Modelling of transient flow in pipeline blowdown problems.

Imperial Users onl

Safe acetoxylation of propylene: The role of oxygen

[[abstract]]Acetoxylation processes are a special type of oxidation process in which the oxygen participates indirectly in the coupling of olefins and carboxylic acids. For example, propylene, acetic acid, and oxygen were catalyzed by Pd catalyst at 433.15 K, 0.5–0.6 MPa to form allyl acetate. As a part of developing safe propylene acetoxylation processes, the effects of excess oxygen are studied directly in the presence of a catalyst or an ignition source. Oxidation and combustion are found to dominate the catalytic reaction when the oxygen feed concentration exceeds the normal level of 6.4%. Temperature runaway is found to occur at feed oxygen concentrations > 14%. Without the presence of catalysts, the ignition and deflagration are possible only when the feed oxygen concentration is >18.6%. The possible mechanism of the catalytic combustion is discussed. The results suggest that using homogeneous flammability limits as the safe operating boundary for catalytic gas-phase acetoxylation processes is unsafe and proper precautions must be taken for potential catalytic oxidation

Characteristics of fire and explosion in semiconductor fabrication processes

[[abstract]]The characteristics of fire and explosion in semiconductor fabrication processes differ from those in the chemical process industries. Case studies are given to illustrate the common, as well as peculiar features of fire and explosion in the fabrication processes. In particular, the process exhaust systems, usually involving flammable, pyrophoric and corrosive gases and vapors, were shown to be a major fire and explosion source. With some preliminary understanding of the semiconductor process, standard chemical process safety knowledge can be readily applied to semiconductor processes

Estimation of waste generation from floods

[[abstract]]A framework of correlation for estimating the amount of waste generation from floods is developed. Flood waste data were collected from four recent typhoons in Taiwan. Parameters affecting the flood waste are analyzed. Population density, flooded area and amount of total rainfall are chosen as the correlating parameters for the model development, and regression diagnostics are performed to check the validity of the collected data. The simple linear model is shown to be incapable of correlating the flood waste data. An exponential model is proposed and shown to give acceptable correlation with the flood waste data spanning five orders of magnitude. The model can be useful in the planning of waste cleanup after floods

Emergency response of toxic chemicals in Taiwan: The system and case studies

[[abstract]]In this paper we describe an emergency response system in Taiwan funded by the Taiwan Environmental Protection Administration and consisted of three local response centers held by the Industrial Technology Research Institute, National Yunlin University of Science and Technology, and National Kaohsiung First University of Science and Technology in the north, central, and south part of the island, respectively. The system is set up for the effective and efficient response to incidents involving toxic chemicals, and reducing the potential impact on the environment from these incidents. Case studies are also provided for the incidents. These incidents range from a fire in a chemical plant to a spillage from a tank truck on the road. The responded incidents are analyzed and possible root causes are identified and classified. The information provided should benefit areas with growing industrial development in developing strategies to prevent or reduce the potential impacts from chemical incidents

A Novel Process of Autoxidation of Cyclohexane Using Pure Oxygen

[[abstract]]Autoxidation of liquid cyclohexane utilizing pure oxygen to produce cyclohexanone, cyclohexanol, and their precursors is achieved in a medium of cyclohexane/water mixture. The addition of water, which acts as an inert component, permits the use of pure oxygen without forming the potentially explosive oxygen/cyclohexane mixtures in the overhead vapor space as well as in the oxygen bubbles. The result is an inherently safer process for cyclohexane oxidation with increased yield and selectivity to the desired products. The use of pure oxygen improves not only the productivity and safety but also reduces the emission and benefits the environment

Experimental studies of ignition and explosions in cyclohexane liquid under oxygen oxidation conditions

[[abstract]]The safe operation of hydrocarbon liquid-phase oxidation by air or oxygen requires the knowledge on the flammability of hydrocarbon/oxygen mixtures in both the vapor space and vapor bubbles. The latter is of particular importance in situation where pure oxygen is used as the oxidant as most bubbles are expected to be flammable and explosive. New experimental findings are presented for ignition and explosion in cyclohexane liquid under oxygen oxidation conditions. A bubble column is constructed and fitted with multiple igniters. Experiments were performed at liquid temperatures between 373.15 and 423.15 K under various flow rates of pure oxygen. Two drastic different ignition and explosion behaviors were observed. The first is a typical bubble explosion from the direct ignition of the flammable bubbles in the liquid. The explosion occurs immediate following the ignition and do not produce significant energy that endanger the system. The other is a remote, delayed ignition and explosion in the vapor space that can produce significant overpressure and endanger the system. The explosion is attributed to the ignition of flammable vapor space by active free radicals from cyclohexyl hydroperoxide decomposition. A mechanism is proposed for the remote, delayed ignition to occur in the oxidation system. It is concluded that explosion in an oxidizing, bubbly liquid is not only a likely scenario but also a severe scenario, and cyclohexane oxidation should not be carried out directly with pure oxygen and without any inerting

An inherently safer process of cyclohexane oxidation using pure oxygen—An example of how better process safety leads to better productivity

[[abstract]]This paper discusses how detailed studies on flammability at elevated pressures and temperatures can be applied to liquid-phase oxidation of cyclohexane using air/oxygen and lead to an inherently safer process with better productivity. Flammability tests of cyclohexane/oxygen vapor and vapor bubbles under actual oxidation conditions were performed. The flammability of the vapor and vapor bubbles was found to be moderated by the addition of water into the cyclohexane liquid. The added water forms minimum boiling azeotrope with cyclohexane and its vapor renders the cyclohexane vapor and vapor bubble inflammable. Oxidations of the cyclohexane/water azeotrope utilizing pure oxygen were carried out and found to outperform the traditional air oxidation process by a factor of 2. This paper summarizes our work during the past few years toward a safer and better process development for the liquid-phase oxidation of cyclohexane

Simple and safe method for determining explosion limits at elevated pressures

[[abstract]]A simple and safe method for determining the explosion limits at elevated pressures and temperatures is developed by using a small explosion test cell with a pressure balancing and containment design. Tests at elevated pressure are achieved by balancing the test-cell pressure and the containment-vessel pressure. If the vapor in the test cell is flammable and ignites, the overpressure will rupture the test cell but remain confined safely by the containment vessel. The method successfully achieved explosion-limit measurement at pressures up to 5.5 MPa with all the equipment components rated at a pressure of only 13.9 MPa. Results are presented for hydrogen and methane at ambient condition and elevated pressures, and shown to be in good agreement with the data in the literature. Preliminary results on the upper explosion limits of cyclohexane at cyclohexane oxidation conditions are also reported. The method will greatly benefit the study of explosion limits at elevated pressures and the safety of hydrocarbon/air oxidation processes