NOVELTY - Separation of isobutane from mixed tetra-carbon isobutene containing isobutene, n-butane, butene-1, cis-2-butene and trans-2-butane involves compressing mixture of isobutane, sent to butane tower (102); dividing tower into tower top carbon four components and bottom carbon four components; carrying out tower bottom carbon four components through throttle valve (103) reducing expansion refrigeration, compressing final return to escape a butane tower bottom, condensing top from butane tower of tower top carbon four component into gas-liquid separator.    USE - For separation of isobutane from mixed tetra-carbon isobutene containing isobutene, n-butane, butene-1, cis-2-butene and trans-2-butane (claimed).    ADVANTAGE - Compared with the existing technology, the energy consumption of the method is low, safe and practical, allows production of high purity isobutene product, isobutane complete separation, in addition, the method has a very wide operating range, which can ensure a content of each component in the hydrocarbon feedstock changes, the system can stably operate, the method using the isobutyl deheavy component tower expansion refrigeration condensing tower top light component, which greatly reduces the system energy consumption.    DETAILED DESCRIPTION - Separation of isobutane from mixed tetra-carbon isobutene containing isobutene, n-butane, butene-1, cis-2-butene and trans-2-butane involves compressing the mixture of isobutane, sent to butane tower (102); dividing the tower into tower top carbon four components and the bottom carbon four components of the fourth tower; carrying out tower bottom carbon four components from fourth tower bottom through throttle valve (103) reducing expansion refrigeration, so as to cool the top carbon four components, compressing final return to escape a butane tower bottom, condensing the top from a removing butane tower of the tower top carbon four component into gas-liquid separator, the separated liquid phase part (isobutane) return to butane tower as isobutene product, where isobutane column inlet pressure is 400-1500kPa, and inlet temperature is 0-90 degrees C; isobutane column overhead outlet pressure is 200-1500 kPa, and outlet temperature is 10-100 degrees C; and isobutane bottoms outlet pressure is 300-1200kPa, and outlet temperature is 25-120 degrees C. In the tower, whose top carbon four major components of a small amount of isobutane and butene, carbon bottoms divided into four groups n-butane, butene-1, cis-2-butene and trans-2-butene.    DESCRIPTION OF DRAWING(S) - The figure shows flow-chart of method for separation of isobutane from mixture of isobutene, n-butane, butene-1, cis-2-butene and trans-2-butane.    Compressor (101)    Fourth tower (102)    Throttle valve (103)    Heat pump compressor (104)    Cooler (105, 106)    Gas-liquid separator (107)    Reflux pump. (108)