Plastics, Rubber, and Paper Recycling - ACS Publications - American

Chapter 22

A Black Filler for Rubber from Tire Pyrolysis Char 1

2

Michael R. Beck and William Klingensmith

1Polymer Valley Chemicals, Inc., 1872 Akron Peninsula Road, Akron, OH 44313 Akron Consulting Company, Akron, OH 44319

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The purpose of this paper is to review the requirements that need to be met by a black filler. This paper reviews two major aspects of rubber technology. The first is a review of the black fillers used in rubber compounding. The second is a discussion of the scrap tire generation and disposal issue and how a black reinforcing filler can be generated using scrap tires and pyrolysis, grinding and beneficiation to produce a useful product. There is over 3 billion pounds of carbon filler used in North America. Over 90% of this is as a reinforcing and/or extender filler for rubber. The three types of black, furnace, thermal, and channel are reviewed and their benefits presented. A typical production specification for several grades of carbon black are shown and the actual production results for over 40 lots of carbon black are analyzed for consistency. In addition a brief history of carbon black development and the specific plant and processing needs of carbon black are discussed.

Carbon black is the major reinforcing agent for rubber. Most rubber articles require the incorporation of reinforcing agents to be useful. Other reinforcing agents that are used include silica, clay and ground carbonates. The rubber compounder selects the reinforcing agent or filler to impart the properties to the rubber compound that make it serve its' intended purpose at the lowest possible cost. Carbon black is made in many different types and grades. These include thermal black with little reinforcing power to N l 10 furnace black with high reinforcing ability. These are discussed in detail in another part of this paper. The total amount of carbon black consumed in the US is estimated at 3.0 billion pounds. About 90% of this is used by the rubber industry with the remaining 10% divided between inks, plastics, coatings, paper and electrodes. These are summarized in Chart 1 (1).

0097-6156/95/0609-0254$12.00/0 © 1995 American Chemical Society Rader et al.; Plastics, Rubber, and Paper Recycling ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

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BECK & KLINGENSMITH

A Black Filler for Rubber

255


There is a significant amount of work being done to recover the carbon black from used rubber goods, especially tires. This has not happened as quickly as many recyclers have desired. This paper will review some of the efforts that have been tried to recycle carbon blackfromtires. The purposes of the paper are the following: 1.0 Review the properties of carbon black used in tire compounding. 2.0 Review the tire disposal needs and properties of a black filler produced from tire pyrolysis char 3.0 Access the potential for black filler from tire pyrolysis char to meet carbon black reinforcing requirements. Carbon black types There are twenty five to thirty grades of carbon black that are commonly used. These are broken into the following classes: N100, N200, N300, N500, N600, N700 and N900. Chart 2 shows the various % of each of the blacks used overall (2). The lower the number the more reinforcing the carbon black. The N100, N200 and N300 series blacks generally used in treads for abrasion resistance while N300 and N500 series are used in carcasses of radial tires. The N600 and N700 series are also used in carcasses and sidewalls of less critical performance bias and slow speed tires. As a result when tires are pyrolyzed a mixture of all the blacks occur along with zinc oxide, titanium dioxide, silica and silicates like clay and talc. The result is a black colored char with a carbon content around 88-90% and an ash of 8-12%. These vary depending on the tire composition used in the pyrolysis operation. The major types of carbon black and the typical applications in which they are used is as follows: Designation

General Rubber Typical uses Properties N110,N121, N166 High Abrasion Resistance Special Tire treads, airplane,off-the-road racing N220, N299, N234 High Abrasion Passenger, off-the-road, Resistance, Good special service tire treads processing Standard tire treads, rail N339, N347, N375, N330 High Abrasion pads, solid wheels, mats, Resistance, easy tire belt, sidewall, processing carcass, retread Tire belt, wire carcass, Low modulus, good tear N326 sidewall,bushings, strength, good fatigue, weather strips, hoses goodflexcracking resistance Tire innerliners, carcass, High modulus, high N550 sidewall, innertubes, hardness, low die swell, hose, extruded goods, Vsmooth extrusion belts

Rader et al.; Plastics, Rubber, and Paper Recycling ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

256

PLASTICS, RUBBER, AND PAPER RECYCLING

CHART #1 Total Carbon Black Sales


Non-

CHART#2 US CARBON BLACK PRODUCTION


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BECK & KLINGENSMITH

N650

N660


N762


High modulus, high hardness, low die swell, smooth extrusion General purpose, low die swell, smooth extrusion

High elongation and resilience, low compression set

257

Tire innerliners, carcass, belt, sidewall, seals, friction, sheeting Carcass, sidewall, bead compounds, innerliners, seals ,cable jackets, hose, soling, flooring, MRG Mechanical goods, footwear, innertubes, innerliners, mats

Carbon black properties The properties of virgin carbon black are closely controlled. They are monitored and the purchaser of the carbon black is provided with a specification sheet. The values reported typically are ash content, heat loss, 325 mesh sieve residue, pellet crush strength, iodine absorption, DBP absorption and physical properties compared to an IRB Reference black in the ASTM D3192 or D3191 recipe (3). A sample of the technical data for a lot of N550 and N762 are shown in Chart 3. As mentioned previously the properties of the black filler obtained from tire pyrolysis char vary widely due to differences in composition of the tires being processed and lack of control of the tire pyrolysis process where temperature and time variations will cause differences in composition. These effects have been studied in great detail in several other studies. To show how consistent carbon black composition can be, lot analysis sheets for 24 lots of N550 and N762 were obtained. These were analyzed and summarized for ash content, pour density, DBP absorption and iodine number. These are all critical composition or performance criteria for carbon black and closely monitored by the end user. These values are all shown in Charts 4 through 11. As the data shows the carbon black properties are very consistent. The quality and consistency of the black along with low grit are considered critical to the carbon performance in rubber. The variations in compositions of black filler from tire char have caused many rubber companies to be cautious in supporting the use of such a filler. It will be necessary to get the composition under control and within acceptable limits for black filler from char to be used by the general rubber industry. History Carbon black has been the major reinforcing filler in the rubber industry for well over 100 years and it will continue to be so for years to come. It has historically been made from natural gas and oil feed stocks using the channel, thermal and furnace processes. The production of carbon black is also possible using a pyrolysis process with worn scrap tires as the feed stock. This paper is not intended to sell the tire pyrolysis process per se, but to review the technology, economics, and business factors that currently affect its development. It will not go into non-tire or plastics pyrolysis potential. It will also show that pyrolysis carbon black can be accepted as a viable alternative reinforcing filler for many rubber applications if properly produced. Rader et al.; Plastics, Rubber, and Paper Recycling ACS Symposium Series; American Chemical Society: Washington, DC, 1995.


258

CHART#3


Physical Chemical Properties Ash,D1506 Heat loss, as packaged D1509

N762 .26 % 0.1 %

N550 .34% 0.1 %

35 Mesh Sieve Residue, D1514 325 Mesh Sieve Residue, D1514

.000 % .003 %

.000% .002 %

Toluene Discoloration 425 m\i 83% Pellet Crush Strength, min 14 grams Pellet Crush Strength, max 41 grams Pellet Crush Strength, avg 27 grams 4.4 % Fines5'Rotap,D1508 Pour Density, D1513 31.2 lb/ft* Iodine Absorption, mg/gm D1510 28.3 DBP,cc/100gm D2414 64.4

95% 8 grams 32 grams 20 grams 3.6% 22.6 lb/ft 43.3 119.9 3

Properties in NR Formula ASTM D3192 o

Cure 30VS).143C femple Difference 300% Modulus Tensile Elongation

IRB#6 Sample Difference

1790 3627 546

1586 3591 543

1765 3740 561

-204 -36 -3

IRB#6

1933 168 3459 -281 496 -65

CHART #4

M

22.5 * 23.5 » 22.8 - 0.27

•••••••••••••••••

l I I l l l l l I I I l l l I l l l l I l I l 1 2 3 4 S 6 7 8 9 10 11 12 13 14 16 16 17 18 18 20 21 22 23 24

Shipment Number CHART #6 DBP of N550 Carbon Black 130 i 128126124 •• 122 • 120118 -

•

•

•

•

•

•

Minimum Maximum Average Std Dev

• •

•

« 117.8 « 124.8 » 120.6 =• 1.44 •

•

• •

Ho-

rn112 «• 110« \ I I -f-+1 2 3 4 6 6 7 8 9 10 11 12 13 14 16 16 17 18 19 20 21 22 23 24

Shipment Number CHART #7 ^

Iodine Adsorption of N550 Carbon Black

" -5f " 1 J;; ©' "

Minimum = 40.9 Maximum * 44.6 Average - 43.1 Std Dev • 0.98

4 9

4 S

4

J

44-

-

42-. * • 41-. • • 40 I I I I | | | | | | | t | | | | | | | | | | | | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 16 17 18 19 20 21 22 23 24

•

•

Shipment Number


260


CHART #8 Ash Content of N762 Carbon Black 1 0.9 0.8 0.7 «


< *

0

8

t


T

0.5 •• 0.4 0.3 0.2^ 0.1 •• 0

• •

« 0.18 =0.33 = 0.26 « 0.04

*

I I l l l I I l I l 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Shipment Number CHART #9 Pour Density of N762 Carbon Black 39--


37..

2

36-.

a 34..

* « • •

31.0 31.9 31.3 0.31

33 + • • • • e• • • • • • * • »• 32 • • • •• • 31 I I I I I I I I I I I I I I I I I I I I I 30 1 2 3 4 6 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Shipment Number #10 Black DBP of CHART N762 Carbon

Mi* *™ s 63.0 11

70-| Maximum 66.8 69Average * 64.8 68Std Dev s 1.11 6766< • • • • • • • • 68• flu64• • • • • • • CQ • 63a 6261 • 601 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 #

Shipment Number



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In America today, we have in excess of two billion scrap tires stockpiled. Regulations have been passed in several states to regulate collection, storage, and disposal of scrap tires. This issue is also being addressed at the federal level. We are recovering less material from our scrap tires today than we did back in 1960 (4). (Chart 12) In 1960, when reclaimed rubber was widely used, there was 36.4% in recovered material obtainedfromthe 1.1 million tons of scrap tires produced. With the advent of the radial tire, compounders removed reclaim rubber to improve green strength and durability. Recovered material dipped to 5.6% in 1988 and is now at 11.6% for 1.8 million tons of scrap tires in 1990 (5). We are currently scrapping 250 million passenger tires per year at an average weight of 20 pounds or 9.1 kilograms each. This equate to a fuel value of 300,000 Btu's per tire (6). (Chart 13) It is evident that the scrap tire disposal problem must continue to be addressed and given more priority. I won't go into detail regarding other alternative disposal measures such as ground rubber as an asphalt additive, or burning as fuel. This paper will show that tire pyrolysis is a viable technical alternative to producing a carbon filler, in essence a new process for carbon black manufacturing. Manufacturing Processes The channel, thermal and furnace processes are the three basic methods used to make carbon black. The century old channel process burns natural gas where the burners impinge on long iron channels depositing the carbon. This is an inefficient and environmentally poor process and is no longer utilized in the U.S.A. Channel black is still made in some parts of the world, with EPC being the most recognized grade to the rubber chemist. (Chart 14) The thermal process was introduced in the 1920's and is still used today to manufacture a coarse particle size black used predominately in non-tire applications. In this process natural gas is introduced to a pre-heated brickwork furnace and thermally decomposes to release hydrogen and carbon. The resulting products are the familiar N800 and N900 series carbons. (Chart 15) The oil furnace process is the most widely utilized and commercially diverse method for making carbon black. Oil feed stocks are injected into heated, refractory lined furnaces where the oxygen content, burner type and furnace geometry are precisely controlled to generate the large number of grades now available ranging from the N100 through the N700 series (7). (Chart 16) With pyrolysis, tires are heated to extremely high temperatures in the absence of oxygen until the components separate yielding oil and carbon "char." (Chart 17) The typical yield for an average passenger tire is: One gallon of oil, seven pounds of carbon, two pounds of steel, two pounds of methane gas, and about onehalf pound of fiber. All of these recovered materials can be re-utilized. (Chart 18) The pyrolysis process will generate a new and different filler material. Pyro black will compete with current materials in narrow, select segments of the market and on a cost performance basis.


262


Chart #11 Iodine Adsorption of N762 Carbon Black 36 34 M A*

Minimum Maximum Avaraga Std Dev

3 3

3 2

6 »

Z

26.0 30.4 28.2 1.37

•

30

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* • » »

* 2»7

•

•

• •

• •

•

•

•

m

1 2 3 4 6 6 7 8 9 10 11 12 13 14 16 16 17 18 19 20 21 22 23 24

Shipment Number Chart #12 SCRAP TIRE DISPOSAL HISTORY Tons

% Recovered Materials

1960 1,100,000

36.4%

1988 1,900,000

5.6%

1990 1,800,000

11.6%

From: Characterization of Municipal Solid Waste in the U.S. 1992 Update Chart #13 We are currently scrapping 250 million passenger tires per year at an average weight of 20 pounds or 9.1 kilograms each.

Fuel Value = 300,000 Btu's / tire Chart #14 CHANNEL BLACK PROCESS • • •

Burn Natural Gas Impinge on iron channels Inefficient: 1% to 5% yield


22. BECK & KLINGENSMITH


Chart #15


THERMAL BLACK PROCESS • •

Thermal decomposition of natural gas Preheated brickwork furnaces Yields 40% to 50% Chart #16 FURNACE BLACK PROCESS • • •

Oil Feed Stock Injected Refractory Lined Furnaces Controlled Conditions • Oxygen Content • Burner Type • Furnace Geometry Chart #17

PYROLYSIS BLACK PROCESS • • •

•

Tire Collection System/ Scrap Tires Tire Preparation • Sorting and Classifying • Shredding Pyrolysis Furnace - Absence of Oxygen Yield • Gas Oil • Steel and Fabric Char Post Treatment


263


264


Carbon Black Market The North American market uses about (1.5 million tons) three billion pounds of carbon black per year that is split almost equally between hard (N100, N200, N300 series) and soft (N500, N600, and N700 series) grades.(Chart 19) Of the three billion pounds (1.5 million tons), about 70% is consumed in tires and tire related products. The remaining 30% is used in non-tire applications such as Molded MRG, Extruded MRG, Foam & Sponge, Wire & Cable, Flooring, Matting, Solid Wheels, and Roofing Membrane. (Chart 20) It is in this non-tire segment, using 450,000 tons of carbon black per year and which is virtually all soft black and thermal black, that pyrolysis blacks will first find a home. (Chart 21) This is because the pyrolysis blacks generated with current technology have a broad particle size distribution that yields reinforcement properties in between the SRF (N762) and MT (N990) range. (Chart 22) It is also quite possible that certain tire applications such as innerliner, carcass and sidewall would be able to utilize pyrolysis carbons in blends with virgin furnace grades.. The fact is that pyrolysis blacks will provide the compounder with an alternative compounding material, and should be viewed accordingly. Pyrolysis blacks are not channel, thermal, or furnace blacks. In order for pyrolysis black to gain initial acceptance, the market will have to overcome a pre-conceived opinion that it is of inferior quality and lacks uniformity. This posture is not unfounded. The many small companies that, in the past have tried and, in some cases, are still producing pyro blacks, have fueled this perception. These blacks are very coarse and contain much extraneous material, and as a result, have limited market potential. They have failed to recognize the quality level that must be achieved through additional processing techniques after they generate the initial char. Technical Requirements A pyrolysis black, when properly produced, will meet the following specification and provide reinforcement as shown in the two ASTM test formulations. The key points to observe in this specification are the low volatiles, the low sieve residue, the soft pellets, the fact that densification is required, and the minimum tensile requirements. (Charts 23 and 24) In the ASTM D3191 SBR formula note that the minimum tensile is achieved and that reinforcement is indeed between that of N774 and N990. (Chart 25) In the ASTM D3192 NR formula the modulus and tensile values exceed those of N990 at equal loading. (Chart 26) These test results reflect data generated from actual pyrolysis carbon produced to the previous specification in pilot plant quantities under current patented processes (Beck, M.R., Polymer Valley Chemicals, unpublished data). The keys to attaining the acceptable reinforcement levels are two-fold. First, the time temperature relationship during pyrolysis must be controlled to produce a black with minimum volatile content on the surface. Secondly, the physical screening, grinding, and classifying techniques employed must remove the extraneous materials and meet the 325 mesh sieve residue specification. (Chart 27) Rader et al.; Plastics, Rubber, and Paper Recycling ACS Symposium Series; American Chemical Society: Washington, DC, 1995.



BECK & KLINGENSMITH



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Chart #20 NORTH AMERICAN CARBON BLACK MARKET


3.0 Billion Pounds = 1.5 Million Tons

Chart #21 NON-TIRE SEGMENT •

450,000 Tons of Carbon Black per Year •

Predominately Soft Blacks & Thermal Black

•

Pyrolysis Black Target Segment Chart #22

Relative Carbon Black Classification

Surface A rea

M»/g

46 -r 40 - 38 - 30 26 20 •15-10 6 0

PYRO

• N660

•N762

* N990

-I— 20

40

Structure

60

DBP


BECK & KLINGENSMITH


Chart #23 PYROLYSIS

CARBON


TARGET SPECIFICATION RUBBER INDUSTRY PftQPggTV Form Specific Gravity Bulk Density pH Ash Volatiles Carbon Content Total Sulfur (Non-Reactive)

*AN

Plastics, Rubber, and Paper Recycling - ACS Publications - American

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