Steam cracking raffinates

Steam cracking raffinate from aromatic extraction units is similar to naphtha cracking. However, because raffinates have more isoparaffins, relatively less ethylene and more propylene is produced. 

Application To produce polymer-grade propylene from ethylene and butenes using Lummus olefins conversion technology (OCT). This technology can be used with a variety of streams, including the mixed C4S produced in steam cracking, raffinate C s from MTBE or butadiene extraction, and C.s produced in FCC units. 

IFP Process for 1-Butene from Ethylene. 1-Butene is widely used as a comonomer in the production of polyethylene, accounting for over 107,000 t in 1992 and 40% of the total comonomer used. About 60% of the 1-butene produced comes from steam cracking and fluid catalytic cracker effluents (10). This 1-butene is typically produced from by-product raffinate from methyl tert-huty ether production. The recovery of 1-butene from these streams is typically expensive and requires the use of large plants to be economical. Institut Francais du Petrole (IFP) has developed and patented the Alphabutol process which produces 1-butene by selectively dimerizing ethylene. 

Liquid feedstocks for olefin production are light naphtha, full range naphtha, reformer raffinate, atmospheric gas oil, vacuum gas oil, residues, and crude oils. The ratio of olefins produced from steam cracking of these feeds depends mainly on the feed type and, to a lesser extent, on the operation variables. For example, steam cracking light naphtha produces about twice the amount of ethylene obtained from steam cracking vacuum gas oil under nearly similar conditions. Liquid feeds are usually... 

Should MTBE be banned, what would be the logical replacement(s) There are several options available. Several refiners opted to build MTBE capacity and avoid purchasing the ether on the open market. MTBE units were an option to use the facility s isobutylenes. Several licensed processes can be used to convert existing MTBE units. Kvaerner and Lyondell Chemical Co. offer technologies to convert an MTBE unit to produce iso-octane, as shown in Fig. 18.27.12 Snamprogetti SpA and CDTECH also have an iso-octene/iso-octane process. These processes can use various feedstocks such as pure iso-butane, steam-cracked C4 raffinate, 50/50 iso-butane/iso-butene feeds, and FCC butane-butane streams. The process selectively dimerizes C4 olefins to iso-octene and then hydrogenates the iso-octene (di-iso-butene) into iso-octane. The processes were developed to provide an alternative to MTBE. The dimerization reactor uses a catalyst similar to that for MTBE processes thus, the MTBE reactor can easily be converted to... 

Thus, butadiene is first recovered from steam-cracked C4 cuts by solvent extraction, an operation that is sometimes facilitated by preliminary selective hydrogenation of the acetylenic compounds. In a number of applications, the raffinate itself must undergo similar treatment to rid it of residual diolefins. The initial cut, after being debutadienized by hydrogenation, can also serve the same purpose. This also applies to catalytic cracker diluents that are very often directly upgradable, but whose albeit low butadiene content may justify hydrogenation pretreatment for certain uses. 

Butenes are usually obtained from Crack C via naphtha steam cracking (Scheme 4.4) [31]. After the removal of butadiene and isobutene from the crude stream, the so-called Raffinate II contains 1-butene, cis/trans-2-hutene, and the isomeric butanes. Alternatively, it has been produced for a subsequent hydroformylation by dehydrogenation of n-butane on a Cr on alumina... 

When steam cracking or naphtha reforming produce an aromatics mixture short in benzene or o- and p-xylene, some interconversion is practiced. Toluene can be hydrodealkylated to benzene. Xylene can be isomerized to increase yields of o- and p-xylene. The analysis for aromatics thus falls into two general types to meet two different needs. Analysis for process optimization assists in obtaining the maximum product at the minimum unit cost. This involves analysis of feeds, products, and raffinate (purge) streams. These analyses must be tailored to the process and the plant streams involved. Generally, it is desirable to have one analytical procedure to apply to a variety of sample types. The final product specification analysis can also be used for process control. The ASTM standard... 

The ethylene feed can be polymer grade or lower purity as long as the impurities are below a certain limit. Any saturated hydrocarbons, such as ethane and methane, do not react. A variety of C4 streams, including mixed C4 s produced by FCC or steam cracking, or C4 Raffinate from butadiene extraction or MTBE production, can be used in the process. In order to achieve the full potential propylene production. However, the raw C4 cut requires pretreatment to maximize its butene-2 content. 

Butenes are usually derived from Crack-C4 from naphtha steam cracking [27]. After the removal of butadiene (by extraction) and isobutene (by conversion into methyl t-butylether) from the crude stream, the so-called Raffinate II contains 1-butene (50-65%), cis/trons-2-butene, and the isomeric butanes. Raffinate II is the cheapest source of butenes, and their most valuable hydroformylation product is n-pentanal, whereas the isomers 2-methylbutyraldehyde and 3-methylbutyraldehyde are less in demand and lower in value. The main application for -valeraldehyde is its transformation into 2-propylheptanol (2-PH) by aldolcondensation and subsequent hydrogenation of the product (Scheme 14.4) [28, 29]. like 2-EH, 2-PH is also an important plasticizer alcohol. n-Valeraldehyde is also used as an ingredient in flavoring mixtures. w-Valeraldehyde can be converted into -valercarboxylic ester by subsequent oxidation and esterification with tertiary valeric alcohol, providing a useful lubricant and a substitute for Freon. 

The dehydrogenation process feed can be refinery streams from the catalytic cracking processes. This mixed C4 stream typically contains less than 20 percent n-butenes. For use in dehydrogenation, however, it should be concentrated to 80-95 percent. The isobutylene generally is removed first by a selective extraction-hydration process. The n-butenes in the raffinate are then separated from the butanes by an extractive distillation. The catalytic dehydrogenation of n-butenes to 1,3-butadiene is carried out in the presence of steam at high temperature (>600°C) and... 

The feedstocks will t3 ically be low value refinery or petrochemical streams, such as steam cracker by-products rich in C4 s, which have poor propylene selectivity when recycled to the steam cracker. The feedstock can include raffinates, catalytic cracked naphtha, coker naphtha, steam cracker pyrolysis gasoline, as well as synthetic chemical streams containing sufficient amounts of C4-C7 olefins. Dienes, sulfur, nitrogen and oxygenates in the feeds are preferably selectively hydrotreated prior to the conversion process. However, feeds with low levels of dienes, sulfur, nitrogen, metal compounds and oxygenates can be processed directly from FCC units, cokers or steam crackers without any pretreatment. 

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