of the most frequent pore diameters (AD,) of at least 10 A. Also, a pore distribution factor (PD) of a t least 5 is preferred. PD =
( 0 8 x mr 104
A comparison of these restraints for the three catalysts is shown in Table VII. From the comparison of Table VII, both catalysts A and B would be expected to have poorer performance than catalyst C, the large pore catalyst. Work by Van Zoonen and Douwes (1963) also supports the necessity of having large pores for good desulfurization.
Summary The effect of changing the most frequent pore radius from 33 to 25 A for a cobalt-molybdate on alumina catalyst resulted in a loss in desulfurization capability while processing a raw anthracene oil, a coal derived liquid. For these catalysts with essentially identical chemical compositions and operating without usual pore diffusion limitations, the shift to a smaller pore size still resulted in lower sulfur removal. A surface phenomenon such as adsorption orientation may be the factor causing differences in desulfurization, although this initial study does not provide for the effect of specific molecular structure on adsorption and desulfurization. The larger pore catalyst was, however, able to cause greater desulfurization of the heavy or higher boiling fractions of the anthracene oil. An empirical method of characterizing catalyst pore properties for petroleum stock hydrotreating, as given in the patent literature (Anderson et al., 1959), also satisfactorily characterized this coal derived liquid. This study represents only initial experiments in a broader program to characterize, develop, and tailor catalysts and support properties explicitly for the removal of heteroatoms from coal liquids. Questions brought out in these experiments are under further study, along with many others. Although a vast amount of work has been given to processing petroleum stocks, and some of this in-
Table VII. Comparison of Pore Factors
Recommended Catalyst C Catalyst A Catalyst B
60 66 50 50
(A)
10 18.5 6.5 10.8
5 6.66 1.62 2.7
formation may be applied to processing coal liquids, there are significant differences between coal and petroleum derived materials which require specific catalyst tailoring for these coal liquids.
Literature Cited Anderson, J. A., Jr., et al. (to Esso Research and Engineering), U S . Patent 2,890,162 (June 9, 1959).. Frye, C. G., Mosby, J. F., Chem. fng. frog.,' 63,66 (1967). Hoog. H., J. lnst. Petrol., 38, 738 (1950). Jones, J. F., et al., "Char Oil Energy Department Final Report," RBD Report No. 56, U.S. Department of the Interior, Office of Coal Research (Dec 3, 1971). Kloepper, D. L., et al., "Solvent Processing of Coal to Produce a De-Ashed Product," R&D Report No. 9, US. Department of the Interior, Office of Coal Research, 1965. LeNoble, J. W., Chaufer, H. H., "Fifth World Petroleum Congress Proceedings," Section IO, Paper 18, Fifth World Petroleum Congress, Inc., New York. N.Y., 1959. Maxted, E. B., Elkins, J. S.,J. Chem. SOC..5086 (1961). Mears, D. E., Chem. fng. Sci., 28, 1361 (1971). Office of Coal Research, "Development of a Process for Producing an Ashless, Low-Sulfur Fuel from Coal," R&D Report No. 53, U.S. Department of the Interior, 1970a. Office of Coal Research, "Economic Evaluation of a Process to Product Ashless, Low-Sulfur Fuel from Coal," R&D Report No. 53, U S . Department of the Interior, 1970b. Satterfield, C. N., "Mass Transfer in Heterogeneous Catalysis," M.I.T. Press, Cambridge, Mass., 1970. Sooter, M. C., Ph.D. Thesis, School of Chemical Engineering, Oklahoma State University, Stillwater, Okla., May, 1974. Van Zoonen, D.. Douwes. C. T.. J. lnst. Petrol, 49 (No.480), 383 (1963). Wilke, C. R., Chang. P., Am. lnst. Chem. fngr. J., 1, 264 (1955).
Receiued for review December 23, 1974 Accepted June 4,1975
Much of this work was supported by funds made available by the Pittsburg and Midway Coal Mining Company and the Office of Coal Research, US.Department of the Interior.
Development of Fire Performance Tests for Carbon-Impregnated Polyurethane Foams Patricia A. Tatem* and Frederick W. Williams Chemical Dynamics Branch, Chemistry Division, Na wal Research Laboratory, Washington, D.C. 20375
Several carbon-impregnated polyurethane foams were evaluated under burning and pyrolysis conditions with the intent of devising dynamic testing procedures for judging their fire safety. The tests were formulated for anechoic chamber material and are intended to assure that a polyurethane foam material classified as fire safe has the ability to self-extinguish deep-seated combustion as well as external or visible flame produced from different sources of ignition. In addition, the tests assess the hazards these foams create by measuring the toxicity levels produced under fire and thermal degradation.
Introduction The number of applications for polymeric materials in the building industry has greatly increased as their tech204
Ind. Eng. Chem., Prod. Res. Dev., Vol. 14, No. 3, 1975
nology expands. These polymers are utilized in various forms-for structural applications, as interior furnishings for the home and office, and in many other products of
day-to-day living. Many of these formulations contain halogens andlor nitrogenous moieties, which can react during combustion or pyrolysis to form toxic products such as hydrogen chloride (HCI) and hydrogen cyanide (HCN). Because of the danger to life and property hy the onset of a major conflagration, all aspects of the behavior of the materials toward fire need to he understood. Polvurethane foam comnrises one class of nolvmeric ma-
,_--..._ potential hazard they may create in a fire. Sumi and Tsuchiya (1973) have investigated several nitrogen-containing polymers, including rigid urethane foam, to assess the importance of HCN, CO, and COz in creating a dangerous atmosphere. However, much of the testing of polyurethane foams involves the deliberate degradation in an inert atmosphere (Woolley, 1972) with subsequent analysis of pyrolysis products. In a real situation where air is present, the combustion products and mechanisms could he different. In addition, in a fire environment the oxygen concentration usually decreases which could lead to incomplete comhus. tion and additional products. Of particular interest is whether the production of HCN and other toxic materials is enhanced in an oxygen deficient environment One application for the polyurethane foams is for covering the walls, floor, and ceiling of modern anechoic chamhers. T o serve as a good microwave absorber, the foam is first impregnated with carbon and a latex hinder to attain this electrical characteristic. The resulting material has a low electrical resistance and is thus a goad conductor. The foam is further treated with a fire retardant, such as a chlorine-containing compound, to an extent sufficient to impart fire resistance without degrading its electrical properties. These fire retardants increase the safety of the materials by reducing flame spread rates. However, when involved in fires, the behavior of the treated foams may he modified. If this modified behavior promotes incomplete comhustion, toxic combustion products containing nitrogen (Woolley, 1972; Napier and Wong, 1972) and halogen may he released that could significantly increase the toxicity of fire gases. The companies that manufacture these anechoic chamher materials have no standard which is uniquely designed for polyurethane foam. They usually adopt the ASTM tests, i.e., D-1692 or D-635, (ASTM Standards, 1974) to meet their specific purposes, hut these ASTM standards are useful only for a qualitative assessment of flammahility. These tests do not give results that can he extrapolated to the fire hazard. In addition no ASTM standard or other type of requirement exists relating to the production of potentially toxic products hy these foams under pyrolysis or fire environment. Although there is limited knowledge on the fire and toxicity hazards contributed by the treated polyurethane foam present in anechoic chambers, two recent fires involving these chambers have indicated the need for flammability and fire retardance controls in the manufacture of these materials. In one fire, the usual firefighting efforts were unsuccessful in extinguishing the fire because of the ability of the foam to continue to smolder after removal of the igntion source. High concentrations of HCN and HCl gases produced extremely hazardous conditions for the firefighters (Carhart and Williams, 1973). T h e investigative report on the second fire indicated that the absorbent materials used in the chamber were manufactured from a self-extinguishing grade of polyurethane foam which was coated with a fire retardant material (Eadens and Connolly, 1974). In an effort to eliminate the potential fire hazard associ ated with anechoic chambers, samples of anechoic chamber
Z:'
Figure I. Fire test chamber, 9.5 ft3, and support equipment. foams produced commercially by four companies were tested extensively to develop tests which would determine flammability and toxic product evolution characteristics of these foams under burning and pyrolysis conditions. The two previous fires indicated a need to evaluate the ability of the foams to self-extinguish flame and smoldering after removal of an electrical, a flaming, or a flameless (hot surface) heat source. Tests with these three sources of ignition would indicate the potential hazard once the material is ignited, if the ignition source is detected and eliminated without delay. High toxic product concentrations during the fires suggested the need for evaluations of toxic product formation when the material is continuously exposed to a source of ignition andlor pyrolytic conditions. As a result of these tests, five proposed performance specifications were devised to set forth a fire retardance and flammability requirements for foams being considered for use in new chambers. Development of Test Procedures Each foam involved in the testing had been impregnated with a fire retardant during the production process. In addition, the manufacturers coated each final product with a fire retardant paint. The ignition sources used were a power supply (capahle of 240 V ac, 8 A), hydrogenlair flame (Ts2100°C), natural gas flame (T =l95ODC), soldering iron (T -5OO"C), and &in. (0.5-in. diameter) long radiative cartridge heater (capahle of temperatures up to 6OOOC). Test leads from the power supply were made of number 10 copper wire from which 1 in. of insulation had been removed a t each end. The hydrogenlair flame was produced on a microhurner (diameter = 0.095 in.) located in a closed comhustion chamber and had a flame height of ?6 in. The natural gas flame was produced on a laboratory Bunsen burner (diameter = 0.438 in.) in the hood and had a flame height of =3 in. The tests which required monitoring of combustion Ind. Eng. Chem., Prod. Res. Dev., Vol. 14, No. 3, 1975
205
CHAMBER 9 . 5 Cu Ft
II
ll
u U
-INLET
FOR CALIBRATION GASES
TO TMOSPHERE
CO ANALYZER
\'
"
Figure 2. Flow diagram of the support facilities for combustion chamber. products were carried out in a 9.5 ft3 closed combustion chamber shown in Figure 1and described in detail in previous work (Tatem et al., 1973). The chamber was modified to sample continuously as shown schematically in Figure 2. The CO2 and CO analyzers (Beckman Instruments, Model 315A) located in the sampling loop have 0-10% and 0-4000 ppm scales, respectively. The 0 2 analyzer (Beckman Instruments, Model F3) range is 0-2596. An auxiliary valve in the rear of the chamber provides an outlet for intermittent colorimetric tube sampling (Drager Tubes, Dragerwork Lubeck, 24 Lubeck Moislinger Allee, Germany) for HC1 and HCN gases. Temperatures were measured with iron-constantan thermocouples referenced to ice water. The samples were contained in an alumina combustion boat during the continuous exposure tests. The boat was located in the center of the chamber and could be manipulated with a remote arm. Also located in the center of the chamber was a nichrome wire, connected to an external power supply, which served as the ignition source for the hydrogen torch. The same power supply was used interchangeably for heating the cartridge heater. Ease of Ignition and Propagation of Flame (Test 1). Tests performed in the laboratory hood involved short exposures (-30 sec) of the foam to the methane flame and soldering iron. During these exposures, care was taken to assure that the surface of the foam subjected to the ignition source was not covered with a surface fire retardant. Specimens were observed for 60 sec after removal of the ignition source for evidence of any visible signs of combustion. Two foams were self-extinguishing and did not propagate smoldering after removal of the ignition sources. Two other foams self-extinguished with respect to open flame and visible smoldering when the heat source was removed, but sample damage observed after these tests indicated that nonluminous reaction, and, hence, potential toxic product formation continued. Therefore, more sophisticated testing was done to determine the extent of smoldering after a flameless heat source was removed. Although a soldering iron was initially used as the flameless heat source, a radiative cartridge heater was used for further testing and is the heat source eventually required by the smoldering test since its temperature can be controlled and monitored better than a soldering iron. Smoldering Test (Test 2). The cartridge heater was inserted snugly into a hole cut in a solid cube of the foam, weighing from 40 to 70 g. The specimen was placed in the chamber and the temperature of the heater was increased 206
Ind. Eng. Chem., Prod. Res. Dev., Vol. 14, No. 3, 1975
/
TIME
(MINI
Figure 3. Production of CO from polyurethane foams in smoldering tests.
to a predetermined value. The interior of one of the foams was hollow, so for this material the heater was wedged into a corner between the 0.5 in. thick walls. The power supply to the heater was disconnected after reaching the desired temperature and the cartridge remotely removed from the sample. The temperature of the cartridge heater and the concentrations of CO, COz, and 0 2 were monitored continuously. Typical examples of toxic product formation in this test are given in Figure 3. In this comparison, the foams were exposed to similar temperatures (300-365OC), but the amounts of toxic products generated following ignition source removal differed widely. Other tests showed that the magnitude of toxic product formation and sample damage varied according to the temperature to which the heater was raised prior to being removed. After removal of the ignition source, the rate of toxic product formation depended on the extent of smoldering since this reaction is a significant producer of toxic products. A rate of zero was evidence that smoldering had halted. These tests can be correlated with the ability of the foam to propagate smoldering. For two of the foams (C and D), the increase in combustion products ceased within 2-4 min after removal of the heater if pyrolysis had been initiated, as can be seen in Figure 3. These foam samples incurred minor damage from smoldering. No pyrolysis occurred for these two foams, as indicated by the absence of gaseous products, below temperatures of 225°C in one case and 300°C in the other. In some tests the temperature of the heater was raised as high as 6OOOC before removal; cessation of smoldering occurred within the same time frame.
Table I. Atmospheric Analyses Following Exposure to Hydrogen Torch (Test 3) Combustion produit
Product concn'
Wt of product/g of sampletmg
HCN HC1
4 PPmb >12 ppm 0.13% 63 PPm 4 PPmb 5.3 670 21
Table 11. Atmospheric Analysis Following Exposure to Cartridge Heater (Test 4) (Smoldering Not Included) Combustion product
Product concn'
Wt of product/g of sample,' mg
HCN HC1 COZ
2 PPm 20 PPm 0.04% 35 PPm 2 PPm 5 PPm 0.04% 130 ppm 3 PPm 2 PPm 0.02% 15 PPm 1 PPm
0.5 9 215 12 0.5 2 215 44 0.6 0.9 110 5 0.24 0.4
~
Foam A
COZ
co Foam B
HCN HC1 COZ
co
Foam C
HCN HC1 COZ
150 ppm; HCl > 20 ppm). For these runs the data collection was terminated 10-15 min after the heater was removed from the sample. At this time the COS concentration was still rising and the 0 2 concentration falling. Visual examination of these samples indicated total destruction. If the maximum heater temperature was lower than the respective temperatures given, the sample did not propagate smoldering and sample damage was not detected. In the procedure for the smoldering test, continuous sampling techniques are not required. After experimentation, it was decided that the involvement of the sample following ignition source removal could be determined from the physical appearance of the sample instead of continuously monitoring the products of combustion. The rapid deterioration of the atmosphere for the foam samples that propagate smoldering (A and B) is immediately evident. The concentrations of CO and HCN gases produced by this quantity of these foams in a 10 ft3 space within 10 min after reaching 300 and 365OC, respectively, would be sufficient to cause death in less than 1 hr (Sax, 1968; ACGIH, 1971). The concentration of HC1 gas produced would cause intense discomfort and irritation in man (Sax, 1968; ACGIH, 1971). Furthermore, toxicity levels reached in the smoldering experiments indicated the need for assessing the hazard these foams would create in a fire or thermal degradation environment. Toxic Gas Emission in a Fire Environment and Due to a Hot Surface (Tests 3 and 4). A known quantity (1g) of each foam was exposed to the hydrogen-air torch for 15-25 min in the chamber. The foams were contained in
FoamA
co Foam B
HCN HC1 COZ
Foam C
HCN HC1 COZ
Foam D
HCN HC1
co
co
1 PPm
COZ
