4 Analytical Instrumentation
NOVEL AND RAPID LSC METHOD FOR THE ANALYSIS OF BIOGENIC CARBON IN FUELS
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Hidex Biofuel Method is novel, easy-to-use, direct LSC measurement for determining the bio-% of biofuels Biofuel analysis at the refi nery
Abstract A novel method based on radiocarbon dating and liquid scintillation counting (LSC) was developed to determine the biocarbon content in biofuels without fuel specifi c background sample. Hidex biofuel method is an easy-to- use measurement that requires no sample preparation, making it well suitable for fast in-house detection needs. It uses a patented algorithm to fi nd the background count rate and counting effi ciency of unknown biofuel samples with variable colour. Hidex biofuel method employs a liquid scintillation counter with triple-double coincidence ratio (TDCR) output and an external standard. The performance of the method was demonstrated by analysing several diff erent types of biofuels with a bio-% ranging from 1 to 100%. Results showed an excellent correlation between Hidex biofuel method and accelerator mass spectrometry (AMS), with detection limit down to 1% biocarbon.
Challenge
Fossil based fuels are increasingly replaced by fuels of biologic origin, such as hydrotreated vegetable oil (HVO) and bioethanol. Percentage of biogenic component in fuel can be determined with accelerator mass spectrometry (AMS) and LSC measurement with benzene synthesis (ASTM D6866 and EN 16640 guidelines), both based on 14C dating principle. These methods provide accurate results but require expensive and time-consuming sample preparation. Direct detection by LSC is an attractive alternative as liquid fuel samples can be measured directly after mixing with scintillation cocktail (DIN 51637, ASTM D8473-22 guidelines and Hurt
et.al., Energy Fuels, 35, 2, 1503–1510, 2021). Fuel samples are often highly variable and intense in colour, which is affecting both counting effi ciency and background. This is a challenge especially with
PIN AUGUST / SEPTEMBER 2024
fuel blends, as a fossil-based background sample with similar quenching properties is rarely available.
Solution
Hidex Biofuel method is an improvement on the direct detection by LSC. The method includes an algorithm, that uses a combination of two different types of quench parameters (external standard TDCR = eTDCR and QPE) to detect simultaneously both colour and chemical quench in the sample. It calculates the background count rate without a fuel specifi c background sample. The same algorithm also fi nds the counting effi ciency for each sample. The method employs a 3-PMT LS counter enabling triple-double coincidence ratio (TDCR) output and an external standard. The biofuel algorithm is derived from background and effi ciency quench curves with chemical and colour quenchers. TDCR and external standard quench parameters are used for the calculation of background and counting effi ciency of unknown samples. The performance of the method has been demonstrated in routine use for over two years at fuel refi neries and contract research organisations.
Calibration of the biofuel method
The biofuel method requires a TDCR counter equipped with cooling and Eu-152 external standard source. The counter used in this study was Hidex 300SL super low-level instrument. The algorithm is derived from background and counting effi ciency quench curves which are measured on-site. Each quench set includes 7 standards with variable amount of chemical quenching agent and 7 standards with variable amount of colour quenching agent. Quench curve sets are available in Tefl on coated plastic vials or in glass vials. After calibration, the algorithm is installed to the instruments measurement protocol and is ready for use in routine analysis of biofuel samples.
Sample preparation
Biofuel sample is mixed directly with MaxiLight+ scintillation cocktail in a vial. The typical sample amount is 10 ml biofuel and 10 ml cocktail. Samples are weighed before measurement,
Hidex LS counters compatible with the Hidex Biofuel Method include the Hidex 300 SL (left) and the Hidex ULLA (right).
Table 1. Comparison of HVO-diesel blends: expected bio-% versus bio-% determined using Hidex biofuel method (with ±1σ uncertainty).
Expected Bio-% 100 78.8 57.7 38.5 19.2 13.9 9.4 4.6 2.7 0.9 0
LSC Hidex Bio-% 99.0 ± 0.7 76.8 ± 0.6 57.7 ± 0.6 37.7 ± 0.5 18.9 ± 0.4 13.8 ± 0.3 9.8 ± 0.3 4.3 ± 0.3 2.7 ± 0.3 1.2 ± 0.3 -0.2 ± 0.2
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