Characteristics of volatile organic compounds emission profiles from hot road bitumens

Avoiding static ignition hazards in chemical operations , Avoiding static ignition hazards in chemical operations , کتابخانه دیجیتال جندی شاپور اهواز

Avoiding Static Ignition Hazards in Chemical Operations

http://chemistry-chemists.com/chemister/Labtechnika/avoiding-static-ignition-hazards_1.pdf

Avoiding Static Ignition Hazards in Chemical Operations: A CCPS Concept Book

The paper presents a new procedure for the determination of oxygenated volatile organic compounds (O-VOCs) in postoxidative effluents from the production of petroleum asphalt using dynamic headspace coupled to gas chromatography-mass spectrometry in the selected ion monitoring (SIM) mode (DHS-GC-MS). Among the GC capillary columns tested, a polar SLB-IL111 column with the ionic liquid stationary phase was found to be superior due to its high selectivity for n-alkanes and individual oxygenated volatile organic compounds. The low detection limit, good reproducibility and a wide linear range allows determination of O-VOCs at low concentration levels and applicability of the procedure to routine analyses of O-VOCs in industrial effluents with a very complex composition. The developed procedure was used for the analysis of real samples – raw effluents from the production of bitumens and effluents treated chemically through oxidation. Thirteen compounds at concentrations ranging from 0.01 μg mL−1 to 118.61 μg mL−1 were identified in the effluents. In addition, nine more compounds, mostly alcohols, aldehydes and ketones, were identified using the SCAN mode. The paper demonstrates the need for monitoring O-VOCs in processes of chemical treatment of effluents. Due to the pathways of oxidation of organic pollutants present in effluents, O-VOCs become secondary pollutants. A substantial increase in the concentration of some groups of compounds, i.e. phenol and its derivatives and aliphatic and cyclic alcohols, was found in oxidized effluents. The presence of these compounds has a negative effect on the activated sludge used in refinery wastewater treatment plants.

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Application of dynamic headspace and gas chromatography coupled to mass spectrometry (DHS-GC-MS) for the determination of oxygenated volatile organic compounds in refinery effluents

The influence of trace impurities is frequently mentioned as a possible or probable cause of accidents in the chemical industry. In process conditions where there is a potential for a fast exothermic decomposition or polymerisation reaction, the contamination of pure chemicals by trace impurities may cause problems. Typical examples of this situation are described concerning the processing of organic nitrocompounds and the storage of reactive monomers, i.e. vinyl acetate and ethylene oxide. In some process instances, i.e. hydrogenation of organic nitrocompounds, trace impurities in the organic substrate are said to have killed the catalyst and caused severe accidents. Many contaminants are known to be catalyst killers in hydrogenation processes. Examples of accidents or runaway reaction hazards caused by trace impurities are given, based on a review of the literature and on our own data. Trace impurities present in common raw materials make their processing more complex and may cause accidents. Two examples are considered, the presence of nitrogen trichloride in chlorine manufacture and the presence of hydrogen sulphide and mercaptans in petrochemical feed-stock. A full literature review is given.

Influence of trace impurities on chemical reaction hazards

Thermal analytical techniques have been used to examine the exothermic nature of the deposits found in heated bitumen storage tanks and to determine if they could act as an ignition source to flammable vapours. The deposits were found to undergo an oxidation/smouldering reaction at temperatures found on the underside of the roof of the tanks. Onset temperatures for exothermic behaviour ranged from 337 to 406 K. Deposits taken from refinery tanks were found to have an activation energy in the range of 80–90 kJ mol −1 . The self-heating found in deposits constitutes a smouldering reaction which could deplete the oxygen concentration and so contribute to the conditions suitable for the formation of pyrophoric material. In a situation where cross-ventilation can occur and air is allowed to pass over the surface of the deposits, the rate of reaction would increase leading to higher temperatures and increasing the risk of fire.

Evidence of the oxidation of deposits in heated bitumen storage tanks

It is thought that pyrophoric iron sulfide may be able to form in heated bitumen storage tanks and act as a source of ignition to the flammable vapours in the ullage space. Electron microscopy has been used to indicate the possible presence of pyrophoric material within a sample of bitumen deposit taken from a refinery tank. High levels of sulfur were found in areas rich in iron and part of this sulfur was in the form of a sulfate, a product of the weathering of pyrite. The sulfur found in the iron-free areas of the deposit was in the form of elemental sulfur.

Study of iron sulfide as a possible ignition source in the storage of heated bitumen

A study has been made of 73 case histories of incidents involving heated bitumen storage tanks. The majority of incidents were found to be due to operations such as charging and discharging of tanks, including overfilling which can lead to lagging fires and exposure of heater tubes. A number of incidents were the result of spontaneous ignition or unknown causes: it is proposed that regular cleaning of tanks would reduce the number of these incidents.

Case histories of incidents in heated bitumen storage tanks

A mathematical model has been developed to simulate the conditions occurring within the deposit layer found on the underside of the roof of a heated bitumen storage tank. The deposit was found to undergo low temperature smouldering, reaching maximum temperatures of around 650–750 K, due to the fact that the reaction took place at the surface of the deposit and any heat generated was easily lost to the surroundings. The rate of reaction was found to be dependent on the rate of diffusion of oxygen into the surface of the deposit. The model can be used to identify potentially hazardous deposits and to determine a maximum safe thickness from which the necessary frequency of removal of deposits can be estimated to ensure a safe system.

F.M. Davie

Papers

Evidence of the oxidation of deposits in heated bitumen storage tanks

Study of iron sulfide as a possible ignition source in the storage of heated bitumen

Case histories of incidents in heated bitumen storage tanks

Mathematical model for the self-heating of deposits found in heated bitumen storage tanks