Fill time synthesis

The FTS was conducted at varying temperatures (from 483 to 513 K) over approximately 50 h of reaction time in order to investigate the reaction kinetics achieved with the respective catalysts. A typical conversion curve using the Co/ HB catalyst as an example is shown in Figure 2.3. After a short settling phase (caused by the pore filling of liquid Fischer-Tropsch products) of only about 4 h, steady-state conditions were reached. In the observed synthesis period of 50 h no deactivation of the catalysts was detected. However, industrially relevant experiments over several weeks are still outstanding. 

The filled ampules are evacuated to a pressure of < 10 3 torr. As described for the synthesis of TiBr3 (previous section) the lower part of the ampule is cooled while sealing quickly with a very hot flame. The sealed ampule is placed in a slightly inclined ( 15 °C) furnace and heated at a rate of 100°Ch-1 to the reaction temperature (Table I). After the reaction time listed in Table I the heating power is switched off, and the system is left to cool down to room temperature. 

N2 adsorption-desorption isotherms and pore size distribution of sample II-IV are shown in Fig. 4. Its isotherm in Fig. 4a corresponds to a reversible type IV isotherm which is typical for mesoporous solids. Two definite steps occur at p/po = 0.18, and 0.3, which indicates the filling of the bimodal mesopores. Using the BJH procedure with the desorption isotherm, the pore diameter in Fig. 4a is approximately 1.74, and 2.5 nm. Furthermore, with the increasing of synthesis time, the isotherm in Fig. 4c presents the silicalite-1 material related to a reversible type I isotherm and mesoporous solids related to type IV isotherm, simultaneously. These isotherms reveals the gradual transition from type IV to type I. In addition, with the increase of microwave irradiation time, Fig. 4c shows a hysteresis loop indicating a partial disintegration of the mesopore structure. These results seem to show a gradual transformation... 

The word amphibolic is often applied to those metabolic sequences that are part of a catabolic cycle and at the same time are involved in a biosynthetic (anabolic) pathway. Another term, anaplerotic, is sometimes used to describe pathways for the synthesis of regenerating substrates. This word, which was suggested by H. L. Komberg, comes from a Greek root meaning "filling up."80... 

Since eukaryotic chromosomes are linear, the ends of these chromosomes require a special solution to ensure complete replication. This can be seen in figure 26.26. At the very end of a linear duplex a primer is necessary to initiate DNA replication. After RNA primer removal there is bound to be a gap at the 5 end of the newly synthesized DNA chains. Since DNA synthesis always requires a primer the usual way of filling this gap is not going to solve the problem. This dilemma is overcome by a special structure at the ends (telomeres) of eukaryotic chromosomes and a special type of reverse transcriptase (telomerase) that synthesizes telomeric DNA. In many eukaryotes the telomeres contain short sequences (frequently hexamers) that are tan-demly repeated many times. Telomerase contains an RNA that binds to the 3 ends and also serves as a template for the extension of these ends. Prior to replication, the 3 ends of the chromosome are extended with additional tandemly repeated hexamers. The 3 ends are extended sufficiently so that there is room to accommodate an RNA primer. In this way there is no net loss of DNA from the 5 ends as a result of replication. After replication the 3 end is somewhat... 

Fig. 6.13 (a) Relation between whole-body glycogen and time redrawn from [93]. The glycogen synthesis rate declines exponentially as the stores are filled up. (b) Relation demonstrating the exponentially decline in glycogen storage rate as the glycogen stores are filled up, for different half times, Ty2. 

Hydrocarbon distributions in the Fischer-Tropsch (FT) synthesis on Ru, Co, and Fe catalysts often do not obey simple Flory kinetics. Flory plots are curved and the chain growth parameter a increases with increasing carbon number until it reaches an asymptotic value. a-Olefin/n-paraffin ratios on all three types of catalysts decrease asymptotically to zero as carbon number increases. These data are consistent with diffusion-enhanced readsorption of a-olefins within catalyst particles. Diffusion limitations within liquid-filled catalyst particles slow down the removal of a-olefins. This increases the residence time and the fugacity of a-olefins within catalyst pores, enhances their probability of readsorption and chain initiation, and leads to the formation of heavier and more paraffinic products. Structural catalyst properties, such as pellet size, porosity, and site density, and the kinetics of readsorption, chain termination and growth, determine the extent of a-olefin readsorption within catalyst particles and control FT selectivity. 

Sample Al203/Si02 (gel) Synthesis time, (h) Solid phase (%crystal.) Composition Al Na b b per unit h2o c cell HM++ d a SiOR e Pore filling (%) f... 

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