Alkylation
catalyzed by concentrated sulfuric acid (H2SO4) is an important process for industrial production
of excellent high octane gasoline blending components. This process
has some vital drawbacks such as extensive side reactions and high
consumption of H2SO4 due to the presence of
the most notorious impurities including H2O, acid soluble
oil (ASO), and esters. In this study, isobutane alkylation was studied
with H2SO4 (275 mL) in a batch reactor at −10
to 0 °C and 0.45 MPa, with the corresponding stirrer speed, feed
rate, acid/hydrocarbon volume ratio, and isobutane/isobutylene volume
ratio being 3000 rpm, 5.0 mL/min, 1.2, and 14.3, respectively. The
effects of the acid strength and composition of acid on the alkylate
quality were investigated. The composition of used acid was analyzed.
The results show that used acid is mainly composed of roughly 89%
free H2SO4, 6% H2O, 2% esters, and
3% ASO. The compounds existing in the ASO extracted from used acid
were identified, and their concentrations were quantitatively determined.
The results show that the most abundant ASO molecules are five-membered
or six-membered cyclic homoannular conjugated olefins such as cyclopentadiene
(15.67%) and cyclohexadiene (14.12%). The effects of acid strength,
H2O, ASO, and esters on alkylation depend strongly on the
concentrations of H2SO4 and these impurities.
Therefore, their optimal concentrations were determined to achieve
advantageous effects on the alkylation. The results are about 93–95%
for H2SO4, 2–4% for H2O, 1.5–2.5%
for ASO, and 0.4–1% for esters, beyond which an adverse effect
will appear. Under the optimal concentrations, the value of the research
octane number, the trimethylpentane (TMP)/dimethylhexane ratio, and
the contents of C8 and TMP remained steady at high levels
of about 92–93, 5.8–6.3, 68–70, and 58–60%,
respectively.
