Diolefin feedstocks

These hydrocarbon resins are produced from the cationic polymerization of mixed olefin and diolefin feedstocks. These raw materials consist of C5 feedstocks such as pentenes, pentadiene, isoprene, and amylene, and C6 streams of hexenes and hexa-dienes. 

The feedstocks used ia the production of petroleum resias are obtaiaed mainly from the low pressure vapor-phase cracking (steam cracking) and subsequent fractionation of petroleum distillates ranging from light naphthas to gas oil fractions, which typically boil ia the 20—450°C range (16). Obtaiaed from this process are feedstreams composed of atiphatic, aromatic, and cycloatiphatic olefins and diolefins, which are subsequently polymerized to yield resias of various compositioas and physical properties. Typically, feedstocks are divided iato atiphatic, cycloatiphatic, and aromatic streams. Table 2 illustrates the predominant olefinic hydrocarbons obtained from steam cracking processes for petroleum resia synthesis (18). 

The largest use of NMP is in extraction of aromatics from lube oils. In this appHcation, it has been replacing phenol and, to some extent, furfural. Other petrochemical uses involve separation and recovery of aromatics from mixed feedstocks recovery and purification of acetylenes, olefins, and diolefins removal of sulfur compounds from natural and refinery gases and dehydration of natural gas. 

Polymerization of raw feedstock. Aliphatic hydrocarbon resins. Raw feedstock contains straight-chain and cyclic molecules and mono- and diolefins. The most common initiator in the polymerization reaction is AICI3/HCI in xylene. The resinification consists of a two-stage polymerization in a reactor at 45°C and high pressure (10 MPa) for several hours. The resulting solution is treated with water and passed to distillation to obtain the aliphatic hydrocarbon resins. Several aliphatic hydrocarbon resins with different softening points can be adjusted. 

CDHydro [Catalytic distillation hydrogenation] A process for hydrogenating diolefins in butylene feedstocks. It combines hydrogenation with fractional distillation. Developed by CDTECH, a partnership between Chemical Research Licensing Company and ABB Lummus Crest. The first plant was built at Shell s Norco, LA, site in 1994. Ten units were operating in 1997. 

Frederick Frey and Walter Shultze were instrumental early researchers. Frey was among the first to dehydrogenate paraffins catalytically to olefins and then the olefins to diolefins that serve as feedstocks to the production of many of today s polymers. In competition with Bakelite, he discovered the preparation of polysulfone polymers made from the reaction of sulfur dioxide and olefins creating a hard Bakelite-like material. Frey and Schultz also developed a process that allowed the production of 1,3-butadiene from butane that allowed the synthesis of SR. 

Improvements in feed preparation and pretreatment have made important contributions to the advances in alkylation technology (12, 17). The ability to design better fractionators has made higher quality feedstocks available, and feed pretreatment facilities have been developed to remove water, mercaptans, sulfides, and diolefins effectively. The benefits of these advances have been realized as higher alkylate yields and octanes, lower acid consumption, and reduced corrosion. 

Description A one-step, fixed-bed catalytic process operates on a single-component or mixed feedstock to selectively produce diolefins. Feed is preheated, then contacted with catalyst in parallel fixed-... 

A lthough coke formation is always of importance during pyrolysis processes that are used for production of ethylene and other valuable olefins, diolefins, aromatics, etc., relatively little is known about the factors affecting such coke formation. It has been found that operating conditions, feedstock, pyrolysis equipment, and materials of construction and pretreatments of the inner walls of the pyrolysis tubes all affect the production of coke. General rules that have been devised empirically at one plant for minimizing coke formation are sometimes different than those for another plant. It can be concluded that there is relatively little understanding of, or at least little application of, fundamentals to commercial units. 

This conversion is conducted at moderate temperature and pressure (100°C, 25.106 Pa absolute), and possibly in the presence of a hydrocarbon diluent, for better control of the temperature rise in the catalyst beds, due to the high exothermidty of the reaction, which is itself related to the high diolefinic content of the initial C3 cut As a rule, the feed is introduced in a downflow stream into the reactor, which contains several beds of a noble metal catalyst on alumina. Quench by recycling and diluent injection is carried out between the beds. The diluent is recovered, by distillation in a depentanizer, after flash to eliminate the inert compounds introduced with hydrogen gas at the same time as the feedstock. The leading licensors inclnde IFP and Shell, etc. 

The trend in chemical feedstocks is towards less expensive, more available ones and away from the expensive, more reactive feeds. For example, the extensive use of acetylene as a feedstock in the 1930-1940 s has been replaced in the 1960-1980 s by olefins and diolefins. The future trend appears to be towards paraffins and synthesis gas (Figure 20). Continued developments in fundamental catalyst science will serve as the basis for the design of the catalytic single-step processes of the future which will efficiently utilize inexpensive, readily available feeds. 

Efforts have been made to maximize the yield of LAB from its feedstocks, improve the quality of LAB, and minimize the production of its by-products such as heavy alkylates and acidic polymeric materials. This has been accomplished by eliminating the diolefins and aromatics from the feed to the alkylation unit. The removal of diolehns has been practiced widely in the industry, whereas the technology for the removal of aromatics has only become available recently and its use is increasing. 

Acid consumption is also highly dependent on certain impurities in the feedstocks to the alkylation reactor. Some more vmdesired impurities include conjugated diolefins, acetylenic hydrocarbons, cyclopentene (found in C5 olefins), methyl f-butyl ethers, sulfur-containing hydrocarbons, and water (in either sulfuric acid as discussed earlier or in hydrocarbon feedstocks). Increased amounts of several of these impurities have resulted in the last 20-30 years because of changes in the operation of the catal3d ic cracking vmits in refineries. There are methods to reduce the impurities to a considerable extent some may be cost-effective. 

During the pyrolysis of hydrocarbons for the production of olefins and diolefins, primary and secondary reactions have been postulated. The primary reactions reflect the decomposition of the reactant essentially by free radical mechanisms. The secondary reactions become important when the reactant conversion through primary reactions has reached high levels. The postulated important secondary reactions are hydrogenation and condensation reactions. In the case of liquid feedstocks, the primary reactions can be represented as first order and the secondary reactions as second order. 

Hydrocarbon Resins. About 50% of the DCPD produced is used in hydrocarbon resins. Crude DCPD with 60-75% purity is t5 ically used in this application. Other components in the feedstock may consist of codimers of CPD with isoprene, piperylene, and methylcyclopentadiene, and a small amoimt of the dimers of methylcyclopentadiene. Both DCPD and the codimers are incorporated into the hydrocarbon resins (46,47). Other C5 diolefins can also be added to the process. 

Downstream units that process FCCU olefins are adversely affected by diolefins. A sudden increase in acid-soluble oils in an HF alkylation unit or a dramatic increase in catalyst consumption on a Dimersol polymerization unit is likely caused by an increase in diolefins in olefin feedstock. 

Personally, I have noted an increase in the diolefin content of FCCU C3-C4 when an ill-advised modification of the feed-injection distributor at the base of the riser reduced feed dispersion up the riser. Incidentally, a selective hydrotreater to destroy diolefins is one of the more cost-effective investments that a refiner can make. It is not uncommon to observe a decrease in sulfuric acid consumption on a sulfuric acid alky unit of 15% when such a hydrotreater is put on-line for butylene feedstock. 

The feedstock can be olefin-rich light hydrocarbons in the carbon range C4 to Cg, and the ideal feedstocks are C4 and C5 streams generated in the steam cracker. Diolefins and acetylenes in the feedstock can be partially hydrogenated to olefins, or the diolefins extracted for other petrochemical applications. Other possible feedstocks are MTBE Rafifinate-2, aromatics plant raffinate and refinery streams that are rich in olefins, such as light naphthas from an FCCU, coker or visbreaker. Refinery streams do not require pretreatment or hydrogenation of dienes - there is no limit on feed aromatic or diene content. 

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