Reforming is an upgrading process in which low octane gasoline is converted to high octane gasoline.

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1 REFORMING Reforming is an upgrading process in which low octane gasoline is converted to high octane gasoline. Catalytic reforming primarily increases the octane of motor gasoline rather than increasing its yield. In this process longer chain molecules are converted to high octane olefins and gases (e.g., n-paraffins to isoparaffins, olefins, and aromatics; and naphthenes to aromatics). Reforming can be Thermal or Catalytic. Thermal Reforming is carried out at high temperatures in a furnace ( o C) with pressures from 400 to 1000 psi. Thermal reforming is not preferred due to its lower conversion and selectivity. 64

2 FEED STOCK The typical feed stocks to catalytic reformers are heavy straight-run (HSR) gasolines and naphthas [ F ( C)] and heavy hydrocracker naphthas. These are composed of the four major hydrocarbon groups: paraffins olefins (PONA) naphthenes aromatics 65

3 REACTIONS Desirable reactions in a catalytic reformer all lead to the formation of aromatics and isoparaffins as follows: 1. Paraffins are isomerized and to some extent converted to naphthenes. The naphthenes are subsequently converted to aromatics. 2. Olefins are saturated to form paraffins which then react as in (1). 3. Naphthenes are converted to aromatics. 4. Aromatics are left essentially unchanged. 66

4 REACTIONS There are four major reactions that take place during reforming. They are: 1. Dehydrogenation of naphthenes to aromatics, as they are the most desirable products of reforming reactions due to their high octane number. 67

5 REACTIONS 2. Dehydrocyclization of paraffins to aromatics 68

6 REACTIONS 3. Isomerization Paraffins rearrange the molecule to give an increase in octane number. Naphtenes may also isomerize but almost immediately undergo dehydrogenation to an aromatic. 69

7 REACTIONS 4. Hydrocracking Hydrogen produced in other reactions is more than the hydrogen required in hydro-cracking, therefore reforming is a source of hydrogen in petroleum refineries. 70

8 CATALYTIC REFORMING The overall reforming reactions are highly endothermic, resulting in rapid temperature drop, which affects the operation efficiency. In general three reactors are used and heating is provided between the reactors. (a fourth reactor may be used as a spare reactor to replace the reactor in regeneration cycle) Fixed bed reactors are used, therefore the process is semi-continuous as catalysts must be regenerated (usually every 6 months or more depending on the feed and catalyst). The reactions are carried out in vapor phase. 71

9 CATALYTIC REFORMING 72

10 PROCESS DESCRIPTION The feed is combined with the hydrogen rich recycled gases and sent to a furnace to be vaporized The partially converted feed is preheated in the second furnace to reach the desired temperature before entering the second reactor. Finally the products are sent to a flash drum, where hydrogen and gaseous unconverted vapors and part of the products are separated and recycled. The products leaving the last reactor are cooled or quenched by the cold feed. 73

11 PROCESS DESCRIPTION (CONT.) A flash drum is used to separate hydrogen rich gases from liquid products. Excess amount of the hydrogen produced is taken out of the recycle stream. A compressor is used to pressurize the recycle stream before entering into the first reactor. The cooled products are separated in a distillation tower where gases and heavy products are separated from high octane gasoline. The liquid product leaving the flash drum is sent to a distillation tower for stabilization. 74

12 REFORMING CATALYST The first catalysts used are chromium oxide and /or molybdenum oxide, supported by alumina or silica, to catalyze hydrogenation-dehydrogenation reactions. In 1949, UOP developed a new catalyst containing platinum or rhenium on a silica or silica-alumina support base, and some contain both platinum and rhenium. Recently new catalysts have been developed based on Platinum, and rhenium with Chlorinated compound of the these metals. 75

13 REFORMING CATALYST (CONT.) Platinum and rhenium sites are used for dehydrogenation reactions while chlorinated alumina provides acid sites for isomerization, cyclization and hydro-cracking reactions. These catalysts are commonly spherical or cylindrical in shape (1/16, 1/8, and ¼ inch in diameter). New catalysts are more efficient and they may last more than two years before regeneration. The activity of the catalyst decreases during the onstream period and the reaction temperature is increased as the catalyst ages to maintain the desired operating severity. 76

14 REFORMING CATALYST (CONT.) Reforming Catalysts are deactivated mainly due to coke deposition over the active sites. Loss of chlorine may also cause deactivation. Catalyst regeneration is carried out by burning coke at high temperatures followed by chlorination. In each regeneration, a fraction of catalyst become permanently deactivated In general after 4 times in-situ regeneration, the catalyst should be replaced by fresh catalyst. 77

15 REFORMING CATALYST (CONT.) There are temporary and permanent poisons for reforming catalysts. Sulfur, Nitrogen, chloride, fluoride and water are temporary poisons and their effects are reversible Arsenic, Lead, Copper, Silica and Phosphorous are permanent poisons and can force a shut down of a reforming unit. Carbon or coke deposited on the catalyst do not fall into either of these two classes, but affect the activity and selectivity of the catalyst. 78

16 CONTINUOUS REFORMING Continuous Catalyst Regeneration (CCR) process was developed in In CCR process the reactors are on top of each other and one furnace is used for all reactors. In 2006, UOP developed a continuous process in which deactivated catalysts are continuously discharged from the reactor and replaced by fresh catalyst. Over 200 units have been installed and commissioned by UOP worldwide. 79