Columns vacuum distillation unit

Where is naphthenic acid corrosion found Naphthenic acid corrosion occurs primarily in crude and vacuum distillation units, and less frequently in thermal and catalytic cracking operations. It usually occurs in furnace coils, transfer lines, vacuum columns and their overhead condensers, sidestream coolers, and pumps. 

The atmospheric reduced crude is the feedstock for the vacuum distillation unit. To prevent thermal decomposition (cracking) of the higher boiling point hydrocarbons in the crude oil, the pressure in the vacuum distillation fractionation column is reduced to about one-twentieth of an atmosphere absolute (one atmosphere pressure is 14.7 psia or 760 mm Fig). This effectively reduces the boiling points of the hydrocarbons several hundred degrees Fahrenheit. The components boiling below about 1050°F (565°C) are vaporized and removed as vacuum gas... 

Figure 3-1. Flow diagram of atmospheric and vacuum distillation units (1,3) heat exchangers (2) desalter, (3,4) heater (5) distillation column, (6) overhead condenser, (7-10) pump around streams, (11) vacuum distillation heater (12) vacuum tower.

Process vapours from the esterification reactors and EG from the EG-vapour jet, as well as from the vacuum stages of the spray condensers, are purified in the distillation unit. The distillation unit commonly consists of two or three columns and is designed for continuous operation. The purified EG is condensed at the top of the third vacuum rectification column and returned to the process via a buffer tank. Gaseous acetaldehyde and other non-condensables are vented or burned and high-boiling residues from the bottom of the third column are discharged or also burned. 

Charge stock for the catalyst testing experiment was prepared by topping a sample of the in situ crude shale oil to 600°F in a batch still equipped with a column having 35 trays and then separating the 600°— 1000°F fraction in a vacuum flash distillation unit. Properties of the 600°-1,000°F fraction of in situ crude shale oil are shown in Table III. 

The 65 per cent peroxide, previously stabilized by adding a small amount of phosphoric acid, is introduced at the rate of 9001 per hr. into a second distillation unit, similar to the first, for re-distillation. Here the process is continuous a4 no solid substances accumulate in the retort. A temperature of 75 °C is njaintained at an absolute pressure of 40 mni Hg. When equilibrium has been reached, the concentration of the liquid in the retort will be about 80 per cent b.w. H2O2 and in the vapour phase will be about 44 per cent b.w. H202. The distilled vapour enters the rectifying column, from where a condensate containing 56 per cent b.w. H202 is continually returned into the retort. Uncondensed water vapour is liquefied in a tubular aluminium condenser connected to a vacuum pump. 

In present-day refineries, the fluid catalytic cracking (FCC) unit has become the major gasoline-producing unit. The FCC s major purpose is to upgrade heavy fractions, that is, gas oil from the atmospheric and vacuum distillation columns and delayed coker, into light products. Atmospheric gas oil has a boiling range of between 650-725°F.9... 

The catalytic cracking unit is often referred to as the gasoline workhorse of a refining unit. As shown in Fig. 18.9, feeds to the catalytic cracking unit are gas oils from the atmospheric and vacuum distillation columns and delayed coker. These heavier fractions also carry metals such as nickel, vanadium, and iron. More important, sulfur compounds concentrate in the heavier product fractions. Table 18.8 lists a typical mass balance for sulfur.25 FCC blend-stocks comprise 36 percent of the volume of the gasoline pool. However, this stream also contributes 98 percent of the sulfur concentration to blended procucts.25 As specifications on sulfur concentrations in diesel and gasoline tighten, more efforts are focused on how feeds and product streams from the FCC are pre- and posttreated for sulfur concentrations. 

Slurry drawn from the crystallizing columns is filtered in rotary vacuum filters where the NaHC03 crystals are water-washed. The filtered liquor then flows to the distillation unit for recovery of ammonia. The crude bicarbonate filter cake contains 3 percent... 

Diphenyl disulfide. In a 100-mL, round-bottomed flask equipped with a magnetic stirrer are placed 11.0 g (10.25 ml, 0.1 mol) of benzenethiol and 50 mL of trifluoroethanol (Note 1). The mixture is stirred and cooled in an ice bath (Note 2) and 12.5 mL (3.73 g, 0.11 mol) of 30% aqueous hydrogen peroxide (Note 3) is added dropwise over a period of 15 min through an addition funnel. After completion of the addition, the ice bath is removed and the reaction mixture is allowed to stir at room temperature for 24 hr. Diphenyl disulfide is sparingly soluble in trifluoroethanol and precipitates out of solution. The solids are collected on a Buchner funnel and dried under vacuum to afford 10.6 g of diphenyl disulfide (97%) (Note 4). Sodium sulfite 2.52 g (0.02 mol) is added to the mother liquor to decompose the excess peroxide and the mixture is heated in a water bath at 50°C for 30 min. A starch iodide test is negative. The liquid is transferred to a 100-mL, round-bottomed flask, fitted with a distillation unit having a Vigreux column (5 cm). The flask is heated in an oil bath and the solvent is distilled to recover the trifluoroethanol (Note 5). 

Dinitrofluorobenzene (Sanger s reagent) [70-34-8] M 186.1, m 25-27", b 133"/2mm, 140-141 /5mm, d 1.483. Crystallise the reagent from Et20 or EtOH. Distil it in a vacuum through a Todd Column (p 11). If it is to be purified by distillation in vacuo, the distillation unit must be allowed to cool before air is allowed into the apparatus otherwise the residue carbonises spontaneously and an EXPLOSION may occur. The material is a skin irritant and may cause serious dermatitis. [Beilstein 5 TV 742.]... 

A more recent test method (ASTM D-5236) is seeing increasing use and appears to be the method of choice for crude assay vacuum distillations. Wiped-wall or thin-fihn molecular stills can also be used to separate the higher-boiUng fractions under conditions that minimize cracking. In these units, however, cut points cannot be directly selected because vapor temperature in the distillation column cannot be measured accurately under... 

In atmospheric or straight-run distillation the crude oil is first pumped into the fractional distillation unit. This is the refinery s tallest unit and some of its columns are used for atmospheric distillation while others are for vacuum distillation. Heated to about 680°F in the gas furnaces, the petroleum reaches the first atmospheric column, which is divided into compartments for fractional distillation. The lighter and more volatile hydrocarbons rise to the upper part. Those that are heavier and less volatile collect in the lower part. While rising, a volatile mass tends to shed its less volatile elements. 

My own technical experience has pretty much followed this history of distillation simulation. My practical experience started back in a high-school chemistry class in which we performed batch distillations. Next came an exposure to some distillation theory and running a pilot-scale batch distillation column as an undergraduate at Penn State, learning from Arthur Rose and Black Mike Cannon. Then, there were five years of industrial experience in Exxon refineries as a technical service engineer on pipestills, vacuum columns, light-ends units, and alkylation units, all of which used distillation extensively. 

The extraction plant was quite complex since it is essential to the economics of the process to recover the quaternary ammonium salt as well as to isolate pure adiponitrile and unreacted acrylonitrile. The sidestream from the catholyte reservoir was cooled and the adiponitrile and unreacted acrylonitrile extracted with further acrylonitrile in a sieve tray column. The organic phase from this unit was counter-currently extracted with water to recover the quaternary ammonium salt and the acrylonitrile was then removed by distillation. The final stage is the vacuum distillation of the adiponitrile. The total process is shown in Fig. 6.5. 

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