PDH

Propylene Production through PDH Technology

The largest volume of propylene is globally produced in NGL or Naphtha steam crackers, which generates ethylene as well. In an olefin plant, propylene is generated by the pyrolysis of the incoming feed, followed by purification. By the way, propylene produced by steam cracking varies according to the severity of the pyrolysis, feedstock composition and also the economic conditions. According to available information, as of 2014, the total nameplate capacity to produce co-product propylene from steam crackers amounted to about 57 million metric tons.

In recent years, the increasing shift to lighter feedstocks, and consequently to lower yield of propylene co-products, driven mainly by the shale gas revolution in North America and a continued advantaged feedstock basis of Middle Eastern producers, has ultimately reduced the output of propylene from steam crackers. As a result, most of the increases in propylene supply for chemical derivatives come from refineries and plants utilizing on-purpose production technologies. In view of this, currently, the markets have evolved to the point where modes of by-product production can no longer satisfy the demand of propylene leads to another reason for new and novel lower cost chemical processes for on-purpose propylene production technologies.
Propane Dehydrogenation as a catalytic process that converts propane into propylene and hydrogen is one of the on-purposed technologies. In fact, catalytic dehydrogenation is especially attractive in those areas where there is an abundant, steady supply of propane, with a stable price structure relative to propylene.

PDH Licensors:

Among five licensed PDH technologies the top three are:
 CATOFIN from Lummus Technology,
 Oleflex from UOP and
 STAR process from Uhde,
The main differences between those technologies are centered on:
1. the type of catalyst and regeneration methods used;
2. the design of the reactor; and
3. the methods used to achieve better conversion rates (e.g. operating pressure; used of diluents, and reaction temperature).

Licensor’s Name	Capacity Range(Kta)	No. of Operating Units	No. of Licensees
CATOFIN	250 ~ 750	14	20
Oleflex	105 ~ 750	23	50
STAR	Up to 550	1	6

Table-2 Process Parameters for Commercial PDH Technologies

Type	Lummus (CATOFIN)	UOP (Oleflex)	Uhde (STAR)
Catalyst	Chromia on alumina	Pt‐Sn on alumina	Pt‐Sn on Zn/Ca aluminate
Reaction System	5 fixed bed, axial flow, adiabatic reactors (2 on‐stream, 2 reheat or cat. Regeneration and 1 evacuation mode)	4 fluidized bed radial flow reactors (all reactors are in series)	Fixed bed, fired tube adiabatic reactors connected in series
Main Heat Source	Heating the catalyst during its regeneration	Pre‐heating of feed and intermediate products before each reactor	External firing of the tubular reactor and H2 combustion in the adiabatic reactor
Operating Mode	Discontinuous	Continuous	Discontinuous
Cycle Time	6‐22 min. for reaction	5‐10 days for catalyst	7/1 normal operation/regeneration hours
Temperature, (ºC)	570‐650	580‐650	570‐590
Pressure, (psig)	<10	29	73
Per‐Pass Conversion of Propane, (%)	48‐65	30‐35	40
Selectivity to Propylene,(mol %)	88	86‐90	89