Hydrofluoric acid recovery

A fairly elaborate hydrofluoric acid recovery system is installed, adapted to batch operation. The concentration of hydrogen fluoride gas fed to the reactor is progressively increased as the reaction tends to slow down. The... 

A basic step in hydrofluoric acid manufacture is the reaction of sulfuric acid with fluorspar (calcium fluoride) to produce hydrogen fluoride and calcium sulfate. Spent alumina is also generated by the defluorination of some hydrofluoric acid alkylation products over alumina. It is disposed of or sent to the alumina supplier for recovery. Other solid residuals from hydrofluoric acid alkylation include any porous materials that may have come in contact with the hydrofluoric acid. 

Severe eye injuries from splashes may occur. In one case of eye burns from a fine spray of hydrofluoric acid in the face, considerable loss of epithelium occurred despite immediate and copious flushing with water and irrigation for 3 hours with a 0.5% solution of benzetho-nium chloride within 19 days, there was recovery of normal vision. ... 

Niobium pentafluoride is obtained as an intermediate during the recovery of niobium metal from its ores (See Niobium). It also can be prepared by direct fluorination of niobium metal at 250 to 300°C, either by fluorine gas or anhydrous hydrofluoric acid. The pentafluoride vapors are condensed in a pyrex or quartz tube from which it is sublimed at 120°C under vacuum and collected as colorless crystals. 

The ore thortveitite may be cracked by fusion with sodium carbonate or by heating with hydrofluoric acid. In a series of steps, scandium is precipitated as hydroxide or oxalate, which on thermal decomposition forms lower yield of oxide. This recovery, however, is tedious and is now obsolete. 

Ionic liquids are successfully being used as replacements for hydrofluoric acid for the commercial oil exploration application discussed previously (Chauvin and Helene, 1995). As we saw in the previous chapter, ionic liquids have potential as extractants in recovery of butyl alcohol from fermentation broth (Fadeev and Meagher, 2001). 

In specialty metal processing such as titanium, the metal is milled with a dilute hydrofluoric acid bath. The bath must be purged of the titanium laden waste acid and replenished with fresh acid periodically. As in the stainless steel case, the titanium waste acid can be neutralized with KOH to precipitate out the metals. The fluoride recovery is greatly dependent upon good pH end point control. If pH is monitored carefully, a greater than 90% fluoride recovery can be achieved. 

Dasher, J., and D. Goldstein. 1963. "Mixed Acid Pickling Waste-Recovery of Nitric and Hydrofluoric Acids." Metal Finishing May 60-63. 

Carlosena et al. [60] and Hirsch and Banin [61] have conducted studies on the speciation of cadmium in soil. Feng and Barrett [62] showed that microwave dissolution of soil and dust samples with nitric-hydrofluoric acid gave recoveries of cadmium (and lead) of over 90% for a 30-minute digestion. Various other workers [65-68] have reviewed methods for the determination of cadmium in soils. 

Adsorption experiments The method developed for the analysis of carbonaceous compounds formed and trapped within the zeolite micropores during catalytic reactions1581 can be adapted for determining the occupancy of micropores by reactant, solvent and product molecules. However, this method cannot be used with compounds sensitive to hydrolysis, such as AA, because of the step of dissolution of the zeolite in a hydrofluoric acid solution necessary for the complete recovery of the organic molecules located within the zeolite micropores.[58] This method was used to determine the composition of the organic compounds retained within the micropores of three different zeolites [H-BEA (zeolite Beta), H-FAU (zeolite Y), and H-MFI (zeolite ZSM-5)] after contact in a stirred batch reactor at 393 K for 4 min of a solution containing 20 mmol of 2-methoxynaphthalene (2-MN), 4 mmol of l-acetyl-2-methoxynaphthalene (1-AMN) and 1 ml of solvent (sulfolane or nitrobenzene) with 500 mg of activated zeolite.[59 61] From the comparison of... 

Tungsten. Both water-soluble and insoluble compounds are determined. Particulate tungsten on a filter is first extracted with water. One ml of 20% w/v sodium sulfate is added to the extract which is then dilute for analysis by rich nitrous oxide-acetylene flame at 255.1 nm. The filter is treated with 1 1 HC1 to remove iron and cobalt interferences before being nitric acid wet ashed and nitric/hydrofluoric acid wet ashed. The residue is heated with 0.5 N NaOH and treated as soluble tungsten. Tungsten carbide is determined at less than 100% recovery when cobalt is present. The detailed method for tungsten developed by Hull and Eller is in Volume Four of the NIOSH Manual of Analytical Methods to be published in Winter 1978. 

These systems are common in liquid extraction and also in a multiphase reactor with an organic and an aqueous phase. Common sources of pollution are incomplete separation and contamination due to trace organics in the aqueous phase. An example is in alkylation reactions (e.g., n-butane reaction with olefins to form isooctanes). Strong acids, such as sulfuric and hydrofluoric acids, are used as catalysts, and the recovery and the recycle of acid need to be optimized in order to reduce the waste generation. 

Both (IV) and (V) are stable in nonpolar solvents but not in acidic or basic solutions 127, 128). Similarly, the integrity of YCN is retained, but only in the structurally intact protein, in the absence of potential enzyme ligands (formic, acetic, or hydrofluoric acids). Such ligands promote a slow hydrolysis of YCN (Table VI) with a concomitant recovery of full enzymic activity 90). Furthermore, acid denaturation of the cyanylated enzyme at pH 2 is followed by complete hydrolysis of YCN (half-time 4 hr at pH 2, 25°) 90), and the formation of carbon dioxide, possibly via Eqs. (8) and (9) ... 

In view of the foregoing, it is not surprising that many attempts have been made by many companies almost from the start of alkylation to develop a recovery process unique to the used sulfuric acid alkylation catalyst. Most of the early attempts were not intensive and continuous. Most of the work is unpublished, since it was of a preliminary nature and not very successful. An added incentive was provided for the users and licensors of the Sulfuric Acid Alkylation Process when it was discovered that hydrofluoric acid was also a good alkylation... 

For the determination of antimony, the digestion efficiency of particulate matter, collected on Whatman 41 cellulose filters, was evaluated by means of radiotracer experiments [6], A quantitative recovery was obtained using 8 ml sulfuric acid and 4 ml hydrogen peroxide, when applied to a quarter fraction of the filter. For the dissolution of residual silicates 0.5 to 4 ml of hydrofluoric acid were added, which were later on evaporated. After digestion the solution was filtered if needed and diluted appropriately. 

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