Debutanizer bottoms

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. 

The HPS liquid consists mostly of C3 s and heavier hydrocarbons however, it also contains small fractions of Cj s, H2S, and entrained water. The stripper removes these light ends. The liquid enters the stripper on the top tray. The heat for stripping is provided by an external reboiler, using steam or debutanizer bottoms as the heat medium. The vapor from the reboiler rises through the tower and strips the lighter fractions from the descending liquid. The rich overhead vapor flows to the HPS via the condenser and is fed to the primary absorber. The stripped naphtha leaves the tower bottoms and goes to the debutanizer. Usually, at least one draw is installed in the tower to remove the entrained water. 

The debutanized gasoline is cooled, first by supplying heat to the stripper reboiler or preheating the debutanizer feed. This is followed by a set of air or water coolers. A portion of the debutanizer bottoms is pumped back to the presaturator or to the primary absorber as lean oil. The balance is treated for sulfur and blended into the refinery gasoline pool. 

The fractionation section of the alkylation plant consists of a deisobutanizer, a debutanizer, and a rerun tower in series, and a depropanizer. The deisobutanizer overhead, which contains about 90% isobutane, recycles to the reactor. The deisobutanizer bottoms stream passes to the debutanizer, which removes normal butane diluent as an overhead stream. The debutanizer bottoms or raw alkylate stream then goes to a rerun tower for removal of the high boiling alkylate bottoms or trimers. The rerun overhead requires no further treatment to be satisfactory as an aviation gasoline blending stock. The depropanizer removes propane diluent from a slip-stream portion of the recycle isobutane stream to prevent propane build-up in the reaction system. 

Condenser duty = 1.31 mmBtu/h Debutanizer Bottom-section Equations (see Fig. 2.6)... 

The reformate produced in the OCR Platforming unit is sent to a debutanizer column, which strips off the light ends. The debutanizer bottoms are sent to a reformate splitter (3). The C7 fraction from the overhead of the reformate splitter is sent to a Sulfolane unit (4). The C8+ fraction from the bottom of the reformate splitter is sent to a xylene fractionation section. The Sulfolane unit extracts the aromatics and then individual high-purity benzene and toluene products are recovered in a BT fractionation section (5 6). 

The deisopentanizer (DIP) tower, shown in Figure 14.8, processes light straight-run naphtha from two sources. The debutanizer bottoms consists of primarily iso and normal pentane (iCs and Cs), with small fractions of butane and Cg-I- components. The overhead from the naphtha fractionator tower contains mostly C5 and Ce paraffin compounds, with some benzene and Ce naphthenes and a small amount of butane. The combined feed to the DIP is typically in the range of 9,000-15,000 bpd. 

A debutanized light naphtha was stored in a floating roof tank. Hydrocarbon vapor emissions from this tank were obviously excessive yet, repeated samples of naphtha, drawn from the debutanizer bottoms, showed a very low butane content. The paradox was resolved when the process engineer observed that the light naphtha sample was taken in a plastic bottle. By the time the lab ran the sample, most of the butane had evaporated. A sample obtained in a pressure bomb revealed the true butane content of the naphtha. 

The overhead product from the lean-oil fractionator, consisting of propane and heavier hydrocarbons, enters the depropanizer. The depropanizer overhead product is treated to remove sulfur and water to provide specification propane. The depropanizer bottoms, containing butane and higher boiling hydrocarbons, enters the debutanizer. Natural gasoHne is produced as a bottom product from the debutanizer. The debutanizer overhead product is mixed butanes, which are treated for removal of sulfur and water, then fed iato the butane spHtter. Isobutane is produced as an overhead product from the spHtter and / -butane is produced as a bottoms product. 

The depropanizer bottoms are further processed in the debutanizer for separation of product from light pyrolysis gasoline. The debutanizer operates at a moderate pressure of 0.4 to 0.5 MPa, and is a conventional fractionator with steam heated reboders and water cooled condensers. 

Butane and heavier bottoms from the depropanizer flow to the debutanizer where the C4 stream (almost entirely olefins and diolefins) is taken overhead and sent to butadiene and isobutylene recovery facilities. 

The stripper bottoms contain Cj s, C4 s, and gasoline the debutanizer separates the Cj s and C4 s from the gasoline. In some units, the hot stripper bottoms can be further preheated before entering the debutanizer. In a number of units, the stripper bottoms is sent directly to the debutanizer. The feed enters about midway in the tower. Debutanizer feed is always partially vaporized because the debutanizer operates at a lower pressure than the stripper. A control valve that regulates stripper bottoms level is the means of this pressure drop. As a result of this drop, part of the feed is vaporized across the valve. 

The debutanizer separates the feed into two products. The overhead product contains a mixture of C3 s and C4 s. The bottoms product is the stabilized gasoline. Heat for separating these products comes from an external reboiler. The heating source is usually the main fractionator heavy cycle oil or slurry. Steam can also be used. 

The LPG stream containing a mixture of C s and C4 s must be treated to remove hydrogen sulfide and mercaptan. This produces a noncorrosive, less odorous, and less hazardous product. The C s and C4 s from the debutanizer accumulator flow to the bottom of the H S contactor. The operation of this contactor is similar to that of the fuel gas absorber, except that this is a liquid-liquid contactor. 

Alkylation generates relatively low volumes of wastewater, primarily from water washing of the liquid reactor products. Wastewater is also generated from steam strippers, depropanizers, and debutanizers, and can be contaminated with oil and other impurities. Liquid process waters (hydrocarbons and acid) originate from minor undesirable side reactions and from feed contaminants, and usually exit as a bottoms stream from the acid regeneration column. The bottoms stream is an acid-water mixture that is sent to the neutralizing drum. The acid in this liquid eventually ends up as insoluble calcium fluoride. 

The feed to a hydrofluoric acid alkylation unit is desiccant dried and then sent to the combined reactor settler (Figure 2.8). The reaction occurs at 90 to 100°F (32 to 38°C), at 250 psia (1,725 kPa), and in the presence of 90% hydrofluoric acid. The effluent from the combined reactor settler is fed to the main fractionator. The hydrofluoric acid goes overhead with the light ends and is condensed and collected in the accumulator. Part of the condensed overhead fluid is recycled from the feed to the combined reactor settler, part is used for reflux to the main fractionator, and the remainder is fed to the hydrofluoric acid stripper. The overhead of the stripper is returned to the main fractionator overhead condenser. The bottom product of the stripper is caustic washed to remove all traces of hydrofluoric acid. The bottom product of the main fractionator is often fed to a debutanizer fractionator column. 

The C3 from the deethanizer bottoms (10) is depropanized (15), hydrogenated (16) to remove methyl acetylene and propadiene (16) and fractionated to recover polymer grade propylene. C4 components are separated from heavier components in the debutanizer (18) to recover a C4 product and a C5 stream. The C5, together with the... 

Description The TAC9 process consists of a fixed-bed reactor and product separation section. The feed is combined with hydrogen-rich recycle gas, preheated in a combined feed exchanger (1) and heated in a fired heater (2). The hot feed vapor goes to a reactor (3). The reactor effluent is cooled in a combined feed exchanger and sent to a product separator (4). Hydrogen-rich gas is taken off the top of the separator, mixed with makeup hydrogen gas, and recycled back to the reactor. Liquid from the bottom of the separator is sent to a stripper column (5). The stripper overhead gas is exported to the fuel gas system. The overhead liquid may be sent to a debutanizer column or a stabilizer. The stabilized product is sent to the product fractionation section of the UOP aromatics complex. 

The cracked gases are cooled and fractionated to remove fuel oil and water (2-5) then compressed (6), processed for acid-gas removal (8) and dried (9). The C3 and lighter material is separated as an overhead product in the depropanizer (10) and acetylene is hydrogenated in the acetylene converter (11). The acetylene converter effluent is processed in the demethanizer system (12-14) to separate the fuel gas and hydrogen products. The demethanizer bottoms is sent to the deethanizer (15) from which the overhead flows to the C2-splitter (16), which produces the polymer-grade ethylene product and the ethane stream, which is recycled to the furnaces as a feedstock. The deethanizer bottoms flows to the C3-splitter (18) where the polymer-grade propylene is recovered as the overhead product. The C3-splitter bottoms product, propane, is typically recycled to the furnaces as a feedstock. The depropanizer bottoms product, C4S and heavier, flow to the debutanizer (19) for recovery of the mixed-C4 product and aromatic-rich pyrolysis gasoline. 

Vised directly. To obtain very pure propylene (99.5 per cent weight), however, it is necessary to remove the propane in a supplementary column. Table 2.10 offers a glance at the specifications that the ethylene and propylene thus separated are required to meet The heavier hydrocarbons obtained at the bottom of the depropanizer are treaty in a debutanizer, which produces a l,3>butadiene-rich cut at the top. In accordance with the severity, Table 2.11 provides a typical example of the composition of this effluent for a naphtha feedstock. The pyrolysis gasoline drawn off at the bottom may, depending on the severity, contain 50 to S5 per cent weight of aromatic hydrocarbons, of which more than half is benzene. Its composition and treatment are discussed separately in Section 2.1.5. 

The operating conditions in the cold separation section arc essentially shown in Fig. Z17. The choice of the gradation in the decreasing operating pressures between the demethanizer and the debutanizer is designed to ensure that the corresponding column bottom temperatures are suf dently low to prevent any undesirable polymerization. 

---