No abstract

in Wiley InterScience (www.interscience.wiley.com).The removal of carbon dioxide (CO 2 ) from industrial emissions has become essential in the fight against climate change. In this study, we employed Zeolite 13X for the capture and recovery of CO 2 in a flow through system where the adsorbent was subjected to five adsorption-desorption cycles. The influent stream contained 1.5% CO 2 at standard conditions. The adsorbent bed was 1 in. in length and 1 in. 3/8 in dia., and was packed with 10 g of the zeolite. Temperature swing adsorption (TSA) was employed as the regeneration method through heating to approximately 135 8C with helium as the purge gas. The adsorbent capacity at 90% saturation was found to decrease from 78 to 60g CO 2 /kg Zeolite13X after the fifth cycle. The CO 2 capture ratio or the mass of CO 2 adsorbed to the total mass that entered the system decreased from 63% to only 61% after the fifth cycle. The CO 2 recovery efficiency ranged from 82 to 93% during desorption, and the CO 2 relative recovery, i.e., CO 2 desorbed for the nth cycle to CO 2 adsorbed for the first cycle, ranged from 88 to 68%. The service life of the adsorbent was determined to be equal to eleven cycles at a useful capacity of 40g CO 2 /kg Zeolite13X .

The polychlorinated biphenyl congener 2,3,4,5,6-pentachlorobiphenyl and hexachlorobenzene were reductively dechlorinated in an aqueous biomimetic model system containing vitamin B12. The products of 2,3,4,5,6-pentachlorobiphenyl dechlorination were 2,3,5,6and 2,3,4,6-tetrachlorobiphenyl. Hexachlorobenzene dechlorinated to pentachlorobenzene and a mixture of 1,2,4,5and 1,2,3,5-tetrachlorobenzene. The proton from water was shown to be the source of the hydrogen atom used for the replacement of chlorine on the biphenyl ring.

No abstract

No abstract

No abstract

No abstract

During the combustion of fuel in Waste-to-Energy (WTE) and coal-fired power plants, all of the mercury input in the feed is volatilized. The primary forms of mercury in stack gas are elemental mercury (Hg0) and mercuric ions (Hg2+) that are predominantly found as mercuric chloride. The most efficient way to remove mercury from the combustion gases is by means of dry scrubbing, followed by activated carbon injection and a fabric filter baghouse. Back in 1988, the U.S. WTE power plants emitted about 90 tons of mercury (Hg). By 2003, implementation of the EPA Maximum Achievable Control Technology (MACT) standards, at a cost of one billion dollars, reduced WTE mercury emissions to less than one ton of mercury. EPA now considers coal-fired power plants to be the largest remaining anthropogenic source of mercury emissions. Approximately 800 million short tons of coal, containing nearly 80 short tons of Hg are combusted annually in the U.S. for electricity production. About 40% of this amount is presently captured in the gas control systems of coal-fired utilities. Since the concentration of mercury in U.S. coal is ten times lower than in the MSW feed and the volume of gas to be cleaned 55 times higher, the cost of implementing MACT by the U.S. coal-fired utilities is estimated to be about $25 billion. However, when this retrofit cost is compared to the total capital investment and revenues of the two industries, it is concluded that MACT should be affordable. Per kilogram of mercury to be captured, the cost of MACT implementation by the utilities will be twenty times higher than was for the WTE industry. However, implementation of MACT by the utilities will also reduce the emissions of other gaseous contaminants and of particulate matter.