High-Pressure Thermobalances

Ghodsi and Neumann-Tilte (63, 64) constructed an isothermal balance with two symmetrical pans for use in the hydrogenation of coal chars to pressures of 5 MPa. Provision was made for the trapping of coal tar and other pyrolysis products that could be analyzed by gas chromatography. 

A similar symmetrical two-pan balance for use up to 3000 bar was described by Sabrowsky and Deckert (65). 

A high-pressure enclosure for the Cahn 1000 electrobalance, for use at pressures up to 1500 psi, is available from Cahn Instruments. The enclosure is machined from two pieces of stainless steel and contains no weld joints. Optional accessories include a reactor and counterweight chambers and O-ring sealed couplings. 

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Tf — T. When a high-pressure thermobalance was used, theTG curves of... 

Williams and Wendlandt (68) have described a high-pressure thermobalance based on the Du Pont Model 950 balance and capable of operation at temperatures of 500°C and 500 atm pressure. A schematic diagram of the balance enclosure is shown in Figure 3.34. The balance chamber was machined in the form of a cylinder from stainless steel. The furnace was insulated with Marinite which was machined to fit inside the pressure vessel and extent from the inner plato to the front of the balance housing. Provision was made for fitting the furnace within the insulated chamber and permitting... 

Figure 3.34. Schematic diagram of the high-pressure thermobalance enclosure. A, end plate with threaded opening for gas inlet fitting B, Buna-N O-ring C. pressure cell D. high-pressure connector for control cable E, balance movement F. furnace chamber G. furnace thermocouple H, furnace heater wire in Marinite insulation J. hexdrive bolts K, end plate with threaded opening for gas outlet fitting (68).

Figure 2. Typical weight-loss curves obtained with high pressure thermobalance for gasification in hydrogen and in nitrogen...

The high pressure thermobalance is very simliar to the balance described by Feldkirchner and Johnson (7). The thermobalance is designed to operate isothermally up to 1000 °C and 2000 psi hydrogen. Details of the balance are shown in Figure 1, and a schematic of the system is shown in Figure 2. The reactor tube is constructed of Haynes 25 superalloy. The mass transducer is a Statham model UC 3 attached to a balance arm (Micro-scale accessory UL 5) and has a full-scale range of 6 grams. 

Buroni, M., et al., Behaviour of calcium-based sorbents towards sulphur-dioxide capture in a high-pressure thermobalance. Fuel, 71(8), 919-924 (1992). 

Dobner, S. Kan, G. Graff, R. A. Squires, A. M. "Modification of a Thermobalance for High Pressure Process Studies," AIChE Meeting, Los Angeles, November 16-20, 1975. 

Enclosure of the Du Pont thermobalance in a high-pressure chamber has been described by Brown et al. (37) and Williams et al. 138). Pressures of up to 20 atm and a maximum temperature of 350°C were possible with the former, while the latter instrument could be operated up to 68 atm and a maximum temperature of 450°C. The modification by Williams et al. (38) also permitted simultaneous magnetic susceptibility measurements on the... 

This kinetic study of catalyzed hydrogasification reactions utilizes a high temperature, high pressure recording balance. A thermobalance is particularly useful in gas-solid reactions because the weight of small solid samples can be measured continuously. Direct kinetic analysis of the weight loss curves are straightforward. 

Fig. 5-4 Magnetic Suspension Thermobalance with High Pressure Oven...

The quality of the furnace atmosphere deserves careful attention. Most commercial thermobalances operate at atmospheric pressure. Vacuum and high-pressure studies normally require specialized equipment, either commercial or home-... 

Perhaps the most widely used TG-MS system, which includes DTG. DTA, and gas pressure measurements, is the Mettler thermoanalyzer. The system, which consists of a precision thermobalance, a high-vacuum system, a mass spectrometer, and a DTA measuring system, has been described in detail by numerous investigators (68-73). 

Knowledge of vapor pressure helps in estimating the volatility of the plasticizer. It is therefore important to find a method of determination which is precise, easy to handle, and uses commonly available equipment, for example, thermobalance. A quick and simple method was developed to determine vapor pressure at different temperatures using thermobalance.Figure 15.2 shows the data measured by the method and data from other studies. It is evident that the results are obtained with high precision. Details of method and the use of modulated temperature programs is described. ... 

Rouquerol [9,10] studied the effect of water vapour pressure on the decomposition, at low pressure, of 1 pm crystallites of gibbsite using a vacuum thermobalance and constant reaction rate regimes. He showed that, at pressures of less than 1,33 Pa, the formation of boehmite is minimised and the gibbsite decomposes directly to produce a highly microporous alumina. He found that the BET surface areas could be varied from 40 to 430 m g" by changing the pressure of water vapour over the solid from 5 to 130 Pa. 

It is obvious from the history of TG-MS [393] that the interface is of crucial importance, fulfils several functions and poses several problems. It operates simultaneously as a gas-input system for the mass analyser and (usually) as a pressure reduction system. Within the interface, conditions are converted from the high temperature and (usually) atmospheric pressure of TG to the room temperature and (usually) high-vacuum conditions in the mass analyser. Both the temperature and geometry of the interface region influence the coupling. The main aspects of the flow in the thermobalance, relevant to hyphenated techniques, are understood. 

All high temperature experiments were carried out in a thermobalance, under an inert argon gas (Ar type U 99.995 vol.% Ar, N2 < 20 ppm, H2 < 10 ppm, CH4 < 5 ppm, H2O < 5 ppm) or synthetic air (80 vol.% N2 20 vol.% O2) atmosphere, at atmospheric pressure. After heat treatment under inert atmosphere, argon was replaced by reconstituted air which marked the beginning of the oxidation of the blank NiCr specimens. Eor coated specimens, the described thermal treatment steps have to be included in the temperature increase. Blank and coated NiCr samples were oxidised for 90 h at 850°C. 

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