Southeast Side Alderman John Pope (10th) elected Tuesday to defer a committee vote on a measure imposing stricter regulations on petroleum coke facilities in Chicago after environmentalists assailed last-second changes to the proposed measure. The deferral further complicates city efforts to regulate petcoke, a by-product of oil refining. Southeast Side residents and public health advocates say the substance causes respiratory illness but state and federal regulators have not judged it to be a hazardous material.