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Analytical Instrumentation


Improve High Temperature Simulated Distillation with MXT®-1HT SimDist Columns


Barry Burger, Restek Corporation 110 Benner Circle, Bellefonte, PA, U.S. Tel: 1-814-353-1300 (outside U.S.) or 1-800-356-1688 (inside U.S.) • Email: support@restek.com • Web: www.restek.com


High temperature simulated distillation of crude oil for the determination of medium and heavy fraction petroleum distillates presents many challenges to refineries and contract laboratories. Due to the high boiling points of the hydrocarbons being analysed, both the column construction and the polymer used as the stationary phase must be robust enough to withstand the high temperatures required for analysis without significant degradation. Columns must yield sharp, symmetrical peaks that meet method requirements for resolution and peak shape. ASTM methods D6352, D7500, D7213, and D7169 all specify C50/C52 resolution values and list criteria for skewness (Table I). Low bleed, high efficiency, metal MXT®-1HT SimDist columns reliably meet all critical parameters and ensure accurate boiling point determination for simulated distillation methods.


Robust Columns are Required for Accurate Boiling Point Data


While fused silica columns can be used for simulated distillation, they deteriorate rapidly at extreme temperatures because of the limited stability of the outer polyimide coating. Metal columns, such as MXT®


-1HT SimDist columns, are a much better choice. The polymer used for


the stationary phase in the column must also be robust enough to exhibit low bleed levels, or retention time shifting, peak skewing, poor resolution, and final boiling point calculation errors can result. High stationary phase bleed eventually leads to shortened retention times, making it necessary to rerun boiling point calibrations more frequently. In contrast, low bleed columns produce stable retention times due to the stationary phase remaining in the column. This results in longer in-calibration periods, extended column lifetimes, and more accurate final boiling point determinations.


MXT®


-1HT SimDist columns are exceptionally stable 100% dimethyl polysiloxane columns that can be used up to 450°C. These columns exhibit very low bleed and reliably meet or exceed requirements for multiple ASTM simulated distillation methods. The example chromatography shown here demonstrates typical results for ASTM Method D6352 (Figures 1 and 2), ASTM Method D7213 (D2887 extended, Figure 3), and ASTM Method D7169 (Figure 4). All method requirements are easily met, and the exceptionally low bleed levels result in precise slice times and accurate final boiling point determination.


Table I: Recommended high temperature columns for use in ASTM simulated distillation methods.


ASTM Method


D2887 D7213 (2887-ext.) Range C5-C44 C5-C60 D3710 D5307


Gasoline up to FBP 260°C (C14)


Crude up to FBP 538°C (C42)


D6352/D7500


C10-C90/C7- C110


Recommended Column


5/10 m x 0.53 mm ID, df = 0.88 - 2.65 µm


5 m x 0.53 mm ID, df = 0.15 - 1.2 µm


10 m x 0.53 mm ID, df = 2.65 µm


5 m x 0.53 mm ID, df = 0.20 µm PDMS


5 m x 0.53 mm ID, df = 0.10 - 0.20 µm


D7169 C5-C100


5 m x 0.53 mm ID, df = 0.10 - 0.20 µm


FBP = final boiling point Method Requirement


C16/C18 resolution (Rs) 3.00


->


C50/C52 resolution: >1 and <10, C50 skewness: >0.5 and <2.0


C12/C13 resolution: >2 and <4


C16/C18 resolution: >3 and <10


C50/C52 resolution: >2 and <4, C50 skewness: >0.5 and <2.0


C50/C52 resolution: >1.8 and <4


Skewness (any C12-C24 paraffin): >0.8 and <1.2


Column: MXT® -1HT SimDist, 5 m, 0.53 mm ID, 0.10 µm (cat.# 70112); Sample: C8-C100 hydrocarbons


(Separation Systems SD-ss3e-05); Diluent: CS2; Conc.: 1%; Injection: 0.5 µL cold on-column; Temp. Program: 53°C to 430°C at 10°C/min. (hold 5 min.); Oven Temp: 50°C to 430°C at 10°C/min. (hold 5 min.); Carrier Gas:


He, constant flow, 18 mL/min.; Detector: FID @ 430 °C; Make-up Gas Flow Rate: 24 mL/min.; Make-up Gas Type: N2; Instrument: Shimadzu 2010 GC.


Figure 2: Excellent resolution and peak shapes are seen on 0.1 µm MXT® more accurate final boiling point determinations (ASTM D6352 conditions).


-1HT SimDist columns, resulting in Figure 1: Low-bleed, high-efficiency 0.2 µm MXT® -1HT SimDist columns perform well under ASTM D6352 conditions.


Column: MXT®


-1HT SimDist, 5 m, 0.53 mm ID, 0.20 µm (cat.# 70115); Sample: C8-C100 hydrocarbons; Diluent: CS2;


Conc.: 1%; Injection: 0.5 µL cold on-column; Temp. Program: 53°C to 430°C at 10°C/min. (hold 5 min.); Oven Temp: 50°C to 430°C at 10°C/min. (hold 5 min.); Carrier Gas: He, constant flow, 18 mL/min.; Detector: FID @ 430°C; Make-up Gas Flow Rate: 24 mL/min.; Make-up Gas Type: N2; Instrument: Shimadzu 2010 GC.


April / May 2012 • www.petro-online.com


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