Spill behaviour using REACTPOOL. Part II. Results for accidental releases of silicon tetrachloride (SiCl(4))

Mechanism of the rapid mechanochemical degradation of hexachlorobenzene with silicon carbide as an additive

Mechanochemical treatment (MCT) is a promising method for degrading hexachlorobenzene (HCB). Silicon carbide (SiC) was proposed in this study as a new additive to accelerate the reaction in MCT. The high performance of SiC was verified, and the relevant mechanism was explored. Graphite, amorphous carbon, CCl₄, SiO₂, and water-soluble chloride were confirmed as predominant products in the proposed method, and only trace-level low chlorinated benzenes were detected. The reaction pathway was revealed as follows: under the attack of free electrons, chlorine atoms were shed from the benzene rings of HCB to form Cl· radicals, which reacted with SiC to form SiCl₄ and CCl₄ and with the in situ-generated iron powder to produce Fe-based chloride. The left benzene rings were translated to graphite and amorphous carbon. As an intermediate product, SiCl₄ further reacted with water vapor in the atmosphere to produce SiO₂ and HCl. The in situ-generated iron powder could not remarkably accelerate the degradation reaction. The major contribution of SiC was the supply of free electrons to trigger the reaction. Two sources of free electrons were discussed. Friction heat resulting from hard SiC also contributed to the endothermic reaction of HCB degradation.

Numerical investigation on three-dimensional dispersion and conversion behaviors of silicon tetrachloride release in the atmosphere

The world has experienced heavy thirst of energy as it has to face a dwindling supply of fossil fuel and polycrystalline silicon photovoltaic solar energy technology has been assigned great importance. Silicon tetrachloride is the main byproducts of polysilicon industry, and it's volatile and highly toxic. Once silicon tetrachloride releases, it rapidly forms a dense gas cloud and reacts violently with water vapor in the atmosphere to form a gas cloud consisting of the mixture of silicon tetrachloride, hydrochloric acid and silicic acid, which endangers environment and people. In this article, numerical investigation is endeavored to explore the three dimensional dispersion and conversion behaviors of silicon tetrachloride release in the atmosphere. The k-ϵ model with buoyancy correction on k is applied for turbulence closure and modified EBU model is applied to describe the hydrolysis reaction of silicon tetrachloride. It is illustrated that the release of silicon tetrachloride forms a dense cloud, which sinks onto the ground driven by the gravity and wind and spreads both upwind and downwind. Complicated interaction occurs between the silicon tetrachloride cloud and the air mass. The main body of the dense cloud moves downwind and reacts with the water vapor on the interface between the dense cloud and the air mass to generate a toxic mixture of silicon tetrachloride, hydrogen chloride and silicic acid. A large coverage in space is formed by the toxic mixture and imposes chemical hazards to the environment. The exothermic hydrolysis reaction consumes water and releases reaction heat resulting in dehydration and temperature rise, which imposes further hazards to the ecosystem over the affected space.

Comparison between solar utilization of a closed microalgae-based bio-loop and that of a stand-alone photovoltaic system

This study compared the solar energy utilization of a closed microalgae-based bio-loop for energy efficient production of biogas with fertilizer recovery against that of a stand-alone photovoltaic (PV) system. The comparison was made from the perspective of broad life cycle assessment, simultaneously taking exergy to be the functional unit. The results indicated that the bio-loop was more environmentally competitive than an equivalent stand-alone PV system, but had higher economic cost due to high energy consumption during the operational phase. To fix the problem, a patented, interior pressurization scheduling method was used to operate the bio-loop, with microalgae and aerobic bacterial placed together in the same reactor. As a result, the overall environmental impact and total investment were respectively reduced by more than 75% and 84%, a vast improvement on the bio-loop.

Quantitative risk assessment for accidental release of titanium tetrachloride in a titanium sponge production plant

This paper outlines the quantitative risk assessment for storage and purification section of a titanium sponge production facility. Based on qualitative HAZAN technique, which involves a detailed FETI and HAZOP study of the entire plant, the storage and the purification section were found to be the most hazardous sections. Titanium tetrachloride (TiCl(4)) is the major reactant used in this plant. TiCl(4) is a toxic, corrosive water reactive chemical and on spillage from containment creates a liquid pool that can either boil or evaporate leading to the evolution of toxic hydrogen chloride (HCl). Fault tree analysis technique has been used to identify the basic events responsible for the top event occurrence and calculate their probabilities. Consequence analysis of the probable scenarios has been carried out and the risk has been estimated in terms of fatality and injuries. These results form the basic inputs for the risk management decisions.

Major intermediates in organophosphate synthesis (PCl3, POCl3, PSCl3, and their diethyl esters) are anticholinesterase agents directly or on activation

Three phosphotrichlorides [phosphorus trichloride (PCl(3)), phosphorus oxychloride (POCl(3)), and thiophosphoryl chloride (PSCl(3))] with an annual U.S. production of >500,000,000 pounds and their diethyl esters are intermediates in the production of organophosphorus pesticides, plastics, flame retardants, and hydraulic fluids. They are classified as highly toxic to mammals based on acute oral and inhalation data with rats. This study considers their mechanisms of toxicity. PCl(3) and POCl(3) inhibit acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) from several species with in vitro IC(50) values of 5-36 and 88-1200 microM, respectively; PSCl(3) is a less potent inhibitor. These phosphotrichlorides have high vapor toxicity to houseflies with in vivo inhibition of brain AChE activity correlating with mortality. PCl(3) and POCl(3) produce cholinergic poisoning signs on ip administration to mice, and all three phosphotrichlorides give marked in vivo inhibition of serum BChE but not brain AChE activity. PCl(3) is a direct acting AChE inhibitor. Our earlier proposed activation of POCl(3) is confirmed here by preparing pure Cl(2)P(O)OH and its potassium and dicyclohexylamine salts that reproduce the action of POCl(3) as in vitro AChE inhibitors and toxicants in mice. PSCl(3) on hydrolysis yields Cl(2)P(O)SH [which oxidizes with peracid to Cl(2)P(O)SOH] as the proposed activation product. Vapors of (EtO)(2)PCl, (EtO)(2)P(O)Cl, and (EtO)(2)P(S)Cl are lethal to houseflies as in vivo AChE inhibitors, the first two acting directly and the last one on oxidative activation to (EtO)(2)P(O)Cl (possibly by P450) or (EtO)(2)P(O)SCl (a phosphorylating agent in a peracid oxidation system). Thus PCl(3), (EtO)(2)PCl, and (EtO)(2)P(O)Cl act directly as AChE inhibitors whereas POCl(3) and PSCl(3) undergo hydrolytic activation and (EtO)(2)P(S)Cl undergoes oxidative activation. In contrast, the toxicity to mice of phosphofluorides [FP(O)Cl(2), F(Cl)P(O)OH, and F(2)P(O)OH; studied as model compounds for comparison] may be due to liberating fluoride ion.

Spill behaviour using REACTPOOL. Part III. Results for accidental releases of phosphorus trichloride (PCl(3)) and oxychloride (POCl(3)) and general discussion

Phosphorus trichloride and oxychloride are aggressive materials, widely used in the process industries. On escape to the atmosphere they create toxic clouds that may cause serious damage to people and to the environment. When spilled onto the ground they create liquid pools that can boil, evaporate or even solidify. The main feature of the pool behaviour is the exothermic reaction of these chemicals with water, which is complicated and depends heavily on the amount of water available for reaction, and as result of which the pool has changing composition and properties. The purpose of this paper is to describe the dangers involved in cases of accidental releases of phosphorus trichloride and oxychloride, to report their properties, referring to toxicity data and major accidents. The spill behaviour of phosphorus trichloride and oxychloride has been incorporated into REACTPOOL [R.F. Kapias, C. Griffiths, J. Haz. Mater.]. Model results indicate that the pool behaviour is strongly affected by the amount of water available for reaction. Surface roughness and wind speed, also have a strong effect on the results. Although there are no experimental data for model validation, it is shown that REACTPOOL gives useful insights into the behaviour of such spills. The paper concludes with a discussion comparing the behaviour for several water reactive chemicals to which REACTPOOL has been applied.

REACTPOOL: a code implementing a new multi-compound pool model that accounts for chemical reactions and changing composition for spills of water reactive chemicals

All chemicals that react violently with water or in contact with water liberate toxic gas are included in the list of substances covered by the majority of the international legislation on major hazards. This category includes a large number of chemicals that are used widely in the process industries. A survey of accidents that occurred in the last 10 years in the USA shows numerous major incidents that involved spillages of these substances. Even so, there are almost no experimental data on the behaviour of these chemicals on release. Furthermore, there are very few published studies on modelling the behaviour of such spillages, except in the case of hydrogen fluoride. In previous work we reported a new theoretical model [J. Haz. Mat. 62 (1998) 101-129, J. Haz. Mat. 62 (1998) 131-142, J. Haz. Mat. A67 (1999) 9-40], that describes accidental spills of SO(3) and oleum, which are substances with very complex behaviour that belong to this category. It describes both the pool [J. Haz. Mat. 62 (1998) 101-129, J. Haz. Mat. 62 (1998) 131-142] and the cloud behaviour [J. Haz. Mat. A67 (1999) 9-40]. In the work reported here the pool model was modified in a generic form in order to include other water reactive chemicals. REACTPOOL is a new code that can be used for both instantaneous and continuous liquid releases under a wide range of input parameters (steady or varying). It can be used for all liquids irrespective of their volatility and reactivity, and it describes pools consisting of more than one liquid that can have changing composition and properties. The purpose of this paper is to present the general procedure followed in REACTPOOL and to show how the new model has been modified and implemented for substances other than SO(3) and oleum. The modelling procedure has been implemented in a computer code written in Visual Basic, and results of the model have been generated using this code. It should be noted that this model requires validation data, but that the availability of such data awaits the performance of suitable experimental investigations.