Steeping stage

The normal source of cellulose is timber, e.g., spruee or eucalyptus, which after debarking, is eut into small ehips, treated with calcium bisulfite as a bleach and pressure cooked with steam to remove lignin. The product is washed with water and the cellulose floating on the surfaee is eollected, compressed and given a further bleach and finally pressed into sheets, or boards, of cellulose eontaining some 30% solids. These sheets, about 95% pure 

Recovery of cellulose as fiber or film by decomposing the derivative 

For every two anhydroglucoside units, only one alcoholate group is formed, mainly at position 2. 

Nine allotropes of alkali-cellulose have been identified. After steeping, the hydraulic ram is closed to give a precise alkali/cellulose ratio, removing the excess spent steeping liquor, which can be recovered by dialysis. The alkali-cellulose containing a controlled amount of residual spent liquor is transferred to a shredder. 

---

One of the commercial methods for production of lysine consists of a two-stage process using two species of bacteria. The carbon sources for production of amino acids are corn, potato starch, molasses, and whey. If starch is used, it must be hydrolysed to glucose to achieve higher yield. Escherichia coli is grown in a medium consisting of glycerol, corn-steep liquor and di-ammonium phosphate under aerobic conditions, with temperature and pH controlled. 

The most widely-accepted dose response model at the present time is the multi-stage model, which has great flexibility in curve-fitting, and also has a strong physiological justification. Although it is difficult to implement, there are already computer codes in existence that estimate the model parameters (13). The two most widely-used models, until recently, were the one-hit model and the log-probit model. They are both easy to implement, and represent opposite extremes in terms of shape - the former represents the linear non-threshold assumption, whereas the latter has a steep threshold-like curvature. In numerous applications with different substances it has been found that these three... 

Fig. 5.19. Evolutionary track in the HR diagram of an AGB model of total mass 0.6 Mq, initial composition (Y, Z) = (0.25, 0.001 Z /20). Heavy dots marked 2 to 11 indicate the start of a series of thermal pulses (see Fig. 5.20), which lead to excursions along the steep diagonal lines. Numbers along the horizontal and descending track indicate times in years relative to the moment when an ionized planetary nebula appears and (in parentheses) the mass of the envelope in units of Mq. R = 0.0285 indicates a line of constant radius (R in solar units) corresponding to the white-dwarf sequence. Shaded areas represent earlier evolutionary stages for stars with initial masses 3,5 and 7 Mq and the steep broken line marks the high-temperature boundary of the instability strip in which stars pulsate in their fundamental mode. The y-axis gives log L/Lq. Adapted from Iben and Renzini (1983).

SINI Also known as the Double Steeping process. A variation of the viscose process for making regenerated cellulose fibers, in which the treatment with sodium hydroxide is done in two stages, at different concentrations. Invented by H. Sihtola, around 1976. 

The second stage of steeping is the sulfur dioxide diffusion stage in which sulfur dioxide diffuses with the water into the corn kernel through the base end of the tip cap and moves through the cross and tube cells of the pericarp to the kernel crown and then slowly into the horny endosperm. The second stage is diffusion limited because of the specific path required for water going into the kernel. 

The majority of physisorption isotherms (Fig. 1.14 Type I-VI) and hysteresis loops (Fig. 1.14 H1-H4) are classified by lUPAC [21]. Reversible Type 1 isotherms are given by microporous (see below) solids having relatively small external surface areas (e.g. activated carbon or zeolites). The sharp and steep initial rise is associated with capillary condensation in micropores which follow a different mechanism compared with mesopores. Reversible Type II isotherms are typical for non-porous or macroporous (see below) materials and represent unrestricted monolayer-multilayer adsorption. Point B indicates the stage at which multilayer adsorption starts and lies at the beginning of the almost linear middle section. Reversible Type III isotherms are not very common. They have an indistinct point B, since the adsorbent-adsorbate interactions are weak. An example for such a system is nitrogen on polyethylene. Type IV isotherms are very common and show characteristic hysteresis loops which arise from different adsorption and desorption mechanisms in mesopores (see below). Type V and Type VI isotherms are uncommon, and their interpretation is difficult. A Type VI isotherm can arise with stepwise multilayer adsorption on a uniform nonporous surface. 

Although an optimum temperature profile may be specified from theoretical calculations, it may not be possible to achieve in practice. The maximum temperature which can be used is usually determined by the materials of reactor construction or the durability of a catalyst. Also, steep axial temperature gradients cannot be realised unless heat transfer rates are high. If heat transfer is poor and the overall process is exothermic, temperature programming of a single reactor may be impossible the reactor becomes virtually adiabatic. In cases such as these, staged reactors (discussed elsewhere in this volume) with intercoolers may be used as a compromise. 

Fig. 5 (a) shows the nitrogen adsorption isotherms of aluminum hydroxy pillared clays after heat-treatment at 300-500°C. These are of the typical Langmuir type isotherm for microporous crystals. Fig, 5 (b) shows the water adsorption isotherms on the same Al-hydroxy pillared clays [27]. Unlike the water adsorption isotherms for hydrophilic zeolites, such as zeolites X and A, apparently these isotherms cannot be explained by Langmuir nor BET adsorption equations the water adsorption in the early stages is greatly suppressed, and shows hydrophobicity. Water adsorption isotherms for several microporous crystals [20] are compared with that of the alumina pillared clay in Fig. 6. Zeolites NaX and 4A have very steep Langmuir type adsorption isotherms, while new microporous crystals such as silicalite and AlPO -S having no cations in the...

C. Although a trace amount of 1 (X=Me) was accidentally generated at the initial stage until the probe temperature had settled, its mole fraction was never increased throughout the observation over a period of 75 min. On the other hand, when the probe temperature was jumped to 25 °C, a steep increase in the mole fraction of 1 (X=Me) was observed. 

---