Slurry loop reactor process

Polymerizations that use supported chromium (Phillips) catalysts are conducted predominantly in slurry processes (though a small portion employs the gas phase process, see below). The historical development of the Phillips process has been expertly reviewed by Hogan (5, 6) and McDaniel (7-9). The slurry process originally developed by Phillips Petroleum (now Chevron Phillips) has been called the "particle form loop slurry process" and the "slurry loop reactor process" for production of HDPE and LLDPE (10). Hexene-1 is most often used as comonomer for LLDPE in the Phillips process. A simplified process flow diagram for the Phillips loop-slurry reactor process is shown in Figure 7.3 and key operating features are summarized in Table 7.4. 

Two modifications of the duidized-bed reactor technology have been developed. In the first, two gas-phase duidized-bed reactors coimected to one another have been used by Mobil Chemical Co. and Union Carbide to manufacture HDPE resins with broad MWD (74,75). In the second development, a combination of two different reactor types, a small slurry loop reactor followed by one or two gas-phase duidized-bed reactors (Sphetilene process), was used by Montedision to accommodate a Ziegler catalyst with a special particle morphology (76,77). This catalyst is able to produce PE resins in the form of dense spheres with a diameter of up to 4—5 mm such resins are ready for shipping without pelletization. 

The loops are pipes of 10- to 20-inch diameters, about 50 feet high, with a total length of 250—300 feet. They hold about 600 cubic feet of slurry and are water-jacketed to control the heat. The reaction temperature in the process is less than 212°F, with pressures of only a couple of hundred pounds, so the process is more economical (energy saving) than the others already discussed. After the slurry is withdrawn from the loop reactor, processing is the same as that downstream of the reactor in Figure 23—2. This process needs only small amounts of catalyst so catalyst separation from the... 

The primary product in the slurry units is HDPE with MDPE as a secondary product. With single-site catalysts production of mLLDPE in slurry loop reactors is also possible. Today for example, Chevron Phillips, BP Solvay, Basell, Borealis and Sumitomo Mitsui have their own slurry process technology-... 

The development of the Borstar PE process, by Borealis, is a relatively recent development in multi-reactor processes. The foundation of this process is the utilization of supercritical propane as diluent in the slurry loop reactor.438 Operating the slurry loop in a supercritical condition provides several advantages over the tradition diluent (isobutane). The solubility of PE drops markedly at the supercritical point of propane, allowing the process to operate... 

Process description The INNOVENE S process utilizes a proprietary vertical slurry-loop reactor, as shown in the flow diagram. Two reactors are used for bimodal capability. Isobutane is normally used as the hydrocarbon diluent in the process, although hexane may be used as an alternative. The diluent is used as a catalyst carrier and as the polymerization reactor suspension and heat transfer medium. Hexene-1 and/or butene-1 can be used as a comonomer. Hydrogen is used for molecular weight control when using the Zieglerg catalyst platform. Titanium-based and chromium-based catalysts are both used. 

A control technique based on high-frequency pressure measurements was developed and implemented to avoid hydrodynamic instabilities in continuous olefin slurry-loop reactors [ 186]. The obtained high-frequency pressure patterns are compared to typical process responses and then used to classify the status of the plant operation. The idea is that pressure fluctuations that do not follow the standard pattern indicate some sort of process instabiUty. When hydrodynamic instabilities are detected, monomer flow rates and/or reactor temperatures are manipulated to reduce the polymer density and the reaction rates and reduce the risks of plant shutdown. Similar procedures can be used for detection and correction of abnormal plant operation in suspension [ 187] and emulsion [188] polymerizations with the help of Raman and near infrared spectroscopy techniques. 

In addition to the general type of slurry loop process described above, slightly different loop reactor processes also exist. A short summary of two of these processes is shown below. 

The process, set up with a loop reactor part and a gas phase reactor part, is similar to corresponding single reactor processes. The catalyst is mixed with propane diluent and fed into a pre-polymerisation reactor. Cocatalyst, ethylene, comonomer and hydrogen are also fed into this reactor. The pre-polymerised slurry, together with the main feeds, is then fed into the slurry loop reactor, designed for supercritical conditions and typically operated at 85 - 100 C and 5.5 - 6.5 MPa. This reactor produces a low molecular weight, high density product. The reactor content is sent to a flash tank where diluent and unreacted components are separated from the polymer produced in the loop reactor. The diluent is condensed and recycled back into the loop reactor. 

Chevron Phillips Chemical Co., LP LPE process from Phillips Petroleum Co., isobutane slurry, loop reactor, very high activity proprietary catalysts comonomers butene-1 hexene-1, 1,4 methyl-1 pentene, and octene-1, no waxes and other by-products, minimum environmental emissions 82 reactor lines, 34% of worldwide capacity slurry-loop reactor. LPE homo- and co-polymers (density 920-970 kg/m ) for films, blow moulding, injection moulding, rotomoulding, pipes, sheets and thermoforming, and wire and cables. 

Polymerization in Hquid monomer was pioneered by RexaH Dmg and Chemical and Phillips Petroleum (United States). In the RexaH process, Hquid propylene is polymerized in a stirred reactor to form a polymer slurry. This suspension is transferred to a cyclone to separate the polymer from gaseous monomer under atmospheric pressure. The gaseous monomer is then compressed, condensed, and recycled to the polymerizer (123). In the Phillips process, polymerization occurs in loop reactors, increasing the ratio of available heat-transfer surface to reactor volume (124). In both of these processes, high catalyst residues necessitate post-reactor treatment of the polymer. 

Slurry phase (or suspension) process. The uniquedooldng equipment in Figure 23—5 is a loop reactor. This process also takes place in a solvent (in this case, normal hexane, isobutane, or isopentane) so that the mixture can be pumped continuously in a loop while the polymerization is taking place. Feeds (the solvent, comonomer if any, ethylene and Ziegler-Natta catalyst) are pumped into the loop and circulated. Polymerization rakes place continuously at temperatures below the melting point of the polyethylene allowing solid polymer particles to form enough to form slurry. The reaction takes place at 185—212°F and 75—150 psi. A slurry of HOPE in hexane is drawn off continuously or intermittently. 

Ever since W. Normann in the beginning of the century invented his process for hydrogenation of fats and oils, it has mainly been performed in the original way, i.e. in a batch reactor where the oil, hydrogen and the catalyst as a slurry are mixed intensively. Alternatively, the loop reactor by Buss AG and some continuous systems have been in operation. 

Borealis A/S Polyethylene Ethylene, butene Slurry-loop process uses supercritical propane and a series gas-phase reactor produce tailor-made MW, enhanced LLDPEs, MDPEs, HDPEs 4 2000... 

Phillips Par tide-forming process (Figure 5) In a double-loop reactor, constructed from wide-bore jaeketed pipe, the catalyst and growing polymer particles are suspended in a slurry and kept in rapid circulation to avoid polymer deposits on the reaetor walls. Due to its high surface-to-volume ratio, this reactor facilitates heat removal and allows short residence times. Typical reaction conditions are 100°C and 30-40 bar. Isobutane, a poor solvent for polyethylene, is used as a diluent and as a vehicle to introduce the catalyst into the reactor. The solid polymer is collected from a sedimentation leg and passed to a flash tank where the monomer and isobutane diluent are separated by evaporation and subsequently recondensed and recycled, while the polymer powder is fed into an extruder and formed into pellets. 

Slurry processes in hydrocarbon diluent are used in the production of HDPE, including bimodal polymers produced in the cascade process in which different hydrogen concentrations are applied in two or more reactors in series. Liquid loop reactors are generally used with a light hydrocarbon diluent such as isobutane, whereas heavier hydrocarbon diluents are typically used in continuous stirred tank reactors. 

In PP manufacture, modern bulk (liquid monomer) and gas-phase processes have largely replaced the earlier slurry processes in which polymerization was carried out in hydrocarbon diluent. The most widely adopted process for PP is Basell s Spheripol process.317 Homopolymer production involves a pre-polymerization step at relatively low temperature, followed by polymerization in a loop reactor using liquid propylene random co-polymers are produced by introducing small quantities of ethylene into the feed. The pre-polymerization step gives a pre-polymer particle with the capacity to withstand the reaction peak, which occurs on entering the main loop reactor. The addition of one or two gas-phase reactors for EP co-polymerization makes it possible to produce heterophasic co-polymers containing up to 40% of E/P rubber within the homopolymer matrix. 

One of the most common hydrogenation processes is the batch process in liquide phase with a slurry catalyst in a stirred tank reactor (STR) or in a loop reactor as Buss Loop for example. 

This process is also carried out in liquid phase with slurry catalyst in STR or loop reactors. It favours hydrodehalogenation and absolutely needs an adapted and selective catalyst. It decreases heavy products and especially suppresses HF formation coming from nucleophilic substitution on the aromatic fluorine atom. 

Stripped for solvent removal. The later Phillips "particle form" process is a slurry process in which the polymer precipitates as it forms. This process uses a circulating-loop reactor. Because of improved catalyst use efficiency, catalyst removal from the polymer is unnecessary. 

Linear polyethylenes are produced in solution, slurry, and increasingly, gas-phase low-pressure processes. The Phillips process developed during the mid 1950s used supported chromium trioxide catalysts in a continuous slurry process (or particle-form process) carried out in loop reactors. Earlier, Standard Oil of Indiana patented a process using a supported molybdenum oxide catalyst. The polyethylenes made by both these processes are HDPE with densities of 0.950-0.965 g/cm and they are linear with very few side-chain branches and have a high degree of crystallinity. 

The Phillips catalyst is mostly applied in ethylene slurry polymerization using loop reactors. It is also now being commercially used in gas phase ethylene polymerization processes. However, it is very difficult to find reports about ethylene gas phase polymerization using Phillips catalysts in the literature because it is a great challenge to perform gas phase polymerization on a laboratory scale. Recently, we carried out gas phase ethylene polymerization over sUica-supported... 

Loop reactors combine the thermal characteristics of the tubular reactors with the residence time distribution of the CSTRs. HDPE and i-PP are produced in loop reactors using coordination catalysts by means of slurry polymerization [22]. HDPE uses isobutane as continuous phase (Chevron-PhilKps process) and i-PP uses the monomer as continuous phase (Spheripol process). 

HIPP presents a complexmorphology consisting of an ethylene-propylene soft copolymer finely dispersed within a semi-crystalline i-PP. In the Spheripol process [22], this material is produced in two steps. In the first one, i-PP is produced in a slurry of propylene in a loop reactor. In the second one, the ethylene-propylene copolymer is produced in a gas phase reactor. The broad residence time distribution of both the loop reactor and the gas phase reactor leads to an uneven distribution of the ethylene-propylene copolymer among the polymer particles, when single reactors are used in each step. A more even distribution is obtained using two loop reactors in the first step [36,37]. 

The overall conversion in the loop polymerization reactor is very high for a polyolefin manufacturing process, and the conversion per pass is limited by the amount of monomer that is needed to carry the polymer out of the reactor. It is desirable to operate the reactor at as high a slurry density as possible to get the highest throughput and the highest conversion. Typically, loop reactors operate at slurry concentrations of about 45-50 wt% polymer. 

Slurry process with horizontal loop reactors... 

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