Plant calorimetry

Hansen L D, Hopkins M S and Griddle R S 1997 Plant calorimetry a window to plant physiology and ecology Thermochim. Acta 300 183-97... 

A new aspect of plant calorimetry was developed in 1939 when a photocalorimeter was used to measure the quantum efficiency of photosynthesis in algae [121. Further improvements in photocalorimetry have occurred only recently and application to plants has been limited [13, 14]. 

The final required measurement for most plant calorimetry is tissue mass. Commonly both sample fresh weight (g FW) and dry weight (g DW) are determined. Dry weights are obtained after drying in a vacuum or convection oven at 75 to 85 "C for at least 24 hr. 

Rapid equilibration time. Minimizing sample equilibration time is important to obtaining the high throughput required for most plant calorimetry studies. 

Temperature scanning capabilities. While many of the measurements required for plant calorimetry studies are best done in an isothermal mode, measurements of metabolic heat rates while. scanning over the viable range of plant growth adds an important dimension for interpretation of plant properties. Studies are facilitated by the ability to scan temperature both up and down. 

No existing calorimeter has all of the above desirable features for plant calorimetry. Mo.st of the commercial calorimeters suitable for plant studies and some characteri.stics related to their function in plant calorimetry. studies are listed... 

Characteristics of calorimeters suitable for plant calorimetry studies, from [37],... 

This di.scussion. so far has discussed limitations to plant calorimetry based only on calorimeter sensitivity, sample size, and Oo depletion. Additional sample-specific problems are encountered, however, and incautious consideration of data can lead to errors in interpretation. 

The potential contributions of plant calorimetry to understanding plant physiology that were postulated years ago by Pierce, Prat, and others were not realizable prior to development of an appropriate model relating plant metabolism, i.e. 0, Rcoi and / o values to growth and substrate carbon conversion efficiency [20],... 

The first major objective for the inherent safety review is the development of a good understanding of the hazards involved in the process. Early understanding of these hazards provides time for the development team to implement recommendations of the inherent safety effort. Hazards associated with flammability, pressure, and temperature are relatively easy to identify. Reactive chemistry hazards are not. They are frequently difficult to identify and understand in the lab and pilot plant. Special calorimetry equipment and expertise are often necessary to fully characterize the hazards of runaway reactions and decompositions. Similarly, industrial hygiene and toxicology expertise is desirable to help define and understand health hazards associated with the chemicals employed. 

Calorimetry shows that the rates of metabolism of plant tissues vary widely with species, with cell types, and with environmental conditions. This provides a means of exploring the mechanisms by which various agents influence the health of a plant community. Studies are being done on beneficial agents such as growth promoters and detrimental ones such as atmospheric pollutants. For example, a correlation has been found between the metabolic heat rates and the extent of damage to pine needles by ozone. 

In our world, most chemical processes occur in contact with the Earth s atmosphere at a virtually constant pressure. For example, plants convert carbon dioxide and water into complex molecules animals digest food water heaters and stoves bum fiiel and mnning water dissolves minerals from the soil. All these processes involve energy changes at constant pressure. Nearly all aqueous-solution chemistry also occurs at constant pressure. Thus, the heat flow measured using constant-pressure calorimetry, gp, closely approximates heat flows in many real-world processes. As we saw in the previous section, we cannot equate this heat flow to A because work may be involved. We can, however, identify a new thermod mamic function that we can use without having to calculate work. Before doing this, we need to describe one type of work involved in constant-pressure processes. 

The worst hazard scenarios (excessive temperature and pressure rise accompanied by emission of toxic substances) must be worked out based upon calorimetric measurements (e.g. means to reduce hazards by using the inherent safety concept or Differential Scanning Calorimetry, DSC) and protection measures must be considered. If handling hazardous materials is considered too risky, procedures for generation of the hazardous reactants in situ in the reactor might be developed. Micro-reactor technology could also be an option. Completeness of the data on flammability, explosivity, (auto)ignition, static electricity, safe levels of exposure, environmental protection, transportation, etc. must be checked. Incompatibility of materials to be treated in a plant must be determined. 

Techniques such as adiabatic calorimetry (Dewar calorimetry) were by then well established [2, 118, 119]. All these techniques can be used for obtaining data to design for the prevention of runaway reactions, that is, to design for inherent plant safety. 

There are a number of different types of adiabatic calorimeters. Dewar calorimetry is one of the simplest calorimetric techniques. Although simple, it produces accurate data on the rate and quantity of heat evolved in an essentially adiabatic process. Dewar calorimeters use a vacuum-jacketed vessel. The apparatus is readily adaptable to simulate plant configurations. They are useful for investigating isothermal semi-batch and batch reactions, and they can be used to study ... 

The PSI element of both the OSHA PSM Standard and the EPA RMP regulation can be improved by requiring the inclusion of all existing information on chemical reactivity. Examples of such information are chemical reactivity test data, such as DSC, thermogravimetric analysis (TGA), or accelerating rate calorimetry and relevant incident reports from the plant, the corporation, industry, and government. OSHA and EPA should require the facility to consult such resources as Bretherick s Handbook of Reactive Chemical Hazards,Sax s Dangerous Properties of Industrial Materials, and computerized tools (e g., CHETAH, The Chemical Reactivity Work Sheet). 

Differential scanning calorimetry (DSC) and dust explosion tests are usually conducted before a new chemical goes into the pilot-plant phase. 

In this context, the term adiabatic refers to calorimetry conducted under conditions that minimize heat losses to the surrounding environment to better simulate conditions in the plant, where bulk quantities of stored or processed material tend to minimize cooling effects. This class of calorimetry includes the accelerating rate calorimeter (ARC), from Arthur D. Little, Inc., and PHI-TEC from Hazard Evaluation Laboratory Ltd. 

The methods for pressure relief system sizing, described in this Workbook, require certain data that are best measured experimentally. It is recommended that the experiment seeks to simulate the plant-scale runaway reaction. Adiabatic calorimetry is required for this purpose (see A2.2 below). It can be dangerous to attempt to extrapolate data for the normal reaction to the higher temperatures experienced during runaway, particularly as unexpected new reactions may begin at higher temperatures. 

R L Rogers, "The Advantages and Limitations of Dewar Calorimetry in Chemical Hazard Testing", Plant/Operations Progress, 8, 109-112, 1989... 

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