Selective Hydrogenation of C4 Stream

SHP A process for purifying 1-butene by selective hydrogenation of C4 streams in petroleum refineries. A hetrogeneous palladium catalyst is used. Developed in Htils and used in 1989 in Germany, the United States, and Japan. In 1991 the licensing rights were acquired by UOP. 

DegussaAG Butadiene-free C4 hydrocarbons C4 hydrocarbons with butadiene Selective hydrogenation of C4 streams without butene-1 isomerization 5 1992... 

BASF/ABB Lummus Global Butadiene-free C4 hydrocarbons, mixed Mixed C4 hydrocarbons Selective hydrogenation of butadiene from mixed C4s stream product—butadiene-free C4 stream 6 2001... 

The selective hydrogenation of C2 - C4 alkynes was studied at atmospheric pressure, using a fully computer-controlled flow apparatus. 0.5 g of catalyst was placed In a copper reactor tube (3/8" O.D.) between glass wool plugs. The catalyst was reduced prior to reaction In a stream of 50 % hydrogen in helium (40 ml/tnin) at 250 C for 4 hours. 

Catalytic distillation hydrogenation is one of the more recent applications of CD that was commercialized by CDTECH for the selective hydrogenation of dienes in C4-C6 streams and the saturation of benzene in the... 

The selective hydrogenation of butadiene from the C4 stream is essential for its conversion to normal butenes to avoid the increased consumption and regeneration cost of acid in alkylation units. RD technology offered by CR L for the C4 stream selectively hydrogenates butadiene in the same column that is used for MTBE. The existing MTBE columns can be conveniently modified to suit this purpose. The butadiene content can be brought down to less than 100 ppm [57, 64). 

LKl cfiemLCoC p oce ycng, syntheses of butynediol from aqueous formaldehyde and acetylene, selective hydrogenation of acetylene to remove it in the presence of butadiene in C4 hydrocarbon streams (31), and hydrogenation of glucose to sorbitol (6). 

The iGi stream can be originated from several sources (Peters et al., 2000) ( ) as coproduct of butadiene production from steam cracker C4 fractions, ( ) as product of selective hydrogenation of butadiene in mixed C4 fractions from steam crackers Hi) as iC4 in the C4 fraction of FCC units (iv) as coproduct of the dehydrogenation of isobutane, and (v) as coproduct of dehydration of t-butanol. 

Purification of olefin-rich C4 cuts, particularly from FCC, is usually performed by selective hydrogenation of undesirable amounts of 1,3-butadiene and acetylene compounds. The use of butene-1 as a monomer in the production of polybutene and comonomer in low-density polyethylene production has high technological appeal and has been the object of recent studies in the literature [2-4], To this end a C4 stream needs to be rich in butene-1 and free from the presence of 1,3-butadiene and acetylenic compounds (content of < than 10 ppm). 

C4 raw cuts of stream crackers typically contain butanes (4-6%), butenes (40-65%) and 1,3-butadiene (30-50%), as well as some vinylacetylene, 1-butyne, propadiene and methylacetylene. First, acetylenes are selectively hydrogenated and the 1,3-butadiene is extracted resulting in butene cut (or raffinate I). Isobutylene is next removed to produce raffinate II which contains linear butenes and some residual 1,3-butadiene. The latter needs to be removed to achieve maximum butene yields. The methods and catalysts for this process are chosen according to the final use of butenes. The demand for polymer-grade... 

A comparative study of nanocomposites (16% Nafion-silica and commercial SAC-13) has been performed by Hoelderich and co-workers169 in the alkylation of isobutane and Raffinate II. Raffinate II, the remaining C4 cut of a stream cracker effluent after removal of dienes, isobutane, propane, and propene, contains butane, isobutylene, and butenes as main components. High conversion with a selectivity of 62% to isooctane was found for Nafion SAC-13 (batch reactor, 80°C). Both the quality of the product and the activity of the catalysts, however, decrease rapidly due to isomerization and oligomerization. Treating under reflux, the deactivated catalysts in acetone followed by a further treatment with aqueous hydrogen peroxide (80°C, 2 h), however, restores the activity. 

A cracker C4 stream contains all of the possible C4 hydrocarbons which are listed in Table 5.2. Of these commercial interest focuses on butenes, isobutene, 1,3-butadiene and butanes. Efficient separation is impossible by distillation alone and complete separation is by a combination of distillation, selective hydrogenation and selective absorption. If butadiene is not required this ean be hydrogenated and the butenes and butane separated by distillation. 

The C3+-fraction of the C2 /C3+ splitter enters the C3/C4+ splitter that separates propane, propene, propadiene, and propyne from all heavier products. The C3 stream undergoes a selective hydrogenation step in a fixed bed reactor that converts propyne and propadiene mainly into propene. Propene and propane are separated in a very similar way as ethane/ethene. Again, distillation columns with more than 100 trays are applied, making these separation units very costly in investment and energy consumption. The bottom fraction of the C3/C4+ splitter is transferred to C4/C5+ splitter. The C4 fraction leaving this column at the top contains mainly butadiene, isobutene, 1-butene, 2-butene, and butane. The further use of this crack-C4 mixture is described in detail in Section 5.3. 

It is important to remove all oxygen, dienes and acetylenes from the feed to the metathesis reactor. Furthermore, the C4 stream needs to contain the minimum practical level of butene-1 and isobutene to minimize the metathesis reaction of the C4 hydrocarbons, which results in the formation of C5 and Ce olefins. The higher olefins lead to polymer formation and catalyst deactivation. An excess of ethylene normally suppresses the C4 reactions. A typical steam cracker C4 stream, which has been subjected to selective hydrogenation to remove impurities and fractionation to provide a suitable butene-2 rich raffinate-2, or the butene-2 rich efflnent from an MTBE unit, can provide a suitable feed for the metathesis reactor. The catalyst operating cycle with a rhenium catalyst is usually fairly long. Regular catalyst regeneration may be necessary and the catalyst can last for several years. 

---