Recycling Used Automotive Oil Filters Kent D. Peaslee

Author's Note: The mention of brand names does not consti­tute an endorsement by the U.S. Bureau of Mines.

Over 400 million used automotive oil fil­ters are discarded in the United States each year, most of which are disposed of in land­fills, wasting valuable resources and risking contamination of ground- and surface-water supplies. This article summarizes U.S. Bu­reau of Mines research evaluating scrap pre­pared from used automotive oil filters. Ex­perimental results show that crushed and drained oil filters have a bulk density that is higher than many typical scrap grades, a chemical analysis low in residual elements (except tin due to use of tin plate in filters), and an overall yield, oil-filter scrap to cast steel, of 76% to 85%, depending on the method used to prepare the scrap.

INTRODUCTION

Every year there are more than 400 million used automotive oil filters discarded in the United States, containing an estimated 91,000 m3 (24 million gallons) of used oil and over 155 kt of steel. Most of these are disposed of in landfills where the motor oil, along with any toxic components that it might contain, may leach from the oil filters into ground- and surface-water supplies. Recycling of oil filters has the potential to recover over 90% of the oil for reuse and/or recycle, 100% of the steel as ferrous scrap, and eliminate the environmental threat from oil-filter landfilling.

Until recently, oil filters were not considered a potential scrap source because of the large volume of residual oil remaining in discarded filters and the small tonnage generated in comparison to the amount of scrap consumed. However, new federal regulations encourage oil-filter recycling, and several states have banned landfilling of oil filters.

Various processes are available for transforming used oil filters into ferrous scrap. Some of the processes are designed to be performed by the generator, while others can only be done by a scrap or waste processor. The selection of the process depends upon state regulations, capital available for equipment, and requirements of the scrap consumer (mill or scrap processor).

The simplest scrap preparation is crushing and draining of individual oil filters using a pneumatic press. Since most local garages have compressed air available, this

process is simple, inexpensive, and fairly effective at removing and recovering oil. Studies at the Iowa Waste Reduction Cen­ter have shown that it is possible to extract 88% of the used oil from discarded filters with this type of equipment.! Processes are also available in which a solvent washes the residual oil from the filter during the crush­ing process to extract a higher percentage of the residual oil and eliminate dripping oil. High-pressure hydraulic crushers, while more expensive, can process several oil fil­ters at one time. The drained oil from each ofthese processes is reused and/ or recycled, and the crushed filter is either directly melted in an electric furnace or sent to a

Figure 1. Used oil filters in various stages of processing. (a) Drained. (b) Shredded. (c) Crushed scrap and/or waste processor for secondary and drained. (d) Oil filter brick containing three filters. scrap preparation. Secondary processing

1.8~------------'

1.6 6" 1.4 ,g 1.2 §.1.0 ·~O.8 ~ 1.6

1.4 1.2

O~L-~~~L-~~~~ #< liM!' liMilJr9rjCD Pi It:: 8/Jshl/'?ilJ?{f Filter

Figure. 2. Apparent density by scrap type (typical). HMS-heavy metal scrap; CD­crushed and drained; OFB-oil filter bricks. No.1 HMS is thicker scrap (>6.35 mm plate) and is generally denser and cleaner than No. 2 HMS (>3.2 mm section thickness). No. 1 bushling consists of flashings from new pro­duction and represents one of the best and most expensive forms of scrap.

44

typically involves shredding of the crushed oil filters, followed by a separation of the clean steel from one or more by-products. The processed scrap is high-yield, low-residual-content material (chemistry similar to those reported later in this paper), and it does not contain the hydrocarbons remaining in the other types of oil-filter scrap. Various types of fuels, recyclable paper, or materials used in the manufacturing of construction materials are produced as typical by-products. Although secondary processing allows for better separation and re­source utilization than direct melting of crushed filters, it requires additional equip­ment and energy. Figure 1 is a photograph of a used Fram PH-8A oil filter and the resulting scrap after processing by each of the above mentioned methods.

A few steel mills in the United States have started recycling used oil filters. The largest oil-filter recycler, Tamco Steel in Rancho Cucamonga, California, started recycling in 1991 and plans to melt approximately 18 million oil filters in 1993.2 Both crushed and drained oil filters and shredded oil filters have been recycled successfully in place of other scrap types in the normal scrap mix. This article summarizes U.S. Bureau of Mines research evaluating scrap prepared from used automotive oil filters.

REGULATORY ASPECTS OF OIL·FIL TER RECYCLING

In 1986, the U.S. Environmental Protection Agency (EPA) decided not to list recycled used oil as a hazardous waste because they believed that a hazardous waste listing might discourage recycling and result in uncontrolled disposal of used oil. This decision was challenged and the District of Columbia's Court of Appeals overturned the EPA's decision in 1988. The Court ruled thatthe EPA had to determine whether any

JOM • February 1994

used oils should be listed as hazardous waste based on the technical criteria for waste listings.3

The EPA promulgated a modification to 40 CFR 261 on May 20, 1992, which ex­empted most used and drained oil filters from definition as hazardous waste.4 The basis for the ruling was a study of the toxicity characteristics (TC) of 46 used oil filters. This study found that none of the 35 light-duty vehicle filters tested exhibited TC, although low levels of lead, chromium, cadmium, and benzene were detected. However, it was determined that of the 11 heavy-duty vehicle filters tested, five ex­hibited TC for lead. The five failed filters were the only terne-plated filters used in the study. (Terne is a lead-based alloy con­taining 10-20% tin.) An unused terne-plated oil filter also failed the test. Therefore, terne­plated oil filters were not included in the exemption and require a hazardous waste determination prior to disposal in a land­fill. Since the ruling, the majority of the U.S. manufacturers have stopped using terne in their filters.2 The same ruling determined that used oil destined for disposal is not a listed hazardous waste. This was decided because the EPA determined that the reduction in lead levels in used oil already observed, in conjunction with the reduc­tions scheduled to occur with the Clean Air Amendments, would further reduce the risk for harm to human health and the environment from mismanagement. The final ruling, in which the EPA determined that recycled used oil does not have to be listed as hazardous waste, was promulgated on September 10, 1992.5 The EPA recommends oil-filter recycling and has encouraged it through promulgating these final rules.

Although the federal regulations make it possible to recycle used oil filters as normal scrap, several states are authorized to administer and enforce the Resource Conserva­tion and Recovery Act program within their state. These states were not required to modify their programs if the federal standards promulgated were less stringent than or reduced the scope of the existing requirements. At least 36 states have more stringent requirements than the federal regulations, placing additional restrictions on the handling, disposal, or recycling of used oil. Of these states, 17 have additional regulations for the disposal or recycling of oil filters. In many of these states, where oil­filter land disposal is banned, oil-filter generators must either pay a processor to prepare the filters for acceptable solid waste disposal, pay to dispose in special landfills, or find recycling outlets. This has provided additional motivation for developing methods of recycling used oil filters.

DENSITY OF RESULTANT SCRAP

The apparent density of oil-filter scrap depended largely upon the method of scrap preparation. Figure 2 compares the apparent density of oil-filter scrap prepared by different methods with typical values of other types of scrap. The crushed and drained oil-filter scrap was crushed with a lower force of compression than the oil filter bricks and was therefore less dense. The oil filter bricks were found to be as dense as most commercial grades of scrap. Although the density of the filters was very good, the bottom of the storage containers had appreciable oil accumulation from seepage out of the crushed filters. Therefore, crushed oil-filter scrap should be used directly out of the transportation containers and not unloaded in the scrap yard, unless the yard is equipped with an area suitable for containment and collection of the oil seepage during storage. The oil in the bottom of the storage containers could be recovered and recycled, avoiding contamination of the scrap yard. A grate above the bottom of the shipping container would prevent crushed oil filters from sitting in oil.

OIL FILTER CONTENT

The average weight loss for each type of filter scrap during the fuming at 900°C in the electric box furnace is shown in Figure 3. The weight loss depended upon the type of scrap preparation. The crushed and drained scrap resulted in the highest percentage weight loss (20%), confirming a suspected larger amount of hydrocarbon remaining in the samples after crushing. This was expected because of the lower crushing forces utilized in the process. The crushed, washed, and drained filters resulted in less weight loss (16.5%) than the crushed and drained filters, indicating a more efficient removal of the oil from the washing process. Less fuming was also observed during the heating, but residual water in the form of an emulsion in the filters sputtered during the fuming process. Of the scrap types tested, only the crushed, washed, and drained filters

1994 February. JOM

25 • Composite

Std. Dev = • PH-BAonly

20 2.5% Std. Dev =

2.0% 15

Std. Dev = ~ 1.7% 2 -' 10 :c: 1 5

o CD Filter CWD Filter OFB Filter

Figure 3. Weight loss during fuming (tempera­ture greater than 900°C). CO-crushed and drained; CWO-crushed, washed, and drained; OFB-oil filter bricks.

Neoprene Rubber Seals-Partially

Removable 2%

Filter Element Cellulose/Glass

Fiber

Used Oil ~---- Steel Can be Recovered Base, Can, Core, by Draining 55-97% Anti-Syphon Valve,

Recovery Spring, etc. 38% 54%

Figure 4. Estimated used oil filter content (by weight).

45

Table I. Mass Balance of Oil Filter Melting showed any significant moisture content (approximately 1 wt.%), which could be a concern to steelmakers during melting. The oil filter bricks were found to have the highest density, the lowest percentage of weight loss (12.8%), and the least amount of fuming.

Scrap Type Charge Weight Charge Composition

Steel Weight Melt Yield

Slag and/or Ash

Losses (Dust and/ or Volatiles)

Calculated Yield

Test 1

Crushed and Drained 26.4 kg

79.6% CD 20.4% pig iron

24.8 kg 94.1 o/c 0.3 kg 1.1 %

1.3 kg 4.9% 76%

CD-crushed and dramed fIlters, OFB-Oll hlter bncks

Table II. Chemical Analysis of Oil Filter Melts (wt.%)

Element Test 1 Test 2 Test 3 Pig Iron

C 2.31 2.43 2.28 4.37 Mn 0.13 0.20 0.19 P 0.053 0.047 0.039 0.036 S 0.055 0.037 0.D25 0.014 Si 0.04 0.05 0.04 0.17 Cu 0.015 0.02 0.015 0.02 Nl 0.02 0.01 0.01 0.06 Cr 0.02 0.02 0.02 0.D2 Mo 0.001 0.002 0.002 Sn 0.026 0.035 0.032

ACKNOWLEDGEMENTS The author thanks Leonard Robinson,

Tamco Steel, for his assistance in obtaining information and samples for this project; Bayou Steel for providing steel samplers and steel sample analysis; Gray Automotive, Enviro-Care Manufacturing, and Oasis In­dustries for providing oil-filter samples; and members of the Filter Manufacturers Coun­cil for their assistance.

References 1 J L Konefes and J A Olson, "Motor VehIcle 011 Filter Recyclmg Demonstration ProJect," unpublIshed report, Iowa Waste ReductIon Center, Um\ ersltv of Northern Iowa (1991) 2 K KIser, "Steel Scrap Challenge~," Scrap ProccsslIIg fmd Reclfe/ms (Marchi ApnI1993), pp 107-113 3 Ha.;:ardous Waste Treatment CounCIl vs EPA, 861 F 2d 270, DC (m IY88) 4 Federal Rex,,!er. \. 57, No 98 IMay 20, 1992), pp 21524-21534 5 Federal RCSJ.:;ft'f, v 57, No 176 (September 10, 19(2), pp 41S66~41586

6 J A Ohlemeler, "Practical InformatIOn About Crushmg Used OIl Filters," UtIII!1f alld Telepholle Flee!s (Marchi Apnl, 1992), pp 20-22 7 J A Obon and J A Ohlemeler, "Motor Vehicle Oil Filter Recyclmg ReVIsIted," unpublIshed report, Iowa Waste Re­ductJOn Center, Um\ efsltv of Northern Iowa (1992) 8 G K Gnggs, FIlter Manufacturers CouncIl, Research Tn­angle Park, NC, pnvatecorrespondence (September21, 1993) 9 L. Theodore and I Revnolds, IlltrodllctlOll to Ha:ardous Waste illClIlt?fatu1I1 (New York John WIley and Sons, 1987)

ABOUT THE AUTHOR

Kent D. Peaslee earned his B.S. in metallur~ gical englneenng at the Colorado School of Mines in 1978. He IS currently a Ph 0 candl~ date at the University of Missouri-Rolla and a metallurgist with the U S. Bureau of Mines, Rolla Research Center. Mr. Peaslee IS also a member of TMS.

For more information on this subject, contact Kent D. Peaslee, U.S. Bureau of Mines, Rolla Research Center, P.O. Box 280, Rolla, Missouri 65401.

46

Test 2

Filter Bricks 25.8 kg

89.2% OFB 10.8% pig iron

24.4 kg 94.6% 0.4 kg 1.6o/c

1.0 kg 3.9% 83o/c

Test 3

Filter Bncks 25.6 kg

90.1% OFB 9.9% pig iron

24.8 kg 96.9% 0.4 kg 1.6o/c

0.4 kg 1.6% 85%

A difference was observed in the weight loss from sample to sample because of the variation in filter content between different filters and inconsistent filter preparation. Of the scrap types tested, the oil filter bricks showed the least variation in weight loss between samples (standard deviation = 1.7%). This consistency was a result of a

combination of the higher crushing forces removing a higher percentage of the oil and an averaging of the differences in content between filters by crushing several filters into one "brick."

Filter media and neoprene make up a large percentage of current oil-filter design. This resulted in a substantial combustible percentage (10-20%) for all used oil-filter scrap, regardless of the scrap preparation method used. The only method available for elimination of all combustible materials from oil-filter scrap is shredding, followed by a separation process.

A new oil filter was dismantled and weighed to establish the typical content of an oil filter. A Fram PH-SA oil filter was selected because it is a size used on a large number of automobiles. These measurements were used to generate the estimated content of used oil filters shown in Figure 4. The maximum steel content of a crushed and drained filter, with the neoprene gasket and 97% of the oil removed, was determined to be 87.5 wt. %. The Iowa Waste Reduction Center found that 97% of the oil was removed from automobile oil filters when a crushing force on the order of 360 kN was used.? The steel content determined in this study was higher than data from a recent survey by the Filter Manufacturers Council, which showed that the average automobile oil filter contains (by weight) 81 % steel, 12% filter media, 4% adhesives, and 3% rubber.8

The results of the induction melting experiments are summarized in Table 1. The metal yields obtained when melting fumed oil filters were between 94% and 97%. The slag formed in all cases was 1.1-1.6 wt. %. The slag appeared to be more of an ash than a typical steelmaking slag because of a very low density (specific gravity < 1). Results of x-ray diffraction and SEM of the slag samples showed a high content of Fe, Ca, Si, and Mg. Iron was expected as a product of oxidation. The presence of calcium, silicon, and magnesium was unexpected because no flux additions were made to the test. However, some of the adhesives used in construction of oil filters contain these elements. The net overall yield, oil-filter scrap to cast steel, was calculated to be between 76% and 85%, depending upon the method of filter preparation. This yield was calculated by combining the 13-20% loss from fuming with the metal yields obtained from melting fumed oil filters.

The recovered iron analysis (detailed in Table II) showed that the oil-filter scrap was low in residual elements and could be used to help dilute typical residual problems (copper, chromium, molybdenum, etc.). Only the tin levels (0.026-0.035% tin) were higher than most low-residual scrap because of the use of tin plate in the construction of the can. The high carbon content (-2.3%) in the iron was a result of the pig iron addition (which contributed 20-40% of the total carbon) and carbon "soot" (which is estimated to have contributed 60-80% of the total carbon). During the process of fuming the oil filters prior to melting, hydrocarbons vaporized into a suffiCiently reducing atmosphere that allowed the high carbon content gas to deposit carbon as a soot on lower temperature regions of oil filters in the furnace. The remainder of the gas eventually decomposed and burned to mainly carbon dioxide and water vapor. Evidence of carbon "soot" was observed on the door of the furnace during several fuming experiments. Used oil is approximately 87% carbon and 12% hydrogen, and filter media is primarily cellulose (CbHIPs),' Both are sources of large amounts of carbon when vaporized.

The energy considerations are very complicated. No experimental work was done to determine the amount of energy saved or used in the melting of oil filters. There is significant potential energy available in the combustion of the hydrocarbons in the filter. Typical fuel oil, similar to used automotive oil, has a net heating value of 45,400 kJ /kg and paper, similar to filter media, has a net heating value of up to 16,300 kJ /kg.9

However, the net heating value is based on combustion of the material to CO2, Since most of the combustion to CO2 occurs by post-combustion above the bath, it would be expected that the largest percentage of the heat would not be reclaimed as usable energy. In fact, the use of a high percentage of oil filters could present problems with excessive heat in the ductwork and baghouse due to postcombustion. Energy would be reclaimed from the oxidation of soot carbon dissolved in the liquid steel and oxidized during the oxygen blow.

JOM • February 1994