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Chapter 4 Instrumentation Used in Pyrolysis
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CHAPTER 4
Instrumentation Used in Pyrolysis 4.1.
OPTIMIZATION OF THE PYROLYTIC PROCESS FOR A SPECIFIC GOAL
General aspects The definition of pyrolysis as a chemical reaction induced by heat alone needs the specification that the process should take place at a temperature significantly higher than ambient. Otherwise, any chemical decomposition caused by thermal energy but taking place at a very low temperature or in a very long period of time would be considered pyrolysis. Even with this restriction, many known chemical processes can be classified as pyrolysis. Some of these pyrolytic processes are unintentional or occur naturally and are typically associated with burning. In other instances, the pyrolytic process is performed intentionally and has a specific purpose. Very common is the pyrolysis performed to obtain analytical information. One common application of analytical pyrolysis is to use it for the characterization of a material after its chemical degradation induced by thermal energy. The type of analytical information can be qualitative, quantitative, or structural. Pyrolysis itself, being a chemical reaction, does not provide analytical data unless it is associated with some kind of measurement process. The measurement is commonly part of a typical analytical technique such as a chromatographic or spectroscopic one. The purpose of the analytical technique is the analysis of the pyrolysis products (i.e., the pyrolysate). This type of application usually is geared toward polymer analysis or composite material analysis. The analysis of intact polymers is typically difficult. Polymers are not volatile and some of them have low solubility in most solvents. Therefore, the direct application of powerful analytical tools such as gas chromatography/mass spectroscopy (GC/MS) or high performance liquid chromatography (HPLC) cannot be done directly on most polymers. The same is true for many composite materials. Pyrolysis of these kinds of samples (polymers, composite organic materials) generates, in most cases, smaller molecules. These can be analyzed using GC/MS, HPLC, or other sensitive analytical procedures. From the ‘‘fingerprint’’ of the pyrolysis products, valuable information can be obtained about the initial sample. In this way, analytical pyrolysis allows the use of sensitive analytical methods for the analysis of samples, either polymeric or non-polymeric, that are not originally fit for a particular analytical method. Quantitation using pyrolytic techniques is feasible although less frequently utilized. The additional variability introduced by the pyrolytic process sometimes diminishes the precision of quantitative analysis. As in other analytical techniques, a calibration is usually necessary for the quantitation (see, e.g., [1]). The addition of an internal standard is possible and may improve the precision [2]. Direct pyrolysis/methylation performed directly in the injection port of a GC instrument is a particular technique very successfully used for quantitative analysis [3,4]. Besides its application as a tool for the analysis of polymers and composite materials, analytical pyrolysis is frequently utilized for the study of pyrolysates obtained from other materials exposed to heat. These materials may include non-polymeric molecules or mixtures of polymeric and nonpolymeric molecules. A convenient way to evaluate the composition of pyrolysates is to use analytical pyrolysis equipment. Numerous examples of such applications will be discussed in Part 2 of this book. Pyrolysis under controlled conditions is also used for synthetic purposes. Synthetic pyrolysis can be performed at laboratory or industrial scale. Industrial-scale pyrolysis has enormous economic implications, for example, for the oil industry and the waste processing industry. A discussion of industrial pyrolysis is beyond the purpose of this book, but in Part 2 there are some references to industrial applications of pyrolysis. Most commonly, the pyrolysis for synthetic purposes at laboratory scale is done in flow mode, when the substance to be pyrolyzed is passed through the hot zone in a flow of diluting gas. The optimization of the conditions for synthetic pyrolysis strongly depends on the chemical nature of the pyrolyzed substances and the goal of the process.
CHAPTER 4
Instrumentation Used in Pyrolysis 4.1.
OPTIMIZATION OF THE PYROLYTIC PROCESS FOR A SPECIFIC GOAL
General aspects The definition of pyrolysis as a chemical reaction induced by heat alone needs the specification that the process should take place at a temperature significantly higher than ambient. Otherwise, any chemical decomposition caused by thermal energy but taking place at a very low temperature or in a very long period of time would be considered pyrolysis. Even with this restriction, many known chemical processes can be classified as pyrolysis. Some of these pyrolytic processes are unintentional or occur naturally and are typically associated with burning. In other instances, the pyrolytic process is performed intentionally and has a specific purpose. Very common is the pyrolysis performed to obtain analytical information. One common application of analytical pyrolysis is to use it for the characterization of a material after its chemical degradation induced by thermal energy. The type of analytical information can be qualitative, quantitative, or structural. Pyrolysis itself, being a chemical reaction, does not provide analytical data unless it is associated with some kind of measurement process. The measurement is commonly part of a typical analytical technique such as a chromatographic or spectroscopic one. The purpose of the analytical technique is the analysis of the pyrolysis products (i.e., the pyrolysate). This type of application usually is geared toward polymer analysis or composite material analysis. The analysis of intact polymers is typically difficult. Polymers are not volatile and some of them have low solubility in most solvents. Therefore, the direct application of powerful analytical tools such as gas chromatography/mass spectroscopy (GC/MS) or high performance liquid chromatography (HPLC) cannot be done directly on most polymers. The same is true for many composite materials. Pyrolysis of these kinds of samples (polymers, composite organic materials) generates, in most cases, smaller molecules. These can be analyzed using GC/MS, HPLC, or other sensitive analytical procedures. From the ‘‘fingerprint’’ of the pyrolysis products, valuable information can be obtained about the initial sample. In this way, analytical pyrolysis allows the use of sensitive analytical methods for the analysis of samples, either polymeric or non-polymeric, that are not originally fit for a particular analytical method. Quantitation using pyrolytic techniques is feasible although less frequently utilized. The additional variability introduced by the pyrolytic process sometimes diminishes the precision of quantitative analysis. As in other analytical techniques, a calibration is usually necessary for the quantitation (see, e.g., [1]). The addition of an internal standard is possible and may improve the precision [2]. Direct pyrolysis/methylation performed directly in the injection port of a GC instrument is a particular technique very successfully used for quantitative analysis [3,4]. Besides its application as a tool for the analysis of polymers and composite materials, analytical pyrolysis is frequently utilized for the study of pyrolysates obtained from other materials exposed to heat. These materials may include non-polymeric molecules or mixtures of polymeric and nonpolymeric molecules. A convenient way to evaluate the composition of pyrolysates is to use analytical pyrolysis equipment. Numerous examples of such applications will be discussed in Part 2 of this book. Pyrolysis under controlled conditions is also used for synthetic purposes. Synthetic pyrolysis can be performed at laboratory or industrial scale. Industrial-scale pyrolysis has enormous economic implications, for example, for the oil industry and the waste processing industry. A discussion of industrial pyrolysis is beyond the purpose of this book, but in Part 2 there are some references to industrial applications of pyrolysis. Most commonly, the pyrolysis for synthetic purposes at laboratory scale is done in flow mode, when the substance to be pyrolyzed is passed through the hot zone in a flow of diluting gas. The optimization of the conditions for synthetic pyrolysis strongly depends on the chemical nature of the pyrolyzed substances and the goal of the process.