Phosphoric acid, losses

The sulphate content of wet acid is generally 2-5% and phosphoric acid losses in the precipitated calcium sulphate (phosphogypsum) are sometimes 3-10%. Most of the fluorine is evolved from the process in gaseous form during acidulation of the rock and consequent evaporation, but some remains in the calcium sulphate and the acid product. Up to 50% of the Cd impurity originally present in the ore is believed to be removed by the calcium sulphate. 

Oh H-S, Cho Y, Lee WH et al (2013) Modification of electrodes using AI2O3 to reduce phosphoric acid loss and increase the performance of high-temperature proton exchange membrane fuel cells. J Mater Chem A 1 2578-2581... 

As for the modeling and simulation of phosphoric acid loss over time, only minor studies are currently available. Based on experimental... 

A nttmber of degradation mechanisms have been proposed for PBI-based MEAs, such as phosphoric acid loss from the membrane, faster catalyst dissolution in the hot acid meditrm, Pt catalyst sintering, thermal stress on fuel cell parts, thermal degradation of the catalyst support and carbon support corrosion. In particttlar, phosphoric acid loss has been specrrlated as a major degradation... 

Phosphoric acid Loss of ECSA, decrease of Evaporation,... 

Vitreous siUca is relatively inert to attack from most acids for temperatures up to 100°C. The weight loss data in acid solutions are summarized in Table 3. The main exceptions are phosphoric acid, which causes some corrosion above approximately 150°C, and hydrofluoric acid, which reacts readily at room temperature (91). This latter dissolution proceeds as follows ... 

For most environments quantitative studies have been reported describing the corrosion rate of various materials including a number of corrosion-resistant alloys (30). For example. Table 4 gives weight losses suffered by corrosion-resistant alloys in a solution of 28% phosphoric acid [7664-38-2] 20—22% sulfuric acid [7664-93-9] and 1—15% duoride (36). 

For commercial appHcation, catalyst activity is only one of the factors to be considered. Equally important is catalyst life, but Htde has been pubHshed on this aspect. Partly because of entrainment losses and partly through loss of acid as volatile triethyl phosphate, the catalyst loses activity unless compensating steps are taken. This decline in activity can be counteracted by the periodic or continuous addition of phosphoric acid to the catalyst during use, a fact that seems to have been disclosed as early as 1940 (94). A catalyst subjected periodically to acid addition could remain in service indefinitely, according to a report by Shell (91). A later Shell patent (85) states that complete reimpregnation with acid is required every 200 mn-days. 

Note The detection limit for aryl- and thioglucosides is 100 — 200 ng substance per chromatogram zone [2]. Reduction of the proportion of phosphoric acid in the reagent leads to loss of sensitivity [2]. 

No No Flow Excess ammonia in reactor. Release to work area. 1. Valve A fails closed. 2. Phosphoric acid supply exhausted. 3. Plug in pipe pipe ruptures. Automatic closure of valve B on loss of flow from phosphoric acid supply... 

The hydration reaction is carried out in a reactor at approximately 300°C and 70 atmospheres. The reaction is favored at relatively lower temperatures and higher pressures. Phosphoric acid on diatomaceous earth is the catalyst. To avoid catalyst losses, a water/ethylene mole ratio less than one is used. Conversion of ethylene is limited to 4-5% under these conditions, and unreacted ethylene is recycled. A high selectivity to ethanol is obtained (95-97%). 

Tests for quality of sealing of anodic coatings have become internationally standardised. They include dye spot tests with prior acid treatment of the surface (ISO 2143 1981 and BS 6161 Part 5 1982), measurement of admittance or impedance (ISO 2931 1983 and BS 6161 Part 6 1984), or measurement of weight loss after acid immersion (ISO 3210 1983 and BS 6161 Part 3 1984, and ISO 2932 1981 and BS 6161 Part 4 1981). Of these the chromic-phosphoric acid immersion test (ISO 3210) has become the generally accepted reference test. 

The relation between free phosphoric acid content and total phosphate content in a processing bath, whether based on iron, manganese or zinc, is very important this relation is generally referred to as the acid ratio. An excess of free acid will retard the dissociation of the primary and secondary phosphates and hinder the deposition of the tertiary phosphate coating sometimes excessive loss of metal takes place and the coating is loose and powdery. When the free acid content is too low, dissociation of phosphates (equations 15.2, 15.3 and 15.4) takes place in the solution as well as at the metal/solution interface and leads to precipitation of insoluble phosphates as sludge. The free acid content is usually determined by titrating with sodium... 

An alternative sequence utilized 2-oxazolidone, which was readily synthesized from urea and ethanolamine, as the glycine equivalent. Subsequent treatment with phosphorous acid and formaldehyde produced iV-phosphonomethyl-2-oxazolidone 12 (16). Upon hydrolysis, and loss of CO2,12 provided the related derivative, iV-phosphonomethylethanolamine 13, which was oxidized at high temperature with a variety of metal catalysts including cadmium oxide (16) or Raney copper (17) to give GLYH3, after acidification. A similar oxidation route has also been reported starting from iV-phosphonomethy 1-morpholine (18). 

One of the critical issues with regard to low temperamre fuel cells is the gradual loss of performance due to the degradation of the cathode catalyst layer under the harsh operating conditions, which mainly consist of two aspects electrochemical surface area (ECA) loss of the carbon-supported Pt nanoparticles and corrosion of the carbon support itself. Extensive studies of cathode catalyst layer degradation in phosphoric acid fuel cells (PAECs) have shown that ECA loss is mainly caused by three mechanisms ... 

Gruver GA, Pascoe RE, Kunz HR. 1980. Surface Area loss of platinum supported on carhon in phosphoric acid electrolyte. J Electrochem Soc 127 1219-1224. 

Degradation of poisoning phosphite [27] may lead to the formation of an aldehyde acid, as shown in Equation 2.8. The concentration of aldehyde acid and phosphorus or phosphoric acids should be monitored and controlled to minimize losses of the desired catalyst modifying ligand. 

Both 1st- and 2nd-order rate expressions gave statistically good fits for the control samples, while the treated samples were statistically best analyzed by 2nd-order kinetics. The rate constants, lst-order activation parameters, and char/residue yields for the untreated samples were related to cellulose crystallinity. In addition, AS+ values for the control samples suggested that the pyrolytic reaction proceeds through an ordered transition state. The mass loss rates and activation parameters for the phosphoric acid-treated samples implied that the mass loss mechanism was different from that for the control untreated samples. The higher rates of mass loss and... 

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