Activated Carbon for Automotive Applications

Ford Motor Company Automotive Components Division Dearborn, Michigan 

The generation of au pollutants, ineluding VOC s, from automotive vehieles was identified to eome from two prineipal sourees vehiele exhaust emissions, and fuel system evaporative emissions [4], Evaporative emissions are defmed as the automotive fuel vapors generated and released from the vehiele s fuel system due to the interactions of the speeific fuel in use, the fuel system characteristics, and environmental factors. The sources of the evaporative emissions are discussed below and, as presented m the remainder of this chapter, control of these evaporative emissions are the focus of the application of activated carbon technology in automotive systems. 

The buyers of motor vehicles have been substantially positive concerning the need to have cleaner running vehicles. Although the required emission control devices and other mandated safety equipment have increased the cost of new motor vehicles, sales have not been significantly effected. The current environmental awareness and concern are evidence of the general population s new found knowledge and acceptance of both mobile and stationary source emission controls. 

The early carbon trap and SHED methods measured two components of evaporative emissions. Hot soak emissions were measured for a one hour period immediately after a vehicle had been driven on a prescribed cycle and the engine turned off. Diurnal emissions were also measured during a one hour event where the fuel tank was artificially heated. The one hour fuel temperature heat build was an accelerated test that was developed to represent a full day temperature heat build. 

The latest CARB/EPA procedures require diurnal emissions to be measured during a real time, three day test that exposes the complete vehicle to daily temperature fluctuations. This test method has been employed to more accurately reflect the real world diurnal emissions that occur. Rutming loss emission measurements were also initiated in the latest test procedures. Evaporative emissions are measured 

Research dating back to the mid 1950 s has shown that volatile orgamc compounds (VOC s) photochemically react m the atmosphere and contribute to the formation of ground level ozone, a precursor to smog [1]. Medical studies have shown that human exposure to ozone can result in eye and smus tract irritation, and can lead to respiratory related illnesses [2]. Due to the unique and severe smog problems that affected many cities in the state of California, studies of the causes of ah pollution were initiated m the 1950 s [3]. Based on its findings, California formed the Motor Vehicle Pollution Control Board m 1960 to regulate pollution from automobiles. 

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Johnson, P.J., Setsuda, D. J., and Williams, R.S. Activated carbon for automotive application. In Carbon Materials for Advanced Technologies, Amsterdam, The Netherlands Pergamon, 1999 235. 

Activated Carbon for Process Water Treatment Activated Carbon from CPL Carbon Link - Activated carbon from CPL Carbon Link for liquid and gas phase purification by adsorption. Activated carbons for all applications including chemical, water, air, solvent recovery, gold recovery, food, automotive, industrial, catalysis.. http //www.activated-carbon.com. 

Properties of activated carbons produced by Westvaco for automotive applications are presented in Table 5. 

The current requirements have led to the development of pellet shaped activated carbon products specifically for automotive applications. These pellets are typically generated as chemically activated, wood-based carbons. 

Applications of activated carbons are discussed in Chapters 8-10, including their use in the automotive arena as evaporative loss emission traps (Chapter 8), and in vehicle natural gas storage tanks (Chapter 9). The use of evaporative loss emission traps has been federally mandated in the U.S. and Europe. Consequently, a significant effort has been expended to develop a carbon adsorbent properly optimized for evaporative loss control, and to design the on board vapor collection and disposal system. The manufacture of activated carbons, and their preferred characteristics for fuel emissions control are discussed in Chapter 8, along with the essential features of a vehicle evaporative loss emission control system. 

In another report, James and Kalinoski [4] performed an estimation of the costs for a direct hydrogen fuel cell system used in automotive applications. The assumed system consisted of an 80 kW system with four fuel cell stacks, each with 93 active cells this represents around 400 MEAs (i.e., 800 DLs) per system. The study was performed assuming that the DL material used for both the anode and cathode sides would be carbon fiber paper with an MPL. In fact, the cost estimate was based on SGL Carbon prices for its DLs with an approximate CEP value of around US 12 m for 500,000 systems per year. Based on this report, the overall value of the DLs (with MPL) is around US 42.98 per kilowatt (for current technology and 1,000 systems per year) and 3.27 per kilowatt (for 2015 technology and 500,000 systems per year). Figure 4.2 shows the cost component distribution for this 80 kW fuel cell system. In conclusion, the diffusion layer materials used for fuel cells not only have to comply with all the technical requirements that different fuel cell systems require, but also have to be cost effective. 

It has been reported in the course of this review that a recent study of the targets of a costless electrocatalyst to replace Pt in automotive applications requires that such non-noble metal catalysts have an activity no less than 1/lOth of the current industrial Pt activity under equivalent conditions. This requires mainly a sizeable increase in the site density (defined as catalytic sites/cm in the electro-catalytic layer) of the non-noble metal catalysts. A knowledge of the molecular structure of the catalytic site for the electrochemical reduction of oxygen in acid medium is, therefore, essential in order to increase the site density on the carbon support for those catalysts. The long-term stabilities of the same catalysts under current industrial conditions are yet to be demonstrated, as weU. 

Gas-phase applications of activated carbon in the USA are mainly concentrated towards granular carbons. Total consumption in 1994 accounted for somewhat <20% of the total market. The main applications are air purification (it includes industrial gas purification), solvent vapor recovery, automotive evaporation control systems, and others, of which the two first constitute the main share of the total. 

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