STATUS OF CONTROLS TO LIMIT VCM EMISSIONS
FROM THE PVC FABRICATION INDUSTRIES

A.    CURRENT CONTROL TECHNIQUES

In 1974, the major emphasis on limitation of VCM emissions was, perforce, concentrated on reduction of VCM content in plant air, in order to minimize risk to the plant workers. These controls measures took two forms:

  1. Massive ventilation and hooding at the points of the process where large amounts of VCM could be expected to be emitted; and
  2. Reduction of the residual VCM levels in input resins so that the total amount of monomer available to be released would be minimized.
In none of the 25 to 30 facilities we visited or interviewed by telephone and letter was there any control equipment used to limit the VCM emission from the fabricating plants into the surrounding atmosphere (aside from the usual stacks).* Manufacturers believed that the most practical way to limit emissions both inside and outside the plant was to reduce the monomer content in the incoming resin. Both resin manufacturers and users of the resins were confident that, by the end of 1975, the residual monomer in resin coming into compounding and fabricating facilities would be sufficiently low that additional control measures to limit external emissions would not be required. (Thus, the OSHA regulations to limit internal plant emissions were expected to result in solving of the "external" emission problem also.)

Compounders and fabricators did not believe that, at present, there were any economically practical ways to control emissions from compounding and fabricating externally without seriously hindering their ability to control internal plant emissions. Not even the more sophisticated and advanced facilities (notably those compounding operations operated by the more research-minded resin-producing firms) had any method for removing VCM from vented air from the plant.

The reason for the lack of control methods available appears to be in the very low level of VCM in the vented air (typically less than 1.0 and 
* It should be noted that VCM emissions from oven-dried PVC coatings 
 (such as coatings on sheet metal and fused plastisol resins on cast 
  sheet and coated fabrics) are inadvertently controlled. The air in 
  the drying ovens is recirculated through the gas burners; both the 
  solvent and the VCM are thereby consumed. The VCM released in coatings, 
  however, is negligible--totaling less than a few thousand lbs/year 
  nationwide.

VI-1

almost always less than 10 ppm even in the air vented directly from the dry blenders and Banbury machines in the compounding facilities) and in the large volumes of air to be processed. These factors made scrubbers, after-burners and absorbers (such as carbon columns) largely impractical.

We should note at this point that activated carbon adsorption of VCM has been suggested as a practical method for removing and recovering VCM from stack gas. Although this method offers some promise for the reduction of VCM emissions from PVC polymerization facilities, its utility appears to be limited to recovery of VCM from low volume, high concentration streams. In the Tenneco pilot plant in which it is currently under investigation, the VCM concentration in the stream is between 10 and 30% (100,000 to 300,000) ppm. The maximum concentrations of VCM in fabricating plant vents is usually 50,000 to 100,000 times lower than this. In addition, much of the emissions from compounding and fabricating plants will also contain larger amounts of volatile plasticizers and other additives-frequently in much larger concentrations than the VCM-which would be expected to compete with VC24 for the carbon adsorption sites, and significantly limit the utility of the carbon.

At present, therefore, it does not appear practical to suggest carbon adsorption for limiting emissions from fabricating and compounding facilities, unless significant and unanticipated breakthroughs in VCM concentrating and adsorption techniques occur.

Similar difficulties arise in attempting to apply other emission control techniques such as condensation, compression and scrubbing which have been suggested for application to PVC polymerization facilities. The levels of VCM are simply too low to be practical.

B.    FUTURE CONTROL TECHNIQUES

1.    Reduction of VCM in Input Resins

The major control technique for the future appears to be reduction of residual VCM content in incoming resins. Since polyvinyl chloride does not generate VCM (decomposition of PVC generally produces HU instead), the only VCM which can be emitted from compounding and fabricating facilities will be that in the incoming resins. We are told by resin manufacturers that they anticipate reducing residual VCM levels in resins to less than 50 ppm. Should this be achieved, the total nationwide emissions from all PVC compounding and fabricating facilities will be less than 110,000 kg/year (230,000 lbs/year) nationwide.

A few resin producers have predicted that a 10 ppm residual monomer content can be achieved by 1976 to 1977. Should this be achieved, the total nationwide emissions should be less than 23,000 kg/year (50,000 lbs/year) by 1977--a negligible quantity. These estimates are summarized in Table VI-1.

VI-2

Table     VI-1
ANTICIPATED FUTURE VCM LOSS RATES FROM C014POUNDING AND FABRICATION 

                                             Total Annual U.S.
                                                VCM Release
     PVC Production     Avg. VCM Content     from Compounding
Year    Rates (kg)     of Raw Resin (ppm)   and Fabricating (kg)
1974    2.0 x 109           300                   600,000
1975    2.1 x 109*           50                   105,000
1980    2.4 x 109 (est)      20                    48,000

*Assumes 7% growth rate.

Finally, it appears that reduction of VCM emissions at later stages of fabricating (after compounding) is best accomplished by reducing the VCM levels either in the input raw resin or in the final compound. Techniques exist for both reductions, and it would appear wasteful to attempt to design and build equipment for removing VCM further downstream if it could be removed before it even entered the fabricating operations.

VI-3

The major difficulty in achieving these low VCM levels appears to be the quality of resin produced. Current techniques for reducing monomer content-many of them proprietary at this time--appear to result in diminished adsorbability of the raw resin for plasticizer and in reduced insulation properties and altered color.

The additional cost of producing resins of lower VCM levels cannot be estimated at this time since techniques are still in the developmental stage and information is proprietary. However, it appears that the pressures from OSHA to reduce in-plant emissions (and the high cost of providing respirators and other controls if emissions cannot be reduced), will place a very high premium on reducing the VCM content in resins. The industry is quite competitive, and it appears that fabricators will favor those manufacturers' resins which have the lowest VCM levels, thus increasing the incentives for the resin manufacturers to reduce these levels.

2.    Auxiliary "External" Control Techniques

For completeness one should consider other techniques which might be applicable for controlling VCM emitted from compounding and fabricating operations. It should be stressed, however, that these techniques are purely speculative at this time, and have not been considered by any manufacturer we interviewed.

The most promising control techniques which we can envision are those which might operate at points of high VCM emissions--notably at the dryblending points of compounding operations. As we have noted, up to 902 of the residual VCM in resins used in flexible formulations is emitted at the dryblending stage. A sizable fraction of the VCM in rigid compounds is also emitted at this stage. At least in theory, it should be possible to totally enclose the dryblending, equipment, and vent it with only small volumes of air, which could then be used as feed air to gas burners or incinerators. The purpose of the small volume of venting sir would be to increase the VCM levels in the air and to reduce the volume of air to be processed to amounts which could be usefully employed in the burners. VCM is highly combustible and decomposes readily at normal burner temperatures.

There are several disadvantages to this technique which must be considered At present, it runs totally counter to current "improvements" in processing equipment designed to sweep away any VCM emissions which might go into the workspace. Thus, equipment would have to be totally redesigned for low flows. Secondly, the dryblend powder would probably need a longer residence time in order to ensure that enough VCM is stripped out under the low-air-flow conditions. Finally, of course, the burners would have to be built of materials that would withstand the HCl emitted when vinyl chloride monomer is burned.

It is not possible at this stage to estimate the cost of equipment redesign for VCM burning since such a system is simply at the speculation stage.

VI-4

[Appendix | Table of Contents]

If you have come to this page from an outside location click here to get back to mindfully.org