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45 NACE INTERNATIONAL: VOL. 56, NO. 10 MATERIALS PERFORMANCE OCTOBER 2017 and dangerous corrosion. Some of these organochloride compounds are not com- plete, and the remaining non-hydrolyzed chlorides usually follow and hydrolyze in the NHT unit. The objective of this work is to identify and quantify the organochloride compounds present in the naphtha feed sample that caused this corrosion threat. Experimental Procedures The chloride analysis of hydrocarbons was conducted using the UOP991 stan- dard, 8 which determines the total chloride, including both inorganic and organic com- pounds. This method is used for determin- ing trace concentrations of chloride, fluo- ride, and bromide in liquid organics by combustion ion chromatography. Screening and quantification of organo- chlorides was performed using a gas chro- matograph (GC) connected to an electron capture detector (GC-µECD). The system was fitt ed with a nonpolar chromato- graphic column (DB1, 60-m long, 0.32-mm inside diameter [ID]), and 1.0-µm film thickn e ss). Th e c o lumn was op erat ed under a constant carrier gas (helium) flow of 1.0 mL/min. The GC oven was ramped from 40 to 310 °C at 10 °C/min. To ensure the reproducibility of the analysis, an auto sampler was used. The compounds were identified by matching their retention times with reference material. Trichloro- ethylen e (TC E) and p erchloroethylen e (PCE) were found to elute (separate out) at 10.03 and 12.28 min , respectively. Th e quantification was achieved by external calibration w hile establishing for each † Trade name. FIGURE 1 Typical naphtha hydrotreater process illustrating the corrosion incident. FIGURE 2 Chromatograms obtained for the naphtha sample collected. compound the relation between the con- centration and the peak areas. For both compounds, a good linear correlation was obtained in the 0.3 to 200 ppm range (R2> 0.999). Identification of organochlorides was performed using a gas comptograph com- bined with a mass spectrometer for organo- chloride speciation analysis 9-13 for the sam- ple with high organic chloride measured by the UOP991 method. The analysis was per- formed on an Agilent 7890 † GC in combina- tion with an Agilent 7200B † Q-TOF mass spectrometer. The sample was directly (neat) injected on a DB-PETRO † column (100 by 0.25 mm ID by 0.5 µm), with injec- tion (0.5 µL) in split mode. Carrier gas was helium (1.5 mL/min) and the oven temper- ature was programmed from 50 °C (5 min) to 270 °C at 2 °C/min. High-resolution accu- rate mass detection was done by Q-TOF, using a scan range from 40 to 400 amu. Electron ionization at 250 °C was used. Results and Discussion In the initial investigation, many ran- dom samples were collected for total chlo- ride analysis from different types of oil crude, oil tanks, and slop stream at differ- ent dates and times. The results showed the chloride level of all these samples was lower than 1 ppm in accordance with the UOP991 method. It is normal practice in the refinery to monitor pH, iron count, and chloride in spent wash water to control the corrosion. The spent wash water was moni- tored over a six-month period after the ini- tial chloride excursion. To ensure the avail- ability of relevant representative samples needed to study the origin of the chloride contamination, samples from the streams feeding the NHT were also collected on a daily basis and stored for further analysis w h e n sp e n t w a s h w a t e r u p s e t s w e re observed. Under normal operating conditions, chloride content in both the spent wash water and the NHT feed naphtha were found to remain below 1 ppm ; however, when a chloride excursion was observed in the spent wash water, an increase in the total chloride content from <1 ppm to 9.6 ppm was also observed in the naphtha feed. Th erefore, th e corresponding naphtha samples were selected to conduct a chlo- ride speciation. The chloride speciation was conducted using gas chromatography coupled to both a GC-µECD and high-resolution mass spec- trometry (GC-HR-TOF-MS). Figure 2 pres- ents the chromatogram for the naphtha sample. As shown in Figure 2, the sample con- tains mainly two halogenated compounds. For identification purposes, the sample was screened by GC-HR-TOF-MS. Twenty- two selected organic chlorinated com- pounds listed in Table 1 were screened in