HF acid

Figure 11.4-2 shows process flows for an HF alkylation unit. The three sections are 1) reaction, 2). settling and 3) fractionation. In the reaction section isobutane feed is mixed with the olefin feed (usually propylene and butylene) in approximately a 10 or 15 to 1 ratio. In the presence of the HF acid catalyst the olefins react to form alkylate for gasoline blending. The exothermic reaction requires water cooling. The hydrocarbon/HF mixture goes to the settling... 

Precipitation of fluoride compounds from solutions of hydrofluoric acid, HF, is performed by the addition of certain soluble compounds to solutions containing niobium or tantalum. Initial solutions can be prepared by dissolving metals or oxides of tantalum or niobium in HF solution. Naturally, a higher concentration of HF leads to a higher dissolution rate, but it is recommended to use a commercial 40-48% HF acid. A 70% HF solution is also available, but it is usually heavily contaminated by H2SiF6 and other impurities, and the handling of such solutions is extremely dangerous. 

HF acid. The acidity (pH) of the solutions was modified by adding HF or NH4OH solutions. The minimums observed on the isotherms are related to the precipitation of complex oxyfluoroniobates of various compositions, namely (NH4)3NbOF6, (NH4)2NbOF5 and (NH4)5Nb3OF,8. 

Which materials are best for cell design depends essentially on the type of electrolyte used. Because HF acid is quite common in the electrochemistry of silicon, materials resistant to HF are preferable. Polyvinyl chloride (PVC), polypropylene (PP), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) can be used for the cell body. PVC is a good choice for most designs because it is inex-... 

This reaction is called displacement deposition, because the nickel ions in solution simply displace the silicon at the surface. The substrate. Si, acts here as a reducing agent, as discussed in Chapter 9. Copper may be deposited on Si from HF acid solutions (69). In the presence of HF, Si is oxidized into [SiF5] . 

Titanium foils were potentiostatically anodized at 25V in an electrolyte of pH 3.5 containing 0.4M ammonium nitrate NH4NO3 and 0.07M HF acid with reference to Fig. 5.26, Sample A was removed after 17 s of anodization, while Sample B was anodized for 240 s. Sample C was anodized for 6 h at 20V in an electrolyte of pH... 

TABLE 2-5. Comparison of Sulfuric Acid and Hydrofluoric (HF) Acid Alkylation Processes... 

Silicon Fluoride or Silicon Tetrafluoride. See in Vol 6, F146-R to F147-L, and G100-L under the history of NG manufacture where the use of SiF4 to separate the liq phases and recover the NG is Silicon Nitride. Si3N4 mw 140.31 grey-white amorph powd mp 1900 (sublimes) d 3.44g/cc. Sol in HF acid, Prepn is by reaction of powd Si and nitrogen in an electric furnace (Refs 1,37 ... 

These compds can be oxidized by peracetic acid to azoxy compds. They are easily reduced, first to hydrazo compds and then to two primary amines. Azocompds are unaffected by aqueous acids and alkalies. They are sol in coned HC1 or HF acids and compds can be obtd from these solns which contain the acid... 

Calculation of paleopressure and thus the success of this approach to determining paleoelevation depend upon our ability to accurately measure the size distribution of vesicles in hand samples of basalt (Fig. 4). In the course of our research, we have developed three techniques for measurement. The first involved injecting hand samples with plastic monomer which subsequently polymerized, and then dissolving away the basalt to leave a large number of plastic casts of vesicles for measurement and counting. The plastic casts were resistant to the effects of HF acid, so they reliably represented the actual vesicle sizes and shapes but were difficult to measure accurately and very tedious to work with (Sahagian et al. 1989). This was a laborious and inefficient technique that should be abandoned in favor of faster and more accurate methods. 

The prototype of a functional group with an appropriate breakable bond is the Wang resin 3, which contains a 4-hydroxybenzyl alcohol linker moiety. The benzyl alcohol hydroxyl group can be functionalized using either electrophilic or nucleophilic substrates (Scheme 6.1.1) to give a benzylic linkage. It is very stable in many reactions, but can be cleaved by acids such as trifluoroacetic acid or HF. Acids, alcohols, esters, and amides can be obtained as products after cleavage. 

Eastman, A., et al., Consider Online Monitoring of HF Acid When Optimizing Alkylation Operations, Hydrocarbon Processing (Aug. 2001). 

Positronium formation was also found in porous Si obtained by anodization of crystalline silicon in HF acid solutions. Itoh, Murakmi and Kinoshita [11] found a long-lived (>10 ns) component in the positron lifetime spectrum measured by conventional PALS. The authors investigated Ps behavior in porous Si at various temperatures by means of PALS with a monoenergetic pulsed positron beam [12],[13]. 

HF acidity-basicity (solute, molality) no Species in solution... 

It is obvious that this reaction is favored by binding the HF acid released during its course, i.e., in the presence of H and F ion acceptors. A weakly coordinating sterically hindered N,N-di(iso-propyl)ethyl amine and boron trifluoride etherate have been used as H+ ion acceptor and electrophilic agent to remove F ions, respectively. In addition, BF3 0(C2H5)2 has prevented the side fluoroboron caps elimination reaction (Scheme 8). 

Monocrystalline, macro- and mesoporous silicon were used for the electrochemical deposition of Pt. A 10 pm thick macroporous silicon layer was formed by anodizing of p-type Si wafers of 12 Ohm-cm resistivity in an aqueous solution of HF acid and DMSO (10 46 by volume parts) at the current density of 8 mA-cm [1]. Pore channels distributed with the surface density of 6T0 cm look like long straight holes with inlet diameters of 1.5 pm. An uniform 1 pm thick mesoporous silicon layer was fabricated by anodizing of n" -type Si wafers of 0.01 Ohm-cm resistivity in a solution of HF acid, water and isopropanol (1 3 1 by volume parts) at the current density of 60 mA-cm . The mesoporous silicon sample formed looks like Si layer perpendicularly pierced through by pore channels with diameter of about 20 nm. The number of pores per square centimetre is up to 2-10 [2]. 

Figure 2.10 Designs of (a) concentric glass nebuliser (Meinhard type) available showing enlarged fine bore tip to suit clear solutions and wide bore tip to suit solutions containing high salt content (b) PTFE nebuliser suitable for HF acids with fittings. (Reproduced with kind permission from E-POND S.A., C.P. 389, CH-1800 Vevey, Switzerland)...

Table 6.7 Microwave acid digestion conditions for HF acid digestion of anaerobic adhesives...

One of the key technical issues is to select suitable material as the substrate. Graphite and silicate glass are widely used because graphite is easily oxidised in air at 700°C and silicate glass can be etched away by HF acid. Sometimes Mo, Ta, W, SiC and Si3N4 are also employed due to their superior stiffness at elevated temperatures and inertness to reactant gases. 

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