Maximization of middle distillates in fluid catalytic cracking
IR@IIP: CSIR-Indian Institute of Petroleum, Dehradun
View Archive Info| Field | Value | |
| Creator |
Krishna, Rajamani
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| Date |
2010-05-11T10:49:42Z
2010-05-11T10:49:42Z 2010-05-11T10:49:42Z |
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| Identifier |
Research and Industry,Vol. 34, March 1989, pp. 30-35
http://hdl.handle.net/123456789/511 |
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| Description |
This paper addresses the problem of maximization of middle distillates in Fluidized Catalytic
Cracking (FCC) with special reference to processing of highly-waxyfeedstocks such as
Bombay High VacuumGas Oil (BHVGO).In operations of sixnewly-designed commercial
riser FCC units in India, employing amorphous silica alumina catalysts, the following was
experienced withBH VGO. (i)The Clarified Oil (CLO) make was much higher than design
expectations and typicallyin the range 10-13per cent wt.Further, the CLO had amuch higher
pour point than expected, coupled withamuch lower density, both signifyingthe predominance
of hydrogen rich paraffinic structures. (ii)The pour point of the Total Cycle Oils
(TCO) was significantlyhigher than expected in the design. (iii)The regenerator temperatures
were about 40°C higher than design expectations. The above operating experiences
can be explained on the basis of the poor reactivity, on an amorphous catalyst, of n-paraffins
present in the feedstock (BHVGO has a total of 45 per cent wt n-paraffins). The poor reactivity
of n-paraffins emanate from their poor adsorbability and lack of tertiary C atoms,
which makes the problem of formation of the intermediate car1o>eniumions quite difficult.
The uncracked n-paraffins concentrate in the CLO (explaining the high pour point) and
those whichescape being stripped in the stripper, enter the regenerator and burn there causing
excessivelyhigh tempeatures. Further, the cracking of n-paraffins leads to a lop-sided
product distribution: a lot of LPG together with a daughter paraffin of slightlyreduced chain
length. The latter first-crack products end up in the TCO causing high pour points. The
problem of sluggishlyreactive n-paraffins on an amorphous catalyst surface can be'overcome
byenhancing their crackability byincorporation ofthe right amount of zeolite crystals
(of the Y-type)of the appropriate size, embedded in an amorphous matrix having sufficient
activity to crack compounds other than n-paraffins. The matrix should possess the right
amount of macroporosity to effect bottoms conversion, i.e.lower CLO make. The use of zeolite-
based catalysts in some locations in India has indeed given some of the expected improvements.
This paper could serve as a guide to catalyst selection for middle distillates
maximization with waxy feedstocks.
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| Language |
en_US
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| Subject |
Catalytic cracking of fluid
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| Title |
Maximization of middle distillates in fluid catalytic cracking
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| Type |
Article
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