Two Types of Natural Graphite Host Matrix for Composite Activated Carbon Adsorbents

Abstract

Two types of host for activated carbon (AC) adsorbents intended for use in compressed systems are studied: expanded natural graphite (ENG) and expanded natural graphite treated with acid (ENG-TA). Results show that compressed ENG-TA has much higher thermal conductivity than the compressed ENG. For a density of 830 kg/m3 the thermal conductivity of compressed ENG-TA is 336 W/(mK), and it is of the order of one hundred times higher compared with compressed ENG having similar density. The permeability of compressed ENG-TA is much more critical than the compressed ENG. For example for similar density of 300 kg/m3, the permeability of compressed ENG-TA is 2.01 × 10−15 m2 while the permeability of compressed ENG is 1.07 × 10−13 m2. Compressed composite adsorbents of AC with ENG as host were produced with a high density in the range 700–720 kg/m3. Considering that the permeability will be too low using composite AC with ENG-TA as host in high density, the density range was restricted to less than 500 kg/m3. The thermal conductivity of AC/ENG-TA composite is much higher than the thermal conductivity of AC/ENG composite, and it is about 7 times higher than the optimal value of AC/ENG composite.