Isoprene recovery

Troublesome amounts of C and Q acetylenes are also produced in cracking. In the butadiene and isoprene recovery processes, the acetylenes in the feed are either hydrogenated, polymerized, or extracted and burned. Acetylene hydrogenation catalyst types include palladium on alumina, and some non-noble metals. 

The principal route for production of isoprene monomer outside of the CIS is recovery from ethylene by-product C streams. This route is most viable where ethylene is produced from naphtha or gas oil and where several ethylene plants are located in relatively close proximity to the isoprene plant. Although the yield of isoprene per mass of ethylene is quite low, there is enough ethylene produced to provide a large portion of demand. Because of the presence of / -pentane in these streams which a2eotropes with isoprene, extractive distillation must be used to recover pure isoprene. Acetonitrile is the most common solvent, but dimethylformamide is also used commercially. 

The demand for isoprene for Butyl rubber led to the development of a recovery process for this Cj diolefin. Extractive distillation with acetone was the first process used but it has been replaced with acetonitrile (ACN ). The first step in the process is the fractionation of steam cracker debutanizer bottoms in a conventional two tower system to produce a C5 cut containing 30% isoprene. The first tower rejects C and heavier while the second rejects C4 and lighter materials. 

Dehydrogenation of t-amylenes over a dehydrogenation catalyst produces isoprene. The overall conversion and recovery of t-amylenes is approximately 70%. 

The mechanical properties at low strain rates, dynamic mechanical properties, creep-recovery behaviour, thermal expansion and thermal conductivity of foams manufactured from blends of LDPE with an EVA and with an isoprene-styrene block copolymer were studied as a function of the LDPE content in the blends. The experimental results demonstrated important aspects related to the modification of the foam properties by blending. 16 refs. 

Head-to-tail rearrangement of four isoprene units results in the formation of diterpenes (C20H32), as seen also in Fig. 4.2. Diterpenes are generally found in resins, e.g. pimaric acid and abietic acid. Some diterpenoids are also constituents of essential oils, e.g. phytol [3, 7-14, 37, 52, 53]. Like sesquiterpenes, diterpenes are heavier than monoterpenes therefore, they require more energy to go to the vapour phase. For this reason, longer distillation times are necessary for their recovery. The DNP lists 118 different structural types for diterpenoids [37]. Important diterpenes found in essential oils will be detailed. Some representatives of volatile diterpenes are as in Structure 4.32. 

Draw carefully a flowsheet for the recovery of isoprene from a mixture of C5 hydrocarbons by extractive distillation with aqueous acetonitrile according to the following description. 

The extract is pumped from the bottom of D-l to a stripper D-2 with 35 trays. The stripped solvent is cooled with water and returned to D-l. An isoprene-acetonitrile azeotrope goes overhead, condenses, and is partly returned as top tray reflux. The net overhead proceeds to an extract wash column D-3 with 20 trays where the solvent is recovered by countercurrent washing with water. The overhead from D-3 is the finished product isoprene. The bottoms is combined with the bottoms from the raffinate wash column D-4 (20 trays) and sent to the solvent recovery column D-5 with 15 trays. 

Overhead from D-l is called the raffinate. It is washed countercurrently with water in D-4 for the recovery of the solvent, and then proceeds beyond the battery limits for further conversion to isoprene. Both wash columns operate at substantially atmospheric pressure and 100°F. The product streams are delivered to the battery limits at 100 psig. 

Extractive Distillation Recovery of Isoprene. A typical flowsketch and material balance of distillation and solvent recovery towers for extracting isoprene from a mixture of cracked products with aqueous acetonitrile appears in Figure 13.26. A description of the flowsheet of a complete plant is given in Example 2.10. In spite of the fact that several trays for washing by reflux are provided, some volatilization of solvent still occurs so that the complete plant... 

Figure 13.26. Flowsketch for the recovery of isoprene from a mixture of C5s with aqueous acetonitrile. Flow quantities in lb/hr, pressures in psia, and temperatures in °F. Conditions are approximate. (Data of The C. W. Nofsinger Co.)...

The principal route for production of isoprene monomer outside of the CIS is recovery from ethylene by-product C< streams. 

The production process of natural rubber in the tree is not yet fully understood. However, it involves a long series of complex biochemical reactions that do not involve isoprene as a monomer, even though the resulting polymer is 100 percent cis 1,4 polyisoprene. Because the tree makes the product, the rubber production process is really one of recovery. 

Ion exchange equipment, 508,512,517 continuous processes, 515, 519,520 fixed bed arrangements, 512 performance. Uranium recovery, 515 sizing example, 513 Isoprene... 

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