Chlorine processing control

Removal of metal chlorides from the bottoms of the Hquid-phase ethylene chlorination process has been studied (43). A detailed summary of production methods, emissions, emission controls, costs, and impacts of the control measures has been made (44). Residues from this process can also be recovered by evaporation, decomposition at high temperatures, and distillation (45). A review of the by-products produced in the different manufacturing processes has also been performed (46). Several processes have been developed to limit ethylene losses in the inerts purge from an oxychlorination reactor (47,48). 

Oxychlorination of Ethylene or Dichloroethane. Ethylene or dichloroethane can be chlorinated to a mixture of tetrachoroethylene and trichloroethylene in the presence of oxygen and catalysts. The reaction is carried out in a fluidized-bed reactor at 425°C and 138—207 kPa (20—30 psi). The most common catalysts ate mixtures of potassium and cupric chlorides. Conversion to chlotocatbons ranges from 85—90%, with 10—15% lost as carbon monoxide and carbon dioxide (24). Temperature control is critical. Below 425°C, tetrachloroethane becomes the dominant product, 57.3 wt % of cmde product at 330°C (30). Above 480°C, excessive burning and decomposition reactions occur. Product ratios can be controlled but less readily than in the chlorination process. Reaction vessels must be constmcted of corrosion-resistant alloys. 

The process control of sulfochlorination, especially the analysis of sulfo-chlorination mixtures, is described elsewhere [15]. 

Small but environrrientallyjnendly. The Chemical Engineer, March 1993 Huge increases in technology in the past distributed manufacturing in small-scale plants miniaturization of processes domestic methanol plant point-of-sale chlorine simpler and cheaper plants economy of plant manufacture process control and automation start-up and shut-down sensor demand [145],... 

At an early stage in the preparation of methyl parathion, it is supposed that the phosphorus ester was being chlorinated to give dimethyl thionophosphorochlori-date. Thermocouple failure indicated a low reaction temperature and the process controller boosted the chlorine feed rate, but when this fault situation was realised, the chlorine flow and agitator were stopped. However, an exothermic runaway reaction developed, eventually leading to a violent explosion. 

Liquid phase chlorination work in the former U.S.S.R. has been summarized by Vereshchinskii (1972). With tetradecane, the reaction is nearly or partially diffusion-controlled at a dose rate of 0.1-0.4 rad s-1. However, during the chlorination process, the liquid phase properties change continuously because of chlorine absorption accompanying the chemical reactions. Due to long chain reactions the chlorination G value is high and can reach 105 per 100 eV of energy absorption. At around 10-30°C the reaction rate is found to vary as the square root of the dose rate. A set of consecutive reactions has been reported in the liquid phase chlorination of 1,1,1,5-tetrachloropentane (Vereshchinskii, 1972). 

Even if few systems are proposed for inorganic compounds (with regard to the number of potential pollutants), instruments or sensors for parameters used for treatment process control are available UV systems for residual chlorine in deodorization, electrochemical sensors for dissolved oxygen (with nowadays a luminescent dissolved-oxygen probe utilizing a sensor coated with a luminescent material) and a colorimetric technique for residual ozone. 

Renal Effects. Although not adverse, dark urine (as a result of oxidation products of phenol or a result of hemoglobin or its breakdown products in the urine) is a common symptom observed in humans exposed to phenol. In persons exposed to about 0.14-3.4 mg/kg/day phenol in drinking water for several weeks after an accidental spill, dark urine was reported by 17.9% of the most highly-exposed individuals, while only 3.4% of the controls reported the effect (Baker et al. 1978). This difference was not statistically significant. A 3.3-fold increase in the prevalence of dark urine was reported by persons exposed to unspecified doses of phenol after an accidental spill in Korea (Kim et al. 1994). It is not known if the chlorination process, which may have converted a majority of the phenol to chlorophenol, contributed to this effect. 

Direct chlorination of ethylene is usually conducted in liquid EDC in a bubble column reactor. Under typical process conditions, the reaction rate is controlled by mass transfer, with absorption of ethylene as the limiting factor. Feme chloride is a highly selective and efficient catalyst for llus reaction, and is widely used commercially. The direct chlorination process may be run with a slight excess of either ethylene or chlorine, depending on how effluent gases from the reactor are subsequently processed. Conversion of the limiting component is essentially 100%. and selectivity to EDC is greater than 99%. The direct chlorination reaction is exothermic (AH = — 180 kJ/mol foreq. 1) and requires heat removal for temperature control. 

Mr. Fellow, the process control engineer—in the script of this satirical article—explains that in the past, interlocks would have been placed on many but not all of the indirect causes of a release. In McMillans example, a steam-heated chlorine vaporizer would have only two direct chemical process causes of a release. These direct causes are high pressure, which can open a relief device, and high temperature. The high temperature can accelerate corrosion. 

In the past, this company s process control design would have placed interlocks on many of the indirect causes of releases. The indirect causes include a wide-open steam control valve, a closed chlorine gas valve downstream of the vaporizer, or a wide open upstream nitrogen regulator. Unfortunately with the large number of interlocks with similar test requirements, there was not sufficient time and money to assure the integrity of all of the interlocks. 

Generation of chloramines requires the same equipment as chlorination (gaseous or aqueous hypochloramination), plus equipment for adding ammonia (gaseous or aqueous). The information for calculating the corrosion indexes for final corrosion control and for determining the CT values for secondary chloramination process control can be found in Appendix A and Appendixes D-E, respectively. 

In most cases, control of breakpoint chlorination requires the use of accurate and reliable automatic equipment to reduce the need for manual process control by operators. However, the operator must give special attention to this equipment and monitoring devices in order to ensure their proper operation. Table 3 indicates how the common process shortcomings can be compensated and improved. Table 4 is a wastewater chlorination process trouble-shooting guide for use by practicing environmental engineers. 

The major parameters used to control the septage chlorination process are treated septage color, effluent pH, and effluent chlorine residual. The chlorine dose can be adjusted until the effluent stream is a hght buff color with a pH of 2-2.5, and a chlorine residual of 150-200 mg/L (43). 

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