Effect of Feed Quality on Aromatic Yield
N = Naphthenes % A = Aromatics %
(1) Benzene = 60-90oC Fraction
(2) To luene = 90-110oC Fraction
(3) Xy lenes = 110-140oC Fraction
(4) Octane blending stock = 90-140oC Fraction
Figure M-VII 7.1: Aromatics Complex
The p-xylene plant consists of five units are:
Pretreatment Unit: This unit is used for reducing sulphur content to 5 ppm (max.) by dehydro - desulphurisation which takes place at 330–370 oC and 24 kg/cm2 pressure in presence of cobalt molybdenum catalyst.
Reformer Unit: To get maximum amount of C8 aromatics by reforming process (Process similar to described earlier).
Fractionation Unit: For separation of o-, m-, and p-xylenes from combined C8 reformate and isomerisate from isomerisation unit (after clay treatment).
Parex Unit: This unit is for the separation of p-xylene by selective adsorption using molecular sieve followed by desorption. Other method for separation of p-xylene is by crystallisation process.
Isomerisation: Isomerisation of C8 stream from Parex unit rich in m- and o-xylene and ethyl benzene to p-xylene, which is sent to fractionation unit for separation of high component. The bottom of the column is recycled for further recovery of xylenes.
Aromatic Conversion Processes
Because of higher demand of benzene and p-xylene in comparison to toluene and m-xylene various processes are commercially available for conversion of toluene and m-xylene to more value added products like benzene and p-xylene. processes are also avialble for conversion of paraffins into aromatics. Some of the major processes are:
Aromatic conversion Process
Isomerizatin of meta xylenes to para and ortho
Transalkylation and Disproportion
Transalkylation and Disproportionation of C7 and C9
Toluene disproportionation to xylenes and benzene
Selective conversion of toluene to para xylene by
Maximization of p-xylene, ethyl benzene (EB)
conversion and EB dealkylation process
Conversion of light hydrocarbons to benzene,
toulenes and xylenes
Research Association of
Cyclar process inexpensive and plentiful LPG requires minimal feed pretreatment and product purification requirements and simplicity in operation. Reaction involved in the cycler process is shown in Figure M-VII 7.2. Process flow diagram of UOP-BP cycler process for LPG aromatisation is shown is Figure M-VII 7.3.
Feed: Propane, Butane, Pentanes or mixture
Liquid Product: Largely BTX essentially free from C6-C9 paraffinic & naphthalenes Preparation of Benzene Toluene and xylene charges very little with the composition of feed. Aromatic yield:
63.6% of Feed for Propane
67.5% of Feed for Butane
→ Very high H2 yield of 5.5 – 6% for feed
→H2 purity of about 95%.
Feed Intermediate Products
Figure M-VII 7.2: Reactions involved in Cyclar Process
Figure M-VII 7.3: UOP-BP Cyclar Process for LPG Aromatisation