McBain-Bakr balance

Adsorption Measurement. The capacities of the molecular sieves to adsorb vapor phase 1,3,5-triisopropylbenzene (97 %, Aldrich) and 1,2,4-triisopropylbenzene (99%, Camegie-Mellon University) were measured at 373 K using a McBain-Bakr balance. The adsorption temperature was chosen such that no chemical reactions of the adsorbates were observed. Prior to the adsorption experiment, the NH4+-forms of the solids (except SAPO-37) were dehydrated at 573 K under a vacuum of 10" 2 Torr. The as-made SAPO-37 was calcined at 793 K in an oxygen flow of 6 L/h in-situ in the adsorption system for removal of organic species and dehydration. The vapor pressure at 296 K of 1,3,5- and 1,2,4-triisopropylbenzene is approximately 0.45 Torr. The adsorption experiments were conducted at this pressure. 

Following crystallization, the solid was separated from the mother liquor by filtration, washed with distilled water, and air dried in an oven at 100 C to remove loosely bound water. Samples of the dried powder were sent routinely to the x-ray laboratory. The fact that we could obtain a strip chart recording of the x-ray powder pattern within 30 minutes was an important factor in the pace of our work. Adsorption evaluations were facilitated by use of multiple, quartz spring, McBain-Bakr balances connected in parallel. As many as 16 adsorbent samples could be evaluated simultaneously. 

The adsorption/desorption isotherms of benzene vapors were measured at 293K by gravimetric method using the McBain-Bakr balance. 

Using Equations (4) and (S), and the effective diffiisivity measurements from Table 16-3, the toms in Equation (3) can be calculated to provide an estimate of the conversion ratio for each of the CMS supported catalysts. There is (Mie additional complication. The McBain-Bakr balance utilized for the molecular probe studies was limited to measurments at ambient temperature. Thus, the effective diffiisivities of prqpylene and isobutylene were determined at 21X. Howevo, beonise the reactor stupes were perfcmned at 12S C, the diffiisivity ratio in Equadai (3) should also be at 12S C, for comparsicxt to the experimental d. Chihara et al. (1978) showed that the diffusion in ca n molecular sieve matoials is an activated diffusion process, and thus has an exprmential dependence on temperature,... 

Apparatus. The sorption of methanol on coal was measured in the apparatus shown schematically in Figure 1. It consisted of three McBain-Bakr tvpe balances, the springs for which were formed from 0.005-inch Ni-Span-C alloy wire annealed at 600°C. The diameters of these springs were about 1.5 cm.,... 

Adsorption of the two butanol isomers at 303 K was performed using a McBain-Bakr gravimetric balance built in-house (details reported previously3). The sample was outgassed at 373 K under vacuum for several hours to remove physisorbed vapour prior to adsorption. Isotherms are presented as plots of amount sorbed (mmol g 1) versus relative pressure, p/p°. 

Water vapour adsorption and desorption isotherms were determined gravimetrically at 298 K with the aid of quartz spring balances of the McBain-Bakr type. Prior to measurement each of the microporous carbons was outgassed at 573 K, the other samples at 673 K, for 16 hours to a vacuum of < 10 torr. The adsorbents used in this study are listed in Table I they have all been employed in other related studies and their properties are described elsewhere (ref. 9). 

Helical spring balances first used by McBain and Bakr have been extensively used for adsorption measurements. The spring is suspended inside a glass tube by attachment to a hook at the top. A bucket containing the adsorbent is connected to the bottom of the spring. The bottom of the tube, containing the sample, is immersed in the coolant. The upper portion of the tube is connected to a vacuum pump, source of adsorbate, and manometer. 

Many improvements in design and material have been made since McBain and Bakr s original paper. Gregg and Sing, as well as Young and Crowell, review some of the more recent developments of spring as well as beam balances. 

A spring balance for the determination of the amount adsorbed (measurement of mass) was first used by McBain and Bakr (1926). In its simplest form the apparatus consists of an adsorbent bucket attached to the lower end of a fused silica spring, which is suspended within a vertical glass tube as in Figure 3.10. 

Figure 3.10. The McBain spring adsorption balance (after McBain and Bakr, 1926).

In another static method of measuring gas adsorption, the amount of gas adsorbed is measured by the increase in the weight of the adsorbent. For this, a very useful balance was developed by McBain and Bakr (Figure 13 2), the essential part of which is a helical spring... 

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