Propane product separation

The volumetric expansion parameter S may thus be taken as 0.9675. The product distribution will vary somewhat with temperature, but the stoichiometry indicated above is sufficient for preliminary design purposes. (We should also indicate that if one s primary goal is the production of ethylene, the obvious thing to do is to recycle the propylene and ethane and any unreacted propane after separation from the lighter components. In such cases the reactor feed would consist of a mixture of propane, propylene, and ethane, and the design analysis that we will present would have to be modified. For our purposes, however, the use of a mixed feed would involve significantly more computation without serving sufficient educational purpose.)... 

Natural Gas Liquids (NGL) - The portions of natural gas that are liquefied at the surface in production separators, field facilities, or gas processing plants, leaving dry natural gas. They include but are not limited to ethane, propane, butane, natural gasoline, and condensate. 

One possible arrangement for a hydrofluoric acid alkylation unit is shown schematically in Fig. 1. Feedstocks are pretreated, mainly to remove sulfur compounds. The hydrocarbons and acid are intimately contacted in the reactor to form an emulsion, within which the reaction occurs. The reaction is exothermic and temperature must be controlled by cooling water. After reaction, the emulsion is allowed to separate in a settler, the hydrocarbon phase rising to the top. The acid phase is recycled. Hydrocarbons from the settler pass to a fractionator which produces an overhead stream rich in isobutane. The isobutane is recycled to the reactor. The alkylate is the bottom product of tile fraetionater (isostripper). If the olefin teed contains propylene and propane, some of the isoshipper overhead goes to a depropanizer where propane is separated as an overhead... 

Enter an alpha value if you have chosen F or T for the method. Enter a K value for a light key component if you chose A. Input the factor alpha or K. Alpha is defined as simply the light key K divided by the heavy key K component. The K factor is simply the particular component s vapor phase mole fraction divided by its liquid mole fraction. The alpha value is therefore a ratio of the chosen two key components. These key components should be those that readily point to how well the fractionator is doing its job of separation. For example, for a depropanizer tower, choose propane as the light key component and butane as the heavy key, since you wish to separate the propane from the butane to make a propane product specification. For a multicomponent system, you may try several components to determine a controlling alpha and/or to factor an average tray efficiency. 

As shown in Fig. 18.23, dry liquid feed containing olefins and isobutane is charged to a combined reactor-settler. In this example, the reactor uses the principle of a differential gravity head to circulate through a cooler before contacting a highly dispersed hydrocarbon feed in the reactor pipe. The hydrocarbon phase, generated in the settler, is sent to a fractionator, which separates LPG-quality propane, isobutane recycle, n-butane, and alkylate products. A small amount of dissolved catalyst is also removed from the propane product by a small stripper tower. 

Propane is separated by distillation and can be either recycled to produce cracker feedstock or purified to a saleable LPG product. 

The thermodynamics of this process are described in detail in references (67 —72, 80,81). Let us examine a typical methanol injection system. In a typical methanol injection and recovery system for a cold-oil absorption or turboexpander plant, feed gas passes through a free-water knockout drum and into a gas-gas exchanger with methanol being sprayed on exchanger tube-sheets. Methanol inhibits hydrate formation and aqueous methanol condenses in the exchanger (and the chiller following it) and is pumped to a primary separator. The methanol-water solution is then flashed in a flash drum and filtered into a methanol still to recover methanol. Normally, methanol dissolves in the hydrocarbon liquids and is distilled as a mixture of propane and methanol. Some of the methanol is recovered as the overhead product to recover the methanol dissolved in the heavier solution, the bottoms of the methanol still (propane product or hydrocarbon liquids from the demethanizer)... 

The development of the preparation of nitroparaffins from laboratory scale through pilot-plant to full-scale operation covered a 20-year-long effort by Commercial Solvents Corporation. A full-scale plant with a capacity of more than 10,000,000 lb per year went on stream in 1955. By a process of nitration of propane, the main production of nitroparafl5ns includes nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane. The nitration is done in the vapor phase. A flow diagram illustrating the process is shown in Fig. 4-17. There are five process sections in the nitroparaffin preparation. These involve (1) nitration, (2) products recovery, (3) products purification, (4) products separation, and (5) reactants recovery. A report by Schecter and Kaplan states that conditions for the nitration of propane are 770 F (410 C) at pressures of 115-175 psi. Initially the vapor-phase... 

The photochlorination of propanes to a mixture of polychloropropanes is accomplished by introducing chlorine and propane in separate streams in a light-activated chamber containing products of the reaction. The composition of the products range from dichlorides up to octachlorides. This mixture is suitable for further chlorination to carbon tetrachloride and perchloroethylene by thermal or catalytic procedures. The over-all reaction is... 

When the reflux accumulator separates two liquid phases, excessive rise or fall of the interface level can carry over one phase into another, and/or reflux the column with the improper phase. In some situations, such carryover can be h2aardous. In one case (7), carryover of hydrofluoric acid into a propane product route from the reflux accumulator of an alkylation depropanizer caused multiple explosions in downstream equipment. The author is familiar with an almost identical incident that overpress u ed downstream equipment but stopped short of exploding. Refluxing an improper phase into a column can also be troublesome this is described in detail in Sec. 13.7. 

In the example distillation system considered in Chapters 3 and 4, we studied the binary propane/isobutane separation in a single distillation column. This is a fairly ideal system from the standpoint of vapor-liquid equilibrium (VLE), and it has only two components, a single feed and two product streams. In this chapter, we will show that the steady-state simulation methods can be extended to multicomponent nonideal systems and to more complex column configurations. 

We are separating 1000 kmol/h of a feed containing propane, n-butane, and n-pentane. The feed pressure is 4.0 atm This feed is 22.4 mol% propane, 44.7 mol% n-butane, and the remainder n-pentane. In the overall process we plan to recover 99.6% of the propane in the propane product, 99% of the n-butane in the n-butane product, and 99.7% of the n-pentane in the n-pentane product. In column 1 recover 99.5% of the n-butane in the bottoms product. For purposes of your initial mass balances, assume 1) There is no n-pentane in the propane product stream, and 2) There is no propane in the n-pentane product stream Check these guesses after you have run the simulations. Both columns operate at 4.0 atm Operate each column at 1.15 L/D minimum Use the optimum feed stage for each column. 

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. 

Some small amount of byproduct formation occurs. The principal byproduct is di-isopropyl ether. The reactor product is cooled, and a phase separation of the resulting vapor-liquid mixture produces a vapor containing predominantly propylene and propane and a liquid containing predominantly the other components. Unreacted propylene is recycled to the reactor, and a purge prevents the buildup of propane. The first distillation in Fig. 10.3a (column Cl) removes... 

The simpler nitrop>arafIins (nitromethane, nitroethane, 1- and 2-nitroproj)ane) are now cheap commercial products. They are obtained by the vapour phase nitration of the hydrocarbons a gaseous mixture of two mols of hydrocarbon and 1 mol of nitric acid vapour is passed through a narrow reaction tube at 420-476°. Thus with methane at 476° a 13 per cent, conversion into nitro methane is obtained ethane at 420° gives a 9 1 mixture of nitroethane (b.p. 114°) and nitromethane (b.p. 102°) propane at 420° afifords a 21 per cent, yield of a complex mixture of 1- (b.p. 130-6°) and 2-nitropropane (b.p. 120°), nitroethane and nitromethane, which are separated by fractional distillation. 

Commercial VPO of propane—butane mixtures was in operation at Celanese Chemical Co. plants in Texas and/or Canada from the 1940s to the 1970s. The principal primary products were acetaldehyde, formaldehyde, methanol, and acetone. The process was mn at low hydrocarbon conversion (3—10%) and a pressure in excess of 790 kPa (7.8 atm). These operations were discontinued because of various economic factors, mainly the energy-intensive purification system required to separate the complex product streams. 

Solid-Bed Dehydration. Sihca gel, bauxite, activated alurnina, or molecular sieves can be used for removing dissolved water to meet propane specifications. The soHd-bed dehydrators are used in a cycHc adsorption process. After an adsorption cycle has completed, the bed is heated with a purge gas or a vaporized Hquid-product stream for regeneration. If the latter is used, the Hquid product is condensed, separated from the free water, and returned to the process. After the beds are regenerated, they are cooled and returned to the adsorption cycle. 

Eor vapor-phase processes, the product stream from the nitrator must be separated. The nitroparaffins, excess propane, and NO plus NO2 (which are converted back to HNO ), are recovered. The oxygenated products are removed, but there are generally insufficient amounts for economic recovery. 

The distillation system is designed to recover a high purity cumene product. The unconverted benzene and polyisopropylbenzenes are separated and recycled to the reaction system. Propane ia the propyleae feed is recovered as fiquid petroleum gas (LPG). 

Zeolite Catalysts. Uaocal has iatroduced a fixed-bed fiquid-phase reactor system based oa a Y-type zeofite catalyst (62). The selectivity to cumene is geaeraHy betweea 70 and 90 wt %. The remaining components are primarily polyisopropylbenzenes, which are transalkylated to cumene ia a separate reactioa zoae to give an overall yield of cumene of about 99 wt %. The distillation requirements iavolve the separation of propane for LPG use, the recycle of excess benzene to the reaction zones, the separation of polyisopropylbenzene for transalkylation to cumene, and the production of a purified cumene product. 

The feed streams should be reasonably pure to limit yield losses and protect the purity of the final products. Typically, polymer-grade propylene with 99.5% purity is employed propane impurity can react to undesirable 1-chloropropane (bp 46.6°C), which is very difficult to separate from aHyl chloride (bp 45°C). Both propylene and chlorine should be dry to prevent corrosion in downstream equipment where mixtures with HCl occur. 

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