Kinetics of Catalytic Oxidation of Benzene,n-Hexane,and Emission Gas from a Refinery Oil/Water Separator over a Chromium Oxide Catalyst

ABSTRACT

With the advances made in the past decade, catalytic incineration of volatile organic compounds (VOCs) has become the technology of choice in a wide range of pollution abatement strategies. In this study, a test was undertaken for the catalytic incineration, over a chromium oxide (Cr₂O₃) catalyst, of n-hexane, benzene, and an emission air/vapor mixture collected from an oil/water separator of a refinery. Reactions were carried out by controlling the feed stream to constant VOC concentrations and temperatures, in the ranges of 1300–14,700 mg/m³ and 240–400 ° C, respectively. The destruction efficiency for each of the three VOCs as a function of influent gas temperature and empty bed gas residence time was obtained.

Results indicate that n-hexane and the oil vapor with a composition of straight- and branch-chain aliphatic hydrocarbons exhibited similar catalytic incineration effects, while benzene required a higher incineration temperature or longer gas retention time to achieve comparable results.

In the range of the VOC concentrations studied, at a given gas residence time, increasing the operating temperature of the catalyst bed increased the destruction efficiency. However, the much higher temperatures required for a destruction efficiency of over 99% may be not cost-effective and are not suggested. A first-order kinetics with respect to VOC concentration and an Arrhenius temperature dependence of the kinetic constant appeared to be an adequate representation for the catalytic oxidation of these volatile organics. Activation energy and kinetic constants were estimated for each of the VOCs. Low-temperature destruction of the target volatile organics could be achieved by using the Cr₂O₃ catalyst.     

Optimization for solidification of low-level-radioactive resin using Taguchi analysis

Solidification of low-level-radioactive (LLW) resin was optimized using Taguchi analytical methodology. The ingredients in LLW mortar which caused the solidification of cement were evaluated through consecutive measurements of the effects of various concentrations of ingredients. Samples selected according to Taguchi's method were separated into 18 different categories and measured at the 7th, 21st, and 28th day after fabrication on developing effects. Evaluations of the various samples focused on whether the compressive and bending strength fulfilled the special criteria of the Taiwan Power Company (TPC). Similar results indicated that both furnace slag and fly ash were the dominant material resulting from the solidification of LLW mortar. The superior combination was obtained as furnace slag 24 wt.%, fly ash 24 wt.%, and cement 8 wt.% to mix 24 wt.% of resin with 20 wt.% of water, to fulfill the contemporary requirements of TPC.     

Biotrickling filtration of nitric oxide

A biotrickling filter with blast-furnace slag packings (sizes = 20-40 mm and specific surface area = 120 m2/m3) was utilized to treat NO in an air stream. The operational stability, as well as the effects of gas empty-bed retention time (EBRT) and nutrient addition on the removal ability of NO, were tested. Approximately six weeks were required for the development of a biofilm for NO degradation, and a two-week organic carbon deficiency resulted in the detachment of biofilms from the packing surfaces. A steady removal rate of 80% was attained at specified influent NO concentrations of 892 to 1237 ppm and an EBRT of 118 sec. The effluent NO concentration diminished exponentially with enlarging EBRT, with influent NO concentrations of 203-898 ppm, and EBRTs of 25 to 118 sec. Nutrient addition is essential for efficient removal of the influent NO. Mass ratios of C: P: N = 7: 1: 30 and NaHCO3: NO-N = 6.3 could be used for practical applications.     

Columnar optical properties of tropospheric aerosol by combined lidar and sunphotometer measurements at Taipei,Taiwan

Vertical extinction profiles and columnar optical properties (optical depth, Angstrom exponent, lidar ratio, and particle depolarization) of aerosols were obtained by simultaneous measurements with a depolarization lidar and a sunphotometer at Taipei, Taiwan from February 2004 to January 2006. Columnar optical depths are high in Feb–Apr (0.61–0.75) by sunphotometer measurements. Lidar measurements show the contribution of aerosols in the free atmosphere on columnar optical depths are about 44–50% in Feb–Apr and about 26–37% in other months. Back-trajectory analyses and depolarization measurements show almost all of non-spherical aerosols originated from Northwest China which indicate Asian dusts frequently transported to Taipei from dust source regions in the free atmosphere. Aerosols with depolarization lower than 5% are found mostly originated from South China or Southeast Asia. Good correlations between columnar lidar ratio, particle depolarization, and Angstrom exponent are found for cases that columnar water vapor less than 1.5 cm. The effect of water vapor on particle depolarization is briefly discussed.     

UV/ozone degradation of gaseous hexamethyldisilazane (HMDS)

As a carcinogen, hexamethyldisilazane (HMDS) is extensively adopted in life science microscopy, materials science and nanotechnology. However, no appropriate technology has been devised for treating HMDS in gas streams. This investigation evaluated the feasibility and effectiveness of the UV (185+254nm) and UV (254nm)/O(3) processes for degradation of gaseous HMDS. Tests were performed in two batch reactors with initial HMDS concentrations of 32-41mgm(-3) under various initial ozone dosages (O(3) (mg)/HMDS (mg)=1-5), atmospheres (N(2), O(2), and air), temperatures (28, 46, 65 and 80 degrees C), relative humilities (20%, 50%, 65%, 99%) and volumetric UV power inputs (0.87, 1.74, 4.07 and 8.16Wl(-1)) to assess their effects on the HMDS degradation rate. Results indicate that for all conditions, the decomposition rates for the UV (185+254nm) irradiation exceeded those for the UV (254nm)/O(3) process. UV (185+254nm) decompositions of HMDS displayed an apparent first-order kinetics. A process with irradiation of UV (185+254nm) to HMDS in air saturated with water at temperatures of 46-80 degrees C favors the HMDS degradation. With the condition as above and a P/V of around 8Wl(-1), k was approximately 0.20s(-1) and a reaction time of just 12s was required to degrade over 90% of the initial HMDS. The main mechanisms for the HMDS in wet air streams irradiated with UV (185+254nm) were found to be caused by OH free-radical oxidation produced from photolysis of water or O((1)D) produced from photolysis of oxygen. The economic evaluation factors of UV (185+254nm) and UV (254nm)/O(3) processes at different UV power inputs were also estimated.     

Assessment and distribution of antimony in soils around three coal mines, Anhui, China

Thirty-three soil samples were collected from the Luling, Liuer, and Zhangji coal mines in the Huaibei and Huainan areas of Anhui Province, China. The samples were analyzed for antimony (Sb) by inductively coupled plasma-optical emission spectrometry (ICP-OES) method. The average Sb content in the 33 samples was 4 mg kg(-1), which is lower than in coals from this region (6.2 mg kg(-1)). More than 75% of the soils sampled showed a significant degree of Sb pollution (enrichment factors [EFs] 5-20). The soils collected near the gob pile and coal preparation plant were higher in Sb content than those collected from residential areas near the mines. The gob pile and tailings from the preparation plant were high in mineral matter content and high in Sb. They are the sources of Sb pollution in surface soils in the vicinity of coal mines. The spatial dispersion of Sb in surface soil in the mine region shows that Sb pollution could reach out as far as 350 m into the local environment conditions. Crops in rice paddies may adsorb some Sb and reduce the Sb content in soils from paddyfields. Vertical distribution of Sb in two soil profiles indicates that Sb is normally relatively immobile in soils.     

采用零排放新工艺处理蚀刻废液

广州市某化工厂开发出一套对线路板蚀刻废液进行大规模集中资源化处理的零排放处理新工艺,该工艺通过在固相条件下生成氧化铜并用重力分选的方法将其分离出来,克服了原有工艺的缺陷,使废液中所有的成分能够在较低的处理成本下全部分离回收,无三废排出,达到了清洁生产的要求.对其工艺条件进行深入研究,通过正交试验优化了工艺条件.     

A Study of Sustainable Material Management Approach in Taiwan

Sustainable material management (SMM) has been initiated by the Organization for Economic Cooperation and Development (OECD) in 2005. SMM is an approach to promote resource conservation, reducing negative environmental impacts and preserving the natural capital of material and the balance of economic efficiency and social equity. Life cycle assessment and material flow analysis have been widely used to estimate the environmental impacts for resource consumption, but economic development has not been taken into account. Before 1984, improper garbage disposal was not an important issue in Taiwan. But over the past three decades, the Taiwan Government has accomplished not only waste disposal but also resource recycling, which are conducive to the essence of SMM. This study is the first research project to develop a SMM conceptual model for policy and strategy in Taiwan. SMM is the suitable waste management concept for the next era. This study reviewed the policy and strategy that has been applied in Taiwan’s waste management, and compares the efficiency of waste management policy in Taiwan with the concept of SMM. A case study of the waste flow will be used to prove that the sustainable material policy can be a suitable management system to achieve sustainable development. This study will open a new chapter of research on global SMM for Taiwan.     

Effect of recycle-to-influent ratio on activities of nitrifiers and denitrifiers in a combined UASB-activated sludge reactor system

A laboratory study using a combined upflow anaerobic sludge bed (UASB)-activated sludge (AS) reactor system was undertaken to explore the effect of recycle-to-influent ratio (R(e)=1, 2, and 3) on the activities of nitrifiers and denitrifiers. Suspended-solids pre-settled piggery wastewater was used as the substrate-feed wastewater. At the R(e) of 1-3, the combined reactor system achieved efficient removal of COD (96-97%), TKN (100%) and total nitrogen TN (54-77%). Methanogenesis occurred with nearly-complete denitrification in the UASB reactor, whereas complete nitrification took place in the AS reactor. A higher R(e) (i.e., accompanied with a shorter solids retention time) resulted in a larger amount of high-activity denitrifiers and thereby achieved a higher TN removal efficiency. Compact granules and a high biomass concentration in the UASB reactor were observed. At the R(e) of 1-3, the maximum specific reaction rate of nitrifiers (0.45-0.49 NH(4)(+)-NmgVSS(-1)d(-1)) and the specific nitrification rates of mixed culture (0.18-0.22mg NH(4)(+)-NmgVSS(-1)d(-1)) in the AS reactor varied slightly; whereas the maximum specific reaction rate of denitrifiers (0.18-0.27mg NO(x)(-)-NmgVSS(-1)d(-1)) and the specific denitrification and COD removal rates of mixed culture (0.025-0.050mg NO(x)(-)-NmgVSS(-1)d(-1); 0.24-0.31mgCODmgVSS(-1)d(-1)) in the UASB reactor increased with increasing R(e). The primary finding of the study is that the combined UASB-AS reactor system should be operated at a higher R(e) to maintain high-activity denitrifiers to remove organic materials and nitrogen from piggery wastewater.     

Regenerative thermal oxidation of airborne N, N-dimethylformamide and its associated nitrogen oxides formation characteristics

In this study, a two-bed electrically heated regenerative thermal oxidizer (RTO) was used to test the thermal destruction and oxides of nitrogen (NOx) formation characteristics in burning airstreams that contain either N, N-dimethylformamide or dimethylformamide (DMF) mixed with methyl ethyl ketone (MEK). The RTO contained two 0.152 m x 0.14 m x 1 m (L x W times] H) beds, both packed with gravel particles with an average diameter of approximately 0.0111 m and a height of up to 1 m with a void fraction of 0.42 in the packed section. The thermal recovery efficiency (TRE) and the gas pressure drop over the beds were also studied. Experimental results reveal that, with a valve shifting time (ts) of 1.5 min, a superficial gas velocity (Ug) of 0.39 m/sec (evaluated at an influent air temperature of around 30 degrees C) and preset maximum destruction temperatures (Ts) of 750-950 degrees C, no NOx was present in the effluent gas from the RTO when it was loaded with DMF-free air. When only DMF was present in the influent air, the average destruction efficiencies exceeded 96%, and increased with the influent DMF concentration from 300 to 750 mg/N x m3. The "NOx-N formation/DMF-N destruction" mass ratios were in the range 0.76-1.05, and decreased as the influent DMF concentration increased within the experimental range. When both DMF and MEK were present in the influent gas, the NO, formation ratio was almost the same and the DMF destruction efficiency increased with the influent MEK/DMF ratio from 150/300 to 4500/300 (mg/mg) and in the preset temperature range. The NOx formation ratios were in the range 0.75-0.96. The TRE decreased as Ug increased but was invariant with Ts. The Ergun equation was found to suffice in the estimation of the pressure drop when the gas flowed over the packing beds.