Slurry processing

Hercules slurry process Hercules viscometer Hercymte... 

Hoechst slurry process Hoeppler viscometer Hoffman degradation Hoffman eliminations Hofmann degradation... 

Phillips PPS process Phillips process Phillips slurry process... 

Fig. 11. Dorr-Ohver type slurry process for manufacture of granular triple superphosphate. Courtesy of TVA.

When pure needle-like crystals of -aminobenzoyl chloride are polymerized in a high temperature, nonsolvent process, or alow temperature, slurry process, polymer is obtained which maintains the needle-like appearance of monomer. PBA of inherent viscosity, 4.1 dL/g, has been obtained in a hexane slurry with pyridine as the acid acceptor. Therefore PBA of fiber-forming molecular weight can be prepared in the soHd state. 

In the case of refractory metals, coatings generaHy are sHicides, appHed by pack cementation or slurry processes. Typical sHicide compositions are... 

An unusual slurry process which works well with sodium hydroxide is based on diffusion of the aqueous reagent into pellets of acid polymer (28). The concentration of ions in the Hquid phase is preferably two to four times the stoichiometric level, and the temperature is maintained at 50—100°C. 

Slurry (Suspension) Polymerization. This polymerization technology is the oldest used for HDPE production and is widely employed because of process engineering refinement and flexibHity. In a slurry process, catalyst and polymer particles are suspended in an inert solvent, ie, a light or a... 

Some slurry processes use continuous stirred tank reactors and relatively heavy solvents (57) these ate employed by such companies as Hoechst, Montedison, Mitsubishi, Dow, and Nissan. In the Hoechst process (Eig. 4), hexane is used as the diluent. Reactors usually operate at 80—90°C and a total pressure of 1—3 MPa (10—30 psi). The solvent, ethylene, catalyst components, and hydrogen are all continuously fed into the reactor. The residence time of catalyst particles in the reactor is two to three hours. The polymer slurry may be transferred into a smaller reactor for post-polymerization. In most cases, molecular weight of polymer is controlled by the addition of hydrogen to both reactors. After the slurry exits the second reactor, the total charge is separated by a centrifuge into a Hquid stream and soHd polymer. The solvent is then steam-stripped from wet polymer, purified, and returned to the main reactor the wet polymer is dried and pelletized. Variations of this process are widely used throughout the world. 

One of the most efficient implementations of the slurry process was developed by Phillips Petroleum Company in 1961 (Eig. 5). Nearly one-third of all HDPE produced in the 1990s is by this process. The reactor consists of a folded loop with four long (- 50 m) vertical mns of a pipe (0.5—1.0 m dia) coimected by short horizontal lengths (around 5 m) (58—60). The entire length of the loop is jacketed for cooling. A slurry of HDPE and catalyst particles in a light solvent (isobutane or isopentane) circulates by a pump at a velocity of 5—12 m/s. This rapid circulation ensures a turbulent flow, removes the heat of polymeriza tion, and prevents polymer deposition on the reactor walls. 

Phillips Petroleum Company developed an efficient slurry process used for the production of both HDPE and LLDPE (Eig. 6). The reactor is built as a large folder loop containing long mns of pipe from 0.5 to 1 m ia diameter coimected by short horizontal stretches of pipe. The reactor is filled with a light solvent (usually isobutane) which circulates through the loop at high speed. A mixed stream containing ethylene and comonomers (1-butene,... 

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. 

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). 

Polymerization Processes. Isotactic PB and PMP are produced commercially in slurry processes in Hquid monomers or monomer mixtures (optionally diluted with light inert hydrocarbons) at 50—70°C. The first commercial process for PB production used a highly isospecific... 

Most commercial processes produce polypropylene by a Hquid-phase slurry process. Hexane or heptane are the most commonly used diluents. However, there are a few examples in which Hquid propylene is used as the diluent. The leading companies involved in propylene processes are Amoco Chemicals (Standard OH, Indiana), El Paso (formerly Dart Industries), Exxon Chemical, Hercules, Hoechst, ICl, Mitsubishi Chemical Industries, Mitsubishi Petrochemical, Mitsui Petrochemical, Mitsui Toatsu, Montedison, Phillips Petroleum, SheU, Solvay, and Sumimoto Chemical. Eastman Kodak has developed and commercialized a Hquid-phase solution process. BASE has developed and commercialized a gas-phase process, and Amoco has developed a vapor-phase polymerization process that has been in commercial operation since early 1980. 

The slurry process requires less coating component. The latter is suspended in a vehicle, eg, lacquer or water, and is painted onto the substrate. The coated part is heated in an alumina retort containing a layer of activator at the bottom. The coating component forms a haHde and is deposited onto and diffused into the substrate. Slurry processes can be either activated or nonactivated. In the latter case, development of the coating reHes purely on diffusion without the possible benefits of vapor deposition. 

In the slurry process, the hydrolysis is accompHshed using two stirred-tank reactors in series (266). Solutions of poly(vinyl acetate) and catalyst are continuously added to the first reactor, where 90% of the conversion occur, and then transferred to the second reactor to reach hiU conversion. Alkyl acetate and alcohols are continuously distilled off in order to drive the equiUbrium of the reaction. The resulting poly(vinyl alcohol) particles tend to be very fine, resulting in a dusty product. The process has been modified to yield a less dusty product through process changes (267,268) and the use of additives (269). Partially hydroly2ed products having a narrow hydrolysis distribution cannot be prepared by this method. 

Forming additives or processing aids (2,33—37) are commonly used to render ceramic powders more processible. Binders and plasticizers (qv) are typically added to improve or aid dry powder and plastic forming, whereas deflocculants, surfactants (qv), and antifoams are commonly used in slurry processing. 

Liquids. Liquids (33) are common forming additives in plastic, paste, and slurry processing. In plastic forming operations, the Hquid aids forming and serves as the binder/plasticizer for the system. In pastes and slurries, other additives are also dissolved or dispersed in the Hquid/solvent. Water is a good, inexpensive solvent that can be recycled. Organic Hquids such as alcohols are used to process water-sensitive materials and to dissolve water-insoluble forming additives, however, at considerably more expense. 

Epichlorohydrin Elastomers without AGE. Polymerization on a commercial scale is done as either a solution or slurry process at 40—130°C in an aromatic, ahphatic, or ether solvent. Typical solvents are toluene, benzene, heptane, and diethyl ether. Trialkylaluniinum-water and triaLkylaluminum—water—acetylacetone catalysts are employed. A cationic, coordination mechanism is proposed for chain propagation. The product is isolated by steam coagulation. Polymerization is done as a continuous process in which the solvent, catalyst, and monomer are fed to a back-mixed reactor. Pinal product composition of ECH—EO is determined by careful control of the unreacted, or background, monomer in the reactor. In the manufacture of copolymers, the relative reactivity ratios must be considered. The reactivity ratio of EO to ECH has been estimated to be approximately 7 (35—37). 

The regulator is hmited to operating on processes with clean, non-slurry process fluids. The small orifice and valve assembhes contained in the regulator can plug and malfunc tion if the process fluid that operates the regulator is not sufficiently clean. 

If the dissolving of a portion of the polymer takes place, diffusional restriction may occur as a result. Such a case was observed in (98) where a decrease of the polymerization rate (slurry process in cyclohexane) with temperature rise from 75° to 90°C was found despite the increase in the number of propagation centers. At a further increase of the polymerization temperature (>115°C) polymerization becomes a solution process that may also proceed with no diffusional restrictions (94). 

The kinetics of ethylene polymerization at temperatures below 90°C (the slurry process) were studied in Bukatov el al. (157, 159). The steady-state polymerization rate was observed the first order in the polymerize tion rate with respect to ethylene and the catalyst concentration was found. The polymerization rate increased on increasing the polymerization temperature from 20° to 80°C (Eeu = 7.5 0.5 kcal/mole). 

Rogers, Pilot Plant Preparation of PBXN-1 By The Stoddard Solvent Slurry Process , NAVORD 5799 (1958). 26) Anon, Thermal And Stability Properties of LASL PBX 9404 , Mason Hanger — Silas Mason Co, Inc, Iowa, nugieS nept a yiyjoj t) n.a. d am bl m,... 

Slurry processes, in which a finely divided catalyst is suspended in a liquid medium which is cooled either by means of heat-transfer surfaces in the reactor or by recirculation of the liquid through external heat exchangers, have been under investigation for this purpose in Germany, the United States, and the United Kingdom (C12, F3, HI, K5, K7, K8, K12). 

In a later publication, Kolbel et al. (K16) have proposed a less empirical model based on the assumption that the rate-determining steps for a slurry process are the catalytic reaction and the mass transfer across the gas-liquid interface. When used for the hydrogenation of carbon monoxide to methane, the process rate is expressed as moles carbon monoxide consumed per hour and per cubic meter of slurry ... 

Gas phase olefin polymerizations are becoming important as manufacturing processes for high density polyethylene (HOPE) and polypropylene (PP). An understanding of the kinetics of these gas-powder polymerization reactions using a highly active TiCi s catalyst is vital to the careful operation of these processes. Well-proven models for both the hexane slurry process and the bulk process have been published. This article describes an extension of these models to gas phase polymerization in semibatch and continuous backmix reactors. 

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