A vacuum double structure includes: a tubular and metal inner wall member; a tubular and metal outer wall member in which the inner wall member is accommodated; and a sealing member provided between a facing surface of the inner wall member and a facing surface of the outer wall member. The sealing member includes an annular spacer, a first annular packing material, and a second annular packing material. The annular spacer is provided between the facing surface of the inner wall member and the facing surface of the outer wall member.

The disclosed invention relates to a process for converting ethylbenzene to styrene, comprising: flowing a feed composition comprising ethylbenzene in at least one process microchannel in contact with at least one catalyst to dehydrogenate the ethylbenzene and form a product comprising styrene; exchanging heat between the process microchannel and at least one heat exchange channel in thermal contact with the process microchannel; and removing product from the process microchannel. Also disclosed is an apparatus comprising a process microchannel, a heat exchange channel, and a heat transfer wall positioned between the process microchannel and heat exchange channel wherein the heat transfer wall comprises a thermal resistance layer.