Abstract

Flash hydropyrolysis experiments have been performed on the vacuum bottoms fraction of Cold Lake bitumen, using zinc chloride as a catalyst. Milligram size samples of vacuum bottoms resid were heated rapidly (120 - 400 °C/s) by passing a large electric current through the reactor tube. The variables studied included temperature, heating rate, catalyst/pitch ratio, vapour phase residence time and pressure. Temperature and catalyst/pitch ratio caused major changes in yi.elds. In contrast pressure had little effect. It was found that high conversions could be obtained at hydrogen pressures which are much lower than those normally used in catalytically hydrocracking residual oils.

Introduction

For many years delayed coking and fluid coking have been the only industrial processes used to upgrade the bitumen derived from Canada's oil sand resources. The hydrocracking process units that are currently being constructed are considered to be the next generation of upgraders. In spite of the success of these commercial processes, alternatives that might have potential advantages merit consideration. Experiments with one such alternative, catalytic flash hydropyrolysis, were performed in order to examine its characteristics. Either pitch from the original bitumen or the unreacted pitch by-product from a bitumen hydrocracking process can be used as the feedstock for a catalytic flash hydropyrolysis unit. During flash hydropyrolysis the feedstock is heated rapidly to the reaction temperature in the presence of hydrogen, is kept at reaction conditions for a short period, and is cooled quickly before extensive secondary reactions can occur. Considerable work describing flash pyrolysis (Scott et al., 1986) and flash hydropyrolysis of coals (Hiteshue et al, 1957; Stangeby and Sears, 1981a) has been reported. Unfor tunately, flash hydropyrolys is experiments with bitumen and heavy oils have been less extensive.

Bunger et al (1981) performed one non-catalytic flash hydropyrolysis experiment on each of three different feedstocks derived from Utah oil Sands. Extremely large gas velocities, 700,000 scf/Bbl (124.7 m3 H2/m3 feed), were used. Subsequently, Bunger (1985) reported a single non-catalytic flash hydropyrolysis experiment on Athabasca bitumen. Stangeby and Sears (1981b) used oil sand samples (bitumen plus the original sand) in their flash hydropyrolysis experiments. Walsh and Chen (1983) measured the effects of several experimental variables: temperature, hydrogen pressure, vapour residence time and feedstock hydrogen to carbon ratio while stunying thp non-catalytic. hydropyrolysis of a heavy petroleum oil. The lowest char yield they obtained was 18 wt %

Shabtai et al (1979) described a general reaction mechanism for flash hydropyrolysis. They suggested that the initiation step is the same as in thermal cracking. Free radicals can be formed from homolytic cloavage of a C-C bond.

Chemical equation (1) (Available in full paper)

The explanation for the react ion rates in hydrupyrolysis being greater than those in thermal cracking involves the formation of hydrogen atoms, 11 °. Atomic hydrogen is produced when some of the free radicals formed by Equation (1) are stabilized, by interacting with molecular hydrogen (H2). Chemical equation (2) (Available in full paper)

Comparatively few hydrogen atoms will be formed directly from molecular hydrogen via Equation 3. Chemical equation (3) (Available in full paper)

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