Catalytic reforming is a major conversion process in petroleum refinery and petrochemical industries. The reforming process is a catalytic process which converts low octane naphthas into higher octane reformate products for gasoline blending and aromatic rich reformate for aromatic production. Basically, the process re-arranges or re-structures the hydrocarbon molecules in the naphtha feedstocks as well as breaking some of the molecules into smaller molecules. Naphtha feeds to catalytic reforming include heavy straight run naphtha. It transforms low octane naphtha into high-octane motor gasoline blending stock and aromatics rich in benzene, toluene, and xylene with hydrogen and liquefied petroleum gas as a byproduct. With the fast growing demand in aromatics and demand of high - octane numbers, catalytic reforming is likely to remain one of the most important unit processes in the petroleum and petrochemical industry. Various commercial catalytic reforming processes is given in Table M-VI 6.1.
Table M-VI 6.1: Various Catalytic Reforming Processes
Altalntic Richfield oil
Octane Number of Hydrocarbons
Octane number is a measurement of antiknock characteristics of fuels
Table M-VI 6.2: Octane Number of Various Hydrocarbons
Naphtha Hydro Treatment
Naphtha hydrotreatment is important steps in the catalytic reforming process for removal of the various catalyst poisons. It eliminates the impurities such as sulfur, nitrogen, halogens, oxygen, water, olefins, di olefins, arsenic and other metals presents in the naphtha feed stock to have longer life catalyst. Figure M-VI 6.1 illustrate hydrotreatment of naphtha.
Various sections in the naphtha hydro treatment unit are:
Charge Heater: Preheating reactor feedstock to reaction temperature of 340 oC. Charge heater has four passes four gas burners. Heater tubes are made up of SS-321
Reaction Section: The reactor consists of two catalyst beds.
Stripping Section: Stripping section uses air for stripping the light ends mainly hydrogen sulfide from reactor product, stripper temperature 14 kg/ cm2 and temp. 172 0C
Stripper Reboiler: Stripper reboiler supply heat required for striper
Operating Variables Naphtha Hydrotreatmernt
Figure M-VI 6.1: Hydrotreatment of Naphtha
Classification of Processes
Various Types of Catalytic Reformers
Semi-Regenerative Fixed Bed reactors: In this type of reformers the catalyst generally has a life of one or more years between regeneration. The time between two regeneration is called a cycle. The catalyst retains its usefulness over multiple regeneration.
Cyclic Fixed Bed Reformers: Cyclic reformers run under more severe operating conditions for improved octane number and yields. Individual reactors are taken offline by a special valving and manifold system and regenerated while the other reformer unit continues to operate.
Continuous Reformers: In these reformers the catalyst is in moving bed and regenerated frequently. This allows operation at much lower pressure with a resulting higher product octane, C5+, and hydrogen yield. These types of reformers are radial flow and are either separated as in regenerative unit or stacked one above the other.
Semi- regenerative Catalytic Reforming Process
A semi-regenerative process uses low platinum and regeneration is required only once a year. The process consists of typically three reactor beds & furnace preheaters. The dehydrogenation is highly endothermic and large temperature drop as the reaction proceeds. Multiple reactors with intermediate reheat is required. Dehydrogenation of naphthene takes place in first reactor and requires less catalyst. Preheat of feed is required. Last reactor for isomerization of paraffins. Typical catalyst distribution in three reactors are 20, 30 and 50percent. Figure M-VI 6.2 shows typical catalytic reforming process.
Performance of the catalyst decreases with respect to time due to deactivation. Reasons for deactivation
Objective of Regeneration
Figure M-VI 6.2: Catalytic Reforming Process
Reactions in Catalytic Reforming
Following are the most prevalent main reactions in catalytic reforming
Dehydrogenation & Dehydrocyclization: Highly endothermic, cause decrease in temperatures, highest reaction rates, aromatics formed have high B.P so end point of gasoline rises Dehydrogenation reactions are very fast, about one order of magnitude faster than the other reactions. The reaction is promoted by the metallic function of catalyst
Methyl cyclohexane → Toluene + H2
MCP→Benzene + H2
Dehydrocyclisation: It involves a dehydrogenation with a release of one hydrogen mole followed by a molecular rearrangement to form a naphthene and the subsequent dehydrogenation of the naphthene.
i-paraffins to aromaticsof paraffins
n-heptane à toluene + H2
Favourable Conditions: High temperature, Low pressure, Low space velocity, Low H2/HC ratio
Isomerisation: Branched isomers increase octane rating, Small heat effect, Fairly rapid reactions.
Favourable Conditions: High temperature, Low pressure, Low space velocity, H2/HC ratio no significant effect
n-Hexane → Neo hexane
Naphthenes dehydro-Isomerisation: A ring re-arrangement reaction, Formed alkyl-cyclohexane dehydrogenate to aromatics." Octane increase is significant, Reaction is slightly exothermic
Coking: Coking is very complex group of chemical reactions. Linked to heavy unsaturated products such as poly-nuclear aromatics. Traces of heavy olefines and di-olefines promote coking. High feed FBP favors coking. Poor feed distribution in the reactor promotes coking favored by high temperature
Hydrocracking: Exothermic reactions, slow reactions, consume hydrogen, produce light gases, Lead to coking, Causes are high paraffin conc feed
Favourable conditions: High temperature, High pressure