The alkylation of benzene with ethylene or propylene to form ethylbenzene (EB) or cumene is an industrially significant transformation. EB is used as an intermediate in the manufacture of styrene, which in turn is an important in the manufacture of many kinds of polymers. The primary use of cumene is in the co-production of phenol and acetone, which in turn are important in the manufacture of many kinds of chemicals and polymers. In industry, EB and cumene are mainly manufactured by the alkylation of benzene with ethene or propene via two methods, the gas and the liquid phase in the presence of Lewis and Brønsted acids. The development of efficient solid catalysts has gained much attention over the last decades. The objective of this chapter is to provide an overview of the history of the alkylation of benzene with ethene and propene, the development of homogeneous and heterogeneous Lewis and Brønsted acids and zeiolite catalysts, the liquid and gas phase alkylation processes, and the industrial technologies for EB and cumene production.
TopIntroduction
Alkylation of aromatics: Alkylation is the transfer of an alkyl substituent from one molecule to another via an alkyl carbocation or carbonuim ion, a carbanion, a free radical, or a carbene, which are generated from electrophilic alkylating agents such as olefin or alkyl halide in the presence of catalyst, such as Brønsted acid, Lewis acid or zeolite.
The ethylene (ethene) feed used for ethylation of benzene is produced from the cracking of fractions obtained from distillation of natural gas and oil. The processes are:
- (a)
the steam cracking of ethane and propane (from natural gas and from crude oil),
- (b)
the steam cracking of naphtha from crude oil,
- (c)
the steam cracking of gas oil from crude oil.
The choice of feedstock depends on availability, price and what other products from cracking are needed for other chemical processes.
The alkylation of benzene with ethylene or propylene to form ethylbenzene or isopropylbenzene (cumene) over acid catalystisan industrially significant and the main commercial route for the production of important petrochemical intermediates, such as ethylbenzene(EB) as the key building block for manufacture polystyrene and isopropylbenzene (IPB - cumene), a precursor to solvents and chemical intermediates such as acetone and phenol; alkyl benzene sulfonates, used extensively in detergent building; and alkylnaphthalenes, precursors to advanced high strength polymers (Yurchak et al., 1979)
Ethylbenzene and isopropylbenzene are commercially the two largest volume derivatives of benzene. Combined, these two basic intermadiat chemicals account for nearly 75% of the world’s consumption of petrochemical grade benzene.
The worldwide capacity amounting to around 30 million metric tons (MMT) per year, and in Chinese the value being about 5 million tons per year (Zhu et al., 2011). The global demand for ethylbenzene increased from 20.5m tons in 2000 to 25.1m tons in 2011 at annual growth rate of 1.9%. The increase in global demand for ethylbenzene has been due largely to ethylbenzene usage growth in developing countries, led by China, which has more than compensated for the declining demand in the US and large markets in Europe.
Figure 1. World and Saudi Arabia Demand of Ethylbenzene
It was reported that in 2012 the world annual demand of EB was estimated to be 37 million metric tons per year, and expected to be about 38 million metric tons in 2016, with an average annual growth rate of approximately 3.5% from 2012 to 2016. In the other forecast period from 2011 to 2020, demand is expected to grow at a rate of 3.7%, with the increasing market dominance of Asia-Pacific region. Moreover furthermore, the overall EB demand in the world will expected to increase at an average annual rate of 3.9% from 2012 to 2022, and over 90% of the production of ethylbenzene is used in the manufacture of styrene. Figure (1) shows the world and Saudi Arabia demand of ethylbenzene (http://www.cmai global.com). (https://www.ihs.com/products/ethylbenzene-chemical-economicshandbook.html).