Jul-2022

AC Analytical Controls productivity center combines full ASTM D86 alternative in a single GC

Distillation is a method that separates a liquid mixture by boiling and subsequent condensation of the gas phase.

PAC

Article Summary

Evidence of the use of distillation has been traced as far back as 800 BC in Asia. Today, it is the most widely used processing method in the hydrocarbon processing industry. In fact, it is one of the first processes that crude oil is subjected to, as it is being distilled in the atmospheric distillation unit. Even if it is not a main goal of the specific processing step in question, it is still frequently used as a post-treatment step of the process. If distillation is employed as an analytical technology, it describes the volatility properties of a material.

Distillation can be used as a quality-control tool for end products. For example, with gasoline, volatility requirements are imposed to ensure vehicle drivability in both hot and cold conditions. Distillation is then used to categorise the volatility class of the fuel. If there is too little light material present in the sample, the engine may not start at low temperatures. However, if there is too much light material in the gasoline, vapour lock may occur where the flow of gasoline in the fuel lines is obstructed by the formation of gas bubbles. Needless to say, refiners use distillation as an analytical technology in various streams in their refinery with the goal to monitor and optimise production processes. As such, various lab and process applications exist for distillation technology.

Methods
A frequently used distillation method in the HPI laboratories is physical distillation, per the methods:
- ASTM D86: “Standard Test Method for Distillation of Petroleum Products and LiquidFuels at Atmospheric Pressure”,
- ISO 3405: “Petroleum and related products from natural or synthetic sources, Determination of distillation characteristics at atmospheric pressure”.

These test methods cover the atmospheric distillation to determine quantitatively the boiling range characteristics of products like gasoline, gasoline feedstocks, aviation fuels diesel (including biodiesel blends), and naphtha’s, etc. The method was introduced in 1927, has been revised numerous times since then, and is still used as the referee method in various fuel specification methods.

Over the last decades, various alternative distillation methods have been developed, such as simulated distillation (also called SIMDIS or SimDist). The huge product portfolio of AC Analytical Controls includes numerous solutions to determine the boiling point distribution for the same sample scope of samples as described by ASTM D86 & ISO 3405. For more than 20 years, AC has offered two ASTM D86 / ISO 3405 alternatives, which have been recently combined in one system, called the Productivity Center. This analyser is reporting D86 data based on two different principles, depending on the product group type as defined in the D86 method:

Group 1 & 2
This application is called the AC8612. It calculates the boiling distribution of a product based on a DHA analysis and a Fugacity Film model. This model uses the sample composition, individual component characteristics, and various thermodynamic processes (and related formulas) to describe the evaporation and condensation processes as they take place in a traditional physical distillation process as described in the ASTM D86.

The application considers the various requirements of this method, like time to IBP, start temperature, distillation rate, etc.

Further details of the calculation are described in Appendix 1. The result is like what D86 reports: IBP, distillation points (evaporated and recovered), FPB, loss, residue, recovery, etc. The AC8612 application is not compliant to any standardisation method. It can, however, be used for intermediate streams like a straight run naphtha, reformate, reformer feed, FCC naphtha, etc. However, regular motor gasolines and reformulated finished gasolines can be analysed as well and fit perfectly in the model.

Group 3 & 4
This application is called the AC8634. It correlates mid-distillate Simdis results (mass percent off) to D86 boiling point distribution (volume percent off), based on mathematical equations. For details of the correlation, see Appendix 2. The correlation is described in both ASTM D2887 and ISO 3924, and currently valid for B7 samples, as well.

There are various fuel specification methods allowing reporting of correlated Simdis data, for which the AC8634 is a great tool:

Hardware configuration
Historically these applications have been sold as separated systems. AC Analytical Controls has taken the introduction of the Agilent 8890 as an opportunity to combine both applications in one dual-channel analyser, known as the Productivity Center.

With the new design that features both applications in one analyser, a laboratory has the option to run both methods (in random order) in one sequence. This translates into increased lab capacity for distillation analysis by a factor of two or three. With the Productivity Center, it is possible to run at least 4-5 samples per hour, while a classic D86 analysis takes about half an hour. Another huge advantage is that the system runs the sequence of samples without user intervention (one cannot operate of both applications simultaneously, since the oven temperature program used is optimised for the applications and thus different).

The AC8634 is configured with the AC temperature programmable inlet (TPI), an inlet specially designed by AC Analytical Controls for Simdis analysis. It has proven industry-leading performance, confirmed by AC’s performance monitoring program, where repeatability and reproducibility results at all levels outperform the method’s accuracy. This translates into tighter control options.

With the Productivity Center setup for dual-channel application (AC8612 & AC8634 in one system), the AC8634 scope is limited to the scope of the ASTM D86 group 3 & 4 type of products (thus not the D2887 scope). Heavier samples (FBP >C36) cannot be analysed due restrictions that oven temperature program may not exceed the MAOT (Maximum Allowable Oven Temperature) of the AC8612 column.

The PAC IRIS-based Simdisxlnc & DHAxlnc software includes the AC8612 calculations and AC8634 correlations and can be installed in a standalone as well as a client server environment. After starting the analysis in the chromatography data system, results are calculated automatically and automatic data transfer into LIMS is an option as well.

Results
Historical data from PTP programs show an excellent correlation of Simdis to D86 or ISO 3405. Below graphs and table shows some results.
For the AC8612 a comparison check has been performed on some of the AC Reference samples. See tables and graphs below.

Conclusion
The AC Productivity Center is a great alternative for classic D86 analysis. It is a huge cost saver for modern laboratories who are tasked with delivering D86 distillation results in shortest possible time with the best possible accuracy:
- Unique AC8612 model allows highly accurate analysis for gasoline and naphtha
- AC8634 listed as alternative method in various jet-fuel and diesel specifications
- High workload and fast turnaround time: 4-5 samples per hour
- Unattended use, high level of automation and lower cost per analysis