click for Chilworth home click for DEKRA Insight home

chemical reaction hazard testing

Chemical Process Development and Optimization

Many existing chemical processes could be run much more efficiently with improved yield, better quality and greater speed. Our experience shows it is quite possible to achieve this without compromising safety or increasing environmental impact. Companies should take advantage of these opportunities to achieve financial gain and increased competitive edge. Yet they often do not pursue this potential for improvement for reasons which include:

  • a false belief that the costs would outweigh the benefits
  • lack of in-house staff time and resources to research the most appropriate solution
  • lack of specialist equipment to try new mechanisms or process changes
  • concerns over safety implications of changing the process over-familiarization with the process so possibilities are not even considered.

What You Should Do
The first action is to carry out a technical review. This brings together existing expertise and data with new knowledge derived from external expertise and laboratory studies. All this can be undertaken with due regard to safety and the environmental implications of change.

How We Can Help
Chilworth has state-of-the-art technology and a wealth of experience in chemical process development and optimization work. We can bring fresh, practical ideas to old processes and have the resources available to test and provide speedy solutions to your process improvement needs. Fully confidentiality is guaranteed.

Chilworth can:

  • review existing processes and develop new ones
  • conduct automated laboratory reaction studies
  • test under reflux and at elevated pressures
  • perform factorial experimental designs
  • assess safety and environmental implications of process change
  • make practical and economical recommendations

Specialist Capabilities

  • Adiabatic Dewar calorimetry
  • Reaction calorimetry using a Mettler RC1
  • Accelerated Rate Calorimetry
  • Differential Scanning Calorimeter
  • Vent Sizing Package 2 (VSP2™)
  • Carius tube
  • Gas evolution rate measurements
  • Mass spectroscopy
  • Evaluation of highly energetic materials including potential explosives
  • Experimental blast chamber facility
  • Handling of toxic and highly active materials

Screening Evaluation

The CHETAH program (The ASTM program for Chemical Thermodynamic and Energy Release Evaluation) is a unique tool for predicting both thermochemical properties and certain “reactive chemical hazards” associated with a pure chemical, a mixture of chemicals or a chemical reaction. This is accomplished through knowledge of only the molecular structures of the components involved by an implementation of Benson’s method of group additivity. CHETAH is useful for classfying materials for their ability to decompose with violence, for estimating heats of reaction or combustion, and for predicting lower flammable limits.

Differential Scanning Calorimetry (DSC)

DSC is a method for thermal analysis using small samples of a few milligrams (micro-thermal analysis). The apparatus consists of a temperature controlled furnace in which two crucibles are placed; one crucible containing the sample and a second crucible the reference (empty or containing an inert substance). The difference in the temperature between the two crucibles is measured as a function of time and can be calibrated in units of heat release rate. Two different methods of measurement can be used; the scanning method where the temperature of the furnace is increased linearly over time or the isothermal mode where the furnace temperature is kept constant. Since DSC works on a micro scale using only a few milligrams of substance, it is possible to investigate highly exothermic processes under extreme conditions without any risk. The relatively small sample quantities used in DSC guarantee sufficient temperature homogeneity within the sample and thus even high heat outputs can be measured quantitatively. In addition the duration of an experiment in the scanning mode is only several hours, making the DSC technique a very rapid and powerful method for screening purposes. DSC can be used for assessing severity (?Tadiabatic), probability (Time to Maximum Rate adiabatic, TMRad), process deviations, and the identification of self accelerating reactions. Samples undergoing extremely rapid deflagrations/detonations can be identified in order to be excluded from further testing (i.e. screening prior to scale up in the laboratory). High pressure gold plated crucibles are used to avoid any loss of material during the experiment and distortion of the result.

Carius Tube with End Gas Analysis

Carius tube is a screening tool for thermal stability screening to search for exothermic activity and gas generation. The following data can be obtained from the Carius tube screening tests. Identification of exothermic activity such as the onset temperatures, identification of pressure effects such as the onset of permanent gas generation and ultimately the knowledge of the quantity of gas generated during the test. The apparatus consists of a 35 cm3 glass tube in which the sample is tested, with a thermocouple pocket in the base and a glass metal seal at the top, which allows for connection to a remote pressure transducer. The glass tube is capable of withstanding pressures up to typically 60 barg. The tube is nominally charged with 10 cc of liquid or an equivalent volume of powder. The tube is then placed in a furnace and the temperature of the furnace is increased at a linear rate (0.5 K/min) from ambient to 400°C. Carius tube can also be run in an isothermal mode.

The permanent gases generated can be analyzed by various analytical techniques such as GC-MS and GC-FID.

Accelerating Rate Calorimeter (ARC)

The ARC is an automated laboratory instrument, which aids in experimentally determining the time, temperature, and pressure relationships of any exothermal reaction in a confined adiabatic environment. In operation the ARC uses an automatic heat-wait-search step scanning mode to determine the onset of exothermic reaction. When detected, the calorimeter will follow this reaction adiabatically, storing time, temperature, and pressure data. The data produced by the ARC can be applied to the evaluation of thermal and pressure hazard potentials of reactive chemicals. The ARC generates data such as heat generation rates, adiabatic self-heating parameters, temperature vs. real time plot, adiabatic reaction temperature, adiabatic reaction pressure, pressure rate data, kinetic data, reaction rate constants, and time to maximum rate. The calorimeter package consist of an insulated aluminum canister package which houses the calorimeter jacket, sample bomb assembly, and connections for thermocouples, heating elements, pressure transducer and jacket cooling air. Samples usually 1- 10 grams are contained in pressure rated holders (bombs) of various masses and materials of construction such s titanium tantalum, Hastelloy – C and 316 stainless steel. The data from an ARC experiment can be used for specifying plant protection measures including emergency relief system design using the DIERS technology.

Reaction Calorimetry (Mettler RC1)

The Mettler RC1 reaction calorimeter is a computer controlled laboratory reactor with balancing of heat and mass flows. It is an excellent tool for studying the thermal characteristic of the desired reactions, and for assuring safe process performance. RC1 data provides information such as energy of reaction, specific heat, adiabatic temperature rise and heat transfer coefficient. RC1 can be used for process development and optimization of chemical processes by studying the behavior of chemical processes in relation to changing process parameters, such as temperature, dosing, stirring, concentration and catalyst. Thanks to a rapid, effective control system, a high cooling capacity and a homogeneous jacket temperature, virtually ideal isothermal measurement conditions are achieved. The calorimeter based on the heat flow principle ensures that the heat dissipation is continuously matched to changes in the heat production in the reactor to variation of the jacket temperature. When operated on the heat balance principle, the reactor temperature is kept at the target value by changing the inlet temperature of the jacket medium. The complete RC1 system comprises the actual reaction calorimeter (with thermostat, stirrer, and electronics cabinet), a chemical reactor (glass or metal) and a computer with a printer. For control of pumps or valves up to three RD 10 dosing controllers can be attached. With the latest WinRC software enhanced evaluation and data handling possibilities are possible. RC1 can be run in isothermal, isoperibolic and adiabatic modes. RC1 reactors can be fitted with baffles and several types of stirrers, and a reflux condenser assembly for distillation and work under reflux. A range of RC1 reactors are available, e.g. small volume reactors and high pressure reactors of various materials of construction.

Adiabatic Pressure Dewar Calorimeter

This instrument enables plant scale runaway reactions to be directly simulated in the laboratory. The use of Dewar vessel with an adiabatic shield results in minimal heat loss both to the calorimeter (low phi factor) and to the environment. The Chilworth ADC III Dewar system consists of a double skinned stainless steel 1.1 dm3 reaction vessel with a 45mm diameter flanged across. The pressure rating is 50 bar at ambient temperature or around 30 bar at 200°C. Direct mechanical agitation is provided. There are range of options to go with the system such as high pressure pump, gas evolution burette to monitor gas evolution rates, injection system for instantaneous addition of liquids to a reaction mixture, alternative materials of construction for Dewar flasks, and different agitators. The benefits of the Dewar calorimeter are large scale operation ensures direct simulation of reactors up to 25 m3, low phi factor means highly accurate test data, accurate representation of multi-phase reaction mixtures, can be run batch, semi batch or gaseous batch and a highly economic solution to combining process safety and development studies. The test method can be described as follows. The Dewar is heated with an internal heater for the flask and the stirrer operates with sufficient speed to prevent the formation of hot spots. Once heated to the launch temperature, the reaction should be left under adiabatic conditions until there is clearly no exothermic activity occurring i.e. a temperature stability of <+/0.2 °C/hr or until after the vessel has vented. A residual pressure present at ambient temperature indicates that the reaction has produced permanent gas, which should be noted. The data from a Dewar experiment can be used for specifying plant protection measures including emergency relief system design using the DIERS technology.

Vent Sizing Package 2 (VSP2™)

The Vent Sizing Package, was originally developed during the DIERS project in the mid-1980’s to collect data for vent sizing calculations on runaway exothermic reactions and decompositions, and later commercialised as the VSP2™. Unlike the Adiabatic Dewar and ARC systems, which use thicker wall test cells to withstand high pressures, the 120 cm3 VSP2™ test cells are thin walled with lower phi factor. The apparatus is capable of studying reactions to high pressures by using pressure balancing, whereby the lightweight test cell is placed in a high pressure chamber where the containment pressure is regulated close to that inside the cell. Maintaining a low differential pressure permits reactions to be studied up to 100 barg and 140 barg, in case of the standard and the high pressure VSP2™ systems respectively. The test is fully adiabatic and operates with very low phi factors typically down to 1.05. The apparatus is agitated either through magnetic or mechanical stirrers and reactions can be conducted under standard sealed cell conditions or to examine the tempering or flow regime characteristics of reaction runaways. The study of semi-batch additions is possible using pressure injection systems. This unit is one of the most well-known adiabatic calorimeters across the world and is particularly popular in the USA for the study of runaway reactions.