Cumene recycling process

Scheme 3.2 shows recently established industrial processes for PO production. The cumene recycling process uses an organic hydroperoxide process combined with hydrogenation of cumyl alcohol to cumene. This process consumes only hydrogen... 

I 14 Au NP-catalysed Propene Epoxidation by Dioxygen and Dihydrogen a) Cumene recycling process by Sumitomo Chemical Co. Ltd. 

In the first step cumene is oxidized to cumene hydroperoxide with atmospheric air or air enriched with oxygen ia one or a series of oxidizers. The temperature is generally between 80 and 130°C and pressure and promoters, such as sodium hydroxide, may be used (17). A typical process iavolves the use of three or four oxidation reactors ia series. Feed to the first reactor is fresh cumene and cumene recycled from the concentrator and other reactors. Each reactor is partitioned. At the bottom there may be a layer of fresh 2—3% sodium hydroxide if a promoter (stabilizer) is used. Cumene enters the side of the reactor, overflows the partition to the other side, and then goes on to the next reactor. The air (oxygen) is bubbled ia at the bottom and leaves at the top of each reactor. 

The yield of acetone from the cumene/phenol process is beUeved to average 94%. By-products include significant amounts of a-methylstyrene [98-83-9] and acetophenone [98-86-2] as well as small amounts of hydroxyacetone [116-09-6] and mesityl oxide [141-79-7]. By-product yields vary with the producer. The a-methylstyrene may be hydrogenated to cumene for recycle or recovered for monomer use. Yields of phenol and acetone decline by 3.5—5.5% when the a-methylstyrene is not recycled (21). 

The oxidation reaction is a radical chain reaction, which can be influenced by radical scavengers, such as phenol. As phenol is produced from GHP, the risk of phenol recycling within the cumene oxidation process is always present. To reduce the... 

Phenol produced by the cumene-phenol process is relatively expensive but Solutia has recently claimed a new process developed in Russia.Benzene is oxidized directly to phenol using nitrous oxide. Phenol is then converted to adipic acid by oxidature procedures. Nitrous oxide from the final nitric acid oxidation to adipic acid is recycled to the first stage. This has been reported as the first new commercial technology since DuPont introduced the direct hydrocya-nation of butadiene to adiponitrile in 1971. 

The recovery area of the plant employs fractionation to recover and purify the phenol and acetone products. Also in this section the alpha-methylstyrene is recovered and may be hydrogenated back to cumene or recovered as AMS product. The hydrogenated AMS is recycled as feedstock to the reaction area. The overall yield for the cumene process is 96 mol %. Figure 1 is a simplified process diagram. 

Propylene feed, fresh benzene feed, and recycle benzene are charged to the upflow reactor, which operates at 3—4 MPa (400—600 psig) and at 200—260°C. The SPA catalyst provides an essentially complete conversion of propylene [115-07-1] on a one-pass basis. A typical reactor effluent yield contains 94.8 wt % cumene and 3.1 wt % diisopropylbenzene [25321-09-9] (DIPB). The remaining 2.1% is primarily heavy aromatics. This high yield of cumene is achieved without transalkylation of DIPB and is unique to the SPA catalyst process. 

Hydroperoxide Process. The hydroperoxide process to propylene oxide involves the basic steps of oxidation of an organic to its hydroperoxide, epoxidation of propylene with the hydroperoxide, purification of the propylene oxide, and conversion of the coproduct alcohol to a useful product for sale. Incorporated into the process are various purification, concentration, and recycle methods to maximize product yields and minimize operating expenses. Commercially, two processes are used. The coproducts are / fZ-butanol, which is converted to methyl tert-huty ether [1634-04-4] (MTBE), and 1-phenyl ethanol, converted to styrene [100-42-5]. The coproducts are produced in a weight ratio of 3—4 1 / fZ-butanol/propylene oxide and 2.4 1 styrene/propylene oxide, respectively. These processes use isobutane (see Hydrocarbons) and ethylbenzene (qv), respectively, to produce the hydroperoxide. Other processes have been proposed based on cyclohexane where aniline is the final coproduct, or on cumene (qv) where a-methyl styrene is the final coproduct. 

Production of a-methylstyrene (AMS) from cumene by dehydrogenation was practiced commercially by Dow until 1977. It is now produced as a by-product in the production of phenol and acetone from cumene. Cumene is manufactured by alkylation of benzene with propylene. In the phenol—acetone process, cumene is oxidized in the Hquid phase thermally to cumene hydroperoxide. The hydroperoxide is spHt into phenol and acetone by a cleavage reaction catalyzed by sulfur dioxide. Up to 2% of the cumene is converted to a-methylstyrene. Phenol and acetone are large-volume chemicals and the supply of the by-product a-methylstyrene is weU in excess of its demand. Producers are forced to hydrogenate it back to cumene for recycle to the phenol—acetone plant. Estimated plant capacities of the U.S. producers of a-methylstyrene are Hsted in Table 13 (80). 

Fig. 1. UOP catalytic condensation process for cumene synthesis. R = reactor RECT = rectifier DP = depropanizer RC = recycle column ...

In the UOP process (Figure 10-5), fresh propylene feed is combined with fresh and recycled benzene, then passed through heat exchangers and a steam preheater before being charged to the reactor.The effluent is separated, and excess benzene recycled. Cumene is finally clay treated and fractionated. The bottom product is mainly diisopropyl benzene, which is reacted with benzene in a transalkylation section ... 

The streams coming out of the reactors will be a mixture of the excess benzene and the product—cumene. A fractionating column is used to separate the two, permitting the benzene to be recycled. A final fractionator takes the cumene overhead any of those miscellaneous compounds accidentally formed in the process go out the bottom. 

Batch Stirred Tank H2S04/Oleum Aromatic Sulfonation Processes. Low molecular weight aromatic hydrocarbons, such as benzene, toluene, xylene, and cumene, are sulfonated using molar quantities of 98—100% H2S04 in stirred glass-lined reactors. A condenser and Dean-Stark-type separator trap are installed on the reactor to provide for the azeotropic distillation and condensation of aromatic and water from the reaction, for removal of water and for recycling aromatic. Sulfone by-product is removed from the neutralized sulfonate by extraction/washing with aromatic which is recycled. 

A substantial amount of a-methylstyrene is produced during the cumene oxidation step in the production of phenol and acetone. Slurry processes applying Raney nickel and a fixed-bed operation with palladium developed by Engelhard326,341 are used to hydrogenate and recycle a-methylstyrene to produce more phenol and acetone. 

The charge to the unit is treated refinery propane-propylene along with recycle benzene from the recycle column overhead. Make-up benzene is added to the recycle. Nitration-grade benzene is usually used so that a drag stream of benzene is not required to remove contaminants from the unit. Table IX shows the component analysis of the various streams in the cumene process. 

Figure 6.1 Conceptual flowsheet for manufacturing cumene by Dow-Kellogg process [3] (R-l) alkykation, (R-2) transalkylation, (C-l) propane column, (C-2) benzene recycle column,...

In the reactor portion of this process, the olefin stock is mixed with benzene (for cumene) or recycle lights (for tetramer). The resulting charge is pumped to the reaction chamber. The catalyst, solid phosphoric acid, is maintained in separate beds in the reactor. Suitable propane quench is provided between beds for temperature control purposes because the reaction is exothermic. 

First commercialized at Georgia Gulfs Pasadena, TX plant in 1994, the Mobil-Badger Cumene process consists of a fixed-bed alkylator, a fixed-bed transalkylator and a separation section (22, 23). Fresh and recycle benzene are combined with liquid propylene in the alkylation reactor where the propylene is completely reacted. Recycled polyisopropylbenzenes are mixed with benzene and sent to the transalkylation unit to produce additional cumene. Trace impurities are removed in the depropanizer column. Byproduct streams consist of LPG (mainly propane contained in the propylene feedstock) and a small residue stream, which can be used as fuel oil. 

Current zeolite catalysts already operate at process temperatures that require minimal external heat addition. Heat integration and heat management will be of increasing concern at the lower benzene to propylene ratios because the cumene synthesis reaction is highly exothermic (AHf= -98 kJ/mole). Recycle, particularly in the alkylation reactor, is likely to become increasingly important as a heat management strategy. The key will be how to limit the build-up of byproducts and feed impurities in these recycle loops, particularly as manufacturers seek cheaper and consequently lower quality feedstocks. As in the case of ethylbenzene, process and catalyst innovations will have to develop concurrently. 

Description The process includes a fixed-bed alkylation reactor, a fixed-bed transalkylation reactor and a distillation section. Liquid propylene and benzene are premixed and fed to the alkylation reactor (1) where propylene is completely reacted. Separately, recycled polyisopropylbenzene (PIPB) is premixed with benzene and fed to the transalkylation reactor (2) where PIPB reacts to form additional cumene. The transalkylation and alkylation effluents are fed to the distillation section. The distillation section consists of as many as four columns in series. The depropanizer (3) recovers propane overhead as LPG. The benzene column (4) recovers excess benzene for recycle to the reactors. The cumene column (5) recovers cumene product overhead. The PIPB column (6) recovers PIPB overhead for recycle to the transalkylation reactor. 

The world production of phenol, of ca. 8.4 Mt/a, is mostly dependent on the cumene process. The yields and selectivities of the process are almost quantitative. However, the per-pass yield is relatively low (< 8.5%) and ca. 0.6 tonne of acetone is co-produced per 1 tonne of phenol. The hydrogenation-dehydration of acetone and its recycle has been considered but is not practised commercially. 

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