OPERATIONS & MAINTENANCE
to ensure the blend is homogeneous. Once the fuel from the blend tank is verifi ed, the product goes through the traditional certifi cation practices according to ASTM specifi cation standard D-4814. Traditionally, a lab uses an octane engine test to analyse the blend. A one-cylinder engine is used to combust the fuel. Two fuel samples are taken to identify and bracket the octane level, which is then compared to a known standard that has been blended by a third-party laboratory for verifi cation. T is analysis typically takes several hours. T e gasoline is then transferred to a rack distribution tank and all lines are closed to protect the integrity of the blend. At this point, the lab will test a sample
from the rack tank to verify the blend’s Research Octane Number (RON), American Petroleum Institute’s (API) gravity and Reid Vapour Pressure (RVP) to ensure it matches what was certifi ed in the blending tank. When the product is deemed “of like kind,” it is ready to be released for distribution via the refi nery’s truck rack. To expedite this verifi cation, refi neries such as US Oil & Refi ning in Tacoma, Washington are increasingly turning to advanced Raman spectroscopy analysers that can produce results in less than a minute using established models, instead of the two to three hours using an Octane engine. “We wanted to fi nd a technology that could improve laboratory effi ciency and expedite our logistics so we can get our gasoline to the customer faster,” says Christopher Sticka, lab manager at US Oil & Refi ning. “So, we purchased a Raman analyser at the beginning of 2022 and began building the associated models for octane.”
EXPEDITING QA Raman spectroscopy is a laser-based optical analysis technique for measuring
Raman’s direct measurement produces readings every few seconds as compared to traditional GC techniques
compositions through the vibrational properties of molecules. Since its discovery in the 1920s, Raman spectroscopy has revolutionised process analysis with its non-destructive mode of operation. For many years Raman equipment has had a reputation for being expensive, cumbersome and diffi cult to use. Now advancements in the stability and portability of solid-state Raman systems and technological improvements in lasers, optics and detectors have made the technique faster and more accessible for real-time inline analysis. With spectroscopy, samples of the gasoline blend are collected using a 785nm excitation laser and a non-contact probe through the sample container that produces a unique spectral fi ngerprint identifying the chemical composition and molecular structure of the gasoline. T e distribution of the spectral peaks describes the molecules’ composition while the signal intensity correlates linearly with concentration. “We have always been interested in [Raman spectroscopy] but the price point 10 years ago was close to three quarters of a million dollars,” says Sticka. “It is hard to fi nd an instrument that you could potentially buy for a laboratory in that context.” Over time, Sticka continued to monitor
With a Raman system, the contact probe can be placed directly into the process stream without having to collect the gas sample
the development of Raman spectroscopy, and in 2022 selected a commercial technology from MarqMetrix. T e MarqMetrix All-in-One that US
Oil purchased is designed to produce identical and repeatable results from unit to unit, in a package 80% smaller
than previous Raman instruments. Each device is nearly an exact copy so common mathematical models can be applied across systems to produce consistent results. To date, results from the Raman
spectroscopy analyser have matched US Oil’s expectations and now its onsite lab is using the unit to additionally analyse the refi nery’s naphtha pre-treats to identify various compositions on the front end before it goes through the reforming process. T ey are also using spectroscopy to measure the net diff erence conversion as those molecules get reformed. According to Sticka, there are other potential advantages. With a Raman system, the contact probe can be placed directly into the process stream without having to collect the gas sample, take it offl ine, or analyse the sample by gas chromatography. Raman’s direct measurement produces readings every few seconds as compared to traditional GC techniques. Online continuous measurement also eliminates a potential safety risk from taking samples directly from the processing line to the lab. “T e analyser can be used to identify sulphur peaks online without having to collect samples,” adds Sticka. Similarly, the spectroscopy can be modelled to identify concentrations of carbon dioxide, carbon monoxide, oxygen level, and hydrogen sulphide ratios. Raman spectroscopy is quickly gaining traction as a highly effi cient, accurate and reliable solution off ering the potential to transform the speed and logistics of sampling gasoline blends so that refi neries can get their product to market faster.
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