Catalyst steam stripping

FIGURE 7.9 Catalyst steam stripping—an annual stripper configuration. (Reprinted from Jack Wilcox, R., Published in Petroleum Technology Quarterly, Troubleshooting Complex FCCU Issues, http //www.ePTQ.com, Q3, 2009. With permission.)... 

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. 

The reaction is completed after 6—8 h at 95°C volatiles, water, and some free phenol are removed by vacuum stripping up to 140—170°C. For resins requiring phenol in only trace amounts, such as epoxy hardeners, steam distillation or steam stripping may be used. Both water and free phenol affect the cure and final resin properties, which are monitored in routine quaHty control testing by gc. OxaHc acid (1—2 parts per 100 parts phenol) does not require neutralization because it decomposes to CO, CO2, and water furthermore, it produces milder reactions and low color. Sulfuric and sulfonic acids are strong catalysts and require neutralization with lime 0.1 parts of sulfuric acid per 100 parts of phenol are used. A continuous process for novolak resin production has been described (31,32). An alternative process for making novolaks without acid catalysis has also been reported (33), which uses a... 

Process water streams from vinyl chloride manufacture are typically steam-stripped to remove volatile organics, neutralized, and then treated in an activated sludge system to remove any nonvolatile organics. If fluidized-bed oxychlorination is used, the process wastewater may also contain suspended catalyst fines and dissolved metals. The former can easily be removed by sedimentation, and the latter by precipitation. Depending on the specific catalyst formulation and outfall limitations, tertiary treatment may be needed to reduce dissolved metals to acceptable levels. 

Emulsion Polymerization. In this method, polymerization is initiated by a water-soluble catalyst, eg, a persulfate or a redox system, within the micelles formed by an emulsifying agent (11). The choice of the emulsifier is important because acrylates are readily hydrolyzed under basic conditions (11). As a consequence, the commonly used salts of fatty acids (soaps) are preferably substituted by salts of long-chain sulfonic acids, since they operate well under neutral and acid conditions (12). After polymerization is complete the excess monomer is steam-stripped, and the polymer is coagulated with a salt solution the cmmbs are washed, dried, and finally baled. 

Fluidized-bed catalytic cracking units (FCCUs) are the most common catalytic cracking units. In the fluidized-bed process, oil and oil vapor preheated to 500 to SOOT is contacted with hot catalyst at about 1,300°F either in the reactor itself or in the feed line (called the riser) to the reactor. The catalyst is in a fine, granular form which, when mixed with the vapor, has many of the properties of a fluid. The fluidized catalyst and the reacted hydrocarbon vapor separate mechanically in the reactor and any oil remaining on the catalyst is removed by steam stripping. 

The spent catalyst is withdrawn from the bottom of the reactor and stripped with steam to vaporize the hydrocarbons remaining on the surface. Stripping also removes most of the hydrocarbon vapors which are entrained between the particles of catalyst. Without stripping, hydrocarbon products would be carried to the regenerator and needlessly burned consuming much of the regeneration air, and decreasing yield of useful products. 

As the spent catalyst falls into the stripper, hydrocarbons are adsorbed on the catalyst surface, hydrocarbon vapors fill the catalyst pores, and the vapors entrained with the catalyst also fall into the stripper. Stripping steam, at a rate of 2 to 5 lbs per 1,000 lbs (2 kg to 5 kg per 1,000 kg,) is primarily used to remove the entrained hydrocarbons between catalyst particles. Stripping steam does not address hydrocarbon desorption and hydrocarbons filling the catalyst pores. However, reactions continue to occur in the stripper. These reactions are... 

Catalyst flux Stripping steam rate Stripping steam superficial velocity Catalyst residence time Steam quality 500-700 Ib/min/ft" (40 to 55 kg/sec/m ) 2-5 lb/1,000 lb of circulating catalyst 0.5-0.75 ft/sec (.15-.25 m/sec) 1-2 minutes Superheated 100°F (55°C)... 

Steam stability, of dehydrogenation catalysts, 23 336 Steam stripping... 

Pilot plant tests were made in a cyclic fixed fluidized bed unit over a range of conditions. Catalyst-to-oil ratio was varied from 3 to 5 and WHSV was varied from 32 to 53, inversely. The reactor temperature was held at 975°F for the cracking and steam stripping cycles, and at 1200°F for the regeneration cycles. After regeneration, carbon on catalyst was effectively zero. 

The larger amounts of coke on the catalyst can be handled by more effective steam stripping, regeneration with heat removal, or using a two-step regenerator. Improved temperature tolerance of the catalyst and of the construction materials in the regenerator also contributes to the handling of the coke problem. 

In a typical fluid catalytic cracker, catalyst particles are continuously circulated from one portion of the operation to another. Figure 9 shows a schematic flow diagram of a typical unit W. Hot gas oil feed (500 -700°F) is mixed with 1250 F catalyst at the base of the riser in which the oil and catalyst residence times (from a few seconds to 1 min.) and the ratio of catalyst to the amount of oil is controlled to obtain the desired level of conversion for the product slate demand. The products are then removed from the separator while the catalyst drops back into the stripper. In the stripper adsorbed liquid hydrocarbons are steam stripped from the catalyst particles before the catalyst particles are transferred to the regenerator. 

During the cracking process, carbon deposits or coke build up on the spent catalyst particles. These deposits can deactivate the catalyst performance and must be removed. This is typically accomplished in two stages. First, the catalyst collected at the bottom of the reactor is steam stripped to remove residual hydrocarbon. The stripped catalyst then passes into the regenerator and is heated with air to temperatures as high as 1,100°F to 1,200°F (539.3°C to 648.9°C). At these temperatures, coke bums off of the catalyst making it ready for reuse within the FCC unit. See FIGURE 2-5. 

STEP 1 Polybutadiene rubber is formulated by feeding butadiene, water, an emulsifier, and catalyst into a glass-lined reactor. This is an exothermic reaction About 80% conversion is achieved in a period of about 50 hours. The residual butadiene monomer is recovered by steam-stripping and recycled. 

The next step.was the removal of ammonia from the crude soln , which was done by steam-stripping in an evaporator to an ammonia recovery system, where NH, was absorbed in w. The resultant NH,-free crude soln was filtered through a Nutsch type filter to remove the catalyst and other insol impurities. The filtrate referred to as clear liquor was stored in a 1000 gal tank from which it could be transferred by suction into either of two 280 gal jacketed evaporators. The evaporation was conducted under 24" vacuum with 50 lb steam press in the jacket. A total of 425 gal of "clear liquor was concentrated until a sample of its "mother liquor showed the strength of 35% NaOH. During this operation the bulk of NaN, being less sol in w than NaOH, pptd. Then the mixt was cooled to 80-90°F (27-32°) (to cause the pptn of addnl NaN,) and dropped to a wringer. The yield was ca 75% NaN, and the overall cycling time was 5 6 hrs... 

The catalyst/oil disengaging system is designed to separate the catalyst from the reaction products and then rapidly remove the reaction products from the reactor vessel. Spent catalyst from the reaction zone is first steam stripped, to remove adsorbed hydrocarbon, and then routed to the regenerator. In the regenerator all of the carbonaceous deposits are removed from the catalyst by combustion, restoring the catalyst to an active state with a very low carbon content. The catalyst is then returned to the bottom of the reactor riser at a controlled rate to achieve the desired conversion and selectivity to the primary products. 

Vanadium is present in crudes mainly in the +4 state (58). In fact, up to 50% of the total vanadium in crude oil can be found as V02+ in organometallic compounds such as porphyrins and naphthenates (59-63). During the cracking reaction in a FCCU, these compounds deposit V (probably in the form of VO+2 cations) on the catalyst surface. Then, after steam-stripping and catalyst regeneration, formation of V+5 surface phases occur. The effects of vanadium on FCC properties are more severe than any of the other metals present in petroleum feedstocks. In fact, vanadium causes an irreversible loss of cracking activity which is the result of a decrease in crystallinity, pore volume and surface area of the catalyst, Figure 5. 

All the solution processes require high efficiency in recovering the solvent. The most widely used process consists of termination of the polymerization and the addition of antioxidant to the polymer solution. The solution may be treated to remove catalyst residue and then transferred into an agitated steam stripping vessel in which unreacted monomer and solvent are flashed off, leaving the rubber as a crumb slurry in water. The water-crumb slurry then is dewatered and dried. The recovered monomer/solvent is recirculated to a... 

Butyl rubber is produced at very low temperature (below — 90°C) to control the rapid exotherm, and to provide high molecular weight. The process consists of charging isobutylene along with isoprene (2-4%) with an inert diluent such as methyl chloride to a reactor to which a Friedel-Crafts catalyst is added. The polymerization is very rapid, and the polymer forms in a crumb or slurry in the diluent. Heat is removed via the reactor jacket. The slurry is steam-stripped to remove all volatiles. The catalyst is neutralized, and antioxidants are added to the slurry prior to drying.53 The halogenated derivatives are produced by the direct addition of the halogen to a solution of the isobutylene-isoprene polymer. 

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