Chemical & Engineering News Digital Edition - January 18, 2010

ISTOCK
ACETYLENE, COKE, and calcium carbide
are no longer part of the vocabulary of
chemists and chemical engineers working at
most modern industrial sites. But in China,
these materials, dating back to the early
days of the chemical industry, are still widely
used to manufacture polyvinyl chloride.
Making an anachronism contemporary,
Chinese firms are building new, larger scale
facilities to produce vinyl from calcium
carbide, a process that most of the world
replaced with a petrochemical one decades
ago. The method has been widely faulted
for using too much energy and creating too
much waste, but Chinese firms are confident
they will be able to modernize it.
China has valid economic reasons for
sticking with the calcium carbide route to
PVC, industry observers say. The country
is endowed with the vast coal and lime
resources necessary for the production of
calcium carbide. In contrast, it does not
have the abundant supply of ethylene required
for making PVC via the petrochemical
route that the rest of the world uses.
China is a major producer and consumer
of PVC. According to figures C&EN obtained
from a major international PVC producer,
the country consumed nearly 10 million
metric tons of PVC in 2009. That year,
BUSINESS
CHINA’S VENERABLE
VINYL PROCESS
Replaced in most of the world, the
CALCIUM CARBIDE ROUTE to PVC gains ground in China
JEAN-FRANÇOIS TREMBLAY , C&EN HONG KONG
it had a production capacity of 19 million
metric tons, about 80% of which was based
on the carbide route. Chemical Market
Associates Inc. (CMAI), a market research
firm, estimates that China represents onethird
of the world’s PVC capacity.
“If you look at the expansion of facilities
in China in the past four to five years, it’s
been mostly plants featuring the carbide
route,” says Eddie Kok, Asian director for
chlor-alkali and vinyls at CMAI. “There’s
little ethylene from the Chinese crackers
available for making PVC because it’s often
allocated to more profitable products.”
PVC, one of the world’s most widely
used plastics, can basically be made in two
ways. The petrochemical route involves
the chlorination of ethylene to yield ethylene
dichloride, which is then cracked to
generate vinyl chloride. Vinyl chloride is
polymerized into PVC. Implementing this
method in an economically viable fashion
typically requires that a chlorine plant be
set up in the vicinity of an ethylene cracker.
The calcium carbide route used in China
WWW.CEN-ONLINE.ORG 18 JANUARY 18, 2010
BUILDER’S CHOICE
Most Chinese
PVC is used in
the construction
industry.
involves heating lime
and coal-derived
coke in an electric
furnace at a temperature
of 2,000 °C
to obtain calcium
carbide. Acetylene is
generated by the hydrolysis of this calcium
carbide. This early part of the process is
labor intensive, requires a lot of energy,
and generates vast quantities of a watery
calcium hydroxide slag. With the use of a
catalyst that is usually based on mercuric
chloride, the acetylene is then reacted with
anhydrous hydrogen chloride to produce
vinyl chloride.
Both methods for making PVC were invented
in the early-20th century. Calcium
carbide even dominated until the 1960s,
when ethylene became the preferred starting
material in most of the world.
The calcium carbide route has a number
of flaws that explain why it has mostly been
replaced. Yet because China is such a big
business partner, chemical industry executives
refuse to be quoted speaking critically
of the practice.
An executive at a major producer of
PVC, who requested anonymity because
China is a big market for his company, tells
C&EN that PVC made by the carbide route
is of inferior quality. “There are a lot of
impurities,” he says. “It can be used in construction
materials, such as in pipes, but
you can’t make film from it.” Others say the
poor quality is the result of inferior polymerization
techniques and is unrelated to the
carbide process.
CALCIUM CARBIDE production requires
huge amounts of power, the executive
further explains, but that issue has been
largely overcome in China. “They can make
cheap electricity with all the coal they
have,” he says. Indeed, most of the PVC
plants in China that employ the calcium
carbide route are located near coal mines,
and some house large on-site generators.
But by far the biggest flaw in the carbide
route is its negative environmental impact.
First of all, there is all the calcium hydroxide
slag to deal with. “It’s the biggest problem,”
the PVC executive says. His Chinese
competitors, he says, endeavor to use the
slag in cement production and are encour-
By far the biggest flaw in the carbide route
is its negative environmental impact.