Carbon Dioxide Sensing

Fundamentals, Principles, and Applications

Gerald Gerlach, Ulrich Guth, Wolfram Oelßner

• Publisher: Wiley-VCH
• Year: 2019
• Print ISBN:
  9783527411825
• Edition: 1
• eBook ISBN:
  9783527688272
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

The book provides the reader with a profound knowledge of basic principles, properties and preferred applications of diverse kinds of CO2 measurement. It shows the advantages, disadvantages and limitations of several methods and gives a comprehensive overview of both possible applications and corresponding boundary conditions. Applications reach from environmental monitoring to safety control to biotechnology and food control and finally to medicine.

Part I
General

1
Introduction

Wolfram Oelßner

Kurt‐Schwabe‐Institut für Mess‐ und Sensortechnik e.V. Meinsberg, Kurt‐Schwabe‐Straße 4, 04736 Waldheim, Germany

Carbon dioxide (CO₂) is one of the key components in our life and without any doubt the most important chemical substance in the global climate system. It presents the feedstock for plant assimilation and for the growth of plants and phyto cells in the biological carbon cycle as well as buffer system in the blood of humans and animals, and hence, it is important for total life on Earth. On the other hand, CO₂ is the “waste” produced by the metabolism of most of the living creatures on our Earth and by combustion of fossil fuels using carbon stocks or biomass, and it is widely understood to be one of the crucial sources of the dangerous greenhouse effect. Observation of CO₂ in the atmosphere and in the oceans yields important signals for long‐term predictions of the world's climate. Furthermore, in process technology, CO₂ is an important reagent for the manufacture of a variety of products. Monitoring of CO₂ in chemical as well as in biotechnological processes is a valuable tool to control the efficiency of the production processes. Since carbon dioxide in higher concentration can be lethal for human beings, CO₂ warning devices are needed. This short listing indicates the general importance of CO₂ and the need to determine it in gases as well as in liquids over a wide range of concentrations from ppm level up to 100% [1].

In publications and regulations the CO₂ concentration is indicated in different units. The general formula for converting the units vol ppm to mg m⁻³ and vice versa is:

1.1

with M being the molar mass in g mol⁻¹ (e.g. for CO₂ M = 44 g mol⁻¹) and V_m being the molar volume in l mol⁻¹ (e.g. for ideal gases at 25 °C V_m = 24.5 l mol⁻¹).

Table 1.1 is intended to simplify the conversion.

Table 1.1 Conversion factors for CO₂ concentrations.

		To
To convert from the units on the left to the units on top, multiply by		vol%	vol ppm	mg m^−3
From	vol%	1	10^4	1.8 × 10^4
	vol ppm	10^−4	1	1.8
	mg m^−3	5.56 × 10^−5	0.56	1

In medicine, the carbon dioxide partial pressure pCO₂ is usually indicated in the unit mm Hg instead of in the SI unit Pa. The conversion is done according to Table 1.2.

Table 1.2 Conversion factors for CO₂ partial pressures.

		To
To convert from the units on the left to the units on top, multiply by		mm Hg	Pa	bar
From	mm Hg	1	133.32	1.33 × 10^−3
	Pa	7.50 × 10^−3	1	10^−5
	bar	750.06	10^5	1

This means that typical CO₂ partial pressures in the range pCO₂ =35–45 mm Hg correspond to 4.6–6.0 kPa.

Depending on the medium in which CO₂ needs to be measured and the requirements for measuring range, accuracy, long‐term stability, selectivity, and maintenance, different methods can be applied [1] :

1. Standard test methods for the analytical determination of total and dissolved carbon dioxide in water require the titration of test samples.
2. CO₂ sensors that are based on various chemical or physical measuring methods are more user‐friendly and therefore preferably applied:

• Because of their simple set‐up and the resulting low costs, membrane‐covered electrochemical CO₂ sensors according to the Severinghaus principle have been manufactured and widely applied already for a long time. Unlike other types of CO₂ sensors, Severinghaus sensors can be applied not only in gases but also for direct measurements in liquid media.
• In comparison with these sensors with aqueous electrolytes, solid electrolyte CO₂ sensors operating at high temperatures have the advantages of a short response time and maintenance‐free operation without calibration. They are used successfully in all cases of long‐term ...

Table of contents

• Cover
• Table of Contents
• Scientific Biographies of the Authors
• Scientific Biographies of the Co-Authors to Chapter 16
• Preface
• Part I: General
• Part II: Principles of Carbon Dioxide Sensors and Measuring Methods
• Part II: Applications
• Index
• End User License Agreement