Catalyst residues, removal

Description The process, with a combination of the most advanced high-yield and high-stereospecificity catalyst, is a nonsolvent, nondeash-ing process. It eliminates atactic polymers and catalyst residue removal. The process can produce various grades of PP with outstanding product quality. Polymer yields of 20,000 to 100,000 kg/kg of supported catalyst are obtained, and the total isotactic index of polymer can reach 98% to 99%. 

General Procedure for the Synthesis of the Quinoline Polymers. In a flame-dried 500-mL Schlenk flask under nitrogen are placed 27b and 5b, 1 mol% of (Ph3P)2PdCl2, 1 mol% of Cul, and piperidine (15mL). The reaction mixture was stirred for 48 h. For workup, chloroform (3 x 50 mL) was added. The solution was washed with water and NH4OH to remove the transition-metal-containing catalyst residues. Removal of solvent and addition of methanol (400 mL) precipitates the polymers, which are isolated by filtration and vacuum dried. 

TiCl catalysts produced by the reduction of TiCl with Al(C2H 2d> subsequentiy treated first with an electron donor (diisoamyl ether), then with TiCl, are highly stereospecific and four to five times more active than d-TiCl (6). These catalysts were a significant advance over the earlier TiCl systems, because removal of atactic polymer was no longer required. They are often referred to as second-generation catalysts. The life of many older slurry process faciUties has been extended by using these catalysts to produce "clean" polymers with very low catalyst residues. 

Gas-phase polymerization of propylene was pioneered by BASF, who developed the Novolen process which uses stirred-bed reactors (Fig. 8) (125). Unreacted monomer is condensed and recycled to the polymerizer, providing additional removal of the heat of reaction. As in the early Hquid-phase systems, post-reactor treatment of the polymer is required to remove catalyst residues (126). The high content of atactic polymer in the final product limits its usefiilness in many markets. 

In the 1970s, Solvay iatroduced an advanced TiCl catalyst with high activity and stereoregulahty (6). When this catalyst was utilized ia Hquid monomer processes, the level of atactic polymer was sufftciendy low so that its removal from the product was not required. Catalyst residues were also reduced so that simplified systems for post-reactor treatment were acceptable. Sumitomo has developed a Hquid monomer process, used by Exxon (United States), ia which polymer slurry is washed ia a countercurrent column with fresh monomer and alcohol to provide highly purified polymer (128). 

Montedison and Mitsui Petrochemical iatroduced MgCl2-supported high yield catalysts ia 1975 (7). These third-generation catalyst systems reduced the level of corrosive catalyst residues to the extent that neutralization or removal from the polymer was not required. Stereospecificity, however, was iasufficient to eliminate the requirement for removal of the atactic polymer fraction. These catalysts are used ia the Montedison high yield slurry process (Fig. 9), which demonstrates the process simplification achieved when the sections for polymer de-ashing and separation and purification of the hydrocarbon diluent and alcohol are eliminated (121). These catalysts have also been used ia retrofitted RexaH (El Paso) Hquid monomer processes, eliminating the de-ashing sections of the plant (Fig. 10) (129). 

The mixture is kept for 3 hours at 105°C after the oxide addition is complete. By this time, the pressure should become constant. The mixture is then cooled to 50°C and discharged into a nitrogen-filled botde. The catalyst is removed by absorbent (magnesium siUcate) treatment followed by filtration or solvent extraction with hexane. In the laboratory, solvent extraction is convenient and effective, since polyethers with a molecular weight above about 700 are insoluble in water. Equal volumes of polyether, water, and hexane are combined and shaken in a separatory funnel. The top layer (polyether and hexane) is stripped free of hexane and residual water. The hydroxyl number, water, unsaturation value, and residual catalyst are determined by standard titration methods. 

After epoxidation a distillation is performed to remove the propylene, propylene oxide, and a portion of the TBHP and TBA overhead. The bottoms of the distillation contains TBA, TBHP, some impurities such as formic and acetic acid, and the catalyst residue. Concentration of this catalyst residue for recycle or disposal is accompHshed by evaporation of the majority of the TBA and other organics (141,143,144), addition of various compounds to yield a metal precipitate that is filtered from the organics (145—148), or Hquid extraction with water (149). Low (<500 ppm) levels of soluble catalyst can be removed by adsorption on soHd magnesium siUcate (150). The recovered catalyst can be treated for recycle to the epoxidation reaction (151). 

The presence of catalyst residues, such as alkali hydroxide or alkali acetate, a by-product of the hydrolysis reaction, is known to decrease the thermal stability of poly(vinyl alcohol). Transforming these compounds into mote inert compounds and removal through washing are both methods that have been pursued. The use of mineral acids such as sulfuric acid (258), phosphoric acid (259), and OfXv o-phosphotic acid (260) has been reported as means for achieving increased thermal stability of the resulting poly(vinyl alcohol). 

Erom 1955—1975, the Ziegler-Natta catalyst (91), which is titanium trichloride used in combination with diethylaluminum chloride, was the catalyst system for propylene polymerization. However, its low activity, which is less than 1000 g polymer/g catalyst in most cases, and low selectivity (ca 90% to isotactic polymer) required polypropylene manufacturers to purify the reactor product by washing out spent catalyst residues and removing unwanted atactic polymer by solvent extraction. These operations added significantly to the cost of pre-1980 polypropylene. 

Catalyst residues, particularly vanadium and aluminum, have to be removed as soluble salts in a water-washing and decanting operation. Vanadium residues in the finished product are kept to a few ppm. If oil-extended EPDM is the product, a metered flow of oil is added at this point. In addition, antioxidant, typically of the hindered phenol type, is added at this point. 

B. Methyl indole-4-carboxylate (30). A mixture of 7.0 g (28 mmol) of methyl trans-2-[ -(dimethylamino)vinyl]-3-nitrobenzoate(29) in 140 mL of dry benzene which contained 1.4 g of 10% Pd/C was shaken in a Parr apparatus under Hj (50 psi) for 1.5 h. The catalyst was removed by filtration, and the benzene solution was washed with 30 mL of 5% aq. HCl, brine and dried over MgS04. After removal of the solvent under reduced pressure, the residue was purified via chromatography on silica gel to furnish 6.9 g (82%) of methyl indole-4-carboxylate (30). 

A solution of 76 g (S)-( + )-mandelic acid in 400 ml methanol and 5 ml acetic acid was reduced over 5% rhodium-on-alumina under 100 psig for 10 h. The catalyst was removed by filtration through Celite, and the methanol was removed in a rotary evaporator. The white, solid residue was dissolved in I 1 of hot diethyl ether and filtered while hot. After reduction of the volume to 400 ml, 250 ml cyclohexane was added. The remainder of the ether was removed, and the cyclohexane solution was stored for several hours in a refrigerator. The white crystals were filtered and dried in vacuo at 40 C the yield of (S)-( + )-hexahydromandelic acid was 71%. 

To a solution of 180 parts of -benzyl N-benzyloxycarbonyl-L-aspartvI-L-phenylalanine methyl ester in 3,000 parts by volume of 75% acetic acid is added 18 parts of palladium black metal catalyst, and the resulting mixture is shaken with hydrogen at atmospheric pressure and room temperature for about 12 hours. The catalyst is removed by filtration, and the solvent is distilled under reduced pressure to afford a solid residue, which is purified by re-crystallization from aqueous ethanol to yield L-aspartyl-L-phenylalanine methyl ester. It displays a double melting point at about 190°C and 245°-247°C. 

This Crude product (15.8 g) In water (360 ml) was added to a prehydrogenated suspension of 10% palladium on charcoal (4 g) in water (400 ml), and hydrogenation was continued for 30 minutes. The catalyst was removed and the filtrate was adjusted to pH 7.5 with sodium bicarbonate, then evaporated at low temperature and pressure. The residue was purified by chromatography on a column of cellulose powder, eluting first with butanol/ ethanol/water mixture and then with acetone/isopropanol/water. The main fraction was evaporated at low temperature and pressure to give a 32% yield of the sodium salt of a-carboxybenzylpenicillin as a white powder. The product was estimated by manometric assay with penicillinase to be 58% pure. 

A solution containing 741 g (5.0 mols) of 1-phenyl-2-propylidenylhydrazine, 300 g (5.0 mols) of glacial acetic acid and 900 cc of absolute ethanol was subjected to hydrogenation at 1,875 psi of hydrogen in the presence of 10 gof platinum oxide catalyst and at a temperature of 30°C to 50°C (variation due to exothermic reaction). The catalyst was removed by filtration and the solvent and acetic acid were distilled. The residue was taken up In water and made strongly alkaline by the addition of solid potassium hydroxide. The alkaline mixture was extracted with ether and the ether extracts dried with potassium carbonate. The product was collected by fractional distillation, BP B5°C (0.30 mm) yield 512 g (68%). 

The reaction takes place at low temperature (40-60 °C), without any solvent, in two (or more, up to four) well-mixed reactors in series. The pressure is sufficient to maintain the reactants in the liquid phase (no gas phase). Mixing and heat removal are ensured by an external circulation loop. The two components of the catalytic system are injected separately into this reaction loop with precise flow control. The residence time could be between 5 and 10 hours. At the output of the reaction section, the effluent containing the catalyst is chemically neutralized and the catalyst residue is separated from the products by aqueous washing. The catalyst components are not recycled. Unconverted olefin and inert hydrocarbons are separated from the octenes by distillation columns. The catalytic system is sensitive to impurities that can coordinate strongly to the nickel metal center or can react with the alkylaluminium derivative (polyunsaturated hydrocarbons and polar compounds such as water). 

Cut Out Separations. This can produce significant savings regardless of the stage of the process to which it is applied, provided efficiency of other parts of the process can be maintained. Avoidance of treatments to feedstocks and intermediates is clearly advantageous as is the removal of the need to clean up catalyst residues in high density polyethylene. 

In contrast to bulk polymerization, solution polymerization provided soluble polymers with high molecular weights using low FeCl3 concentration at 120-140 C.31 A major disadvantage of the above approaches is that all the metal-halide catalysts need to be removed, since the catalyst residue will deteriorate die thermal stability and electrical and other properties. 

Under argon, a mixture of 145 (0.046 mmol), 132 (0.046 mmol), Pd(PPli3)4 (0.2 (junol), Cul (0.2 [miol), and diisopropylamine (0.015 mmol) in THF (4 mL) was stirred in the dark at 50°C for 2 days. Ethynylbenzene (0.92 mmol) was then added and stirred at 50°C overnight. After concentration, die residue was dissolved in CHCI3 and filtered. The filtrate was subjected to preparative SEC with CHCI3 as eluent in order to remove catalyst residues and unreacted starting materials. Polymer 42 was obtained as a yellow solid in 85% yield. SEC analysis (THF, polystyrene standards) Mw = 280,000 (PDI = 6.5). 

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