Solid Alkalis

Solid alkalis might catalyse the cracking reactions of polymers as is the case with acidic catalysts. According to experimental work solid alkalis catalyse the degradation of polystyrene more efficiently than acidic catalysts [53]. This phenomenon could be explained by differences in the cracking mechanism of polymers. The main components in the oils obtained by solid acids were styrene monomer and dimer. Since cracking of hydrocarbons on solid acids has been explained in terms of P-scission of C-C bonds [19, 20], these were probably produced by P-scission of C-C bonds in the PS main chains as follows  

Gnlyurtulu and 1. Cabrita, Pyrolysis of plastic waste 2. Effect of catalyst on product yield. Journal of Analytical and Applied Pyrolysis, 51, 57-71 (1999). 

Miskolczi, L. Bartha, Gy Deak, B. lover and D. Kallo, Kinetic model of the chemical recycling of waste polyethylene into fuels. Process Safety and Environmental Protection, 82, 223-229 (2004). 

Masuda, H. Kuwahara, S. R Mukai and K. Hashimoto, Production of high quality gasoline from waste polyethylene derived heavy oil over Ni-REY catalyst in steam atmosphere. Chemical Engineering Science, 54, 2773-2779 (1999). 

Lee and D. -H. Shin, Investigation of catalytic degradation of high density polyethylene by hydrocarbon group type analysis. Journal of Analytical and Applied Pyrolysis, 70, 383-398 (2003). 

---

Semidry Scrubbers The advantage of semidry scrubbers is in that they remove contaminants by way of a solid waste that is easier to dispose of (less expensive). Initially, the scrubbing medium is wet (such as a lime or soda ash slurry). Then a spray dryer is used to atomize the slurry into the gas which evaporates the water in the droplets. As this takes place, the acid in the gas neutralizes the alkali material and forms a fine white solid. Most of the white solids are removed at the bottom of the scrubber while some are carried into the gas stream and have to be removed by a filter or electrostatic precipitator (discussed later). Although semidry systems cost 5-15% more than wet systems, when combined with a fabric filter, they can achieve 90-95% efficiencies. Dry scrubbers are sometimes used in a very similar fashion, but without the help of gas-liquid-solid mass transfer, these systems use much higher amounts of the solid alkali materials. 

Solid alkalis Solid alkalis may be used, in principle, for the corrosion control of drum boilers at all pressures but other factors, e.g. carryover or hideout a (reversible disappearance from solution on-load), may preclude them in some cases. However, they are used for feed-line treatment only in lower pressure plant where the boiler has increased tolerance to the higher solids burden which their use entails. Sodium hydroxide or, at very low pressures, sodium carbonate, (which is hydrolysed to the hydroxide at boiler temperatures) have been used, as have potassium and lithium hydroxides and various phosphate mixtures. (For a comparison of various alkalis for this purpose see References.)... 

Solid alkalis may hide-out in some boilers so that the operator has little choice but to apply all volatile treatment (AVT)... 

Consensus Solid alkali AVT With reheat Without reheat ... 

When impure, the material is unstable towards heat or light and decomposes to give an explosive residue. The pine material is more stable to light, but detonates on heating or in contact with solid alkalies [1], Preparation by action of oxygen on diallylzinc gives improved yields, but there is a risk of explosion. The peroxide is also impact-sensitive if sand is admixed [2],... 

Like the lower homologue ethyleneimine, it may polymerise explosively if exposed to acids or acidic fumes, so it must always be stored over solid alkali. 

Alkali-washed material, stabilised with 0.25% of pyrogallol, was distilled at 103°C/4 mbar until slight decomposition began. The heating mantle was then removed and the still-pot temperature had fallen below its maximum value of 135°C when the residue exploded violently [1], The presence of solid alkali [2] or 5% of phenolic inhibitor is recommended, together with low-temperature high-vacuum distillation, to avoid formation of acidic decomposition products, which catalyse rapid exothermic polymerisation. 

Cotton linters or wood pulp, usually in the form of sheets, is steeped in strong alkali (18-50%). The swollen sheets are then pressed to force out most of the excess alkali solution. This alkali cellulose is then shredded, and aged if low viscosity is desired. The aging process is the one followed in the viscose industry and is fully explained in any discussion of that process. More alkali may be introduced during the shredding, either as a concentrated solution or as solid alkali.18 The alkali... 

Some halo-substituted anilines are of limited thermal stability, tending to eliminate hydrogen halide which may catalyse further decomposition. To avoid decomposition during distillation, this should be conducted in the presence of solid alkali or magnesium oxide at minimum temperature (under relatively high vacuum) and/or with exclusion of air by inert gas. Individually indexed compounds are 4-Bromoaniline, 2296... 

Mochida, M., H. Akimoto, H. van den Bergh, and M. J. Rossi, Heterogeneous Kinetics of the Uptake of HOBr on Solid Alkali... 

A. A. Noyes 5 to the belief that the number of molecules in the soln. is not changed by the addition of more iodine because polyiodides are formed MI+mI2=MI2 +i. Y. Osaka showed that the rise of the f.p. which occurs when iodine is added to hydriodic acid or to aq. soln. of potassium iodide is proportional to the amount of iodine added, and is greater for hydriodic acid than for the potassium salt. Hence, the total concentration of the ions and of unionized molecules is decreased by the addition of iodine. A. A. Jakowkin inferred from the partition coeff. of iodine in dil. soln. that potassium tri-iodide was formed, and that with more cone. soln. still more complex polyiodides are produced. Still further, the change in the partition coeff. of iodine between aq. soln. of potassium iodide and nitrobenzene led H. M. Dawson and R. Gawler to infer that polyiodides as high as potassium ennea-iodide, KI9, are probably present in soln., although no such compound has been obtained in the solid state. H. L. Wells and H. L. Wheeler and others, however, have prepared several solid alkali polyiodides for example ... 

Table XX.-—Vapour Pressure of Solid Alkali Polyiodides (Iodine Unity).

When working with solid alkalies (the crushing of large lumps, the filling of desiccators with an alkali, the preparation of mixtures for fusion, etc.), wear eye protection. Handle the alkali only with a spatula, tong, or pincers. Carefully remove all surplus alkali from your workplace. Observe the same safety measures when w orking with phosphorous anhydride. 

Table 19 Vibrational Frequencies for Solid Alkali Hexafluorometallates...

Reduction of Alkali Dichromates. In industrial processes, solid alkali dichromates are reacted with reducing agents such as sulfur or carbon compounds. The reaction is strongly exothermic, and with sulfur proceeds as follows ... 

Twenty grams of powdered green chromic chloride are placed in a smaU rpund-bottomed flask and 60ml of freshly-distilled thionyl chloride are added. When evolution of gas has ceased, the mixture is refluxed for two hours, the excess liquid evaporated off in v and the product stored in a vacuum desiccator over pellets of solid alkali for at least ttheura. 

The moist precipitate thus obtained, after being suction-filtered and pressed down well, is carefully separated from the adhering filter paper by peeling the latter away cleanly and then stirred with 20ml of a 85% solution of sodium hydroxide (1 part solid alkali to 2 parts of water) until only... 

Twelve grams of stannous chloride 2-hydrate are dissolved in 76ml of 3Af hydrochloric add contained in a 250ml suction flask fitted with a stopper and gas delivery tube leading well under the surface of the solution. The flask and contents are immersed in an ice hath and chlorine is passed in (2-8 bubbles/sec) until oxidation is complete. This is indicated by a persistent yellow color in the reaction mixture due to excess chlorine. The chlorination will take 15 to 30 minutes at the above rate of introducing the gas. The solution of hexachlorostannic (IV) acid is now warmed to 50°C and a solution of 6g of ammonium chloride in 25ml of 3Af Hydrochloric add at the same temperature are mixed together. The warm solution is evaporated to crystallization on the steam bath, cooled, filtered by suction, and drained well. The complex salt is dried in vacua over solid alkali. The mother liquor is worked up for further batches of crystals. 

A solution of 7g of arsenic trioxide in 100ml of concentrated hydrochloric acid is mixed with a solution of 35g of potassium iodide in 35ml of water, After standing for 5 minutes tile orange precipitate of product Is filtered off, drained thoroughly, and dried in vacuo over solid alkali. The product is freed from adhering potassium chloride hy... 

A solution of 1.25 of silver nitrate in 25ml of distilled water is mixed with 10ml of pure pyridine, and the mixture is stirred into 15 of fresh potassium persulfate dissolved in 500ml of cold distilled water. The liquid immediately assumes an orange color the product soon begins to precipitate, and this is complete in about 30 minutes. After it is filtered, the orange material is washed with two 10ml portions of ice-cold water and then dried for an hour or two in vacuo over solid alkali. 

If the anhydrous (98-100%) ethylenediamine is not available, it may be prepared from the aqueous 70% product as follows One hundred grams of solid sodium hydroxide and 175ml of 70% ethylenediamine are heated in a flask with an air condenser on the steam bath overnight. (As the amine attacks corks and rubber stoppers readily, these should be covered with tin foil.) The two layers that form are separated after cooling and the upper one is heated again for several hours with 30g more of the solid alkali. When distilled, the yield of amine, boiling at 115-118°C, is almost quantitative. This method is also used to dehydrate propylenediamine b.p. 118-120° C. 

---