Effect of Thermal Defocusing on Backward Stimulated Raman Scattering in CH4

The conversion efficiency of stimulated Raman scattering （SRS） in CH4 is studied by using a single longitudinal mode second-harmonic Nd：YAG laser （532 nm, linewidth 0.003 cm^-1, pulse-width （FWHM） 6.5 ns）. Due to the heat release from vibrationally excited particles, SRS processes often suffer from the thermal defocusing effect （TDE）. In view of 6.5 ns laser pulse width is much shorter than the vibrational relaxation time of CH4 molecules, TDE can only affect the SRS processes afterwards. In the cases of low laser repetition, TDE will be not serious, because it will be removed by the thermal diffusion in Raman medium before the next pulse arrives. At the laser repetition rate 2 Hz, CH4 pressure 1.1 MPa and pump laser energy 95 mJ, the quantum conversion efficiency of backward first-Stokes （BS1） has attained 73%. This represents the highest first-stokes conversion efficiency in CH4. Furthermore, due to the relaxation oscillation, the BS1 pulses are narrowed to about 1.2 ns. As a result, the BS1 peak power turns out to be 2.7 times that of the pump. Its beam quality is also much better and is only slightly affected by TDE. This reason is that BS1 represents a wave-front-reversed replica of the pump beam, which can compensate the thermal distortions in Raman amplify process. Under the same conditions, but pump laser repetition rate as 10 Hz, the conversion efficiency of BS1 goes down to 36% due to TDE. From this study, we expect that a well-behaved 630 nm Raman laser may be designed by using a closed CH4/He circulating-cooling system, which may have some important applications.

The Effect of Pressure on the Dissociation of H_2/CH_4Gas Mixture during Diamond Films Growth via Chemical Vapor Deposition

Monte Carlo simulations are adopted to study the electron motion in the mixture of H2 and CH4 during diamond synthesis via Glow Plasma-assisted Chemical Vapor Deposition (GPCVD). The non-uniform electric field is used and the avalanche of electrons is taken into account in this simulation. The average energy distribution of electrons and the space distribution of effective species such as CH3, CH+3, CH+ and H at various gas pressures are given in this paper, and optimum experimental conditions are inferred from these results.

Distinguished discriminatory separation of CO2 from its methane-containing gas mixture via PEBAX mixed matrix membrane

Highly selective separation of CO_2 from its methane-containing binary gas mixture can be achieved by using Poly(ether-block-amide)(PEBAX)mixed matrix membranes(MMMs).According to FESEM and AFM analyses,silica-based nanoparticles were homogenously integrated within the polymer matrix,facilitating penetration of CO_2 through the membrane while acting as barrier for methane gas.The membrane containing 4.6 wt% fumed silica(FS)(PEBAX/4.6 wt%FS)exhibits astonishing selectivity results where binary gas mixture of CO_2/CH_4 was used as feed gas.As detected by gas chromatography,in the permeate side,data showed a significant increase of CO_2 permeance,while CH_4 transport through the mixed matrix membrane was not detectable.Moreover,PEBAX/4.6 wt%FS greatly exceeds the Robeson limit.According to data reported on CO_2/CH_4 gas pair separation in the literature,the results achieved in this work are beyond those data reported in the literature,particularly when PEBAX/4.6 wt%FS membrane was utilized.

Greenhouse gas emissions during co-composting of cattle feedlot manure with construction and demolition （C＆D） waste

Manure management strategies should reflect current animal feeding practices and encourage recycling of organic waste to help protect our environment. This research investigated greenhouse gas （GHG） emissions during cattle manure stockpiling or composting with and without construction and demolition （C＆D） waste. Manure was collected from cattle fed a typical finishing diet （CK manure） and from cattle on diets which included 30% dried distillers grains with solubles （DG manure）. The CK and DG manures were co-composted with （4：1） C＆D waste （treatments： CK CD, DG CD）, composted alone （treatments： CK and DG） in 13 m3 bins or stockpiled without C＆D ~vaste （treatments： CK ST and DGST） for 99 days. Manure type （CK vs. DG manure） had no effect on GHG emissions-over the 99 day manure composting or stockpiling. Composting with C＆D waste 2 produced similar CO2 emissions, about double that from manure stockpthng （7.9 kgC.m^-2）. In contrast, CH4 emissions were reduced by the inclusion of C＆D waste （64 gC.m^-1 with C＆D vs. 244 gC.m 2 without C＆D） while the manure stockpile emitted the greatest amount of CH4 （464 gC. m 2）. Additionally, only 0.48% of C was emitted in CH4 form with C＆D waste, compared to 1.68% when composting without C＆D waste and 7.00% when cattle manure was stockpiled. The N2O emissions （12.4 to 18.0 gN.m ） were similar across all treatments. The lower CH4 emissions with C＆D waste are beneficial in reducing overall GHG emissions from manure composting, while reducing the amount of material entering landfills.