Application Note · multi N/C® 2100S

TOC/TNb Determination in Refinery EffluentsIntroduction
The petrochemical industry generates large volumes of wastewater or effluentsthat need to be treated before they can be reused or released into natural
waterways. Total organic carbon (TOC) and the total nitrogen bound (TNb) content
is routinely determined, as these contaminants lead to eutrophication of surface
water recourses, endangering aquatic life and groundwater supplies.

Challenge
Reproducible and reliable
determination of TOC andTNb contents in demanding
wastewater samples.

Solution
Fully automated and simultaneous
TOC/TNb measurement using
catalytic high-temperature
combustion and direct injection
technology providing optimum
particle handling and minimized
carry-over.

According to the European Industrial Emissions Directive (IED), Best Available
Techniques (BAT) have to be implemented within the EU for direct wastewater
discharges from the refining of mineral oil and gas.1 The BAT reference document(BREF) indicates that, among other parameters, TOC and TNb are of growing
importance. They need to be monitored on a daily basis. Furthermore, apreference for the parameter TOC instead of COD is given, as TOC does not require
the use of highly toxic compounds, such as dichromate (Cr VI) and mercury.
In many cases, the COD and TN contents are still measured using separate
methods. This is a labor- and time-consuming process and is often associated withthe formation of chromium-VI-contaminated waste. Through correlation studies,
an empirical conversion factor for TOC to COD conversion can be established.
Hence, a fully automated analytical process for TOC/TNb determinationaccording to EN 1484 and EN 12260 (also the planned new ISO 20236 for bothparameters) can be applied to save resources and time.

2TOC/TNb Determination in Refinery Effluents

Effluent waters from refining processes usually represent demanding samples for TOC/TNb analyzers, since tubing and valve
technique feeding the sample into the combustion process are prone to carry-over. Direct injection as applied in themulti N/C® 2100S using a septum-free injection port and a wide-bore needle for optimum particle handling can overcome
this problem. Direct injection ensures a sample transfer without particle losses and prevents blockages, hence increasingsystem uptime and reducing wear and tear on sensitive Teflon parts inside the dosing system. In addition, the injectionneedle is fully thermally cleaned before injecting the next sample, since it stays in the hot furnace inlet zone during analysis
time, thus reliably avoiding carry-over. multi N/C® 2100S thus offers a robust solution for simultaneous TOC/TNb analysis ofparticulate or oily samples.
Materials and Methods
Samples and Reagents
Samples from different prozess streams and clean-up stages have been collected and measured alongside with a referencestandard.
Sample Preparation and measurement
The samples were stored in a refridgerator at 4 degrees Celsius until analysis. For measurement, the samples were transferred
into suitable autosampler vials. The wastewater samples were analyzed in direct mode using an NPOC/TN method.
Using 2 M HCl, the samples were adjusted to pH < 2 and subsequently purged for 5 minutes. An injection volume of 250 µl
was used for these measurement sequences. The samples were catalytically oxidized at a temperature of 800 degrees Celsius
in an oxygen-rich atmosphere. A combustion tube filled with platinum catalyst was used for complete sample oxidation. The
formed nitrogen oxides were detected by means of a chemiluminescence detector (alternatively ChD detector can be utilized),
CO2 detection was done by focus radiation none-dispersive infrared detection (FR-NDIR).
Calibration
The multi N/C® analyzer was calibrated between 1 and 500 mg/l with a potassium hydrogen phthalate standard solution
for TOC determination. A multi-point calibration was used to evaluate the results of NPOC measurement. For total boundnitrogen a calibration was carried out from 1 to 50 mg/l using an ammonium sulfate and a potassium nitrate (50:50 mix)
solution according to the standard EN 12260.

Table 1: TC and TN calibration curves

Figure 1 and 2: Example of NPOC and TN calibration and method characteristics

Within the method up to 3 calibration ranges can be linked to each parameter in order to cover an over-all working range ofup to 3 magnitudes. Detection limits and limits of quantification are depending on the selected working range and can bederived from the method characteristics given above.

TOC/TNb Determination in Refinery Effluents

Instrumentation
The analysis was done on a multi N/C® 2100S using an NPOC/TN method.
Parameter

Specification Analyzer

Analytical Parameters

TC, TOC, NPOC, NPOC+, POC, TIC and TNb

Norm complianceEN 1484, US EPA 9060,US EPA 415, ASTM G144, EN 12260

User confidence and comfort

multiWin® control and evaluation software, VITA® technology, self-check system, etc.

Sample feeding

Direct injection at variable volumes 50 – 500 µL

Automation

AS 60 up to 112 pos. (8 ml / 2 ml vials)

Digestion

Thermocatalytic up to 950 °C

Detection

Focus Radiation NDIR, Chemilumineszenz Detection (CLD) or electrochemical detection (ChD)

Measuring range

Carbon: 50 ppb–30000 ppm,
Nitrogen: 5 ppb – 200 ppm (CLD) or 50 ppb – 100 ppm (ChD)

Measuring timeappr. 3 - 5 min.

Gas supply

Oxygen 4.5 or better, alternatively: HC- and CO2-free synthetic / cleaned-up air

Method Parameters
The following method settings were used to determine the NPOC and TNb contents:Parameter

multi N/C 2100S

Measurement parameter

NPOC / TNbDigestion

High temperature digestion at 800° C with platinum catalyst

Number of repetitionsmin. 3, max. 4

Rinse with sample before injection

3 times

Sample purge time

300 sec.

Injection volume

250 µlResults and Discussion
The table below shows the mean values of three replicate injections with relative standard deviations for different real
samples (anonymized) and recoveries for TOC and TNb reference solutions. According to the Best Available Techniques (BAT)
reference document issued under the Industrial emission directive 2010 / 75 / EU1), the associated average emission levels(BAT-AEL) for direct waste water discharges from refining processes can be expected as in the following ranges:
COD: 30 – 125 mg/L equals to: TOC: 7 – 32 mg/L
TNb: 1 – 25 mg/L
Table 2: Results
Sample ID

NPOC Average [mg/L]

TOC RSD [%]TNb [mg/L]

TNb RSD [%]Sample 1

26.2

2.1

19.5

1.4

Sample 2

161

0.9

41.3

1.1

Sample 3

12.9

1.2

5.38

0.8

Check Standard Nicotinic
Acid (TOC 20.0 / TNb 3.88)

19.8

0.6

4.06

0.7

3

4TOC/TNb Determination in Refinery Effluents

Fig. 3: example for a TOC and TNb measurement curve of sample 3Conclusion
The data analyzed covered undiluted wastewater samples from different sampling points in the wastewater treatment
process and with varying TOC and TNb concentrations. All samples were measured with outstanding accuracy and precision.
Nicotinic acid was used as an analytical quality-assurance standard (AQA) to simultaneously check for TOC and TNb
recoveries. Very good recoveries were achieved for the reference material for organically bound nitrogen.
This outstanding performance of multi N/C® analyzers for such demanding wastewater matrices is based on the optimized
combustion process with freely selectable combustion temperatures up to 950 degrees Celsius. The direct injection with aseptum-free pneumatic injection head in combination with a wide-bore needle of 0.7 µm inner diameter, as well as proper
sample homogenization on the auto sampler rack and the valve- and tubing-free sample transfer into the combustion system,
contribute to this performance. An operation mode keeping the stainless-steel injection needle in the oven head at elevatedtemperatures during peak integration time to assure complete evaporation of TOC components and a clean needle for further
sample processing in combination with an effective rinsing of the microliter injection syringe minimize carry-over effects.
A high degree of automation combined with the well-proven Self Check System for trouble-free unattended system operation
make light work of TOC/TNb analyses, even in challenging samples. In addition, the patented VITA flow-management systemcompensates flow fluctuations inside the system caused by sample evaporation, providing TOC calibration stability for up to
one year and saving valuable measurement time.
References1)O fficial Journal of the European Union, L 307/38, 28.10.2014, Commission Implementing Decision of 09. October 2014
“Establishing vest available techniques (BAT) conclusions, under Directive 2010/75/EU of the European Parliament and of
the Council on industrial emissions, for the refining of mineral oil and gas”

This document is true and correct at the time of publication; the information within is subject to change. Other documents may supersede this document, including technical modifications andcorrections.

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