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Estimation of Static Dissipater Additives (SDA) in Aviation Turbine Fuels (ATF) using ASTM D 7524 and ASTM D2624; Observation, Precautions and Suggestion thereof. Anil Yadav, Maya Chakradhar, Anju Chopra, Jayaraj Christopher, and Gurpreet Singh Kapur Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03341 • Publication Date (Web): 10 Jan 2018 Downloaded from http://pubs.acs.org on January 11, 2018
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Energy & Fuels
Estimation of Static Dissipater Additives (SDA) in Aviation Turbine Fuels (ATF) using ASTM D 7524 and ASTM D2624; Observation, Precautions and Suggestion thereof. Anil Yadav*, Maya Chakradhar, Anju Chopra ,J.Christopher and G S Kapur Research & Development Centre, Indian Oil Corporation Ltd., Sector-13, Faridabad121007, Haryana, India.
Highlights The work started with the estimation of Static Dissipator Additive (SDA) in Aviation turbine fuel (ATF) using two standard methods ASTM D2624 and ASTM D7524. However, during experiments it was observed that one have to be cautious while using the mentioned standard methods. This work describes the observations made during targeted analysis and precaution one has to take while using mentioned standard methods.
Abstract Static Dissipater Additives (SDA) is conductivity improver additives that are added to ATF to avoid sudden increase in conductivity that may occur during transfer/pumping of ATF. STADIS 450 has been used globally as the SDA in aviation jet A1. The dosage of SDA into jet fuels is very closely specified (1-3 ppm). Due to surface active nature, SDA dosage may deplete with time. The monitoring of concentration of SDA is very critical and is generally carried out using conductivity measurement as per ASTM D2624 or as per liquid chromatographic technique based ASTM D7524 method that provides for “Determination of Static Dissipater Additive (SDA) in Aviation turbine fuel using HPLC technique with UV detector in the range of 1 to 12 ppm”. In this work, SDA blended ATF in range of 1 to 5 ppm have been analyzed for estimation of SDA using both HPLC based ASTM D7524 and conductivity measurement based ASTM D2624. This paper suggests precautions that need to be taken while using two methods. The work also recommends suggestions that can make the ASTM D 7524 findings more specific, precise and ensures better recoveries. While the initial procedure were adopted from ASTM D7524, multiple collections during cartridge extraction process and use of HPLC with Photodiode detector instead of UV detector bring down the detection level to 0.5 ppm SDA in ATF. Keywords: Static Dissipator Additive, Aviation turbine Fuel, HPLC, Conductivity, Photodiode array. 1 ACS Paragon Plus Environment
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1.0 Introduction Hydrocarbon fuels typically have low electrical conductivity and consequently are susceptible to retaining a static charge. Static charges are induced, especially, when the fuel is pumped at high rates through filters. Due to the relatively low conductivity, the static charge does not readily dissipate and is retained for a considerable period of time. This condition can result in an fire/explosion (1, 2). As fuels have become ‘cleaner’, the risks of electro-static ignition have further increased. The high severity refinery processes used to remove trace materials from low sulfur fuels, also reduce the natural conductivity of the fuel. It is therefore essential to use additives that increase the electrical conductivity of fuels, reducing the risk of electrostatic hazards. STADIS® 450 is the premium SDA in use today for Aviation turbine fuel (ATF). It reduces the risk of static discharge and electro-static ignition at minimal treat rates even when dosed at (typically 0.5 to 3 mg/l). Its use is mandatory in most aviation turbine fuels for either civil or military use. The active component in SDA is DINNSA (~12%w/W) (Dinonyl naphthalene sulphonic acid). This is surface active component and its concentration depletes with time and it has to be regularly added to ATF to maintain it at the required concentration. There are two standard methods available for the monitoring of the concentration of SDA. These are ASTM D 2624 and ASTM D 7524. The conductivity measurement as per ASTM D2624 has been used for the quick monitoring (3). However, the robustness of the conductivity test can be at times questionable, because it measures the total conductivity of the fuel and not selectively measure the static dissipater present in the fuel. Further, the conductivity values are found to depend not only on SDA but ATF also (4). In this work conductivity values have been collected for SDA in two different ATF from two different sources doped at level of 0.5 ppm to 4 ppm. It has been observed that different ATF samples show difference in response w.r.t to conductivity towards SDA. Same concentration of SDA leads to different values of conductivity in different ATF samples. ASTM D7524 is liquid chromatography technique based method that estimates Static Dissipater Additive (SDA) in Aviation turbine fuel in the range of 1 to 12 ppm (5). It is specific for SDA containing active component that is structurally alkyl substituted aromatic sulfonic acid. The ASTM method involves two stages; stage 1 involves enrichment of 2 ACS Paragon Plus Environment
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Energy & Fuels
DINNSA by passing the ATF through solid phase extraction cartridges and stage 2 involves HPLC analysis of enriched sample from stage 1 using UV detection at 234 nm. Multiple experiments were conducted which showed that the ASTMD 7524 method has to be used but with due precautions and slight modifications adapted to available laboratory analytical condition. The present work discusses the experimental observations associated with using two standard methods and the precautions one has to take while using these methods. 2. Experimental 2.1
Reagents/chemicals
Solid phase extraction Cartridges of two make were used (a) NH2
Solid Phase Extraction
(SPE) tube, 100 mg (Make-A) and (b) Discovery DSC- NH2 Solid Phase Extraction (SPE) tube, SUPELCO, 100 mg. The average particle size and pore diameter for both the types of cartridges falls in the range of 45- 60 µm and 60-80 A° respectively. Commercial Dinonylnapthalene Sulfonic Acid (DINNSA)(50%w/w), Stadis 450(with ~ 12wt % DINNSA), HPLC grade Tetrahydrofuran, Methanol, Heptane, Buffered Phosphoric Acid, 1 M Sodium Hydroxide Solution, Aviation Turbine Fuel (ATF) from two different sources Two different ATF samples; namely ATF (A) and ATF (B) from different sources were used. The conductivity studies were carried using both the ATF samples. 2.2 Preparation of Mobile Phase as mentioned in ASTM D 7524. 400 ml Tetrahydro Furan (THF), 400 ml Methanol and 50 ml buffered phosphoric acid were mixed well and maintained at 2.5 pH. 2.3 Preparation of DINNSA calibration Standards. The calibration standards(w/V) of commercially available DINNSA(50%w/w) were prepared as mentioned in ASTM D 7524 in range of 0.64 ppm to 16 ppm. In terms of active component, these calibration standards have concentration in range of 0.32 ppm to 8 ppm. These standards were used to make the calibration plot. 2.4 Preparation of SDA blended ATF to establish ASTM D7524 method in Lab All standards were prepared in ATF (A). 0.1g of SDA was weighed in 100 ml volumetric flask and made up to volume with ATF to make 0.1% or 1000 ppm solution of SDA in ATF solution (labelled as S1). The S1 solution was diluted with ATF to prepare 50 ppm stock solution (labelled as S2). The stock solution S2 was used to prepare blend solution of 0.5 ppm to 5 ppm SDA in ATF solution. All the dilutions were carried out with the help of ATF (A). 2.5. High Performance Liquid Chromatography (HPLC) Instrumentation
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The HPLC analysis was carried on Shimadzu model no.LC-2010 CHT comprised of a degasser unit(DGU-20A) for extracting any dissolved air from the solvents, quaternary pump(LC-30AD) for isocratic and gradient solvent program, an auto sampler(SIL-30AC)for sample injection, column oven (CTO-20AC) to maintain the temperature and UV-DAD (SPD-M20A) detector . 2.6 Conductivity measurement Instrumentation: The electrical conductivity measurements were carried on EMCEE 1152 model digital conductivity meter as per ASTM D2624. 2.7 Liquid Chromatography Analytical Conditions Stage 1: Stage 1 was associated with enrichment procedure. In the step, known volume of sample was loaded on the solid phase cartridges. The elution was carried using the procedure provided in ASTM D 7524 with slight modification. The original ASTM 7524 elution scheme along with modified elution scheme are tabulated in Table 1 and Table 1a respectively. Stage II: This stage involved the HPLC analysis of the enriched extract obtained from Stage 1. 50ul of the extract solution was injected. The C8 (Enable C-8H) was used as stationary phase. The mobile phase conditions are mentioned at 2.2. 3.0 Results and Discussion Calibration: The calibration standards (w/V) of commercially available DINNSA (50%w/w) were prepared in range of 0.64 ppm to 16 ppm in mobile phase and were analyzed by HPLC technique as mentioned at 2.7. The overlaid HPLC chromatogram is given at figure.1. The area under the DINNSA component peak (retention time between 4.5 - 5 minutes) was measured using software. The concentration vs. area data is shown in Table 2. Fig. 2 show the calibration curve and equation. The repeatability studies under HPLC experimental condition w.r.t Retention time (RT) and area were carried by analyzing 1 ppm DINNSA standard ten times. The precision value was found to be less than
