Hydrocarbon Processing - April 2021 - 38

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pressure (RVP) were computed using the gas chromatography
product analysis and confirmed by independent engine testing.
In general, the octane values for alkylate produced by the
proprietary catalyst tend to be higher than those obtained
by either liquid acids or ionic liquids for three main reasons.
Those include:
1. The proprietary catalyst has an inherent functionality
that converts n-butenes to a mixture of 1-butene,
trans-2-butene and cis-2-butene. As a result,
irrespective of the type of normal butene used as feed,
the product composition of the alkylate is identical.
TABLE 1. Proprietary catalyst performance with various
reﬁnery feedstocks
FCC offgas
with ethylene Propyleneand propylene rich feeds

FCC
oleﬁns

MTBE
raffinate

Research octane
number (RON)

Motor octane
number (MON)

RVP, psi

3.3

2.8

4.1

3.8

Yield, vol/vol
oleﬁn

1.88

1.86

1.85

TABLE 2. Typical contaminants in alkylation feedstock
Contaminant

FCC oleﬁns

Water, ppm wt
Mercaptans, ppm wt
Hydrogen sulﬁde, ppm wt
Butadiene, wt%

MTBE raffinate

300

25-100

0.4-1

Dimethyl ether, ppm wt

500

MTBE, ppm wt

Tert-butyl alcohol, ppm wt

Methanol, ppm wt

2. The trimethyl pentanes-to-dimethyl hexanes (TMP/
DMH) ratio for alkylate produced by the proprietary
catalyst is roughly double the value for TMP/DMH
ratios produced by liquid acids or ionic liquids. The
octane values for TMPs range from 100-109,
while those for DMH range from 55-75. High
TMP/DMH ratios boost the alkylate octane rating.
3. The distribution of TMP molecules produced by
the proprietary catalyst is different from those
produced via other processes. While the dominant
TMP produced by most alkylation processes is
2,2,4-trimethyl pentane, which has a RON of 100,
the proprietary catalyst tends to favor 2,3,4-trimethyl
pentane and 2,3,3-trimethyl pentane, which have
RON ratings of 103 and 106, respectively.
A combination of these three effects boosts the octane rating of alkylate produced by the proprietary catalyst vs. other
technologies.
Feed contaminants. Poisoning is the strong chemisorption of
reactants, products or impurities on acid sites otherwise available for catalysis. Certain feed contaminants act as catalyst poisons and increase the rate of deactivation of the catalyst. Typical
feed impurities for alkylation units are shown in TABLE 2.
These feed impurities lead to an increase in liquid acid consumption for sulfuric and HF acid alkylation technologies. In
general, the recommended limits for feed contaminants using
these liquid acids are less than 10 ppm each for sulfur, dienes
and oxygenates. For solid-acid catalysts, the feed contaminant

TABLE 3. Effect of feed contaminants on alkylate quality
Base
Case
feed

Highoxygenate
feed

Highsulfur
feed

Highdiene
feed
FIG. 2. Innovations in the proprietary solid-acid catalyst system.

Oleﬁn composition, wt%
Propylene

Butenes

210

Amylenes

Contaminants, wt ppm
Oxygenates
Mercaptans

33
22

220

903

910

2,120

RON

MON

Dienes
Alkylate properties

APRIL 2021 | HydrocarbonProcessing.com

FIG. 3. The proprietary catalysta can trap most feed contaminants
(e.g., mercaptans, dienes and oxygenates), while allowing
high-octane alkylate molecules to diffuse out easily.

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Hydrocarbon Processing - April 2021

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